merge in latest release

Merge branch 'develop' into release/v1.2.0
Feature/prioritise surb retransmission (#1883 )
2022-12-13 12:32:40 +01:00 · 2022-12-13 11:21:05 +00:00 · 2022-12-12 13:27:20 +00:00 · 2022-12-09 11:09:57 +00:00 · 2022-12-08 17:10:42 +00:00 · 2022-12-08 14:01:07 +00:00
121 changed files with 9041 additions and 2580 deletions
@@ -37,4 +37,5 @@ validator-config
 *.patch
 validator-api-config.toml
 dist
-storybook-static
+storybook-static
+envs/qwerty.env
@@ -0,0 +1,14 @@
+[
+    {
+      "id": "Coconut",
+      "description": "Bandwidth Test",
+      "items": [
+        {
+          "id": "cocos",
+          "description": "testing",
+          "address": "51RhttA7LhKp573QWUU74uaFuoyb4Bg2cqNUaiuTRAMb.GW9e3T5TQvn5iyvdTVnhTWaZ9WLCaBvA8XVdnw4xL9DW@EVupP2tRUeZo5Y6RpBHAbm8kSntpgNyZNL6yCr7BDEoG",
+          "gateway": "EVupP2tRUeZo5Y6RpBHAbm8kSntpgNyZNL6yCr7BDEoG"
+        }
+      ]
+    }
+]
@@ -2,6 +2,24 @@

 Post 1.0.0 release, the changelog format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

+## Unreleased (multi-surb branch breaking)
+
+### Added
+
+-clients: ability to use multi-reply SURBs to send arbitrarily long messages fully anonymously whilst requesting additional reply blocks whenever they're about to run out ([#1796], [#1801], [#1804], [#1835], [#1858], [#1883]))
+
+### Changed
+
+- clients: improve message logging when received message fails to get reconstructed ([#1803])
+
+[#1796]: https://github.com/nymtech/nym/pull/1796
+[#1801]: https://github.com/nymtech/nym/pull/1801
+[#1803]: https://github.com/nymtech/nym/pull/1803
+[#1804]: https://github.com/nymtech/nym/pull/1804
+[#1835]: https://github.com/nymtech/nym/pull/1835
+[#1858]: https://github.com/nymtech/nym/pull/1858
+[#1883]: https://github.com/nymtech/nym/pull/1883
+
 ## [Unreleased]

 ### Changed
@@ -131,9 +131,9 @@ dependencies = [

 [[package]]
 name = "async-trait"
-version = "0.1.53"
+version = "0.1.58"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ed6aa3524a2dfcf9fe180c51eae2b58738348d819517ceadf95789c51fff7600"
+checksum = "1e805d94e6b5001b651426cf4cd446b1ab5f319d27bab5c644f61de0a804360c"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -588,9 +588,11 @@ dependencies = [
 name = "client-core"
 version = "1.1.2"
 dependencies = [
+ "async-trait",
 "client-connections",
 "config",
 "crypto",
+ "dashmap 5.4.0",
 "dirs",
 "futures",
 "gateway-client",
@@ -604,11 +606,12 @@ dependencies = [
 "rand 0.7.3",
 "serde",
 "serde_json",
- "sled",
+ "sqlx 0.6.2",
 "tap",
 "task",
 "tempfile",
 "thiserror",
+ "time 0.3.17",
 "tokio",
 "tokio-stream",
 "topology",
@@ -617,6 +620,7 @@ dependencies = [
 "wasm-bindgen",
 "wasm-bindgen-futures",
 "wasm-timer",
+ "wasm-utils",
 ]

 [[package]]
@@ -782,7 +786,7 @@ dependencies = [
 "rand 0.8.5",
 "sha2 0.10.2",
 "subtle 2.4.1",
- "time 0.3.14",
+ "time 0.3.17",
 "version_check",
 ]

@@ -1350,6 +1354,19 @@ dependencies = [
 "num_cpus",
 ]

+[[package]]
+name = "dashmap"
+version = "5.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "907076dfda823b0b36d2a1bb5f90c96660a5bbcd7729e10727f07858f22c4edc"
+dependencies = [
+ "cfg-if 1.0.0",
+ "hashbrown 0.12.3",
+ "lock_api",
+ "once_cell",
+ "parking_lot_core 0.9.4",
+]
+
 [[package]]
 name = "der"
 version = "0.5.1"
@@ -1798,16 +1815,6 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c8cbd1169bd7b4a0a20d92b9af7a7e0422888bd38a6f5ec29c1fd8c1558a272e"

-[[package]]
-name = "fs2"
-version = "0.4.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9564fc758e15025b46aa6643b1b77d047d1a56a1aea6e01002ac0c7026876213"
-dependencies = [
- "libc",
- "winapi",
-]
-
 [[package]]
 name = "fuchsia-cprng"
 version = "0.1.1"
@@ -1920,15 +1927,6 @@ dependencies = [
 "slab",
 ]

-[[package]]
-name = "fxhash"
-version = "0.2.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c31b6d751ae2c7f11320402d34e41349dd1016f8d5d45e48c4312bc8625af50c"
-dependencies = [
- "byteorder",
-]
-
 [[package]]
 name = "gateway-client"
 version = "0.1.0"
@@ -2274,13 +2272,14 @@ checksum = "7ebdb29d2ea9ed0083cd8cece49bbd968021bd99b0849edb4a9a7ee0fdf6a4e0"

 [[package]]
 name = "hidapi"
-version = "1.4.2"
+version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9d26e1151deaab68f34fbfd16d491a2a0170cf98d69d3efa23873b567a4199e1"
+checksum = "798154e4b6570af74899d71155fb0072d5b17e6aa12f39c8ef22c60fb8ec99e7"
 dependencies = [
 "cc",
 "libc",
 "pkg-config",
+ "winapi",
 ]

 [[package]]
@@ -2611,9 +2610,9 @@ dependencies = [

 [[package]]
 name = "js-sys"
-version = "0.3.55"
+version = "0.3.60"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7cc9ffccd38c451a86bf13657df244e9c3f37493cce8e5e21e940963777acc84"
+checksum = "49409df3e3bf0856b916e2ceaca09ee28e6871cf7d9ce97a692cacfdb2a25a47"
 dependencies = [
 "wasm-bindgen",
 ]
@@ -2759,9 +2758,9 @@ dependencies = [

 [[package]]
 name = "lock_api"
-version = "0.4.7"
+version = "0.4.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "327fa5b6a6940e4699ec49a9beae1ea4845c6bab9314e4f84ac68742139d8c53"
+checksum = "435011366fe56583b16cf956f9df0095b405b82d76425bc8981c0e22e60ec4df"
 dependencies = [
 "autocfg 1.1.0",
 "scopeguard",
@@ -2913,7 +2912,7 @@ dependencies = [
 "serde_json",
 "serde_repr",
 "thiserror",
- "time 0.3.14",
+ "time 0.3.17",
 "ts-rs",
 ]

@@ -3090,15 +3089,6 @@ dependencies = [
 "libc",
 ]

-[[package]]
-name = "num_threads"
-version = "0.1.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aba1801fb138d8e85e11d0fc70baf4fe1cdfffda7c6cd34a854905df588e5ed0"
-dependencies = [
- "libc",
-]
-
 [[package]]
 name = "nym-bity-integration"
 version = "0.1.0"
@@ -3161,7 +3151,7 @@ dependencies = [
 "serde_json",
 "tap",
 "thiserror",
- "time 0.3.14",
+ "time 0.3.17",
 "toml",
 "url",
 "validator-client",
@@ -3194,7 +3184,6 @@ dependencies = [
 "rand 0.7.3",
 "serde",
 "serde_json",
- "sled",
 "tap",
 "task",
 "thiserror",
@@ -3223,7 +3212,7 @@ dependencies = [
 "config",
 "credentials",
 "crypto",
- "dashmap",
+ "dashmap 4.0.2",
 "dirs",
 "dotenv",
 "futures",
@@ -3464,7 +3453,7 @@ dependencies = [
 "tap",
 "task",
 "thiserror",
- "time 0.3.14",
+ "time 0.3.17",
 "tokio",
 "tokio-stream",
 "topology",
@@ -3537,6 +3526,7 @@ dependencies = [
 "nymsphinx-types",
 "rand 0.7.3",
 "rand_distr",
+ "thiserror",
 "tokio",
 "topology",
 ]
@@ -3562,6 +3552,7 @@ dependencies = [
 "nymsphinx-types",
 "rand 0.7.3",
 "serde",
+ "thiserror",
 ]

 [[package]]
@@ -3575,7 +3566,9 @@ dependencies = [
 "nymsphinx-types",
 "rand 0.7.3",
 "serde",
+ "thiserror",
 "topology",
+ "wasm-bindgen",
 ]

 [[package]]
@@ -3587,6 +3580,7 @@ dependencies = [
 "nymsphinx-params",
 "nymsphinx-types",
 "rand 0.7.3",
+ "thiserror",
 ]

 [[package]]
@@ -3601,6 +3595,7 @@ dependencies = [
 "nymsphinx-params",
 "nymsphinx-types",
 "rand 0.7.3",
+ "thiserror",
 "topology",
 ]

@@ -3652,9 +3647,9 @@ dependencies = [

 [[package]]
 name = "once_cell"
-version = "1.13.0"
+version = "1.16.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18a6dbe30758c9f83eb00cbea4ac95966305f5a7772f3f42ebfc7fc7eddbd8e1"
+checksum = "86f0b0d4bf799edbc74508c1e8bf170ff5f41238e5f8225603ca7caaae2b7860"

 [[package]]
 name = "oorandom"
@@ -3756,7 +3751,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "87f5ec2493a61ac0506c0f4199f99070cbe83857b0337006a30f3e6719b8ef58"
 dependencies = [
 "lock_api",
- "parking_lot_core 0.9.2",
+ "parking_lot_core 0.9.4",
 ]

 [[package]]
@@ -3775,15 +3770,15 @@ dependencies = [

 [[package]]
 name = "parking_lot_core"
-version = "0.9.2"
+version = "0.9.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "995f667a6c822200b0433ac218e05582f0e2efa1b922a3fd2fbaadc5f87bab37"
+checksum = "4dc9e0dc2adc1c69d09143aff38d3d30c5c3f0df0dad82e6d25547af174ebec0"
 dependencies = [
 "cfg-if 1.0.0",
 "libc",
 "redox_syscall",
 "smallvec 1.8.0",
- "windows-sys 0.34.0",
+ "windows-sys 0.42.0",
 ]

 [[package]]
@@ -4059,11 +4054,11 @@ dependencies = [

 [[package]]
 name = "proc-macro2"
-version = "1.0.37"
+version = "1.0.47"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ec757218438d5fda206afc041538b2f6d889286160d649a86a24d37e1235afd1"
+checksum = "5ea3d908b0e36316caf9e9e2c4625cdde190a7e6f440d794667ed17a1855e725"
 dependencies = [
- "unicode-xid",
+ "unicode-ident",
 ]

 [[package]]
@@ -4622,7 +4617,7 @@ dependencies = [
 "serde_json",
 "state",
 "tempfile",
- "time 0.3.14",
+ "time 0.3.17",
 "tokio",
 "tokio-stream",
 "tokio-util 0.7.3",
@@ -4684,7 +4679,7 @@ dependencies = [
 "smallvec 1.8.0",
 "stable-pattern",
 "state",
- "time 0.3.14",
+ "time 0.3.17",
 "tokio",
 "uncased",
 ]
@@ -5165,22 +5160,6 @@ version = "0.4.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "eb703cfe953bccee95685111adeedb76fabe4e97549a58d16f03ea7b9367bb32"

-[[package]]
-name = "sled"
-version = "0.34.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7f96b4737c2ce5987354855aed3797279def4ebf734436c6aa4552cf8e169935"
-dependencies = [
- "crc32fast",
- "crossbeam-epoch",
- "crossbeam-utils",
- "fs2",
- "fxhash",
- "libc",
- "log",
- "parking_lot 0.11.2",
-]
-
 [[package]]
 name = "smallvec"
 version = "0.6.14"
@@ -5198,9 +5177,9 @@ checksum = "f2dd574626839106c320a323308629dcb1acfc96e32a8cba364ddc61ac23ee83"

 [[package]]
 name = "snafu"
-version = "0.7.1"
+version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5177903bf45656592d9eb5c0e22f408fc023aae51dbe2088889b71633ba451f2"
+checksum = "a152ba99b054b22972ee794cf04e5ef572da1229e33b65f3c57abbff0525a454"
 dependencies = [
 "doc-comment",
 "snafu-derive",
@@ -5208,9 +5187,9 @@ dependencies = [

 [[package]]
 name = "snafu-derive"
-version = "0.7.1"
+version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "410b26ed97440d90ced3e2488c868d56a86e2064f5d7d6f417909b286afe25e5"
+checksum = "d5e79cdebbabaebb06a9bdbaedc7f159b410461f63611d4d0e3fb0fab8fed850"
 dependencies = [
 "heck 0.4.0",
 "proc-macro2",
@@ -5239,7 +5218,7 @@ dependencies = [
 [[package]]
 name = "sphinx"
 version = "0.1.0"
-source = "git+https://github.com/nymtech/sphinx?rev=c494250f2a78bed33a618d470792418eee932859#c494250f2a78bed33a618d470792418eee932859"
+source = "git+https://github.com/nymtech/sphinx?rev=e05a1992522ed0afd3c6fcac160313ffc9bb306a#e05a1992522ed0afd3c6fcac160313ffc9bb306a"
 dependencies = [
 "aes 0.7.5",
 "arrayref",
@@ -5597,13 +5576,13 @@ dependencies = [

 [[package]]
 name = "syn"
-version = "1.0.91"
+version = "1.0.104"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b683b2b825c8eef438b77c36a06dc262294da3d5a5813fac20da149241dcd44d"
+checksum = "4ae548ec36cf198c0ef7710d3c230987c2d6d7bd98ad6edc0274462724c585ce"
 dependencies = [
 "proc-macro2",
 "quote",
- "unicode-xid",
+ "unicode-ident",
 ]

 [[package]]
@@ -5692,7 +5671,7 @@ dependencies = [
 "subtle 2.4.1",
 "subtle-encoding",
 "tendermint-proto",
- "time 0.3.14",
+ "time 0.3.17",
 "zeroize",
 ]

@@ -5725,7 +5704,7 @@ dependencies = [
 "serde",
 "serde_bytes",
 "subtle-encoding",
- "time 0.3.14",
+ "time 0.3.17",
 ]

 [[package]]
@@ -5753,7 +5732,7 @@ dependencies = [
 "tendermint-config",
 "tendermint-proto",
 "thiserror",
- "time 0.3.14",
+ "time 0.3.17",
 "tokio",
 "tracing",
 "url",
@@ -5827,22 +5806,31 @@ dependencies = [

 [[package]]
 name = "time"
-version = "0.3.14"
+version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3c3f9a28b618c3a6b9251b6908e9c99e04b9e5c02e6581ccbb67d59c34ef7f9b"
+checksum = "a561bf4617eebd33bca6434b988f39ed798e527f51a1e797d0ee4f61c0a38376"
 dependencies = [
 "itoa 1.0.1",
- "libc",
- "num_threads",
+ "js-sys",
 "serde",
+ "time-core",
 "time-macros",
 ]

 [[package]]
-name = "time-macros"
-version = "0.2.4"
+name = "time-core"
+version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "42657b1a6f4d817cda8e7a0ace261fe0cc946cf3a80314390b22cc61ae080792"
+checksum = "2e153e1f1acaef8acc537e68b44906d2db6436e2b35ac2c6b42640fff91f00fd"
+
+[[package]]
+name = "time-macros"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d967f99f534ca7e495c575c62638eebc2898a8c84c119b89e250477bc4ba16b2"
+dependencies = [
+ "time-core",
+]

 [[package]]
 name = "tinytemplate"
@@ -5856,9 +5844,9 @@ dependencies = [

 [[package]]
 name = "tokio"
-version = "1.21.2"
+version = "1.22.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a9e03c497dc955702ba729190dc4aac6f2a0ce97f913e5b1b5912fc5039d9099"
+checksum = "d76ce4a75fb488c605c54bf610f221cea8b0dafb53333c1a67e8ee199dcd2ae3"
 dependencies = [
 "autocfg 1.1.0",
 "bytes",
@@ -6070,6 +6058,7 @@ dependencies = [
 "nymsphinx-addressing",
 "nymsphinx-types",
 "rand 0.7.3",
+ "thiserror",
 "version-checker",
 ]

@@ -6329,6 +6318,12 @@ version = "0.3.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1a01404663e3db436ed2746d9fefef640d868edae3cceb81c3b8d5732fda678f"

+[[package]]
+name = "unicode-ident"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ceab39d59e4c9499d4e5a8ee0e2735b891bb7308ac83dfb4e80cad195c9f6f3"
+
 [[package]]
 name = "unicode-normalization"
 version = "0.1.9"
@@ -6499,7 +6494,7 @@ dependencies = [
 "rustc_version 0.4.0",
 "rustversion",
 "thiserror",
- "time 0.3.14",
+ "time 0.3.17",
 ]

 [[package]]
@@ -6772,19 +6767,6 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"

-[[package]]
-name = "windows-sys"
-version = "0.34.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5acdd78cb4ba54c0045ac14f62d8f94a03d10047904ae2a40afa1e99d8f70825"
-dependencies = [
- "windows_aarch64_msvc 0.34.0",
- "windows_i686_gnu 0.34.0",
- "windows_i686_msvc 0.34.0",
- "windows_x86_64_gnu 0.34.0",
- "windows_x86_64_msvc 0.34.0",
-]
-
 [[package]]
 name = "windows-sys"
 version = "0.36.1"
@@ -6799,10 +6781,25 @@ dependencies = [
 ]

 [[package]]
-name = "windows_aarch64_msvc"
-version = "0.34.0"
+name = "windows-sys"
+version = "0.42.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "17cffbe740121affb56fad0fc0e421804adf0ae00891205213b5cecd30db881d"
+checksum = "5a3e1820f08b8513f676f7ab6c1f99ff312fb97b553d30ff4dd86f9f15728aa7"
+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc 0.42.0",
+ "windows_i686_gnu 0.42.0",
+ "windows_i686_msvc 0.42.0",
+ "windows_x86_64_gnu 0.42.0",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc 0.42.0",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41d2aa71f6f0cbe00ae5167d90ef3cfe66527d6f613ca78ac8024c3ccab9a19e"

 [[package]]
 name = "windows_aarch64_msvc"
@@ -6811,10 +6808,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9bb8c3fd39ade2d67e9874ac4f3db21f0d710bee00fe7cab16949ec184eeaa47"

 [[package]]
-name = "windows_i686_gnu"
-version = "0.34.0"
+name = "windows_aarch64_msvc"
+version = "0.42.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2564fde759adb79129d9b4f54be42b32c89970c18ebf93124ca8870a498688ed"
+checksum = "dd0f252f5a35cac83d6311b2e795981f5ee6e67eb1f9a7f64eb4500fbc4dcdb4"

 [[package]]
 name = "windows_i686_gnu"
@@ -6823,10 +6820,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "180e6ccf01daf4c426b846dfc66db1fc518f074baa793aa7d9b9aaeffad6a3b6"

 [[package]]
-name = "windows_i686_msvc"
-version = "0.34.0"
+name = "windows_i686_gnu"
+version = "0.42.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9cd9d32ba70453522332c14d38814bceeb747d80b3958676007acadd7e166956"
+checksum = "fbeae19f6716841636c28d695375df17562ca208b2b7d0dc47635a50ae6c5de7"

 [[package]]
 name = "windows_i686_msvc"
@@ -6835,10 +6832,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e2e7917148b2812d1eeafaeb22a97e4813dfa60a3f8f78ebe204bcc88f12f024"

 [[package]]
-name = "windows_x86_64_gnu"
-version = "0.34.0"
+name = "windows_i686_msvc"
+version = "0.42.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cfce6deae227ee8d356d19effc141a509cc503dfd1f850622ec4b0f84428e1f4"
+checksum = "84c12f65daa39dd2babe6e442988fc329d6243fdce47d7d2d155b8d874862246"

 [[package]]
 name = "windows_x86_64_gnu"
@@ -6847,10 +6844,16 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4dcd171b8776c41b97521e5da127a2d86ad280114807d0b2ab1e462bc764d9e1"

 [[package]]
-name = "windows_x86_64_msvc"
-version = "0.34.0"
+name = "windows_x86_64_gnu"
+version = "0.42.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d19538ccc21819d01deaf88d6a17eae6596a12e9aafdbb97916fb49896d89de9"
+checksum = "bf7b1b21b5362cbc318f686150e5bcea75ecedc74dd157d874d754a2ca44b0ed"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09d525d2ba30eeb3297665bd434a54297e4170c7f1a44cad4ef58095b4cd2028"

 [[package]]
 name = "windows_x86_64_msvc"
@@ -6858,6 +6861,12 @@ version = "0.36.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c811ca4a8c853ef420abd8592ba53ddbbac90410fab6903b3e79972a631f7680"

+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40009d85759725a34da6d89a94e63d7bdc50a862acf0dbc7c8e488f1edcb6f5"
+
 [[package]]
 name = "winreg"
 version = "0.10.1"
@@ -7,18 +7,20 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

 [dependencies]
+async-trait = { version = "0.1.58" }
 dirs = "4.0"
+dashmap = "5.4.0"
 futures = "0.3"
 humantime-serde = "1.0"
 log = "0.4"
 rand = { version = "0.7.3", features = ["wasm-bindgen"] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0.89"
-sled = { version = "0.34", optional = true }
 tap = "1.0.1"
 thiserror = "1.0.34"
-tokio = { version = "1.21.2", features = ["time", "macros"]}
 url = { version ="2.2", features = ["serde"] }
+tokio = { version = "1.21.2", features = ["macros"]}
+time = "0.3.17"

 # internal
 config = { path = "../../common/config" }
@@ -38,6 +40,15 @@ task = { path = "../../common/task" }
 version = "0.1.9"
 features = ["time"]

+[target."cfg(not(target_arch = \"wasm32\"))".dependencies.tokio]
+version = "1.21.2"
+features = ["time"]
+
+[target."cfg(not(target_arch = \"wasm32\"))".dependencies.sqlx]
+version = "0.6.2"
+features = ["runtime-tokio-rustls", "sqlite", "macros", "migrate"]
+optional = true
+
 [target."cfg(target_arch = \"wasm32\")".dependencies.wasm-bindgen-futures]
 version = "0.4"

@@ -52,15 +63,23 @@ rev = "b9d1a54ad514c2f230a026afe0dde341e98cd7b6"
 version = "0.2.4"
 features = ["futures"]

-#[target."cfg(not(target_arch = \"wasm32\"))".dependencies.task]
-#path = "../../common/task"
+[target."cfg(target_arch = \"wasm32\")".dependencies.wasm-utils]
+path = "../../common/wasm-utils"
+
+[target."cfg(target_arch = \"wasm32\")".dependencies.time]
+version = "0.3.17"
+features = ["wasm-bindgen"]

 [dev-dependencies]
 tempfile = "3.1.0"

+[build-dependencies]
+tokio = { version = "1.21.2", features = ["rt-multi-thread", "macros"] }
+sqlx = { version = "0.6.2", features = ["runtime-tokio-rustls", "sqlite", "macros", "migrate"] }
+
 [features]
-default = ["reply-surb"]
+default = []
+fs-surb-storage = ["sqlx"]
 wasm = ["gateway-client/wasm"]
 coconut = ["gateway-client/coconut", "gateway-requests/coconut"]
-reply-surb = ["sled"]

@@ -0,0 +1,31 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+#[tokio::main]
+async fn main() {
+    #[cfg(feature = "fs-surb-storage")]
+    {
+        use sqlx::{Connection, SqliteConnection};
+        use std::env;
+
+        let out_dir = env::var("OUT_DIR").unwrap();
+        let database_path = format!("{}/fs-surbs-example.sqlite", out_dir);
+
+        let mut conn = SqliteConnection::connect(&format!("sqlite://{}?mode=rwc", database_path))
+            .await
+            .expect("Failed to create SQLx database connection");
+
+        sqlx::migrate!("./fs_surbs_migrations")
+            .run(&mut conn)
+            .await
+            .expect("Failed to perform SQLx migrations");
+
+        #[cfg(target_family = "unix")]
+        println!("cargo:rustc-env=DATABASE_URL=sqlite://{}", &database_path);
+
+        #[cfg(target_family = "windows")]
+        // for some strange reason we need to add a leading `/` to the windows path even though it's
+        // not a valid windows path... but hey, it works...
+        println!("cargo:rustc-env=DATABASE_URL=sqlite:///{}", &database_path);
+    }
+}
@@ -0,0 +1,40 @@
+CREATE TABLE status
+(
+    flush_in_progress        INTEGER NOT NULL,
+    previous_flush_timestamp INTEGER NOT NULL,
+    client_in_use            INTEGER NOT NULL
+);
+
+CREATE TABLE reply_surb_storage_metadata
+(
+    min_reply_surb_threshold INTEGER NOT NULL,
+    max_reply_surb_threshold INTEGER NOT NULL
+);
+
+CREATE TABLE sender_tag
+(
+    recipient BLOB NOT NULL UNIQUE,
+    tag       BLOB NOT NULL UNIQUE
+);
+
+CREATE TABLE reply_key
+(
+    key_digest        BLOB    NOT NULL UNIQUE,
+    reply_key         BLOB    NOT NULL UNIQUE,
+    sent_at_timestamp INTEGER NOT NULL
+);
+
+CREATE TABLE reply_surb_sender
+(
+    id                  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
+    last_sent_timestamp INTEGER NOT NULL,
+    tag                 BLOB    NOT NULL UNIQUE
+);
+
+CREATE TABLE reply_surb
+(
+    reply_surb_sender_id INTEGER NOT NULL,
+    reply_surb           BLOB    NOT NULL,
+
+    FOREIGN KEY (reply_surb_sender_id) REFERENCES reply_surb_sender (id)
+);
@@ -10,13 +10,19 @@ use crate::client::real_messages_control::RealMessagesController;
 use crate::client::received_buffer::{
    ReceivedBufferRequestReceiver, ReceivedBufferRequestSender, ReceivedMessagesBufferController,
 };
+use crate::client::replies::reply_controller;
+use crate::client::replies::reply_controller::{ReplyControllerReceiver, ReplyControllerSender};
+use crate::client::replies::reply_storage::{
+    CombinedReplyStorage, PersistentReplyStorage, ReplyStorageBackend, SentReplyKeys,
+};
 use crate::client::topology_control::{
    TopologyAccessor, TopologyRefresher, TopologyRefresherConfig,
 };
 use crate::config::{Config, DebugConfig, GatewayEndpointConfig};
 use crate::error::ClientCoreError;
+use crate::spawn_future;
 use client_connections::{ConnectionCommandReceiver, ConnectionCommandSender, LaneQueueLengths};
-use crypto::asymmetric::identity;
+use crypto::asymmetric::{encryption, identity};
 use futures::channel::mpsc;
 use gateway_client::bandwidth::BandwidthController;
 use gateway_client::{
@@ -24,18 +30,17 @@ use gateway_client::{
    MixnetMessageSender,
 };
 use log::{debug, info};
+use nymsphinx::acknowledgements::AckKey;
 use nymsphinx::addressing::clients::Recipient;
 use nymsphinx::addressing::nodes::NodeIdentity;
-#[cfg(feature = "reply-surb")]
-use std::path::PathBuf;
+use std::sync::Arc;
+use std::time::Duration;
 use tap::TapFallible;
 use task::{ShutdownListener, ShutdownNotifier};
 use url::Url;

-// it's fine to do this disgusting compilation flag business here as this problem
-// is going to go away in 1.2.0
-#[cfg(feature = "reply-surb")]
-use crate::client::reply_key_storage::ReplyKeyStorage;
+#[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+pub mod non_wasm_helpers;

 pub struct ClientInput {
    pub shared_lane_queue_lengths: LaneQueueLengths,
@@ -75,35 +80,36 @@ impl ClientOutputStatus {
    }
 }

-pub struct BaseClientBuilder<'a> {
+pub struct BaseClientBuilder<'a, B> {
    // due to wasm limitations I had to split it like this : (
    gateway_config: &'a GatewayEndpointConfig,
    debug_config: &'a DebugConfig,
    disabled_credentials: bool,
    validator_api_endpoints: Vec<Url>,
-
-    #[cfg(feature = "reply-surb")]
-    reply_surb_keys_store_path: PathBuf,
+    reply_storage_backend: B,

    bandwidth_controller: Option<BandwidthController>,
    key_manager: KeyManager,
 }

-impl<'a> BaseClientBuilder<'a> {
+impl<'a, B> BaseClientBuilder<'a, B>
+where
+    B: ReplyStorageBackend + Send + Sync + 'static,
+{
    pub fn new_from_base_config<T>(
        base_config: &'a Config<T>,
        key_manager: KeyManager,
        bandwidth_controller: Option<BandwidthController>,
-    ) -> BaseClientBuilder<'a> {
+        reply_storage_backend: B,
+    ) -> BaseClientBuilder<'a, B> {
        BaseClientBuilder {
            gateway_config: base_config.get_gateway_endpoint_config(),
            debug_config: base_config.get_debug_config(),
            disabled_credentials: base_config.get_disabled_credentials_mode(),
            validator_api_endpoints: base_config.get_validator_api_endpoints(),
            bandwidth_controller,
+            reply_storage_backend,
            key_manager,
-            #[cfg(feature = "reply-surb")]
-            reply_surb_keys_store_path: base_config.get_reply_encryption_key_store_path(),
        }
    }

@@ -112,19 +118,18 @@ impl<'a> BaseClientBuilder<'a> {
        debug_config: &'a DebugConfig,
        key_manager: KeyManager,
        bandwidth_controller: Option<BandwidthController>,
+        reply_storage_backend: B,
        disabled_credentials: bool,
        validator_api_endpoints: Vec<Url>,
-        #[cfg(feature = "reply-surb")] reply_surb_keys_store_path: PathBuf,
-    ) -> BaseClientBuilder<'a> {
+    ) -> BaseClientBuilder<'a, B> {
        BaseClientBuilder {
            gateway_config,
            debug_config,
            disabled_credentials,
            validator_api_endpoints,
            bandwidth_controller,
+            reply_storage_backend,
            key_manager,
-            #[cfg(feature = "reply-surb")]
-            reply_surb_keys_store_path,
        }
    }

@@ -141,7 +146,9 @@ impl<'a> BaseClientBuilder<'a> {
    // future constantly pumping loop cover traffic at some specified average rate
    // the pumped traffic goes to the MixTrafficController
    fn start_cover_traffic_stream(
-        &self,
+        debug_config: &DebugConfig,
+        ack_key: Arc<AckKey>,
+        self_address: Recipient,
        topology_accessor: TopologyAccessor,
        mix_tx: BatchMixMessageSender,
        shutdown: ShutdownListener,
@@ -149,16 +156,16 @@ impl<'a> BaseClientBuilder<'a> {
        info!("Starting loop cover traffic stream...");

        let mut stream = LoopCoverTrafficStream::new(
-            self.key_manager.ack_key(),
-            self.debug_config.average_ack_delay,
-            self.debug_config.average_packet_delay,
-            self.debug_config.loop_cover_traffic_average_delay,
+            ack_key,
+            debug_config.average_ack_delay,
+            debug_config.average_packet_delay,
+            debug_config.loop_cover_traffic_average_delay,
            mix_tx,
-            self.as_mix_recipient(),
+            self_address,
            topology_accessor,
        );

-        if let Some(size) = self.debug_config.use_extended_packet_size {
+        if let Some(size) = debug_config.use_extended_packet_size {
            log::debug!("Setting extended packet size: {:?}", size);
            stream.set_custom_packet_size(size.into());
        }
@@ -168,32 +175,18 @@ impl<'a> BaseClientBuilder<'a> {

    #[allow(clippy::too_many_arguments)]
    fn start_real_traffic_controller(
-        &self,
+        controller_config: real_messages_control::Config,
        topology_accessor: TopologyAccessor,
        ack_receiver: AcknowledgementReceiver,
        input_receiver: InputMessageReceiver,
        mix_sender: BatchMixMessageSender,
+        reply_storage: CombinedReplyStorage,
+        reply_controller_sender: ReplyControllerSender,
+        reply_controller_receiver: ReplyControllerReceiver,
        lane_queue_lengths: LaneQueueLengths,
        client_connection_rx: ConnectionCommandReceiver,
        shutdown: ShutdownListener,
-        #[cfg(feature = "reply-surb")] reply_key_storage: ReplyKeyStorage,
    ) {
-        let mut controller_config = real_messages_control::Config::new(
-            self.key_manager.ack_key(),
-            self.debug_config.ack_wait_multiplier,
-            self.debug_config.ack_wait_addition,
-            self.debug_config.average_ack_delay,
-            self.debug_config.message_sending_average_delay,
-            self.debug_config.average_packet_delay,
-            self.debug_config.disable_main_poisson_packet_distribution,
-            self.as_mix_recipient(),
-        );
-
-        if let Some(size) = self.debug_config.use_extended_packet_size {
-            log::debug!("Setting extended packet size: {:?}", size);
-            controller_config.set_custom_packet_size(size.into());
-        }
-
        info!("Starting real traffic stream...");

        RealMessagesController::new(
@@ -202,10 +195,11 @@ impl<'a> BaseClientBuilder<'a> {
            input_receiver,
            mix_sender,
            topology_accessor,
+            reply_storage,
+            reply_controller_sender,
+            reply_controller_receiver,
            lane_queue_lengths,
            client_connection_rx,
-            #[cfg(feature = "reply-surb")]
-            reply_key_storage,
        )
        .start_with_shutdown(shutdown);
    }
@@ -213,19 +207,20 @@ impl<'a> BaseClientBuilder<'a> {
    // buffer controlling all messages fetched from provider
    // required so that other components would be able to use them (say the websocket)
    fn start_received_messages_buffer_controller(
-        &self,
+        local_encryption_keypair: Arc<encryption::KeyPair>,
        query_receiver: ReceivedBufferRequestReceiver,
        mixnet_receiver: MixnetMessageReceiver,
+        reply_key_storage: SentReplyKeys,
+        reply_controller_sender: ReplyControllerSender,
        shutdown: ShutdownListener,
-        #[cfg(feature = "reply-surb")] reply_key_storage: ReplyKeyStorage,
    ) {
        info!("Starting received messages buffer controller...");
        ReceivedMessagesBufferController::new(
-            self.key_manager.encryption_keypair(),
+            local_encryption_keypair,
            query_receiver,
            mixnet_receiver,
-            #[cfg(feature = "reply-surb")]
            reply_key_storage,
+            reply_controller_sender,
        )
        .start_with_shutdown(shutdown)
    }
@@ -235,7 +230,7 @@ impl<'a> BaseClientBuilder<'a> {
        mixnet_message_sender: MixnetMessageSender,
        ack_sender: AcknowledgementSender,
        shutdown: ShutdownListener,
-    ) -> Result<GatewayClient, ClientCoreError> {
+    ) -> Result<GatewayClient, ClientCoreError<B>> {
        let gateway_id = self.gateway_config.gateway_id.clone();
        if gateway_id.is_empty() {
            return Err(ClientCoreError::GatewayIdUnknown);
@@ -286,13 +281,14 @@ impl<'a> BaseClientBuilder<'a> {
    // future responsible for periodically polling directory server and updating
    // the current global view of topology
    async fn start_topology_refresher(
-        &mut self,
+        validator_api_urls: Vec<Url>,
+        refresh_rate: Duration,
        topology_accessor: TopologyAccessor,
        shutdown: ShutdownListener,
-    ) -> Result<(), ClientCoreError> {
+    ) -> Result<(), ClientCoreError<B>> {
        let topology_refresher_config = TopologyRefresherConfig::new(
-            self.validator_api_endpoints.clone(),
-            self.debug_config.topology_refresh_rate,
+            validator_api_urls,
+            refresh_rate,
            env!("CARGO_PKG_VERSION").to_string(),
        );
        let mut topology_refresher =
@@ -302,13 +298,12 @@ impl<'a> BaseClientBuilder<'a> {
        info!("Obtaining initial network topology");
        topology_refresher.refresh().await;

-        // TODO: a slightly more graceful termination here
-        if !topology_refresher.is_topology_routable().await {
+        if let Err(err) = topology_refresher.ensure_topology_is_routable().await {
            log::error!(
                "The current network topology seem to be insufficient to route any packets through \
-                - check if enough nodes and a gateway are online"
+                - check if enough nodes and a gateway are online - source: {err}"
            );
-            return Err(ClientCoreError::InsufficientNetworkTopology);
+            return Err(ClientCoreError::InsufficientNetworkTopology(err));
        }

        info!("Starting topology refresher...");
@@ -330,7 +325,27 @@ impl<'a> BaseClientBuilder<'a> {
        mix_tx
    }

-    pub async fn start_base(mut self) -> Result<BaseClient, ClientCoreError> {
+    async fn setup_persistent_reply_storage(
+        backend: B,
+        shutdown: ShutdownListener,
+    ) -> Result<CombinedReplyStorage, ClientCoreError<B>> {
+        let persistent_storage = PersistentReplyStorage::new(backend);
+        let mem_store = persistent_storage
+            .load_state_from_backend()
+            .await
+            .map_err(|err| ClientCoreError::SurbStorageError { source: err })?;
+
+        let store_clone = mem_store.clone();
+        spawn_future(async move {
+            persistent_storage
+                .flush_on_shutdown(store_clone, shutdown)
+                .await
+        });
+
+        Ok(mem_store)
+    }
+
+    pub async fn start_base(mut self) -> Result<BaseClient, ClientCoreError<B>> {
        info!("Starting nym client");
        // channels for inter-component communication
        // TODO: make the channels be internally created by the relevant components
@@ -351,32 +366,42 @@ impl<'a> BaseClientBuilder<'a> {
        let (ack_sender, ack_receiver) = mpsc::unbounded();
        let shared_topology_accessor = TopologyAccessor::new();

-        #[cfg(feature = "reply-surb")]
-        let reply_key_storage =
-            ReplyKeyStorage::load(&self.reply_surb_keys_store_path).tap_err(|err| {
-                log::error!("Failed to load reply key storage - is it perhaps already in use?");
-                log::error!("{:?}", err);
-            })?;
-
        // Shutdown notifier for signalling tasks to stop
        let shutdown = ShutdownNotifier::default();

+        // channels responsible for dealing with reply-related fun
+        let (reply_controller_sender, reply_controller_receiver) =
+            reply_controller::new_control_channels();
+
+        let self_address = self.as_mix_recipient();
+
        // the components are started in very specific order. Unless you know what you are doing,
        // do not change that.
-        self.start_topology_refresher(shared_topology_accessor.clone(), shutdown.subscribe())
-            .await?;
-        self.start_received_messages_buffer_controller(
-            received_buffer_request_receiver,
-            mixnet_messages_receiver,
-            shutdown.subscribe(),
-            #[cfg(feature = "reply-surb")]
-            reply_key_storage.clone(),
-        );
-
        let gateway_client = self
            .start_gateway_client(mixnet_messages_sender, ack_sender, shutdown.subscribe())
            .await?;

+        let reply_storage =
+            Self::setup_persistent_reply_storage(self.reply_storage_backend, shutdown.subscribe())
+                .await?;
+
+        Self::start_topology_refresher(
+            self.validator_api_endpoints.clone(),
+            self.debug_config.topology_refresh_rate,
+            shared_topology_accessor.clone(),
+            shutdown.subscribe(),
+        )
+        .await?;
+
+        Self::start_received_messages_buffer_controller(
+            self.key_manager.encryption_keypair(),
+            received_buffer_request_receiver,
+            mixnet_messages_receiver,
+            reply_storage.key_storage(),
+            reply_controller_sender.clone(),
+            shutdown.subscribe(),
+        );
+
        // The sphinx_message_sender is the transmitter for any component generating sphinx packets
        // that are to be sent to the mixnet. They are used by cover traffic stream and real
        // traffic stream.
@@ -392,20 +417,36 @@ impl<'a> BaseClientBuilder<'a> {
        // primarily to throttle incoming connections (e.g socks5 for attached network-requesters)
        let shared_lane_queue_lengths = LaneQueueLengths::new();

-        self.start_real_traffic_controller(
+        let mut controller_config = real_messages_control::Config::new(
+            self.debug_config,
+            self.key_manager.ack_key(),
+            self_address,
+        );
+
+        if let Some(size) = self.debug_config.use_extended_packet_size {
+            log::debug!("Setting extended packet size: {:?}", size);
+            controller_config.set_custom_packet_size(size.into());
+        }
+
+        Self::start_real_traffic_controller(
+            controller_config,
            shared_topology_accessor.clone(),
            ack_receiver,
            input_receiver,
            sphinx_message_sender.clone(),
+            reply_storage,
+            reply_controller_sender,
+            reply_controller_receiver,
            shared_lane_queue_lengths.clone(),
            client_connection_rx,
            shutdown.subscribe(),
-            #[cfg(feature = "reply-surb")]
-            reply_key_storage,
        );

        if !self.debug_config.disable_loop_cover_traffic_stream {
-            self.start_cover_traffic_stream(
+            Self::start_cover_traffic_stream(
+                self.debug_config,
+                self.key_manager.ack_key(),
+                self_address,
                shared_topology_accessor,
                sphinx_message_sender,
                shutdown.subscribe(),
@@ -413,7 +454,7 @@ impl<'a> BaseClientBuilder<'a> {
        }

        debug!("Core client startup finished!");
-        debug!("The address of this client is: {}", self.as_mix_recipient());
+        debug!("The address of this client is: {self_address}");

        Ok(BaseClient {
            client_input: ClientInputStatus::AwaitingProducer {
@@ -0,0 +1,51 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::replies::reply_storage::{
+    fs_backend, CombinedReplyStorage, ReplyStorageBackend,
+};
+use crate::config::DebugConfig;
+use crate::error::ClientCoreError;
+use log::{error, info};
+use std::path::Path;
+
+pub async fn setup_fs_reply_surb_backend<P: AsRef<Path>>(
+    db_path: P,
+    debug_config: &DebugConfig,
+) -> Result<fs_backend::Backend, ClientCoreError<fs_backend::Backend>> {
+    // if the database file doesnt exist, initialise fresh storage, otherwise attempt to load the existing one
+    let db_path = db_path.as_ref();
+    if db_path.exists() {
+        info!("loading existing surb database");
+        match fs_backend::Backend::try_load(db_path).await {
+            Ok(backend) => Ok(backend),
+            Err(err) => {
+                error!("failed to setup persistent storage backend for our reply needs: {err}");
+                Err(ClientCoreError::SurbStorageError { source: err })
+            }
+        }
+    } else {
+        info!("creating fresh surb database");
+        let mut storage_backend = match fs_backend::Backend::init(db_path).await {
+            Ok(backend) => backend,
+            Err(err) => {
+                error!("failed to setup persistent storage backend for our reply needs: {err}");
+                return Err(ClientCoreError::SurbStorageError { source: err });
+            }
+        };
+
+        // while I kinda hate that we're going to be creating `CombinedReplyStorage` twice,
+        // it will only be happening on the very first run and in practice won't incur huge
+        // costs since the storage is going to be empty
+        let mem_store = CombinedReplyStorage::new(
+            debug_config.minimum_reply_surb_storage_threshold,
+            debug_config.maximum_reply_surb_storage_threshold,
+        );
+        storage_backend
+            .init_fresh(&mem_store)
+            .await
+            .map_err(|err| ClientCoreError::SurbStorageError { source: err })?;
+
+        Ok(storage_backend)
+    }
+}
@@ -161,15 +161,16 @@ impl LoopCoverTrafficStream<OsRng> {
        // poisson delay, but is it really a problem?
        let topology_permit = self.topology_access.get_read_permit().await;
        // the ack is sent back to ourselves (and then ignored)
-        let topology_ref_option = topology_permit.try_get_valid_topology_ref(
+        let topology_ref = match topology_permit.try_get_valid_topology_ref(
            &self.our_full_destination,
            Some(&self.our_full_destination),
-        );
-        if topology_ref_option.is_none() {
-            warn!("No valid topology detected - won't send any loop cover message this time");
-            return;
-        }
-        let topology_ref = topology_ref_option.unwrap();
+        ) {
+            Ok(topology) => topology,
+            Err(err) => {
+                warn!("We're not going to send any loop cover message this time, as the current topology seem to be invalid - {err}");
+                return;
+            }
+        };

        let cover_message = generate_loop_cover_packet(
            &mut self.rng,
@@ -241,19 +242,4 @@ impl LoopCoverTrafficStream<OsRng> {
            log::debug!("LoopCoverTrafficStream: Exiting");
        })
    }
-
-    pub fn start(mut self) {
-        // we should set initial delay only when we actually start the stream
-        let sampled =
-            sample_poisson_duration(&mut self.rng, self.average_cover_message_sending_delay);
-        self.set_next_delay(sampled);
-
-        spawn_future(async move {
-            debug!("Started LoopCoverTrafficStream without graceful shutdown support");
-
-            while self.next().await.is_some() {
-                self.on_new_message().await;
-            }
-        })
-    }
 }
@@ -1,40 +1,80 @@
 use client_connections::TransmissionLane;
 use nymsphinx::addressing::clients::Recipient;
-use nymsphinx::anonymous_replies::ReplySurb;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;

 pub type InputMessageSender = tokio::sync::mpsc::Sender<InputMessage>;
 pub type InputMessageReceiver = tokio::sync::mpsc::Receiver<InputMessage>;

 #[derive(Debug)]
 pub enum InputMessage {
-    Fresh {
+    /// The simplest message variant where no additional information is attached.
+    /// You're simply sending your `data` to specified `recipient` without any tagging.
+    ///
+    /// Ends up with `NymMessage::Plain` variant
+    Regular {
        recipient: Recipient,
        data: Vec<u8>,
-        with_reply_surb: bool,
        lane: TransmissionLane,
    },
-    Reply {
-        reply_surb: ReplySurb,
+
+    /// Creates a message used for a duplex anonymous communication where the recipient
+    /// will never learn of our true identity. This is achieved by carefully sending `reply_surbs`.
+    ///
+    /// Note that if reply_surbs is set to zero then
+    /// this variant requires the client having sent some reply_surbs in the past
+    /// (and thus the recipient also knowing our sender tag).
+    ///
+    /// Ends up with `NymMessage::Repliable` variant
+    Anonymous {
+        recipient: Recipient,
        data: Vec<u8>,
+        reply_surbs: u32,
+        lane: TransmissionLane,
+    },
+
+    /// Attempt to use our internally received and stored `ReplySurb` to send the message back
+    /// to specified recipient whilst not knowing its full identity (or even gateway).
+    ///
+    /// Ends up with `NymMessage::Reply` variant
+    Reply {
+        recipient_tag: AnonymousSenderTag,
+        data: Vec<u8>,
+        lane: TransmissionLane,
    },
 }

 impl InputMessage {
-    pub fn new_fresh(
-        recipient: Recipient,
-        data: Vec<u8>,
-        with_reply_surb: bool,
-        lane: TransmissionLane,
-    ) -> Self {
-        InputMessage::Fresh {
+    pub fn new_regular(recipient: Recipient, data: Vec<u8>, lane: TransmissionLane) -> Self {
+        InputMessage::Regular {
            recipient,
            data,
-            with_reply_surb,
            lane,
        }
    }

-    pub fn new_reply(reply_surb: ReplySurb, data: Vec<u8>) -> Self {
-        InputMessage::Reply { reply_surb, data }
+    pub fn new_anonymous(
+        recipient: Recipient,
+        data: Vec<u8>,
+        reply_surbs: u32,
+        lane: TransmissionLane,
+    ) -> Self {
+        InputMessage::Anonymous {
+            recipient,
+            data,
+            reply_surbs,
+            lane,
+        }
+    }
+
+    pub fn new_reply(
+        recipient_tag: AnonymousSenderTag,
+        data: Vec<u8>,
+        lane: TransmissionLane,
+    ) -> Self {
+        InputMessage::Reply {
+            recipient_tag,
+            data,
+            lane,
+        }
    }
 }
@@ -91,14 +91,4 @@ impl MixTrafficController {
            log::debug!("MixTrafficController: Exiting");
        })
    }
-
-    pub fn start(mut self) {
-        spawn_future(async move {
-            debug!("Started MixTrafficController without graceful shutdown support");
-
-            while let Some(mix_packets) = self.mix_rx.recv().await {
-                self.on_messages(mix_packets).await;
-            }
-        })
-    }
 }
@@ -8,6 +8,5 @@ pub mod key_manager;
 pub mod mix_traffic;
 pub mod real_messages_control;
 pub mod received_buffer;
-#[cfg(feature = "reply-surb")]
-pub mod reply_key_storage;
+pub mod replies;
 pub mod topology_control;
@@ -1,7 +1,7 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-use super::action_controller::{Action, ActionSender};
+use super::action_controller::{AckActionSender, Action};
 use futures::StreamExt;
 use gateway_client::AcknowledgementReceiver;
 use log::*;
@@ -16,14 +16,14 @@ use std::sync::Arc;
 pub(super) struct AcknowledgementListener {
    ack_key: Arc<AckKey>,
    ack_receiver: AcknowledgementReceiver,
-    action_sender: ActionSender,
+    action_sender: AckActionSender,
 }

 impl AcknowledgementListener {
    pub(super) fn new(
        ack_key: Arc<AckKey>,
        ack_receiver: AcknowledgementReceiver,
-        action_sender: ActionSender,
+        action_sender: AckActionSender,
    ) -> Self {
        AcknowledgementListener {
            ack_key,
@@ -49,11 +49,6 @@ impl AcknowledgementListener {
        if frag_id == COVER_FRAG_ID {
            trace!("Received an ack for a cover message - no need to do anything");
            return;
-        } else if frag_id.is_reply() {
-            info!("Received an ack for a reply message - no need to do anything! (don't know what to do!)");
-            // TODO: probably there will need to be some extra procedure here, something to notify
-            // user that his reply reached the recipient (since we got an ack)
-            return;
        }

        trace!("Received {} from the mix network", frag_id);
@@ -90,14 +85,4 @@ impl AcknowledgementListener {
        shutdown.recv_timeout().await;
        log::debug!("AcknowledgementListener: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    pub(super) async fn run(&mut self) {
-        debug!("Started AcknowledgementListener without graceful shutdown support");
-
-        while let Some(acks) = self.ack_receiver.next().await {
-            self.handle_ack_receiver_item(acks).await
-        }
-    }
 }
@@ -3,7 +3,7 @@

 use super::PendingAcknowledgement;
 use crate::client::real_messages_control::acknowledgement_control::RetransmissionRequestSender;
-use futures::channel::mpsc::{self, UnboundedReceiver, UnboundedSender};
+use futures::channel::mpsc;
 use futures::StreamExt;
 use log::*;
 use nonexhaustive_delayqueue::{Expired, NonExhaustiveDelayQueue, QueueKey};
@@ -13,7 +13,8 @@ use std::collections::HashMap;
 use std::sync::Arc;
 use std::time::Duration;

-pub(crate) type ActionSender = UnboundedSender<Action>;
+pub(crate) type AckActionSender = mpsc::UnboundedSender<Action>;
+pub(crate) type AckActionReceiver = mpsc::UnboundedReceiver<Action>;

 // The actual data being sent off as well as potential key to the delay queue
 type PendingAckEntry = (Arc<PendingAcknowledgement>, Option<QueueKey>);
@@ -95,7 +96,7 @@ pub(super) struct ActionController {
    pending_acks_timers: NonExhaustiveDelayQueue<FragmentIdentifier>,

    /// Channel for receiving `Action`s from other modules.
-    incoming_actions: UnboundedReceiver<Action>,
+    incoming_actions: AckActionReceiver,

    /// Channel for notifying `RetransmissionRequestListener` about expired acknowledgements.
    retransmission_sender: RetransmissionRequestSender,
@@ -105,18 +106,15 @@ impl ActionController {
    pub(super) fn new(
        config: Config,
        retransmission_sender: RetransmissionRequestSender,
-    ) -> (Self, ActionSender) {
-        let (sender, receiver) = mpsc::unbounded();
-        (
-            ActionController {
-                config,
-                pending_acks_data: HashMap::new(),
-                pending_acks_timers: NonExhaustiveDelayQueue::new(),
-                incoming_actions: receiver,
-                retransmission_sender,
-            },
-            sender,
-        )
+        incoming_actions: AckActionReceiver,
+    ) -> Self {
+        ActionController {
+            config,
+            pending_acks_data: HashMap::new(),
+            pending_acks_timers: NonExhaustiveDelayQueue::new(),
+            incoming_actions,
+            retransmission_sender,
+        }
    }

    fn handle_insert(&mut self, pending_acks: Vec<PendingAcknowledgement>) {
@@ -138,13 +136,18 @@ impl ActionController {
        trace!("{} is starting its timer", frag_id);

        if let Some((pending_ack_data, queue_key)) = self.pending_acks_data.get_mut(&frag_id) {
-            if queue_key.is_some() {
-                // this branch should be IMPOSSIBLE under ANY condition. It would imply starting
-                // timer TWICE for the SAME PendingAcknowledgement
-                panic!("Tried to start an already started ack timer!")
-            }
-            let timeout = (pending_ack_data.delay.clone() * self.config.ack_wait_multiplier)
-                .to_duration()
+            // the fact that this branch is now POSSIBLE is a sign of a need to refactor this whole
+            // retransmission procedure
+            //
+            // (it can happen as timer is started when ack expires to make sure it's not stuck in memory
+            // and the second instance can be fired when we finally get reply surbs for data we failed to retransmit)
+
+            // if queue_key.is_some() {
+            //     // this branch should be IMPOSSIBLE under ANY condition. It would imply starting
+            //     // timer TWICE for the SAME PendingAcknowledgement
+            //     panic!("Tried to start an already started ack timer!")
+            // }
+            let timeout = (pending_ack_data.delay * self.config.ack_wait_multiplier).to_duration()
                + self.config.ack_wait_addition;

            let new_queue_key = self.pending_acks_timers.insert(frag_id, timeout);
@@ -192,7 +195,8 @@ impl ActionController {
        trace!("{} is updating its delay", frag_id);
        // TODO: is it possible to solve this without either locking or temporarily removing the value?
        if let Some((pending_ack_data, queue_key)) = self.pending_acks_data.remove(&frag_id) {
-            // this Action is triggered by `RetransmissionRequestListener` which held the other potential
+            // this Action is triggered by `RetransmissionRequestListener` (for 'normal' packets)
+            // or `ReplyController` (for 'reply' packets) which held the other potential
            // reference to this Arc. HOWEVER, before the Action was pushed onto the queue, the reference
            // was dropped hence this unwrap is safe.
            let mut inner_data = Arc::try_unwrap(pending_ack_data).unwrap();
@@ -277,17 +281,4 @@ impl ActionController {
            .expect("Task stopped without shutdown called");
        log::debug!("ActionController: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    pub(super) async fn run(&mut self) {
-        debug!("Started ActionController without graceful shutdown support");
-
-        loop {
-            tokio::select! {
-                action = self.incoming_actions.next() => self.process_action(action.unwrap()),
-                expired_ack = self.pending_acks_timers.next() => self.handle_expired_ack_timer(expired_ack.unwrap())
-            }
-        }
-    }
 }
@@ -1,23 +1,14 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-use super::action_controller::{Action, ActionSender};
-use super::PendingAcknowledgement;
-use crate::client::{
-    inbound_messages::{InputMessage, InputMessageReceiver},
-    real_messages_control::real_traffic_stream::{BatchRealMessageSender, RealMessage},
-    topology_control::TopologyAccessor,
-};
+use crate::client::inbound_messages::{InputMessage, InputMessageReceiver};
+use crate::client::real_messages_control::message_handler::MessageHandler;
+use crate::client::replies::reply_controller::ReplyControllerSender;
 use client_connections::TransmissionLane;
 use log::*;
-use nymsphinx::anonymous_replies::ReplySurb;
-use nymsphinx::preparer::MessagePreparer;
-use nymsphinx::{acknowledgements::AckKey, addressing::clients::Recipient};
+use nymsphinx::addressing::clients::Recipient;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
 use rand::{CryptoRng, Rng};
-use std::sync::Arc;
-
-#[cfg(feature = "reply-surb")]
-use crate::client::reply_key_storage::ReplyKeyStorage;

 /// Module responsible for dealing with the received messages: splitting them, creating acknowledgements,
 /// putting everything into sphinx packets, etc.
@@ -26,15 +17,9 @@ pub(super) struct InputMessageListener<R>
 where
    R: CryptoRng + Rng,
 {
-    ack_key: Arc<AckKey>,
-    ack_recipient: Recipient,
    input_receiver: InputMessageReceiver,
-    message_preparer: MessagePreparer<R>,
-    action_sender: ActionSender,
-    real_message_sender: BatchRealMessageSender,
-    topology_access: TopologyAccessor,
-    #[cfg(feature = "reply-surb")]
-    reply_key_storage: ReplyKeyStorage,
+    message_handler: MessageHandler<R>,
+    reply_controller_sender: ReplyControllerSender,
 }

 impl<R> InputMessageListener<R>
@@ -45,153 +30,83 @@ where
    // some considerable refactoring
    #[allow(clippy::too_many_arguments)]
    pub(super) fn new(
-        ack_key: Arc<AckKey>,
-        ack_recipient: Recipient,
        input_receiver: InputMessageReceiver,
-        message_preparer: MessagePreparer<R>,
-        action_sender: ActionSender,
-        real_message_sender: BatchRealMessageSender,
-        topology_access: TopologyAccessor,
-        #[cfg(feature = "reply-surb")] reply_key_storage: ReplyKeyStorage,
+        message_handler: MessageHandler<R>,
+        reply_controller_sender: ReplyControllerSender,
    ) -> Self {
        InputMessageListener {
-            ack_key,
-            ack_recipient,
            input_receiver,
-            message_preparer,
-            action_sender,
-            real_message_sender,
-            topology_access,
-            #[cfg(feature = "reply-surb")]
-            reply_key_storage,
+            message_handler,
+            reply_controller_sender,
        }
    }

-    // we require topology for replies to generate surb_acks
-    async fn handle_reply(&mut self, reply_surb: ReplySurb, data: Vec<u8>) -> Option<RealMessage> {
-        let topology_permit = self.topology_access.get_read_permit().await;
-        let topology = match topology_permit.try_get_valid_topology_ref(&self.ack_recipient, None) {
-            Some(topology_ref) => topology_ref,
-            None => {
-                warn!("Could not process the message - the network topology is invalid");
-                return None;
-            }
-        };
-
-        match self
-            .message_preparer
-            .prepare_reply_for_use(data, reply_surb, topology, &self.ack_key)
-            .await
-        {
-            Ok((mix_packet, reply_id)) => {
-                // TODO: later probably write pending ack here
-                // and deal with them....
-                // ... somehow
-                Some(RealMessage::new(mix_packet, reply_id))
-            }
-            Err(err) => {
-                // TODO: should we have some mechanism to indicate to the user that the `reply_surb`
-                // could be reused since technically it wasn't used up here?
-                warn!("failed to deal with received reply surb - {:?}", err);
-                None
-            }
-        }
+    async fn handle_reply(
+        &mut self,
+        recipient_tag: AnonymousSenderTag,
+        data: Vec<u8>,
+        lane: TransmissionLane,
+    ) {
+        // offload reply handling to the dedicated task
+        self.reply_controller_sender
+            .send_reply(recipient_tag, data, lane)
    }

-    async fn handle_fresh_message(
+    async fn handle_plain_message(
        &mut self,
        recipient: Recipient,
        content: Vec<u8>,
-        with_reply_surb: bool,
-    ) -> Option<Vec<RealMessage>> {
-        log::trace!("handling msg size: {}", content.len());
-        let topology_permit = self.topology_access.get_read_permit().await;
-        let topology = match topology_permit
-            .try_get_valid_topology_ref(&self.ack_recipient, Some(&recipient))
+        lane: TransmissionLane,
+    ) {
+        if let Err(err) = self
+            .message_handler
+            .try_send_plain_message(recipient, content, lane)
+            .await
        {
-            Some(topology_ref) => topology_ref,
-            None => {
-                warn!("Could not process the message - the network topology is invalid");
-                return None;
-            }
-        };
-
-        // split the message, attach optional reply surb
-        let (split_message, reply_key) = self
-            .message_preparer
-            .prepare_and_split_message(content, with_reply_surb, topology)
-            .expect("somehow the topology was invalid after all!");
-
-        #[cfg(feature = "reply-surb")]
-        if let Some(reply_key) = reply_key {
-            self.reply_key_storage
-                .insert_encryption_key(reply_key)
-                .expect("Failed to insert surb reply key to the store!")
+            warn!("failed to send a plain message - {err}")
        }
+    }

-        #[cfg(not(feature = "reply-surb"))]
-        let _reply_key = reply_key;
-
-        // encrypt chunks, put them inside sphinx packets and generate acks
-        let mut pending_acks = Vec::with_capacity(split_message.len());
-        let mut real_messages = Vec::with_capacity(split_message.len());
-        for message_chunk in split_message {
-            // we need to clone it because we need to keep it in memory in case we had to retransmit
-            // it. And then we'd need to recreate entire ACK again.
-            let chunk_clone = message_chunk.clone();
-            let prepared_fragment = self
-                .message_preparer
-                .prepare_chunk_for_sending(chunk_clone, topology, &self.ack_key, &recipient)
-                .unwrap();
-
-            real_messages.push(RealMessage::new(
-                prepared_fragment.mix_packet,
-                message_chunk.fragment_identifier(),
-            ));
-
-            pending_acks.push(PendingAcknowledgement::new(
-                message_chunk,
-                prepared_fragment.total_delay,
-                recipient,
-            ));
+    async fn handle_repliable_message(
+        &mut self,
+        recipient: Recipient,
+        content: Vec<u8>,
+        reply_surbs: u32,
+        lane: TransmissionLane,
+    ) {
+        if let Err(err) = self
+            .message_handler
+            .try_send_message_with_reply_surbs(recipient, content, reply_surbs, lane)
+            .await
+        {
+            warn!("failed to send a repliable message - {err}")
        }
-
-        // tells the controller to put this into the hashmap
-        self.action_sender
-            .unbounded_send(Action::new_insert(pending_acks))
-            .unwrap();
-
-        Some(real_messages)
    }

    async fn on_input_message(&mut self, msg: InputMessage) {
-        let (real_messages, lane) = match msg {
-            InputMessage::Fresh {
+        match msg {
+            InputMessage::Regular {
                recipient,
                data,
-                with_reply_surb,
                lane,
-            } => (
-                self.handle_fresh_message(recipient, data, with_reply_surb)
-                    .await,
+            } => self.handle_plain_message(recipient, data, lane).await,
+            InputMessage::Anonymous {
+                recipient,
+                data,
+                reply_surbs,
                lane,
-            ),
-            InputMessage::Reply { reply_surb, data } => (
-                self.handle_reply(reply_surb, data)
+            } => {
+                self.handle_repliable_message(recipient, data, reply_surbs, lane)
                    .await
-                    .map(|message| vec![message]),
-                TransmissionLane::Reply,
-            ),
+            }
+            InputMessage::Reply {
+                recipient_tag,
+                data,
+                lane,
+            } => {
+                self.handle_reply(recipient_tag, data, lane).await;
+            }
        };
-
-        // there's no point in trying to send nothing
-        if let Some(real_messages) = real_messages {
-            // tells real message sender (with the poisson timer) to send this to the mix network
-            self.real_message_sender
-                .send((real_messages, lane))
-                .await
-                .expect("BatchRealMessageReceiver has stopped receiving!");
-        }
    }

    pub(super) async fn run_with_shutdown(&mut self, mut shutdown: task::ShutdownListener) {
@@ -216,13 +131,4 @@ where
        shutdown.recv_timeout().await;
        log::debug!("InputMessageListener: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    pub(super) async fn run(&mut self) {
-        debug!("Started InputMessageListener without graceful shutdown support");
-        while let Some(input_msg) = self.input_receiver.recv().await {
-            self.on_input_message(input_msg).await;
-        }
-    }
 }
@@ -7,18 +7,20 @@ use self::{
    retransmission_request_listener::RetransmissionRequestListener,
    sent_notification_listener::SentNotificationListener,
 };
-use super::real_traffic_stream::BatchRealMessageSender;
-use crate::client::{inbound_messages::InputMessageReceiver, topology_control::TopologyAccessor};
+use crate::client::inbound_messages::InputMessageReceiver;
+use crate::client::real_messages_control::message_handler::MessageHandler;
+use crate::client::replies::reply_controller::ReplyControllerSender;
 use crate::spawn_future;
+use action_controller::AckActionReceiver;
 use futures::channel::mpsc;
 use gateway_client::AcknowledgementReceiver;
 use log::*;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
 use nymsphinx::params::PacketSize;
 use nymsphinx::{
    acknowledgements::AckKey,
    addressing::clients::Recipient,
    chunking::fragment::{Fragment, FragmentIdentifier},
-    preparer::MessagePreparer,
    Delay as SphinxDelay,
 };
 use rand::{CryptoRng, Rng};
@@ -27,8 +29,7 @@ use std::{
    time::Duration,
 };

-#[cfg(feature = "reply-surb")]
-use crate::client::reply_key_storage::ReplyKeyStorage;
+pub(crate) use action_controller::{AckActionSender, Action};

 mod acknowledgement_listener;
 mod action_controller;
@@ -50,24 +51,64 @@ pub(super) type SentPacketNotificationSender = mpsc::UnboundedSender<FragmentIde
 /// that it is about to be sent to the mix network and its timeout timer should be started.
 type SentPacketNotificationReceiver = mpsc::UnboundedReceiver<FragmentIdentifier>;

+#[derive(Debug)]
+pub(crate) enum PacketDestination {
+    Anonymous {
+        recipient_tag: AnonymousSenderTag,
+        // special flag to indicate whether this was an ack for requesting additional surbs,
+        // in that case we have to do everything we can to get it through, even if it means going
+        // below our stored reply surb threshold
+        extra_surb_request: bool,
+    },
+    KnownRecipient(Box<Recipient>),
+}
+
 /// Structure representing a data `Fragment` that is on-route to the specified `Recipient`
 #[derive(Debug)]
 pub(crate) struct PendingAcknowledgement {
    message_chunk: Fragment,
    delay: SphinxDelay,
-    recipient: Recipient,
+    destination: PacketDestination,
 }

 impl PendingAcknowledgement {
    /// Creates new instance of `PendingAcknowledgement` using the provided data.
-    fn new(message_chunk: Fragment, delay: SphinxDelay, recipient: Recipient) -> Self {
+    pub(crate) fn new_known(
+        message_chunk: Fragment,
+        delay: SphinxDelay,
+        recipient: Recipient,
+    ) -> Self {
        PendingAcknowledgement {
            message_chunk,
            delay,
-            recipient,
+            destination: PacketDestination::KnownRecipient(recipient.into()),
        }
    }

+    pub(crate) fn new_anonymous(
+        message_chunk: Fragment,
+        delay: SphinxDelay,
+        recipient_tag: AnonymousSenderTag,
+        extra_surb_request: bool,
+    ) -> Self {
+        PendingAcknowledgement {
+            message_chunk,
+            delay,
+            destination: PacketDestination::Anonymous {
+                recipient_tag,
+                extra_surb_request,
+            },
+        }
+    }
+
+    pub(crate) fn inner_fragment_identifier(&self) -> FragmentIdentifier {
+        self.message_chunk.fragment_identifier()
+    }
+
+    pub(crate) fn fragment_data(&self) -> Fragment {
+        self.message_chunk.clone()
+    }
+
    fn update_delay(&mut self, new_delay: SphinxDelay) {
        self.delay = new_delay;
    }
@@ -76,10 +117,6 @@ impl PendingAcknowledgement {
 /// AcknowledgementControllerConnectors represents set of channels for communication with
 /// other parts of the system in order to support acknowledgements and retransmission.
 pub(super) struct AcknowledgementControllerConnectors {
-    /// Channel used for forwarding prepared sphinx messages into the poisson sender
-    /// to be sent to the mix network.
-    real_message_sender: BatchRealMessageSender,
-
    /// Channel used for receiving raw messages from a client. The messages need to be put
    /// into sphinx packets first.
    input_receiver: InputMessageReceiver,
@@ -91,20 +128,28 @@ pub(super) struct AcknowledgementControllerConnectors {

    /// Channel used for receiving acknowledgements from the mix network.
    ack_receiver: AcknowledgementReceiver,
+
+    /// Channel used for sending request to `ActionController` to deal with anything ack-related,
+    ack_action_sender: AckActionSender,
+
+    /// Channel used for receiving request by `ActionController` to deal with anything ack-related,
+    ack_action_receiver: AckActionReceiver,
 }

 impl AcknowledgementControllerConnectors {
    pub(super) fn new(
-        real_message_sender: BatchRealMessageSender,
        input_receiver: InputMessageReceiver,
        sent_notifier: SentPacketNotificationReceiver,
        ack_receiver: AcknowledgementReceiver,
+        ack_action_sender: AckActionSender,
+        ack_action_receiver: AckActionReceiver,
    ) -> Self {
        AcknowledgementControllerConnectors {
-            real_message_sender,
            input_receiver,
            sent_notifier,
            ack_receiver,
+            ack_action_sender,
+            ack_action_receiver,
        }
    }
 }
@@ -117,28 +162,15 @@ pub(super) struct Config {
    /// Given ack timeout in the form a * BASE_DELAY + b, it specifies the multiplier `a`
    ack_wait_multiplier: f64,

-    /// Average delay an acknowledgement packet is going to get delayed at a single mixnode.
-    average_ack_delay: Duration,
-
-    /// Average delay a data packet is going to get delayed at a single mixnode.
-    average_packet_delay: Duration,
-
    /// Predefined packet size used for the encapsulated messages.
    packet_size: PacketSize,
 }

 impl Config {
-    pub(super) fn new(
-        ack_wait_addition: Duration,
-        ack_wait_multiplier: f64,
-        average_ack_delay: Duration,
-        average_packet_delay: Duration,
-    ) -> Self {
+    pub(super) fn new(ack_wait_addition: Duration, ack_wait_multiplier: f64) -> Self {
        Config {
            ack_wait_addition,
            ack_wait_multiplier,
-            average_ack_delay,
-            average_packet_delay,
            packet_size: Default::default(),
        }
    }
@@ -162,68 +194,51 @@ where

 impl<R> AcknowledgementController<R>
 where
-    R: 'static + CryptoRng + Rng + Clone + Send,
+    R: 'static + CryptoRng + Rng + Clone + Send + Sync,
 {
-    #[allow(clippy::too_many_arguments)]
    pub(super) fn new(
        config: Config,
-        rng: R,
-        topology_access: TopologyAccessor,
        ack_key: Arc<AckKey>,
-        ack_recipient: Recipient,
        connectors: AcknowledgementControllerConnectors,
-        #[cfg(feature = "reply-surb")] reply_key_storage: ReplyKeyStorage,
+        message_handler: MessageHandler<R>,
+        reply_controller_sender: ReplyControllerSender,
    ) -> Self {
        let (retransmission_tx, retransmission_rx) = mpsc::unbounded();

        let action_config =
            action_controller::Config::new(config.ack_wait_addition, config.ack_wait_multiplier);
-        let (action_controller, action_sender) =
-            ActionController::new(action_config, retransmission_tx);
-
-        let message_preparer = MessagePreparer::new(
-            rng,
-            ack_recipient,
-            config.average_packet_delay,
-            config.average_ack_delay,
-        )
-        .with_custom_real_message_packet_size(config.packet_size);
+        let action_controller = ActionController::new(
+            action_config,
+            retransmission_tx,
+            connectors.ack_action_receiver,
+        );

        // will listen for any acks coming from the network
        let acknowledgement_listener = AcknowledgementListener::new(
            Arc::clone(&ack_key),
            connectors.ack_receiver,
-            action_sender.clone(),
+            connectors.ack_action_sender.clone(),
        );

        // will listen for any new messages from the client
        let input_message_listener = InputMessageListener::new(
-            Arc::clone(&ack_key),
-            ack_recipient,
            connectors.input_receiver,
-            message_preparer.clone(),
-            action_sender.clone(),
-            connectors.real_message_sender.clone(),
-            topology_access.clone(),
-            #[cfg(feature = "reply-surb")]
-            reply_key_storage,
+            message_handler.clone(),
+            reply_controller_sender.clone(),
        );

        // will listen for any ack timeouts and trigger retransmission
        let retransmission_request_listener = RetransmissionRequestListener::new(
-            Arc::clone(&ack_key),
-            ack_recipient,
-            message_preparer,
-            action_sender.clone(),
-            connectors.real_message_sender,
+            connectors.ack_action_sender.clone(),
+            message_handler,
            retransmission_rx,
-            topology_access,
+            reply_controller_sender,
        );

        // will listen for events indicating the packet was sent through the network so that
        // the retransmission timer should be started.
        let sent_notification_listener =
-            SentNotificationListener::new(connectors.sent_notifier, action_sender);
+            SentNotificationListener::new(connectors.sent_notifier, connectors.ack_action_sender);

        AcknowledgementController {
            acknowledgement_listener,
@@ -278,35 +293,4 @@ where
            debug!("The controller has finished execution!");
        });
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    pub(super) fn start(self) {
-        let mut acknowledgement_listener = self.acknowledgement_listener;
-        let mut input_message_listener = self.input_message_listener;
-        let mut retransmission_request_listener = self.retransmission_request_listener;
-        let mut sent_notification_listener = self.sent_notification_listener;
-        let mut action_controller = self.action_controller;
-
-        spawn_future(async move {
-            acknowledgement_listener.run().await;
-            error!("The acknowledgement listener has finished execution!");
-        });
-        spawn_future(async move {
-            input_message_listener.run().await;
-            error!("The input listener has finished execution!");
-        });
-        spawn_future(async move {
-            retransmission_request_listener.run().await;
-            error!("The retransmission request listener has finished execution!");
-        });
-        spawn_future(async move {
-            sent_notification_listener.run().await;
-            error!("The sent notification listener has finished execution!");
-        });
-        spawn_future(async move {
-            action_controller.run().await;
-            error!("The controller has finished execution!");
-        });
-    }
 }
@@ -1,82 +1,101 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

 use super::{
-    action_controller::{Action, ActionSender},
+    action_controller::{AckActionSender, Action},
    PendingAcknowledgement, RetransmissionRequestReceiver,
 };
-use crate::client::{
-    real_messages_control::real_traffic_stream::{BatchRealMessageSender, RealMessage},
-    topology_control::TopologyAccessor,
-};
-
+use crate::client::real_messages_control::acknowledgement_control::PacketDestination;
+use crate::client::real_messages_control::message_handler::{MessageHandler, PreparationError};
+use crate::client::real_messages_control::real_traffic_stream::RealMessage;
+use crate::client::replies::reply_controller::ReplyControllerSender;
 use client_connections::TransmissionLane;
 use futures::StreamExt;
 use log::*;
-use nymsphinx::{
-    acknowledgements::AckKey, addressing::clients::Recipient, preparer::MessagePreparer,
-};
+use nymsphinx::addressing::clients::Recipient;
+use nymsphinx::chunking::fragment::Fragment;
+use nymsphinx::preparer::PreparedFragment;
 use rand::{CryptoRng, Rng};
 use std::sync::{Arc, Weak};

 // responsible for packet retransmission upon fired timer
-pub(super) struct RetransmissionRequestListener<R>
-where
-    R: CryptoRng + Rng,
-{
-    ack_key: Arc<AckKey>,
-    ack_recipient: Recipient,
-    message_preparer: MessagePreparer<R>,
-    action_sender: ActionSender,
-    real_message_sender: BatchRealMessageSender,
+pub(super) struct RetransmissionRequestListener<R> {
+    action_sender: AckActionSender,
+    message_handler: MessageHandler<R>,
    request_receiver: RetransmissionRequestReceiver,
-    topology_access: TopologyAccessor,
+    reply_controller_sender: ReplyControllerSender,
 }

 impl<R> RetransmissionRequestListener<R>
 where
    R: CryptoRng + Rng,
 {
-    #[allow(clippy::too_many_arguments)]
    pub(super) fn new(
-        ack_key: Arc<AckKey>,
-        ack_recipient: Recipient,
-        message_preparer: MessagePreparer<R>,
-        action_sender: ActionSender,
-        real_message_sender: BatchRealMessageSender,
+        action_sender: AckActionSender,
+        message_handler: MessageHandler<R>,
        request_receiver: RetransmissionRequestReceiver,
-        topology_access: TopologyAccessor,
+        reply_controller_sender: ReplyControllerSender,
    ) -> Self {
        RetransmissionRequestListener {
-            ack_key,
-            ack_recipient,
-            message_preparer,
            action_sender,
-            real_message_sender,
+            message_handler,
            request_receiver,
-            topology_access,
+            reply_controller_sender,
        }
    }

-    async fn on_retransmission_request(&mut self, timed_out_ack: Weak<PendingAcknowledgement>) {
-        let timed_out_ack = match timed_out_ack.upgrade() {
+    async fn prepare_normal_retransmission_chunk(
+        &mut self,
+        packet_recipient: Recipient,
+        chunk_data: Fragment,
+    ) -> Result<PreparedFragment, PreparationError> {
+        debug!("retransmitting normal packet...");
+
+        self.message_handler
+            .try_prepare_single_chunk_for_sending(packet_recipient, chunk_data)
+            .await
+    }
+
+    async fn on_retransmission_request(
+        &mut self,
+        weak_timed_out_ack: Weak<PendingAcknowledgement>,
+    ) {
+        let timed_out_ack = match weak_timed_out_ack.upgrade() {
            Some(timed_out_ack) => timed_out_ack,
            None => {
                debug!("We received an ack JUST as we were about to retransmit [1]");
                return;
            }
        };
-        let packet_recipient = &timed_out_ack.recipient;
-        let chunk_clone = timed_out_ack.message_chunk.clone();
-        let frag_id = chunk_clone.fragment_identifier();

-        let topology_permit = self.topology_access.get_read_permit().await;
-        let topology_ref = match topology_permit
-            .try_get_valid_topology_ref(&self.ack_recipient, Some(packet_recipient))
-        {
-            Some(topology_ref) => topology_ref,
-            None => {
-                warn!("Could not retransmit the packet - the network topology is invalid");
+        let maybe_prepared_fragment = match &timed_out_ack.destination {
+            PacketDestination::Anonymous {
+                recipient_tag,
+                extra_surb_request,
+            } => {
+                // if this is retransmission for reply, offload it to the dedicated task
+                // that deals with all the surbs
+                return self.reply_controller_sender.send_retransmission_data(
+                    *recipient_tag,
+                    weak_timed_out_ack,
+                    *extra_surb_request,
+                );
+            }
+            PacketDestination::KnownRecipient(recipient) => {
+                self.prepare_normal_retransmission_chunk(
+                    **recipient,
+                    timed_out_ack.message_chunk.clone(),
+                )
+                .await
+            }
+        };
+
+        let frag_id = timed_out_ack.message_chunk.fragment_identifier();
+
+        let prepared_fragment = match maybe_prepared_fragment {
+            Ok(prepared_fragment) => prepared_fragment,
+            Err(err) => {
+                warn!("Could not retransmit the packet - {err}");
                // we NEED to start timer here otherwise we will have this guy permanently stuck in memory
                self.action_sender
                    .unbounded_send(Action::new_start_timer(frag_id))
@@ -85,11 +104,6 @@ where
            }
        };

-        let prepared_fragment = self
-            .message_preparer
-            .prepare_chunk_for_sending(chunk_clone, topology_ref, &self.ack_key, packet_recipient)
-            .unwrap();
-
        // if we have the ONLY strong reference to the ack data, it means it was removed from the
        // pending acks
        if Arc::strong_count(&timed_out_ack) == 1 {
@@ -101,7 +115,6 @@ where
        // we no longer need the reference - let's drop it so that if somehow `UpdateTimer` action
        // reached the controller before this function terminated, the controller would not panic.
        drop(timed_out_ack);
-
        let new_delay = prepared_fragment.total_delay;

        // We know this update will be reflected by the `StartTimer` Action performed when this
@@ -116,13 +129,12 @@ where
            .unwrap();

        // send to `OutQueueControl` to eventually send to the mix network
-        self.real_message_sender
-            .send((
+        self.message_handler
+            .forward_messages(
                vec![RealMessage::new(prepared_fragment.mix_packet, frag_id)],
                TransmissionLane::Retransmission,
-            ))
+            )
            .await
-            .expect("BatchRealMessageReceiver has stopped receiving!");
    }

    pub(super) async fn run_with_shutdown(&mut self, mut shutdown: task::ShutdownListener) {
@@ -145,14 +157,4 @@ where
        shutdown.recv_timeout().await;
        log::debug!("RetransmissionRequestListener: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    pub(super) async fn run(&mut self) {
-        debug!("Started RetransmissionRequestListener without graceful shutdown support");
-
-        while let Some(timed_out_ack) = self.request_receiver.next().await {
-            self.on_retransmission_request(timed_out_ack).await;
-        }
-    }
 }
@@ -1,7 +1,7 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-use super::action_controller::{Action, ActionSender};
+use super::action_controller::{AckActionSender, Action};
 use super::SentPacketNotificationReceiver;
 use futures::StreamExt;
 use log::*;
@@ -13,13 +13,13 @@ use nymsphinx::chunking::fragment::{FragmentIdentifier, COVER_FRAG_ID};
 /// accidentally fire retransmission way quicker than we should have.
 pub(super) struct SentNotificationListener {
    sent_notifier: SentPacketNotificationReceiver,
-    action_sender: ActionSender,
+    action_sender: AckActionSender,
 }

 impl SentNotificationListener {
    pub(super) fn new(
        sent_notifier: SentPacketNotificationReceiver,
-        action_sender: ActionSender,
+        action_sender: AckActionSender,
    ) -> Self {
        SentNotificationListener {
            sent_notifier,
@@ -31,11 +31,6 @@ impl SentNotificationListener {
        if frag_id == COVER_FRAG_ID {
            trace!("sent off a cover message - no need to start retransmission timer!");
            return;
-        } else if frag_id.is_reply() {
-            debug!("sent off a reply message - no need to start retransmission timer!");
-            // TODO: probably there will need to be some extra procedure here, like it would
-            // be nice to know that our reply actually reached the recipient (i.e. we got the ack)
-            return;
        }
        self.action_sender
            .unbounded_send(Action::new_start_timer(frag_id))
@@ -64,14 +59,4 @@ impl SentNotificationListener {
        assert!(shutdown.is_shutdown_poll());
        log::debug!("SentNotificationListener: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    pub(super) async fn run(&mut self) {
-        debug!("Started SentNotificationListener without graceful shutdown support");
-
-        while let Some(frag_id) = self.sent_notifier.next().await {
-            self.on_sent_message(frag_id).await;
-        }
-    }
 }
@@ -0,0 +1,548 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::real_messages_control::acknowledgement_control::PendingAcknowledgement;
+use crate::client::real_messages_control::real_traffic_stream::{
+    BatchRealMessageSender, RealMessage,
+};
+use crate::client::real_messages_control::{AckActionSender, Action};
+use crate::client::replies::reply_storage::{ReceivedReplySurbsMap, SentReplyKeys, UsedSenderTags};
+use crate::client::topology_control::{TopologyAccessor, TopologyReadPermit};
+use client_connections::TransmissionLane;
+use log::{debug, error, info, trace, warn};
+use nymsphinx::acknowledgements::AckKey;
+use nymsphinx::addressing::clients::Recipient;
+use nymsphinx::anonymous_replies::requests::{AnonymousSenderTag, RepliableMessage, ReplyMessage};
+use nymsphinx::anonymous_replies::{ReplySurb, SurbEncryptionKey};
+use nymsphinx::chunking::fragment::{Fragment, FragmentIdentifier};
+use nymsphinx::message::NymMessage;
+use nymsphinx::params::{PacketSize, DEFAULT_NUM_MIX_HOPS};
+use nymsphinx::preparer::{MessagePreparer, PreparedFragment};
+use nymsphinx::Delay;
+use rand::{CryptoRng, Rng};
+use std::sync::Arc;
+use std::time::Duration;
+use thiserror::Error;
+use topology::{NymTopology, NymTopologyError};
+
+// TODO: move that error elsewhere since it seems to be contaminating different files
+#[derive(Debug, Clone, Error)]
+pub enum PreparationError {
+    #[error(transparent)]
+    NymTopologyError(#[from] NymTopologyError),
+
+    #[error("The received message cannot be sent using a single reply surb. It ended up getting split into {fragments} fragments.")]
+    MessageTooLongForSingleSurb { fragments: usize },
+
+    #[error("Not enough reply SURBs to send the message. We have {available} available and require at least {required}.")]
+    NotEnoughSurbs { available: usize, required: usize },
+}
+
+impl PreparationError {
+    fn return_surbs(self, returned_surbs: Vec<ReplySurb>) -> SurbWrappedPreparationError {
+        SurbWrappedPreparationError {
+            source: self,
+            returned_surbs: Some(returned_surbs),
+        }
+    }
+}
+
+#[derive(Debug, Error)]
+#[error("Failed to prepare packets - {source}. {} reply surbs will be returned", .returned_surbs.as_ref().map(|s| s.len()).unwrap_or_default())]
+pub struct SurbWrappedPreparationError {
+    #[source]
+    source: PreparationError,
+
+    returned_surbs: Option<Vec<ReplySurb>>,
+}
+
+impl<T> From<T> for SurbWrappedPreparationError
+where
+    T: Into<PreparationError>,
+{
+    fn from(err: T) -> Self {
+        SurbWrappedPreparationError {
+            source: err.into(),
+            returned_surbs: None,
+        }
+    }
+}
+
+impl SurbWrappedPreparationError {
+    pub(crate) fn return_unused_surbs(
+        self,
+        surb_storage: &ReceivedReplySurbsMap,
+        target: &AnonymousSenderTag,
+    ) -> PreparationError {
+        if let Some(reply_surbs) = self.returned_surbs {
+            surb_storage.insert_surbs(target, reply_surbs)
+        }
+        self.source
+    }
+}
+
+#[derive(Clone)]
+pub(crate) struct Config {
+    /// Key used to decrypt contents of received SURBAcks
+    ack_key: Arc<AckKey>,
+
+    /// Address of this client which also represent an address to which all acknowledgements
+    /// and surb-based are going to be sent.
+    sender_address: Recipient,
+
+    /// Average delay a data packet is going to get delay at a single mixnode.
+    average_packet_delay: Duration,
+
+    /// Average delay an acknowledgement packet is going to get delay at a single mixnode.
+    average_ack_delay: Duration,
+
+    /// Number of mix hops each packet ('real' message, ack, reply) is expected to take.
+    /// Note that it does not include gateway hops.
+    num_mix_hops: u8,
+
+    /// Predefined packet size used for the encapsulated messages.
+    packet_size: PacketSize,
+}
+
+impl Config {
+    pub fn new(
+        ack_key: Arc<AckKey>,
+        sender_address: Recipient,
+        average_packet_delay: Duration,
+        average_ack_delay: Duration,
+    ) -> Self {
+        Config {
+            ack_key,
+            sender_address,
+            average_packet_delay,
+            average_ack_delay,
+            num_mix_hops: DEFAULT_NUM_MIX_HOPS,
+            packet_size: PacketSize::default(),
+        }
+    }
+
+    /// Allows setting non-default number of expected mix hops in the network.
+    #[allow(dead_code)]
+    pub fn with_mix_hops(mut self, hops: u8) -> Self {
+        self.num_mix_hops = hops;
+        self
+    }
+
+    /// Allows setting non-default size of the sphinx packets sent out.
+    pub fn with_custom_packet_size(mut self, packet_size: PacketSize) -> Self {
+        self.packet_size = packet_size;
+        self
+    }
+}
+
+#[derive(Clone)]
+pub(crate) struct MessageHandler<R> {
+    config: Config,
+    rng: R,
+    message_preparer: MessagePreparer<R>,
+    action_sender: AckActionSender,
+    real_message_sender: BatchRealMessageSender,
+    topology_access: TopologyAccessor,
+    reply_key_storage: SentReplyKeys,
+    tag_storage: UsedSenderTags,
+}
+
+impl<R> MessageHandler<R>
+where
+    R: CryptoRng + Rng,
+{
+    pub(crate) fn new(
+        config: Config,
+        rng: R,
+        action_sender: AckActionSender,
+        real_message_sender: BatchRealMessageSender,
+        topology_access: TopologyAccessor,
+        reply_key_storage: SentReplyKeys,
+        tag_storage: UsedSenderTags,
+    ) -> Self
+    where
+        R: Copy,
+    {
+        let message_preparer = MessagePreparer::new(
+            rng,
+            config.sender_address,
+            config.average_packet_delay,
+            config.average_ack_delay,
+        )
+        .with_custom_real_message_packet_size(config.packet_size)
+        .with_mix_hops(config.num_mix_hops);
+
+        MessageHandler {
+            config,
+            rng,
+            message_preparer,
+            action_sender,
+            real_message_sender,
+            topology_access,
+            reply_key_storage,
+            tag_storage,
+        }
+    }
+
+    fn get_or_create_sender_tag(&mut self, recipient: &Recipient) -> AnonymousSenderTag {
+        if let Some(existing) = self.tag_storage.try_get_existing(recipient) {
+            trace!("we already had sender tag for {recipient}");
+            existing
+        } else {
+            info!("creating new sender tag for {recipient}");
+            let new_tag = AnonymousSenderTag::new_random(&mut self.rng);
+            self.tag_storage.insert_new(recipient, new_tag);
+            info!("we'll be using {new_tag} for all anonymous messages sent to {recipient}");
+            new_tag
+        }
+    }
+
+    fn get_topology<'a>(
+        &self,
+        permit: &'a TopologyReadPermit<'a>,
+    ) -> Result<&'a NymTopology, PreparationError> {
+        match permit.try_get_valid_topology_ref(&self.config.sender_address, None) {
+            Ok(topology_ref) => Ok(topology_ref),
+            Err(err) => {
+                warn!("Could not process the packet - the network topology is invalid - {err}");
+                Err(err.into())
+            }
+        }
+    }
+
+    async fn generate_reply_surbs_with_keys(
+        &mut self,
+        amount: usize,
+    ) -> Result<(Vec<ReplySurb>, Vec<SurbEncryptionKey>), PreparationError> {
+        let topology_permit = self.topology_access.get_read_permit().await;
+        let topology = self.get_topology(&topology_permit)?;
+
+        let reply_surbs = self
+            .message_preparer
+            .generate_reply_surbs(amount, topology)?;
+
+        let reply_keys = reply_surbs
+            .iter()
+            .map(|s| *s.encryption_key())
+            .collect::<Vec<_>>();
+
+        Ok((reply_surbs, reply_keys))
+    }
+
+    pub(crate) async fn try_send_single_surb_message(
+        &mut self,
+        target: AnonymousSenderTag,
+        message: ReplyMessage,
+        reply_surb: ReplySurb,
+        is_extra_surb_request: bool,
+    ) -> Result<(), SurbWrappedPreparationError> {
+        let mut fragment = self
+            .message_preparer
+            .pad_and_split_message(NymMessage::new_reply(message));
+        if fragment.len() > 1 {
+            // well, it's not a single surb message
+            return Err(SurbWrappedPreparationError {
+                source: PreparationError::MessageTooLongForSingleSurb {
+                    fragments: fragment.len(),
+                },
+                returned_surbs: Some(vec![reply_surb]),
+            });
+        }
+
+        let chunk = fragment.pop().unwrap();
+        let chunk_clone = chunk.clone();
+        let prepared_fragment = self
+            .try_prepare_single_reply_chunk_for_sending(reply_surb, chunk_clone)
+            .await?;
+
+        let real_messages =
+            RealMessage::new(prepared_fragment.mix_packet, chunk.fragment_identifier());
+        let delay = prepared_fragment.total_delay;
+        let pending_ack =
+            PendingAcknowledgement::new_anonymous(chunk, delay, target, is_extra_surb_request);
+
+        let lane = if is_extra_surb_request {
+            TransmissionLane::ReplySurbRequest
+        } else {
+            TransmissionLane::General
+        };
+
+        self.forward_messages(vec![real_messages], lane).await;
+        self.insert_pending_acks(vec![pending_ack]);
+        Ok(())
+    }
+
+    pub(crate) async fn try_request_additional_reply_surbs(
+        &mut self,
+        from: AnonymousSenderTag,
+        reply_surb: ReplySurb,
+        amount: u32,
+    ) -> Result<(), SurbWrappedPreparationError> {
+        debug!("requesting {amount} reply SURBs from {from:?}");
+
+        let surbs_request =
+            ReplyMessage::new_surb_request_message(self.config.sender_address, amount);
+        self.try_send_single_surb_message(from, surbs_request, reply_surb, true)
+            .await
+    }
+
+    // // TODO: this will require additional argument to make it use different variant of `ReplyMessage`
+    pub(crate) fn split_reply_message(&mut self, message: Vec<u8>) -> Vec<Fragment> {
+        self.message_preparer
+            .pad_and_split_message(NymMessage::new_reply(ReplyMessage::new_data_message(
+                message,
+            )))
+    }
+
+    // the only difference between this method and `try_send_reply_chunks` is that
+    // here we are not creating acks as acks are already in memory waiting to get cleared.
+    // we are only updating their existing delays
+    pub(crate) async fn try_send_retransmission_reply_chunks(
+        &mut self,
+        fragments: Vec<Fragment>,
+        reply_surbs: Vec<ReplySurb>,
+        lane: TransmissionLane,
+    ) -> Result<(), SurbWrappedPreparationError> {
+        let prepared_fragments = self
+            .prepare_reply_chunks_for_sending(fragments.clone(), reply_surbs)
+            .await?;
+
+        let mut real_messages = Vec::with_capacity(prepared_fragments.len());
+
+        for prepared in prepared_fragments {
+            self.update_ack_delay(prepared.fragment_identifier, prepared.total_delay);
+            real_messages.push(prepared.into())
+        }
+
+        self.forward_messages(real_messages, lane).await;
+        Ok(())
+    }
+
+    pub(crate) async fn try_send_reply_chunks(
+        &mut self,
+        target: AnonymousSenderTag,
+        fragments: Vec<Fragment>,
+        reply_surbs: Vec<ReplySurb>,
+        lane: TransmissionLane,
+    ) -> Result<(), SurbWrappedPreparationError> {
+        let prepared_fragments = self
+            .prepare_reply_chunks_for_sending(fragments.clone(), reply_surbs)
+            .await?;
+
+        let mut pending_acks = Vec::with_capacity(fragments.len());
+        let mut real_messages = Vec::with_capacity(fragments.len());
+
+        for (raw, prepared) in fragments.into_iter().zip(prepared_fragments.into_iter()) {
+            let real_message = RealMessage::new(prepared.mix_packet, prepared.fragment_identifier);
+            let delay = prepared.total_delay;
+            let pending_ack = PendingAcknowledgement::new_anonymous(raw, delay, target, false);
+
+            real_messages.push(real_message);
+            pending_acks.push(pending_ack);
+        }
+
+        self.forward_messages(real_messages, lane).await;
+        self.insert_pending_acks(pending_acks);
+        Ok(())
+    }
+
+    pub(crate) async fn try_send_plain_message(
+        &mut self,
+        recipient: Recipient,
+        message: Vec<u8>,
+        lane: TransmissionLane,
+    ) -> Result<(), PreparationError> {
+        let message = NymMessage::new_plain(message);
+        self.try_split_and_send_non_reply_message(message, recipient, lane)
+            .await
+    }
+
+    pub(crate) async fn try_split_and_send_non_reply_message(
+        &mut self,
+        message: NymMessage,
+        recipient: Recipient,
+        lane: TransmissionLane,
+    ) -> Result<(), PreparationError> {
+        // TODO: I really dislike existence of this assertion, it implies code has to be re-organised
+        debug_assert!(!matches!(message, NymMessage::Reply(_)));
+
+        // TODO2: it's really annoying we have to get topology permit again here due to borrow-checker
+        let topology_permit = self.topology_access.get_read_permit().await;
+        let topology = self.get_topology(&topology_permit)?;
+
+        let fragments = self.message_preparer.pad_and_split_message(message);
+
+        let mut pending_acks = Vec::with_capacity(fragments.len());
+        let mut real_messages = Vec::with_capacity(fragments.len());
+        for fragment in fragments {
+            // we need to clone it because we need to keep it in memory in case we had to retransmit
+            // it. And then we'd need to recreate entire ACK again.
+            let chunk_clone = fragment.clone();
+            let prepared_fragment = self.message_preparer.prepare_chunk_for_sending(
+                chunk_clone,
+                topology,
+                &self.config.ack_key,
+                &recipient,
+            )?;
+
+            let real_message =
+                RealMessage::new(prepared_fragment.mix_packet, fragment.fragment_identifier());
+            let delay = prepared_fragment.total_delay;
+            let pending_ack = PendingAcknowledgement::new_known(fragment, delay, recipient);
+
+            real_messages.push(real_message);
+            pending_acks.push(pending_ack);
+        }
+
+        self.insert_pending_acks(pending_acks);
+        self.forward_messages(real_messages, lane).await;
+
+        Ok(())
+    }
+
+    pub(crate) async fn try_send_additional_reply_surbs(
+        &mut self,
+        recipient: Recipient,
+        amount: u32,
+    ) -> Result<(), PreparationError> {
+        let sender_tag = self.get_or_create_sender_tag(&recipient);
+        let (reply_surbs, reply_keys) =
+            self.generate_reply_surbs_with_keys(amount as usize).await?;
+
+        let message = NymMessage::new_repliable(RepliableMessage::new_additional_surbs(
+            sender_tag,
+            reply_surbs,
+        ));
+
+        self.try_split_and_send_non_reply_message(
+            message,
+            recipient,
+            TransmissionLane::AdditionalReplySurbs,
+        )
+        .await?;
+
+        log::trace!("storing {} reply keys", reply_keys.len());
+        self.reply_key_storage.insert_multiple(reply_keys);
+
+        Ok(())
+    }
+
+    pub(crate) async fn try_send_message_with_reply_surbs(
+        &mut self,
+        recipient: Recipient,
+        message: Vec<u8>,
+        num_reply_surbs: u32,
+        lane: TransmissionLane,
+    ) -> Result<(), SurbWrappedPreparationError> {
+        let sender_tag = self.get_or_create_sender_tag(&recipient);
+        let (reply_surbs, reply_keys) = self
+            .generate_reply_surbs_with_keys(num_reply_surbs as usize)
+            .await?;
+
+        let message =
+            NymMessage::new_repliable(RepliableMessage::new_data(message, sender_tag, reply_surbs));
+
+        self.try_split_and_send_non_reply_message(message, recipient, lane)
+            .await?;
+
+        log::trace!("storing {} reply keys", reply_keys.len());
+        self.reply_key_storage.insert_multiple(reply_keys);
+
+        Ok(())
+    }
+
+    pub(crate) async fn try_prepare_single_chunk_for_sending(
+        &mut self,
+        recipient: Recipient,
+        chunk: Fragment,
+    ) -> Result<PreparedFragment, PreparationError> {
+        let topology_permit = self.topology_access.get_read_permit().await;
+        let topology = self.get_topology(&topology_permit)?;
+
+        let prepared_fragment = self
+            .message_preparer
+            .prepare_chunk_for_sending(chunk, topology, &self.config.ack_key, &recipient)
+            .unwrap();
+
+        Ok(prepared_fragment)
+    }
+
+    async fn prepare_reply_chunks_for_sending(
+        &mut self,
+        fragments: Vec<Fragment>,
+        reply_surbs: Vec<ReplySurb>,
+    ) -> Result<Vec<PreparedFragment>, SurbWrappedPreparationError> {
+        debug_assert_ne!(
+            fragments.len(),
+            reply_surbs.len(),
+            "attempted to send {} fragments with {} reply surbs",
+            fragments.len(),
+            reply_surbs.len()
+        );
+
+        let topology_permit = self.topology_access.get_read_permit().await;
+        let topology = match self.get_topology(&topology_permit) {
+            Ok(topology) => topology,
+            Err(err) => return Err(err.return_surbs(reply_surbs)),
+        };
+
+        Ok(fragments
+            .into_iter()
+            .zip(reply_surbs.into_iter())
+            .map(|(fragment, reply_surb)| {
+                // unwrap here is fine as we know we have a valid topology
+                self.message_preparer
+                    .prepare_reply_chunk_for_sending(
+                        fragment,
+                        topology,
+                        &self.config.ack_key,
+                        reply_surb,
+                    )
+                    .unwrap()
+            })
+            .collect())
+    }
+
+    pub(crate) async fn try_prepare_single_reply_chunk_for_sending(
+        &mut self,
+        reply_surb: ReplySurb,
+        chunk: Fragment,
+    ) -> Result<PreparedFragment, SurbWrappedPreparationError> {
+        let topology_permit = self.topology_access.get_read_permit().await;
+        let topology = match self.get_topology(&topology_permit) {
+            Ok(topology) => topology,
+            Err(err) => return Err(err.return_surbs(vec![reply_surb])),
+        };
+
+        let prepared_fragment = self
+            .message_preparer
+            .prepare_reply_chunk_for_sending(chunk, topology, &self.config.ack_key, reply_surb)
+            .unwrap();
+
+        Ok(prepared_fragment)
+    }
+
+    pub(crate) fn update_ack_delay(&self, id: FragmentIdentifier, new_delay: Delay) {
+        self.action_sender
+            .unbounded_send(Action::UpdateDelay(id, new_delay))
+            .expect("action control task has died")
+    }
+
+    pub(crate) fn insert_pending_acks(&self, pending_acks: Vec<PendingAcknowledgement>) {
+        self.action_sender
+            .unbounded_send(Action::new_insert(pending_acks))
+            .expect("action control task has died")
+    }
+
+    // tells real message sender (with the poisson timer) to send this to the mix network
+    pub(crate) async fn forward_messages(
+        &self,
+        messages: Vec<RealMessage>,
+        transmission_lane: TransmissionLane,
+    ) {
+        self.real_message_sender
+            .send((messages, transmission_lane))
+            .await
+            .expect("real message receiver task (OutQueueControl) has died");
+    }
+}
@@ -8,6 +8,11 @@
 use self::{
    acknowledgement_control::AcknowledgementController, real_traffic_stream::OutQueueControl,
 };
+use crate::client::real_messages_control::message_handler::MessageHandler;
+use crate::client::replies::reply_controller::{
+    ReplyController, ReplyControllerReceiver, ReplyControllerSender,
+};
+use crate::client::replies::reply_storage::CombinedReplyStorage;
 use crate::{
    client::{
        inbound_messages::InputMessageReceiver, mix_traffic::BatchMixMessageSender,
@@ -27,11 +32,13 @@ use rand::{rngs::OsRng, CryptoRng, Rng};
 use std::sync::Arc;
 use std::time::Duration;

-#[cfg(feature = "reply-surb")]
-use crate::client::reply_key_storage::ReplyKeyStorage;
+use crate::client::replies::reply_controller;
+use crate::config;
+pub(crate) use acknowledgement_control::{AckActionSender, Action};

-mod acknowledgement_control;
-mod real_traffic_stream;
+pub(crate) mod acknowledgement_control;
+pub(crate) mod message_handler;
+pub(crate) mod real_traffic_stream;

 // TODO: ack_key and self_recipient shouldn't really be part of this config
 pub struct Config {
@@ -62,31 +69,102 @@ pub struct Config {

    /// Predefined packet size used for the encapsulated messages.
    packet_size: PacketSize,
+
+    /// Defines the minimum number of reply surbs the client would request.
+    minimum_reply_surb_request_size: u32,
+
+    /// Defines the maximum number of reply surbs the client would request.
+    maximum_reply_surb_request_size: u32,
+
+    /// Defines the maximum number of reply surbs a remote party is allowed to request from this client at once.
+    maximum_allowed_reply_surb_request_size: u32,
+
+    /// Defines maximum amount of time the client is going to wait for reply surbs before explicitly asking
+    /// for more even though in theory they wouldn't need to.
+    maximum_reply_surb_waiting_period: Duration,
+
+    /// Defines maximum amount of time given reply surb is going to be valid for.
+    /// This is going to be superseded by key rotation once implemented.
+    maximum_reply_surb_age: Duration,
+
+    /// Defines maximum amount of time given reply key is going to be valid for.
+    /// This is going to be superseded by key rotation once implemented.
+    maximum_reply_key_age: Duration,
+}
+
+impl<'a> From<&'a Config> for acknowledgement_control::Config {
+    fn from(cfg: &'a Config) -> Self {
+        acknowledgement_control::Config::new(cfg.ack_wait_addition, cfg.ack_wait_multiplier)
+            .with_custom_packet_size(cfg.packet_size)
+    }
+}
+
+impl<'a> From<&'a Config> for real_traffic_stream::Config {
+    fn from(cfg: &'a Config) -> Self {
+        real_traffic_stream::Config::new(
+            Arc::clone(&cfg.ack_key),
+            cfg.self_recipient,
+            cfg.average_ack_delay_duration,
+            cfg.average_packet_delay_duration,
+            cfg.average_message_sending_delay,
+            cfg.disable_main_poisson_packet_distribution,
+        )
+        .with_custom_cover_packet_size(cfg.packet_size)
+    }
+}
+
+impl<'a> From<&'a Config> for reply_controller::Config {
+    fn from(cfg: &'a Config) -> Self {
+        reply_controller::Config::new(
+            cfg.minimum_reply_surb_request_size,
+            cfg.maximum_reply_surb_request_size,
+            cfg.maximum_allowed_reply_surb_request_size,
+            cfg.maximum_reply_surb_waiting_period,
+            cfg.maximum_reply_surb_age,
+            cfg.maximum_reply_key_age,
+        )
+    }
+}
+
+impl<'a> From<&'a Config> for message_handler::Config {
+    fn from(cfg: &'a Config) -> Self {
+        message_handler::Config::new(
+            Arc::clone(&cfg.ack_key),
+            cfg.self_recipient,
+            cfg.average_packet_delay_duration,
+            cfg.average_ack_delay_duration,
+        )
+        .with_custom_packet_size(cfg.packet_size)
+    }
 }

 impl Config {
-    // TODO: change the config into a builder
-    #[allow(clippy::too_many_arguments)]
    pub fn new(
+        base_client_debug_config: &config::DebugConfig,
        ack_key: Arc<AckKey>,
-        ack_wait_multiplier: f64,
-        ack_wait_addition: Duration,
-        average_ack_delay_duration: Duration,
-        average_message_sending_delay: Duration,
-        average_packet_delay_duration: Duration,
-        disable_main_poisson_packet_distribution: bool,
        self_recipient: Recipient,
    ) -> Self {
        Config {
            ack_key,
-            ack_wait_addition,
-            ack_wait_multiplier,
            self_recipient,
-            average_message_sending_delay,
-            average_packet_delay_duration,
-            average_ack_delay_duration,
-            disable_main_poisson_packet_distribution,
            packet_size: Default::default(),
+            ack_wait_addition: base_client_debug_config.ack_wait_addition,
+            ack_wait_multiplier: base_client_debug_config.ack_wait_multiplier,
+            average_message_sending_delay: base_client_debug_config.message_sending_average_delay,
+            average_packet_delay_duration: base_client_debug_config.average_packet_delay,
+            average_ack_delay_duration: base_client_debug_config.average_ack_delay,
+            disable_main_poisson_packet_distribution: base_client_debug_config
+                .disable_main_poisson_packet_distribution,
+            minimum_reply_surb_request_size: base_client_debug_config
+                .minimum_reply_surb_request_size,
+            maximum_reply_surb_request_size: base_client_debug_config
+                .maximum_reply_surb_request_size,
+            maximum_allowed_reply_surb_request_size: base_client_debug_config
+                .maximum_allowed_reply_surb_request_size,
+            maximum_reply_surb_waiting_period: base_client_debug_config
+                .maximum_reply_surb_waiting_period,
+            maximum_reply_surb_age: base_client_debug_config.maximum_reply_surb_age,
+            maximum_reply_key_age: base_client_debug_config.maximum_reply_key_age,
        }
    }

@@ -95,75 +173,84 @@ impl Config {
    }
 }

-pub struct RealMessagesController<R>
+pub(crate) struct RealMessagesController<R>
 where
    R: CryptoRng + Rng,
 {
    out_queue_control: OutQueueControl<R>,
    ack_control: AcknowledgementController<R>,
+    reply_control: ReplyController<R>,
 }

 // obviously when we finally make shared rng that is on 'higher' level, this should become
 // generic `R`
 impl RealMessagesController<OsRng> {
    #[allow(clippy::too_many_arguments)]
-    pub fn new(
+    pub(crate) fn new(
        config: Config,
        ack_receiver: AcknowledgementReceiver,
        input_receiver: InputMessageReceiver,
        mix_sender: BatchMixMessageSender,
        topology_access: TopologyAccessor,
+        reply_storage: CombinedReplyStorage,
+        // so much refactoring needed, but this is temporary just to test things out
+        reply_controller_sender: ReplyControllerSender,
+        reply_controller_receiver: ReplyControllerReceiver,
        lane_queue_lengths: LaneQueueLengths,
        client_connection_rx: ConnectionCommandReceiver,
-        #[cfg(feature = "reply-surb")] reply_key_storage: ReplyKeyStorage,
    ) -> Self {
        let rng = OsRng;

+        // create channels for inter-task communication
        let (real_message_sender, real_message_receiver) = tokio::sync::mpsc::channel(1);
        let (sent_notifier_tx, sent_notifier_rx) = mpsc::unbounded();
-
+        let (ack_action_tx, ack_action_rx) = mpsc::unbounded();
        let ack_controller_connectors = AcknowledgementControllerConnectors::new(
-            real_message_sender,
            input_receiver,
            sent_notifier_rx,
            ack_receiver,
+            ack_action_tx.clone(),
+            ack_action_rx,
        );

-        let ack_control_config = acknowledgement_control::Config::new(
-            config.ack_wait_addition,
-            config.ack_wait_multiplier,
-            config.average_ack_delay_duration,
-            config.average_packet_delay_duration,
-        )
-        .with_custom_packet_size(config.packet_size);
+        // create all configs for the components
+        let ack_control_config = (&config).into();
+        let out_queue_config = (&config).into();
+        let reply_controller_config = (&config).into();
+        let message_handler_config = (&config).into();
+
+        // create the actual components
+        let message_handler = MessageHandler::new(
+            message_handler_config,
+            rng,
+            ack_action_tx,
+            real_message_sender,
+            topology_access.clone(),
+            reply_storage.key_storage(),
+            reply_storage.tags_storage(),
+        );

        let ack_control = AcknowledgementController::new(
            ack_control_config,
-            rng,
-            topology_access.clone(),
            Arc::clone(&config.ack_key),
-            config.self_recipient,
            ack_controller_connectors,
-            #[cfg(feature = "reply-surb")]
-            reply_key_storage,
+            message_handler.clone(),
+            reply_controller_sender,
        );

-        let out_queue_config = real_traffic_stream::Config::new(
-            config.average_ack_delay_duration,
-            config.average_packet_delay_duration,
-            config.average_message_sending_delay,
-            config.disable_main_poisson_packet_distribution,
-        )
-        .with_custom_cover_packet_size(config.packet_size);
+        let reply_control = ReplyController::new(
+            reply_controller_config,
+            message_handler,
+            reply_storage,
+            reply_controller_receiver,
+        );

        let out_queue_control = OutQueueControl::new(
            out_queue_config,
-            Arc::clone(&config.ack_key),
+            rng,
            sent_notifier_tx,
            mix_sender,
            real_message_receiver,
-            rng,
-            config.self_recipient,
            topology_access,
            lane_queue_lengths,
            client_connection_rx,
@@ -172,30 +259,26 @@ impl RealMessagesController<OsRng> {
        RealMessagesController {
            out_queue_control,
            ack_control,
+            reply_control,
        }
    }

    pub fn start_with_shutdown(self, shutdown: task::ShutdownListener) {
        let mut out_queue_control = self.out_queue_control;
        let ack_control = self.ack_control;
+        let mut reply_control = self.reply_control;

        let shutdown_handle = shutdown.clone();
        spawn_future(async move {
            out_queue_control.run_with_shutdown(shutdown_handle).await;
            debug!("The out queue controller has finished execution!");
        });
+        let shutdown_handle = shutdown.clone();
+        spawn_future(async move {
+            reply_control.run_with_shutdown(shutdown_handle).await;
+            debug!("The reply controller has finished execution!");
+        });
+
        ack_control.start_with_shutdown(shutdown);
    }
-
-    #[cfg(target_arch = "wasm32")]
-    pub fn start(self) {
-        let mut out_queue_control = self.out_queue_control;
-        let ack_control = self.ack_control;
-
-        spawn_future(async move {
-            out_queue_control.run().await;
-            debug!("The out queue controller has finished execution!");
-        });
-        ack_control.start();
-    }
 }
@@ -16,6 +16,7 @@ use nymsphinx::chunking::fragment::FragmentIdentifier;
 use nymsphinx::cover::generate_loop_cover_packet;
 use nymsphinx::forwarding::packet::MixPacket;
 use nymsphinx::params::PacketSize;
+use nymsphinx::preparer::PreparedFragment;
 use nymsphinx::utils::sample_poisson_duration;
 use rand::{CryptoRng, Rng};
 use std::pin::Pin;
@@ -47,6 +48,12 @@ fn get_time_now() -> wasm_timer::Instant {

 /// Configurable parameters of the `OutQueueControl`
 pub(crate) struct Config {
+    /// Key used to encrypt and decrypt content of an ACK packet.
+    ack_key: Arc<AckKey>,
+
+    /// Represents full address of this client.
+    our_full_destination: Recipient,
+
    /// Average delay an acknowledgement packet is going to get delay at a single mixnode.
    average_ack_delay: Duration,

@@ -66,12 +73,16 @@ pub(crate) struct Config {

 impl Config {
    pub(crate) fn new(
+        ack_key: Arc<AckKey>,
+        our_full_destination: Recipient,
        average_ack_delay: Duration,
        average_packet_delay: Duration,
        average_message_sending_delay: Duration,
        disable_poisson_packet_distribution: bool,
    ) -> Self {
        Config {
+            ack_key,
+            our_full_destination,
            average_ack_delay,
            average_packet_delay,
            average_message_sending_delay,
@@ -93,9 +104,6 @@ where
    /// Configurable parameters of the `ActionController`
    config: Config,

-    /// Key used to encrypt and decrypt content of an ACK packet.
-    ack_key: Arc<AckKey>,
-
    /// Channel used for notifying of a real packet being sent out. Used to start up retransmission timer.
    sent_notifier: SentPacketNotificationSender,

@@ -119,9 +127,6 @@ where
    /// before being sent out into the network.
    real_receiver: BatchRealMessageReceiver,

-    /// Represents full address of this client.
-    our_full_destination: Recipient,
-
    /// Instance of a cryptographically secure random number generator.
    rng: R,

@@ -144,6 +149,16 @@ where
 pub(crate) struct RealMessage {
    mix_packet: MixPacket,
    fragment_id: FragmentIdentifier,
+    // TODO: add info about it being constructed with reply-surb
+}
+
+impl From<PreparedFragment> for RealMessage {
+    fn from(fragment: PreparedFragment) -> Self {
+        RealMessage {
+            mix_packet: fragment.mix_packet,
+            fragment_id: fragment.fragment_identifier,
+        }
+    }
 }

 impl RealMessage {
@@ -175,25 +190,21 @@ where
    #[allow(clippy::too_many_arguments)]
    pub(crate) fn new(
        config: Config,
-        ack_key: Arc<AckKey>,
+        rng: R,
        sent_notifier: SentPacketNotificationSender,
        mix_tx: BatchMixMessageSender,
        real_receiver: BatchRealMessageReceiver,
-        rng: R,
-        our_full_destination: Recipient,
        topology_access: TopologyAccessor,
        lane_queue_lengths: LaneQueueLengths,
        client_connection_rx: ConnectionCommandReceiver,
    ) -> Self {
        OutQueueControl {
            config,
-            ack_key,
            sent_notifier,
            next_delay: None,
            sending_delay_controller: Default::default(),
            mix_tx,
            real_receiver,
-            our_full_destination,
            rng,
            topology_access,
            transmission_buffer: Default::default(),
@@ -220,24 +231,23 @@ where
                // poisson delay, but is it really a problem?
                let topology_permit = self.topology_access.get_read_permit().await;
                // the ack is sent back to ourselves (and then ignored)
-                let topology_ref_option = topology_permit.try_get_valid_topology_ref(
-                    &self.our_full_destination,
-                    Some(&self.our_full_destination),
-                );
-                if topology_ref_option.is_none() {
-                    warn!(
-                        "No valid topology detected - won't send any loop cover message this time"
-                    );
-                    return;
-                }
-                let topology_ref = topology_ref_option.unwrap();
+                let topology_ref = match topology_permit.try_get_valid_topology_ref(
+                    &self.config.our_full_destination,
+                    Some(&self.config.our_full_destination),
+                ) {
+                    Ok(topology) => topology,
+                    Err(err) => {
+                        warn!("We're not going to send any loop cover message this time, as the current topology seem to be invalid - {err}");
+                        return;
+                    }
+                };

                (
                    generate_loop_cover_packet(
                        &mut self.rng,
                        topology_ref,
-                        &self.ack_key,
-                        &self.our_full_destination,
+                        &self.config.ack_key,
+                        &self.config.our_full_destination,
                        self.config.average_ack_delay,
                        self.config.average_packet_delay,
                        self.config.cover_packet_size,
@@ -547,16 +557,6 @@ where
        }
        log::debug!("OutQueueControl: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    pub(super) async fn run(&mut self) {
-        debug!("Started OutQueueControl without graceful shutdown support");
-
-        while let Some(next_message) = self.next().await {
-            self.on_message(next_message).await;
-        }
-    }
 }

 impl<R> Stream for OutQueueControl<R>
@@ -1,26 +1,26 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

+use crate::client::replies::reply_controller::ReplyControllerSender;
+use crate::client::replies::reply_storage::SentReplyKeys;
 use crate::spawn_future;
 use crypto::asymmetric::encryption;
+use crypto::Digest;
 use futures::channel::mpsc;
 use futures::lock::Mutex;
 use futures::StreamExt;
 use gateway_client::MixnetMessageReceiver;
 use log::*;
+use nymsphinx::anonymous_replies::requests::{
+    RepliableMessage, RepliableMessageContent, ReplyMessage, ReplyMessageContent,
+};
+use nymsphinx::anonymous_replies::{encryption_key::EncryptionKeyDigest, SurbEncryptionKey};
+use nymsphinx::message::{NymMessage, PlainMessage};
+use nymsphinx::params::ReplySurbKeyDigestAlgorithm;
 use nymsphinx::receiver::{MessageReceiver, MessageRecoveryError, ReconstructedMessage};
 use std::collections::HashSet;
 use std::sync::Arc;

-#[cfg(feature = "reply-surb")]
-use crate::client::reply_key_storage::ReplyKeyStorage;
-#[cfg(feature = "reply-surb")]
-use crypto::{symmetric::stream_cipher, Digest};
-#[cfg(feature = "reply-surb")]
-use nymsphinx::anonymous_replies::{encryption_key::EncryptionKeyDigest, SurbEncryptionKey};
-#[cfg(feature = "reply-surb")]
-use nymsphinx::params::{ReplySurbEncryptionAlgorithm, ReplySurbKeyDigestAlgorithm};
-
 // Buffer Requests to say "hey, send any reconstructed messages to this channel"
 // or to say "hey, I'm going offline, don't send anything more to me. Just buffer them instead"
 pub type ReceivedBufferRequestSender = mpsc::UnboundedSender<ReceivedBufferMessage>;
@@ -46,26 +46,15 @@ struct ReceivedMessagesBufferInner {
 }

 impl ReceivedMessagesBufferInner {
-    fn process_received_fragment(&mut self, raw_fragment: Vec<u8>) -> Option<ReconstructedMessage> {
-        let fragment_data = match self
-            .message_receiver
-            .recover_plaintext(self.local_encryption_keypair.private_key(), raw_fragment)
-        {
-            Err(e) => {
-                warn!("failed to recover fragment data: {:?}. The whole underlying message might be corrupted and unrecoverable!", e);
-                return None;
-            }
-            Ok(frag_data) => frag_data,
-        };
-
-        if nymsphinx::cover::is_cover(&fragment_data) {
+    fn recover_from_fragment(&mut self, fragment_data: &[u8]) -> Option<NymMessage> {
+        if nymsphinx::cover::is_cover(fragment_data) {
            trace!("The message was a loop cover message! Skipping it");
            return None;
        }

-        let fragment = match self.message_receiver.recover_fragment(&fragment_data) {
-            Err(e) => {
-                warn!("failed to recover fragment from raw data: {:?}. The whole underlying message might be corrupted and unrecoverable!", e);
+        let fragment = match self.message_receiver.recover_fragment(fragment_data) {
+            Err(err) => {
+                warn!("failed to recover fragment from raw data: {err}. The whole underlying message might be corrupted and unrecoverable!");
                return None;
            }
            Ok(frag) => frag,
@@ -79,9 +68,10 @@ impl ReceivedMessagesBufferInner {
        // if we returned an error the underlying message is malformed in some way
        match self.message_receiver.insert_new_fragment(fragment) {
            Err(err) => match err {
-                MessageRecoveryError::MalformedReconstructedMessage(message_sets) => {
+                MessageRecoveryError::MalformedReconstructedMessage { source, used_sets } => {
+                    error!("message reconstruction failed - {source}. Attempting to re-use the message sets...");
                    // TODO: should we really insert reconstructed sets? could this be abused for some attack?
-                    for set_id in message_sets {
+                    for set_id in used_sets {
                        if !self.recently_reconstructed.insert(set_id) {
                            // or perhaps we should even panic at this point?
                            error!("Reconstructed another message containing already used set id!")
@@ -107,6 +97,34 @@ impl ReceivedMessagesBufferInner {
            },
        }
    }
+
+    fn process_received_reply(
+        &mut self,
+        reply_ciphertext: &mut [u8],
+        reply_key: SurbEncryptionKey,
+    ) -> Option<NymMessage> {
+        // note: this performs decryption IN PLACE without extra allocation
+        self.message_receiver
+            .recover_plaintext_from_reply(reply_ciphertext, reply_key);
+        let fragment_data = reply_ciphertext;
+
+        self.recover_from_fragment(fragment_data)
+    }
+
+    fn process_received_regular_packet(&mut self, mut raw_fragment: Vec<u8>) -> Option<NymMessage> {
+        let fragment_data = match self.message_receiver.recover_plaintext_from_regular_packet(
+            self.local_encryption_keypair.private_key(),
+            &mut raw_fragment,
+        ) {
+            Err(err) => {
+                warn!("failed to recover fragment data: {err}. The whole underlying message might be corrupted and unrecoverable!");
+                return None;
+            }
+            Ok(frag_data) => frag_data,
+        };
+
+        self.recover_from_fragment(fragment_data)
+    }
 }

 #[derive(Debug, Clone)]
@@ -114,17 +132,15 @@ impl ReceivedMessagesBufferInner {
 // You should always use .clone() to create additional instances
 struct ReceivedMessagesBuffer {
    inner: Arc<Mutex<ReceivedMessagesBufferInner>>,
-
-    /// Storage containing keys to all [`ReplySURB`]s ever sent out that we did not receive back.
-    // There's no need to put it behind a Mutex since it's already properly concurrent
-    #[cfg(feature = "reply-surb")]
-    reply_key_storage: ReplyKeyStorage,
+    reply_key_storage: SentReplyKeys,
+    reply_controller_sender: ReplyControllerSender,
 }

 impl ReceivedMessagesBuffer {
    fn new(
        local_encryption_keypair: Arc<encryption::KeyPair>,
-        #[cfg(feature = "reply-surb")] reply_key_storage: ReplyKeyStorage,
+        reply_key_storage: SentReplyKeys,
+        reply_controller_sender: ReplyControllerSender,
    ) -> Self {
        ReceivedMessagesBuffer {
            inner: Arc::new(Mutex::new(ReceivedMessagesBufferInner {
@@ -134,8 +150,8 @@ impl ReceivedMessagesBuffer {
                message_sender: None,
                recently_reconstructed: HashSet::new(),
            })),
-            #[cfg(feature = "reply-surb")]
            reply_key_storage,
+            reply_controller_sender,
        }
    }

@@ -177,34 +193,139 @@ impl ReceivedMessagesBuffer {
        guard.message_sender = Some(sender);
    }

-    async fn add_reconstructed_messages(&mut self, msgs: Vec<ReconstructedMessage>) {
-        debug!("Adding {:?} new messages to the buffer!", msgs.len());
-        trace!("Adding new messages to the buffer! {:?}", msgs);
-        self.inner.lock().await.messages.extend(msgs)
+    fn handle_reconstructed_plain_messages(
+        &mut self,
+        msgs: Vec<PlainMessage>,
+    ) -> Vec<ReconstructedMessage> {
+        msgs.into_iter().map(Into::into).collect()
    }

-    #[cfg(feature = "reply-surb")]
-    fn process_received_reply(
-        reply_ciphertext: &[u8],
-        reply_key: SurbEncryptionKey,
-    ) -> Option<ReconstructedMessage> {
-        let zero_iv = stream_cipher::zero_iv::<ReplySurbEncryptionAlgorithm>();
+    fn handle_reconstructed_repliable_messages(
+        &mut self,
+        msgs: Vec<RepliableMessage>,
+    ) -> Vec<ReconstructedMessage> {
+        let mut reconstructed = Vec::new();
+        for msg in msgs {
+            let (reply_surbs, from_surb_request) = match msg.content {
+                RepliableMessageContent::Data {
+                    message,
+                    reply_surbs,
+                } => {
+                    trace!(
+                        "received message that also contained additional {} reply surbs from {:?}!",
+                        reply_surbs.len(),
+                        msg.sender_tag
+                    );

-        let mut reply_msg = stream_cipher::decrypt::<ReplySurbEncryptionAlgorithm>(
-            reply_key.inner(),
-            &zero_iv,
-            reply_ciphertext,
-        );
-        if let Err(err) = MessageReceiver::remove_padding(&mut reply_msg) {
-            warn!("Received reply had malformed padding! - {:?}", err);
-            None
-        } else {
-            // TODO: perhaps having to say it doesn't have a surb an indication the type should be changed?
-            Some(ReconstructedMessage {
-                message: reply_msg,
-                reply_surb: None,
-            })
+                    reconstructed.push(ReconstructedMessage::new(message, msg.sender_tag));
+
+                    (reply_surbs, false)
+                }
+                RepliableMessageContent::AdditionalSurbs { reply_surbs } => {
+                    trace!(
+                        "received additional {} reply surbs from {:?}!",
+                        reply_surbs.len(),
+                        msg.sender_tag
+                    );
+                    (reply_surbs, true)
+                }
+                RepliableMessageContent::Heartbeat {
+                    additional_reply_surbs,
+                } => {
+                    error!("received a repliable heartbeat message - we don't know how to handle it yet (and we won't know until future PRs)");
+                    (additional_reply_surbs, false)
+                }
+            };
+
+            self.reply_controller_sender.send_additional_surbs(
+                msg.sender_tag,
+                reply_surbs,
+                from_surb_request,
+            )
        }
+        reconstructed
+    }
+
+    fn handle_reconstructed_reply_messages(
+        &mut self,
+        msgs: Vec<ReplyMessage>,
+    ) -> Vec<ReconstructedMessage> {
+        let mut reconstructed = Vec::new();
+        for msg in msgs {
+            match msg.content {
+                ReplyMessageContent::Data { message } => reconstructed.push(message.into()),
+                ReplyMessageContent::SurbRequest { recipient, amount } => {
+                    debug!("received request for {amount} additional reply SURBs from {recipient}");
+                    self.reply_controller_sender
+                        .send_additional_surbs_request(*recipient, amount);
+                }
+            }
+        }
+        reconstructed
+    }
+
+    async fn handle_reconstructed_messages(&mut self, msgs: Vec<NymMessage>) {
+        if msgs.is_empty() {
+            return;
+        }
+
+        let mut plain_messages = Vec::new();
+        let mut repliable_messages = Vec::new();
+        let mut reply_messages = Vec::new();
+
+        for msg in msgs {
+            match msg {
+                NymMessage::Plain(plain) => plain_messages.push(plain),
+                NymMessage::Repliable(repliable) => repliable_messages.push(repliable),
+                NymMessage::Reply(reply) => reply_messages.push(reply),
+            }
+        }
+
+        let mut reconstructed_messages = self.handle_reconstructed_plain_messages(plain_messages);
+        reconstructed_messages
+            .append(&mut self.handle_reconstructed_repliable_messages(repliable_messages));
+        reconstructed_messages
+            .append(&mut self.handle_reconstructed_reply_messages(reply_messages));
+
+        let mut inner_guard = self.inner.lock().await;
+        debug!(
+            "Adding {:?} new messages to the buffer!",
+            reconstructed_messages.len()
+        );
+
+        if let Some(sender) = &inner_guard.message_sender {
+            trace!("Sending reconstructed messages to announced sender");
+            if let Err(err) = sender.unbounded_send(reconstructed_messages) {
+                warn!("The reconstructed message receiver went offline without explicit notification (relevant error: - {err})");
+                inner_guard.message_sender = None;
+                inner_guard.messages.extend(err.into_inner());
+            }
+        } else {
+            trace!("No sender available - buffering reconstructed messages");
+            inner_guard.messages.extend(reconstructed_messages)
+        }
+    }
+
+    // this function doesn't really belong here...
+    fn get_reply_key<'a>(
+        &self,
+        raw_message: &'a mut [u8],
+    ) -> Option<(SurbEncryptionKey, &'a mut [u8])> {
+        let reply_surb_digest_size = ReplySurbKeyDigestAlgorithm::output_size();
+        if raw_message.len() < reply_surb_digest_size {
+            return None;
+        }
+
+        let possible_key_digest =
+            EncryptionKeyDigest::clone_from_slice(&raw_message[..reply_surb_digest_size]);
+        self.reply_key_storage
+            .try_pop(possible_key_digest)
+            .map(|reply_encryption_key| {
+                (
+                    *reply_encryption_key,
+                    &mut raw_message[reply_surb_digest_size..],
+                )
+            })
    }

    async fn handle_new_received(&mut self, msgs: Vec<Vec<u8>>) {
@@ -217,69 +338,27 @@ impl ReceivedMessagesBuffer {
        let mut inner_guard = self.inner.lock().await;

        // first check if this is a reply or a chunked message
-        // TODO: verify with @AP if this way of doing it is safe or whether it could
-        // cause some attacks due to, I don't know, stupid edge case collisions?
-        // Update: this DOES introduce a possible leakage: https://github.com/nymtech/nym/issues/296
-        for msg in msgs {
-            // TODO:
-            // 1. make it nicer
-            // 2. make it not feature-locked
-
-            #[cfg(feature = "reply-surb")]
-            {
-                let reply_surb_digest_size = ReplySurbKeyDigestAlgorithm::output_size();
-
-                let possible_key_digest =
-                    EncryptionKeyDigest::clone_from_slice(&msg[..reply_surb_digest_size]);
-
-                // check first `HasherOutputSize` bytes if they correspond to known encryption key
-                // if yes - this is a reply message
-
-                // TODO: this might be a bottleneck - since the keys are stored on disk we, presumably,
-                // are doing a disk operation every single received fragment
-                if let Some(reply_encryption_key) = self
-                    .reply_key_storage
-                    .get_and_remove_encryption_key(possible_key_digest)
-                    .expect("storage operation failed!")
-                {
-                    if let Some(completed_message) = Self::process_received_reply(
-                        &msg[reply_surb_digest_size..],
-                        reply_encryption_key,
-                    ) {
-                        completed_messages.push(completed_message)
-                    }
+        // note: there's a possible information leakage associated with this check https://github.com/nymtech/nym/issues/296
+        for mut msg in msgs {
+            // check first `HasherOutputSize` bytes if they correspond to known encryption key
+            // if yes - this is a reply message
+            let completed_message =
+                if let Some((reply_key, reply_message)) = self.get_reply_key(&mut msg) {
+                    inner_guard.process_received_reply(reply_message, reply_key)
                } else {
-                    // otherwise - it's a 'normal' message
-                    if let Some(completed_message) = inner_guard.process_received_fragment(msg) {
-                        completed_messages.push(completed_message)
-                    }
-                }
-            }
+                    inner_guard.process_received_regular_packet(msg)
+                };

-            #[cfg(not(feature = "reply-surb"))]
-            if let Some(completed_message) = inner_guard.process_received_fragment(msg) {
-                completed_messages.push(completed_message)
+            if let Some(completed) = completed_message {
+                info!("received {completed}");
+                completed_messages.push(completed)
            }
        }

+        drop(inner_guard);
+
        if !completed_messages.is_empty() {
-            if let Some(sender) = &inner_guard.message_sender {
-                trace!("Sending reconstructed messages to announced sender");
-                if let Err(err) = sender.unbounded_send(completed_messages) {
-                    warn!("The reconstructed message receiver went offline without explicit notification (relevant error: - {:?})", err);
-                    // make sure to drop the lock to not deadlock
-                    // (it is required by `add_reconstructed_messages`)
-                    inner_guard.message_sender = None;
-                    drop(inner_guard);
-                    self.add_reconstructed_messages(err.into_inner()).await;
-                }
-            } else {
-                // make sure to drop the lock to not deadlock
-                // (it is required by `add_reconstructed_messages`)
-                drop(inner_guard);
-                trace!("No sender available - buffering reconstructed messages");
-                self.add_reconstructed_messages(completed_messages).await;
-            }
+            self.handle_reconstructed_messages(completed_messages).await
        }
    }
 }
@@ -342,16 +421,6 @@ impl RequestReceiver {
        shutdown.recv_timeout().await;
        log::debug!("RequestReceiver: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    async fn run(&mut self) {
-        debug!("Started RequestReceiver without graceful shutdown support");
-
-        while let Some(message) = self.query_receiver.next().await {
-            self.handle_message(message).await
-        }
-    }
 }

 struct FragmentedMessageReceiver {
@@ -391,34 +460,25 @@ impl FragmentedMessageReceiver {
        shutdown.recv_timeout().await;
        log::debug!("FragmentedMessageReceiver: Exiting");
    }
-
-    // todo: think whether this is still required
-    #[allow(dead_code)]
-    async fn run(&mut self) {
-        debug!("Started FragmentedMessageReceiver without graceful shutdown support");
-
-        while let Some(new_messages) = self.mixnet_packet_receiver.next().await {
-            self.received_buffer.handle_new_received(new_messages).await;
-        }
-    }
 }

-pub struct ReceivedMessagesBufferController {
+pub(crate) struct ReceivedMessagesBufferController {
    fragmented_message_receiver: FragmentedMessageReceiver,
    request_receiver: RequestReceiver,
 }

 impl ReceivedMessagesBufferController {
-    pub fn new(
+    pub(crate) fn new(
        local_encryption_keypair: Arc<encryption::KeyPair>,
        query_receiver: ReceivedBufferRequestReceiver,
        mixnet_packet_receiver: MixnetMessageReceiver,
-        #[cfg(feature = "reply-surb")] reply_key_storage: ReplyKeyStorage,
+        reply_key_storage: SentReplyKeys,
+        reply_controller_sender: ReplyControllerSender,
    ) -> Self {
        let received_buffer = ReceivedMessagesBuffer::new(
            local_encryption_keypair,
-            #[cfg(feature = "reply-surb")]
            reply_key_storage,
+            reply_controller_sender,
        );

        ReceivedMessagesBufferController {
@@ -444,16 +504,4 @@ impl ReceivedMessagesBufferController {
            request_receiver.run_with_shutdown(shutdown).await;
        });
    }
-
-    #[cfg(target_arch = "wasm32")]
-    pub fn start(self) {
-        let mut fragmented_message_receiver = self.fragmented_message_receiver;
-        let mut request_receiver = self.request_receiver;
-        spawn_future(async move {
-            fragmented_message_receiver.run().await;
-        });
-        spawn_future(async move {
-            request_receiver.run().await;
-        });
-    }
 }
@@ -0,0 +1,5 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+pub mod reply_controller;
+pub mod reply_storage;
@@ -0,0 +1,928 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::real_messages_control::acknowledgement_control::PendingAcknowledgement;
+use crate::client::real_messages_control::message_handler::{MessageHandler, PreparationError};
+use crate::client::replies::reply_storage::CombinedReplyStorage;
+use client_connections::TransmissionLane;
+use futures::channel::mpsc;
+use futures::StreamExt;
+use log::{debug, error, info, trace, warn};
+use nymsphinx::addressing::clients::Recipient;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
+use nymsphinx::anonymous_replies::ReplySurb;
+use nymsphinx::chunking::fragment::{Fragment, FragmentIdentifier};
+use rand::{CryptoRng, Rng};
+use std::cmp::{max, min};
+use std::collections::btree_map::Entry;
+use std::collections::{BTreeMap, HashMap, VecDeque};
+use std::sync::{Arc, Weak};
+use std::time::Duration;
+use time::OffsetDateTime;
+
+#[cfg(not(target_arch = "wasm32"))]
+type IntervalStream = tokio_stream::wrappers::IntervalStream;
+
+#[cfg(target_arch = "wasm32")]
+type IntervalStream = gloo_timers::future::IntervalStream;
+
+pub(crate) fn new_control_channels() -> (ReplyControllerSender, ReplyControllerReceiver) {
+    let (tx, rx) = mpsc::unbounded();
+    (tx.into(), rx)
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct ReplyControllerSender(mpsc::UnboundedSender<ReplyControllerMessage>);
+
+impl From<mpsc::UnboundedSender<ReplyControllerMessage>> for ReplyControllerSender {
+    fn from(inner: mpsc::UnboundedSender<ReplyControllerMessage>) -> Self {
+        ReplyControllerSender(inner)
+    }
+}
+
+impl ReplyControllerSender {
+    pub(crate) fn send_retransmission_data(
+        &self,
+        recipient: AnonymousSenderTag,
+        timed_out_ack: Weak<PendingAcknowledgement>,
+        extra_surb_request: bool,
+    ) {
+        self.0
+            .unbounded_send(ReplyControllerMessage::RetransmitReply {
+                recipient,
+                timed_out_ack,
+                extra_surb_request,
+            })
+            .expect("ReplyControllerReceiver has died!")
+    }
+
+    pub(crate) fn send_reply(
+        &self,
+        recipient: AnonymousSenderTag,
+        message: Vec<u8>,
+        lane: TransmissionLane,
+    ) {
+        self.0
+            .unbounded_send(ReplyControllerMessage::SendReply {
+                recipient,
+                message,
+                lane,
+            })
+            .expect("ReplyControllerReceiver has died!")
+    }
+
+    pub(crate) fn send_additional_surbs(
+        &self,
+        sender_tag: AnonymousSenderTag,
+        reply_surbs: Vec<ReplySurb>,
+        from_surb_request: bool,
+    ) {
+        self.0
+            .unbounded_send(ReplyControllerMessage::AdditionalSurbs {
+                sender_tag,
+                reply_surbs,
+                from_surb_request,
+            })
+            .expect("ReplyControllerReceiver has died!")
+    }
+
+    pub(crate) fn send_additional_surbs_request(&self, recipient: Recipient, amount: u32) {
+        self.0
+            .unbounded_send(ReplyControllerMessage::AdditionalSurbsRequest {
+                recipient: Box::new(recipient),
+                amount,
+            })
+            .expect("ReplyControllerReceiver has died!")
+    }
+}
+
+pub(crate) type ReplyControllerReceiver = mpsc::UnboundedReceiver<ReplyControllerMessage>;
+
+#[derive(Debug)]
+pub(crate) enum ReplyControllerMessage {
+    RetransmitReply {
+        recipient: AnonymousSenderTag,
+        timed_out_ack: Weak<PendingAcknowledgement>,
+        extra_surb_request: bool,
+    },
+
+    SendReply {
+        recipient: AnonymousSenderTag,
+        message: Vec<u8>,
+        lane: TransmissionLane,
+    },
+
+    AdditionalSurbs {
+        sender_tag: AnonymousSenderTag,
+        reply_surbs: Vec<ReplySurb>,
+        from_surb_request: bool,
+    },
+
+    // Should this also be handled in here? it's technically a completely different side of the pipe
+    // let's see how it works when combined, might split it before creating PR
+    AdditionalSurbsRequest {
+        recipient: Box<Recipient>,
+        amount: u32,
+    },
+}
+
+pub struct Config {
+    min_surb_request_size: u32,
+    max_surb_request_size: u32,
+    maximum_allowed_reply_surb_request_size: u32,
+    max_surb_waiting_period: Duration,
+    max_reply_surb_age: Duration,
+    max_reply_key_age: Duration,
+}
+
+impl Config {
+    pub(crate) fn new(
+        min_surb_request_size: u32,
+        max_surb_request_size: u32,
+        maximum_allowed_reply_surb_request_size: u32,
+        max_surb_waiting_period: Duration,
+        max_reply_surb_age: Duration,
+        max_reply_key_age: Duration,
+    ) -> Self {
+        Self {
+            min_surb_request_size,
+            max_surb_request_size,
+            maximum_allowed_reply_surb_request_size,
+            max_surb_waiting_period,
+            max_reply_surb_age,
+            max_reply_key_age,
+        }
+    }
+}
+
+// the purpose of this task:
+// - buffers split messages from input message listener if there were insufficient surbs to send them
+// - upon getting extra surbs, resends them
+// - so I guess it will handle all 'RepliableMessage' and requests from 'ReplyMessage'
+// - replies to "give additional surbs" requests
+// - will reply to future heartbeats
+
+// TODO: this should be split into ingress and egress controllers
+// because currently its trying to perform two distinct jobs
+pub struct ReplyController<R> {
+    config: Config,
+
+    // TODO: incorporate that field at some point
+    // and use binomial distribution to determine the expected required number
+    // of surbs required to send the message through
+    // expected_reliability: f32,
+    request_receiver: ReplyControllerReceiver,
+    pending_replies: HashMap<AnonymousSenderTag, VecDeque<Fragment>>,
+
+    /// Retransmission packets that have already timed out and are waiting for additional reply SURBs
+    /// so that they could be sent back to the network. Once we receive more SURBs, we should send them ASAP.
+    // TODO: when purging stale entries, we must take extra care to also purge all pending ACK data!!
+    pending_retransmissions:
+        HashMap<AnonymousSenderTag, BTreeMap<FragmentIdentifier, Weak<PendingAcknowledgement>>>,
+
+    message_handler: MessageHandler<R>,
+    full_reply_storage: CombinedReplyStorage,
+}
+
+impl<R> ReplyController<R>
+where
+    R: CryptoRng + Rng,
+{
+    pub(crate) fn new(
+        config: Config,
+        message_handler: MessageHandler<R>,
+        full_reply_storage: CombinedReplyStorage,
+        request_receiver: ReplyControllerReceiver,
+    ) -> Self {
+        ReplyController {
+            config,
+            request_receiver,
+            pending_replies: HashMap::new(),
+            pending_retransmissions: HashMap::new(),
+            message_handler,
+            full_reply_storage,
+        }
+    }
+
+    /// Inserts the pending replies into the BACK of the queue fn insert_pending_replies<V: Into<VecDeque<Fragment>>>(
+    fn insert_pending_replies<V: Into<VecDeque<Fragment>>>(
+        &mut self,
+        recipient: &AnonymousSenderTag,
+        fragments: V,
+    ) {
+        if let Some(existing) = self.pending_replies.get_mut(recipient) {
+            existing.append(&mut fragments.into())
+        } else {
+            self.pending_replies.insert(*recipient, fragments.into());
+        }
+    }
+
+    fn re_insert_pending_retransmission(
+        &mut self,
+        recipient: &AnonymousSenderTag,
+        data: Vec<Arc<PendingAcknowledgement>>,
+    ) {
+        // the underlying entry MUST exist as we've just got data from there
+        let map_entry = self
+            .pending_retransmissions
+            .get_mut(recipient)
+            .expect("our pending retransmission entry is somehow gone!");
+
+        for pending in data {
+            // if it's 0, we don't need to do anything - we just got that ack!
+            if Arc::strong_count(&pending) > 1 {
+                let id = pending.inner_fragment_identifier();
+                let downgraded = Arc::downgrade(&pending);
+                map_entry.insert(id, downgraded);
+            }
+        }
+    }
+
+    fn should_request_more_surbs(&self, target: &AnonymousSenderTag) -> bool {
+        trace!("checking if we should request more surbs from {:?}", target);
+
+        let pending_queue_size = self
+            .pending_replies
+            .get(target)
+            .map(|pending_queue| pending_queue.len())
+            .unwrap_or_default();
+
+        let retransmission_queue = self
+            .pending_retransmissions
+            .get(target)
+            .map(|pending_queue| pending_queue.len())
+            .unwrap_or_default();
+
+        let total_queue = pending_queue_size + retransmission_queue;
+
+        // simple as that - there's absolutely nothing to retransmit
+        if total_queue == 0 {
+            return false;
+        }
+
+        let available_surbs = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .available_surbs(target);
+        let pending_surbs = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .pending_reception(target) as usize;
+        let min_surbs_threshold = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .min_surb_threshold();
+        let max_surbs_threshold = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .max_surb_threshold();
+
+        debug!("total queue size: {total_queue} = pending data {pending_queue_size} + pending retransmission {retransmission_queue}, available surbs: {available_surbs} pending surbs: {pending_surbs} threshold range: {min_surbs_threshold}..{max_surbs_threshold}");
+
+        (pending_surbs + available_surbs) < max_surbs_threshold
+            && (pending_surbs + available_surbs) < (total_queue + min_surbs_threshold)
+    }
+
+    async fn handle_send_reply(
+        &mut self,
+        recipient_tag: AnonymousSenderTag,
+        data: Vec<u8>,
+        lane: TransmissionLane,
+    ) {
+        if !self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .contains_surbs_for(&recipient_tag)
+        {
+            warn!("received reply request for {:?} but we don't have any surbs stored for that recipient!", recipient_tag);
+            return;
+        }
+
+        trace!("handling reply to {:?}", recipient_tag);
+        let fragments = self.message_handler.split_reply_message(data);
+
+        let required_surbs = fragments.len();
+        trace!("This reply requires {:?} SURBs", required_surbs);
+
+        // TODO: edge case:
+        // we're making a lot of requests and have to request a lot of surbs
+        // (but at some point we run out of surbs for surb requests)
+
+        let (surbs, _surbs_left) = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .get_reply_surbs(&recipient_tag, required_surbs);
+
+        if let Some(reply_surbs) = surbs {
+            if let Err(err) = self
+                .message_handler
+                .try_send_reply_chunks(recipient_tag, fragments, reply_surbs, lane)
+                .await
+            {
+                let err = err.return_unused_surbs(
+                    self.full_reply_storage.surbs_storage_ref(),
+                    &recipient_tag,
+                );
+                warn!("failed to send reply to {:?} - {err}", recipient_tag);
+
+                // TODO: should we buffer that data to try again?
+            }
+        } else {
+            // we don't have enough surbs for this reply
+            self.insert_pending_replies(&recipient_tag, fragments);
+
+            if self.should_request_more_surbs(&recipient_tag) {
+                self.request_reply_surbs_for_queue_clearing(recipient_tag)
+                    .await;
+            }
+        }
+    }
+
+    async fn request_additional_reply_surbs(
+        &mut self,
+        target: AnonymousSenderTag,
+        amount: u32,
+    ) -> Result<(), PreparationError> {
+        let reply_surb = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .get_reply_surb_ignoring_threshold(&target)
+            .and_then(|(reply_surb, _)| reply_surb)
+            .ok_or(PreparationError::NotEnoughSurbs {
+                available: 0,
+                required: 1,
+            })?;
+
+        if let Err(err) = self
+            .message_handler
+            .try_request_additional_reply_surbs(target, reply_surb, amount)
+            .await
+        {
+            let err = err.return_unused_surbs(self.full_reply_storage.surbs_storage_ref(), &target);
+            warn!(
+                "failed to request additional surbs from {:?} - {err}",
+                target
+            );
+            return Err(err);
+        } else {
+            self.full_reply_storage
+                .surbs_storage_ref()
+                .increment_pending_reception(&target, amount);
+        }
+
+        Ok(())
+    }
+
+    async fn try_clear_pending_retransmission(&mut self, target: AnonymousSenderTag) {
+        trace!("trying to clear pending retransmission queue");
+        let available_surbs = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .available_surbs(&target);
+        let min_surbs_threshold = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .min_surb_threshold();
+
+        let max_to_clear = if available_surbs > min_surbs_threshold {
+            available_surbs - min_surbs_threshold
+        } else {
+            trace!("we don't have enough surbs for retransmission queue clearing...");
+            return;
+        };
+        trace!("we can clear up to {max_to_clear} entries");
+
+        let Some(pending) = self.pending_retransmissions.get_mut(&target) else {
+            trace!("there are no pending retransmissions for {target}!");
+            return;
+        };
+
+        let mut to_take = Vec::new();
+        let mut to_remove = Vec::new();
+
+        // TODO: once rust 1.66.0 is stabilised on 15.12.22, just change it to
+        // `.pop_front()` to directly take ownership
+        for (k, data) in pending.iter() {
+            let upgraded = match data.upgrade() {
+                Some(upgraded) => upgraded,
+                None => {
+                    // we got the ack while the data was waiting in the queue
+                    to_remove.push(*k);
+                    continue;
+                }
+            };
+
+            to_take.push(upgraded);
+
+            // we have taken as many entries as we could have
+            if to_take.len() >= max_to_clear {
+                break;
+            }
+            // TODO: use if upgraded.is_extra_surb_request() to bypass the limit
+        }
+
+        for ack in &to_take {
+            pending.remove(&ack.inner_fragment_identifier());
+        }
+
+        for id in to_remove {
+            pending.remove(&id);
+        }
+
+        if to_take.is_empty() {
+            // no need to do anything
+            return;
+        }
+
+        let (surbs_for_reply, _) = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .get_reply_surbs(&target, to_take.len());
+
+        let Some(surbs_for_reply) = surbs_for_reply else {
+            error!("somehow different task has stolen our reply surbs! - this should have been impossible");
+            self.re_insert_pending_retransmission(&target, to_take);
+            return;
+        };
+
+        let to_send_vec = to_take.iter().map(|ack| ack.fragment_data()).collect();
+
+        if let Err(err) = self
+            .message_handler
+            .try_send_retransmission_reply_chunks(
+                to_send_vec,
+                surbs_for_reply,
+                TransmissionLane::Retransmission,
+            )
+            .await
+        {
+            let err = err.return_unused_surbs(self.full_reply_storage.surbs_storage_ref(), &target);
+            self.re_insert_pending_retransmission(&target, to_take);
+
+            warn!(
+                "failed to clear pending retransmission queue for {:?} - {err}",
+                target
+            );
+        }
+    }
+
+    fn pop_at_most_pending_replies(
+        &mut self,
+        from: &AnonymousSenderTag,
+        amount: usize,
+    ) -> Option<VecDeque<Fragment>> {
+        // if possible, pop all pending replies, if not, pop only entries for which we'd have a reply surb
+        let total = self.pending_replies.get(from)?.len();
+        trace!("pending queue has {total} elements");
+        if total == 0 {
+            return None;
+        }
+        if total < amount {
+            self.pending_replies.remove(from)
+        } else {
+            Some(
+                self.pending_replies
+                    .get_mut(from)?
+                    .drain(..amount)
+                    .collect(),
+            )
+        }
+    }
+
+    async fn try_clear_pending_queue(&mut self, target: AnonymousSenderTag) {
+        trace!("trying to clear pending queue");
+        let available_surbs = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .available_surbs(&target);
+        let min_surbs_threshold = self
+            .full_reply_storage
+            .surbs_storage_ref()
+            .min_surb_threshold();
+
+        let max_to_clear = if available_surbs > min_surbs_threshold {
+            available_surbs - min_surbs_threshold
+        } else {
+            trace!("we don't have enough surbs for queue clearing...");
+            return;
+        };
+        trace!("we can clear up to {max_to_clear} entries");
+
+        // we're guaranteed to not get more entries than we have reply surbs for
+        if let Some(to_send) = self.pop_at_most_pending_replies(&target, max_to_clear) {
+            let to_send_vec = to_send.iter().cloned().collect::<Vec<_>>();
+
+            if to_send_vec.is_empty() {
+                panic!(
+                    "please let the devs know if you ever see this message (reply_controller.rs)"
+                );
+            }
+
+            let (surbs_for_reply, _) = self
+                .full_reply_storage
+                .surbs_storage_ref()
+                .get_reply_surbs(&target, to_send_vec.len());
+
+            let Some(surbs_for_reply) = surbs_for_reply else {
+                error!("somehow different task has stolen our reply surbs! - this should have been impossible");
+                self.insert_pending_replies(&target, to_send);
+                return;
+            };
+
+            if let Err(err) = self
+                .message_handler
+                .try_send_reply_chunks(
+                    target,
+                    to_send_vec,
+                    surbs_for_reply,
+                    TransmissionLane::General,
+                )
+                .await
+            {
+                let err =
+                    err.return_unused_surbs(self.full_reply_storage.surbs_storage_ref(), &target);
+                self.insert_pending_replies(&target, to_send);
+                warn!("failed to clear pending queue for {:?} - {err}", target);
+            }
+        } else {
+            trace!("the pending queue is empty");
+        }
+    }
+
+    async fn handle_received_surbs(
+        &mut self,
+        from: AnonymousSenderTag,
+        reply_surbs: Vec<ReplySurb>,
+        from_surb_request: bool,
+    ) {
+        trace!("handling received surbs");
+
+        // clear the requesting flag since we should have been asking for surbs
+        self.full_reply_storage
+            .surbs_storage_ref()
+            .reset_surbs_last_received_at(&from);
+        if from_surb_request {
+            self.full_reply_storage
+                .surbs_storage_ref()
+                .decrement_pending_reception(&from, reply_surbs.len() as u32);
+        }
+
+        // store received surbs
+        self.full_reply_storage
+            .surbs_storage_ref()
+            .insert_surbs(&from, reply_surbs);
+
+        // use as many as we can for clearing pending retransmission queue
+        self.try_clear_pending_retransmission(from).await;
+
+        // use as many as we can for clearing pending 'normal' queue
+        self.try_clear_pending_queue(from).await;
+
+        // if we have to, request more
+        if self.should_request_more_surbs(&from) {
+            self.request_reply_surbs_for_queue_clearing(from).await;
+        }
+    }
+
+    async fn handle_surb_request(&mut self, recipient: Recipient, mut amount: u32) {
+        // 1. check whether we sent any surbs in the past to this recipient, otherwise
+        // they have no business in asking for more
+        if !self
+            .full_reply_storage
+            .tags_storage_ref()
+            .exists(&recipient)
+        {
+            warn!("{recipient} asked us for reply SURBs even though we never sent them any anonymous messages before!");
+            return;
+        }
+
+        // 2. check whether the requested amount is within sane range
+        if amount > self.config.maximum_allowed_reply_surb_request_size {
+            warn!("The requested reply surb amount is larger than our maximum allowed ({amount} > {}). Lowering it to a more sane value...", self.config.maximum_allowed_reply_surb_request_size);
+            amount = self.config.maximum_allowed_reply_surb_request_size;
+        }
+
+        // 3. construct and send the surbs away
+        // (send them in smaller batches to make the experience a bit smoother
+        let mut remaining = amount;
+        while remaining > 0 {
+            let to_send = min(remaining, 100);
+            if let Err(err) = self
+                .message_handler
+                .try_send_additional_reply_surbs(recipient, to_send)
+                .await
+            {
+                warn!("failed to send additional surbs to {recipient} - {err}");
+            } else {
+                trace!("sent {to_send} reply SURBs to {recipient}");
+            }
+
+            remaining -= to_send;
+        }
+    }
+
+    fn buffer_pending_ack(
+        &mut self,
+        recipient: AnonymousSenderTag,
+        ack_ref: Arc<PendingAcknowledgement>,
+        weak_ack_ref: Weak<PendingAcknowledgement>,
+    ) {
+        let frag_id = ack_ref.inner_fragment_identifier();
+        if let Some(existing) = self.pending_retransmissions.get_mut(&recipient) {
+            if let Entry::Vacant(e) = existing.entry(frag_id) {
+                e.insert(weak_ack_ref);
+            } else {
+                warn!("we're already trying to retransmit {frag_id}. We must be really behind in surbs!");
+            }
+        } else {
+            let mut inner = BTreeMap::new();
+            inner.insert(frag_id, weak_ack_ref);
+            self.pending_retransmissions.insert(recipient, inner);
+        }
+    }
+
+    async fn handle_reply_retransmission(
+        &mut self,
+        recipient_tag: AnonymousSenderTag,
+        timed_out_ack: Weak<PendingAcknowledgement>,
+        extra_surbs_request: bool,
+    ) {
+        // seems we got the ack in the end
+        let ack_ref = match timed_out_ack.upgrade() {
+            Some(ack) => ack,
+            None => {
+                debug!("we received the ack for one of the reply packets as we were putting it in the retransmission queue");
+                return;
+            }
+        };
+
+        // if this is retransmission for obtaining additional reply surbs,
+        // we can dip below the storage threshold
+        let (maybe_reply_surb, _) = if extra_surbs_request {
+            self.full_reply_storage
+                .surbs_storage_ref()
+                .get_reply_surb_ignoring_threshold(&recipient_tag)
+        } else {
+            self.full_reply_storage
+                .surbs_storage_ref()
+                .get_reply_surb(&recipient_tag)
+        }
+        .expect("attempted to retransmit a packet to an unknown recipient - we shouldn't have sent the original packet in the first place!");
+
+        if let Some(reply_surb) = maybe_reply_surb {
+            match self
+                .message_handler
+                .try_prepare_single_reply_chunk_for_sending(reply_surb, ack_ref.fragment_data())
+                .await
+            {
+                Ok(prepared) => {
+                    // drop the ack ref so that controller would not panic on `UpdateTimer` if that task
+                    // got to handle the action before this function terminated (which is very much
+                    // possible if `forward_messages` takes a while)
+                    drop(ack_ref);
+
+                    self.message_handler
+                        .update_ack_delay(prepared.fragment_identifier, prepared.total_delay);
+                    self.message_handler
+                        .forward_messages(vec![prepared.into()], TransmissionLane::Retransmission)
+                        .await;
+                }
+                Err(err) => {
+                    let err = err.return_unused_surbs(
+                        self.full_reply_storage.surbs_storage_ref(),
+                        &recipient_tag,
+                    );
+                    warn!("failed to prepare message for retransmission - {err}");
+                    // we buffer that packet and to try another day
+                    self.buffer_pending_ack(recipient_tag, ack_ref, timed_out_ack);
+
+                    if self.should_request_more_surbs(&recipient_tag) {
+                        self.request_reply_surbs_for_queue_clearing(recipient_tag)
+                            .await;
+                    }
+                }
+            };
+        } else {
+            self.buffer_pending_ack(recipient_tag, ack_ref, timed_out_ack);
+
+            if self.should_request_more_surbs(&recipient_tag) {
+                self.request_reply_surbs_for_queue_clearing(recipient_tag)
+                    .await;
+            }
+        }
+    }
+
+    async fn handle_request(&mut self, request: ReplyControllerMessage) {
+        match request {
+            ReplyControllerMessage::RetransmitReply {
+                recipient,
+                timed_out_ack,
+                extra_surb_request,
+            } => {
+                self.handle_reply_retransmission(recipient, timed_out_ack, extra_surb_request)
+                    .await
+            }
+            ReplyControllerMessage::SendReply {
+                recipient,
+                message,
+                lane,
+            } => self.handle_send_reply(recipient, message, lane).await,
+            ReplyControllerMessage::AdditionalSurbs {
+                sender_tag,
+                reply_surbs,
+                from_surb_request,
+            } => {
+                self.handle_received_surbs(sender_tag, reply_surbs, from_surb_request)
+                    .await
+            }
+            ReplyControllerMessage::AdditionalSurbsRequest { recipient, amount } => {
+                self.handle_surb_request(*recipient, amount).await
+            }
+        }
+    }
+
+    async fn request_reply_surbs_for_queue_clearing(&mut self, target: AnonymousSenderTag) {
+        trace!("requesting surbs for queues clearing");
+
+        let pending_queue_size = self
+            .pending_replies
+            .get(&target)
+            .map(|pending_queue| pending_queue.len())
+            .unwrap_or_default();
+
+        let retransmission_queue = self
+            .pending_retransmissions
+            .get(&target)
+            .map(|pending_queue| pending_queue.len())
+            .unwrap_or_default();
+
+        let total_queue = (pending_queue_size + retransmission_queue) as u32;
+
+        if total_queue == 0 {
+            trace!("the pending queues for {:?} are already empty", target);
+            return;
+        }
+
+        let request_size = min(
+            self.config.max_surb_request_size,
+            max(total_queue, self.config.min_surb_request_size),
+        );
+
+        if let Err(err) = self
+            .request_additional_reply_surbs(target, request_size)
+            .await
+        {
+            warn!("failed to request additional surbs... - {err}")
+        }
+    }
+
+    async fn inspect_stale_entries(&mut self) {
+        let mut to_request = Vec::new();
+        let mut to_remove = Vec::new();
+
+        let now = OffsetDateTime::now_utc();
+        for (pending_reply_target, vals) in &self.pending_replies {
+            if vals.is_empty() {
+                continue;
+            }
+
+            let Some(last_received) = self.full_reply_storage.surbs_storage_ref().surbs_last_received_at(pending_reply_target) else {
+                error!("we have {} pending replies for {pending_reply_target}, but we somehow never received any reply surbs from them!", vals.len());
+                to_remove.push(*pending_reply_target);
+                continue;
+            };
+
+            // this should never ever happen (famous last words, eh?), but in case it DOES happen eventually
+            // purge that malformed data
+            let Ok(last_received_time) = OffsetDateTime::from_unix_timestamp(last_received) else {
+                error!("somehow our stored timestamp ({last_received}) for surbs from {pending_reply_target} is corrupted!. Going to remove all the associated entries");
+                to_remove.push(*pending_reply_target);
+                continue;
+            };
+
+            let diff = now - last_received_time;
+
+            if diff > self.config.max_surb_waiting_period {
+                warn!("We haven't received any surbs in {:?} from {pending_reply_target}. Going to explicitly ask for more", diff);
+                to_request.push(*pending_reply_target);
+            }
+        }
+
+        for pending_reply_target in to_request {
+            self.request_reply_surbs_for_queue_clearing(pending_reply_target)
+                .await;
+            self.full_reply_storage
+                .surbs_storage_ref()
+                .reset_pending_reception(&pending_reply_target)
+        }
+        for to_remove in to_remove {
+            self.pending_replies.remove(&to_remove);
+        }
+    }
+
+    async fn invalidate_old_data(&self) {
+        let now = OffsetDateTime::now_utc();
+
+        let mut to_remove_surbs = Vec::new();
+        let mut to_remove_keys = Vec::new();
+        for map_ref in self.full_reply_storage.surbs_storage_ref().as_raw_iter() {
+            let (sender, received) = map_ref.pair();
+            // TODO: handle the following edge case:
+            // there's a malicious client sending us exactly one reply surb just before we should have invalidated
+            // the data thus making us keep everything in memory
+            // possible solution: keep timestamp PER reply surb (but that seems like an overkill)
+            // but I doubt this is ever going to be a problem...
+            // ...
+            // However, if you're reading this message, it probably became a legit problem,
+            // so I guess add timestamp per surb then? chop-chop.
+
+            let last_received = received.surbs_last_received_at();
+            // this should never ever happen (famous last words, eh?), but in case it DOES happen eventually
+            // purge that malformed data
+            let Ok(last_received_time) = OffsetDateTime::from_unix_timestamp(last_received) else {
+                error!("somehow our stored timestamp ({last_received}) for surbs from {sender} is corrupted!. Going to remove all the associated entries");
+                to_remove_surbs.push(*sender);
+                continue;
+            };
+            let diff = now - last_received_time;
+
+            if diff > self.config.max_reply_surb_age {
+                info!("it's been {diff:?} since we last received any reply surb from {sender}. Going to remove all stored entries...");
+
+                to_remove_surbs.push(*sender);
+            }
+        }
+
+        for map_ref in self.full_reply_storage.key_storage_ref().as_raw_iter() {
+            let (digest, reply_key) = map_ref.pair();
+
+            // this should never ever happen (famous last words, eh?), but in case it DOES happen eventually
+            // purge that malformed data
+            let Ok(sent_at) = OffsetDateTime::from_unix_timestamp(reply_key.sent_at_timestamp) else {
+                error!("somehow our stored timestamp ({}) for one of our reply key is corrupted!. Going to remove all the entry", reply_key.sent_at_timestamp);
+                to_remove_keys.push(*digest);
+                continue;
+            };
+
+            let diff = now - sent_at;
+
+            if diff > self.config.max_reply_key_age {
+                debug!("it's been {diff:?} since we created this reply key. it's probably never going to get used, so we're going to purge it...");
+                to_remove_keys.push(*digest);
+            }
+        }
+
+        for to_remove in to_remove_surbs {
+            self.full_reply_storage
+                .surbs_storage_ref()
+                .remove(&to_remove);
+        }
+
+        for to_remove in to_remove_keys {
+            self.full_reply_storage.key_storage().remove(to_remove)
+        }
+    }
+
+    fn create_interval_stream(polling_rate: Duration) -> IntervalStream {
+        #[cfg(not(target_arch = "wasm32"))]
+        return tokio_stream::wrappers::IntervalStream::new(tokio::time::interval(polling_rate));
+
+        #[cfg(target_arch = "wasm32")]
+        return gloo_timers::future::IntervalStream::new(polling_rate.as_millis() as u32);
+    }
+
+    pub(crate) async fn run_with_shutdown(&mut self, mut shutdown: task::ShutdownListener) {
+        debug!("Started ReplyController with graceful shutdown support");
+
+        let polling_rate = Duration::from_secs(5);
+        let mut stale_inspection = Self::create_interval_stream(polling_rate);
+
+        // this is in the order of hours/days so we don't have to poll it that often
+        let polling_rate = Duration::from_secs(self.config.max_reply_surb_age.as_secs() / 10);
+        let mut invalidation_inspection = Self::create_interval_stream(polling_rate);
+
+        while !shutdown.is_shutdown() {
+            tokio::select! {
+                biased;
+                _ = shutdown.recv() => {
+                    log::trace!("ReplyController: Received shutdown");
+                },
+                req = self.request_receiver.next() => match req {
+                    Some(req) => self.handle_request(req).await,
+                    None => {
+                        log::trace!("ReplyController: Stopping since channel closed");
+                        break;
+                    }
+                },
+                _ = stale_inspection.next() => {
+                    self.inspect_stale_entries().await
+                },
+                _ = invalidation_inspection.next() => {
+                    self.invalidate_old_data().await
+                }
+            }
+        }
+        assert!(shutdown.is_shutdown_poll());
+        log::debug!("ReplyController: Exiting");
+    }
+}
@@ -0,0 +1,43 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::replies::reply_storage::backend::Empty;
+use crate::client::replies::reply_storage::{CombinedReplyStorage, ReplyStorageBackend};
+use async_trait::async_trait;
+
+// well, right now we don't have the browser storage : (
+// so we keep everything in memory
+pub struct Backend {
+    empty: Empty,
+}
+
+impl Backend {
+    pub fn new(min_surb_threshold: usize, max_surb_threshold: usize) -> Self {
+        Backend {
+            empty: Empty {
+                min_surb_threshold,
+                max_surb_threshold,
+            },
+        }
+    }
+}
+
+#[async_trait]
+impl ReplyStorageBackend for Backend {
+    type StorageError = <Empty as ReplyStorageBackend>::StorageError;
+
+    async fn flush_surb_storage(
+        &mut self,
+        storage: &CombinedReplyStorage,
+    ) -> Result<(), Self::StorageError> {
+        self.empty.flush_surb_storage(storage).await
+    }
+
+    async fn init_fresh(&mut self, fresh: &CombinedReplyStorage) -> Result<(), Self::StorageError> {
+        self.empty.init_fresh(fresh).await
+    }
+
+    async fn load_surb_storage(&self) -> Result<CombinedReplyStorage, Self::StorageError> {
+        self.empty.load_surb_storage().await
+    }
+}
@@ -0,0 +1,53 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use std::io;
+use std::path::PathBuf;
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum StorageError {
+    #[error("the provided database path doesn't have a filename defined")]
+    DatabasePathWithoutFilename { provided_path: PathBuf },
+
+    #[error("failed to rename our databse file - {source}")]
+    DatabaseRenameError {
+        #[source]
+        source: io::Error,
+    },
+
+    #[error("failed to rename our old databse file - {source}")]
+    DatabaseOldFileRemoveError {
+        #[source]
+        source: io::Error,
+    },
+
+    #[error("failed to perform sqlx migration: {source}")]
+    MigrationError {
+        #[source]
+        #[from]
+        source: sqlx::migrate::MigrateError,
+    },
+
+    #[error("failed to connect to the underlying connection pool: {source}")]
+    DatabaseConnectionError {
+        #[source]
+        source: sqlx::error::Error,
+    },
+
+    #[error("failed to run the SQL query: {source}")]
+    QueryError {
+        #[source]
+        #[from]
+        source: sqlx::error::Error,
+    },
+
+    #[error("The loaded data is inconsistent - it seems that on the last shutdown the client hasn't finished the data flush. You may have to remove the entire storage manually")]
+    IncompleteDataFlush,
+
+    #[error("data retrieved from the underlying storage is corrupted: {details}")]
+    CorruptedData {
+        details: String,
+        // err: Option<Box<dyn std::error::Error>>
+    },
+}
@@ -0,0 +1,257 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::replies::reply_storage::backend::fs_backend::error::StorageError;
+use crate::client::replies::reply_storage::backend::fs_backend::models::{
+    ReplySurbStorageMetadata, StoredReplyKey, StoredReplySurb, StoredSenderTag, StoredSurbSender,
+};
+use log::{error, info};
+use sqlx::ConnectOptions;
+use std::path::Path;
+
+#[derive(Debug, Clone)]
+pub(crate) struct StorageManager {
+    pub(crate) connection_pool: sqlx::SqlitePool,
+}
+
+// all SQL goes here
+impl StorageManager {
+    pub(crate) async fn init<P: AsRef<Path>>(
+        database_path: P,
+        fresh: bool,
+    ) -> Result<Self, StorageError> {
+        let mut opts = sqlx::sqlite::SqliteConnectOptions::new()
+            .filename(database_path)
+            .create_if_missing(fresh);
+
+        opts.disable_statement_logging();
+
+        let connection_pool = match sqlx::SqlitePool::connect_with(opts).await {
+            Ok(pool) => pool,
+            Err(err) => {
+                error!("Failed to connect to SQLx database: {err}");
+                return Err(StorageError::DatabaseConnectionError { source: err });
+            }
+        };
+
+        if let Err(err) = sqlx::migrate!("./fs_surbs_migrations")
+            .run(&connection_pool)
+            .await
+        {
+            error!("Failed to initialize SQLx database: {err}");
+            return Err(err.into());
+        }
+
+        info!("Database migration finished!");
+        Ok(StorageManager { connection_pool })
+    }
+
+    #[allow(dead_code)]
+    pub(crate) async fn status_table_exists(&self) -> Result<bool, sqlx::Error> {
+        sqlx::query!("SELECT name FROM sqlite_master WHERE type='table' AND name='status'")
+            .fetch_optional(&self.connection_pool)
+            .await
+            .map(|r| r.is_some())
+    }
+
+    pub(crate) async fn create_status_table(&self) -> Result<(), sqlx::Error> {
+        sqlx::query!("INSERT INTO status(flush_in_progress, previous_flush_timestamp, client_in_use) VALUES (0, 0, 1)")
+            .execute(&self.connection_pool)
+            .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn get_flush_status(&self) -> Result<bool, sqlx::Error> {
+        sqlx::query!("SELECT flush_in_progress FROM status;")
+            .fetch_one(&self.connection_pool)
+            .await
+            .map(|r| r.flush_in_progress > 0)
+    }
+
+    pub(crate) async fn set_previous_flush_timestamp(
+        &self,
+        timestamp: i64,
+    ) -> Result<(), sqlx::Error> {
+        sqlx::query!("UPDATE status SET previous_flush_timestamp = ?", timestamp)
+            .execute(&self.connection_pool)
+            .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn get_previous_flush_timestamp(&self) -> Result<i64, sqlx::Error> {
+        sqlx::query!("SELECT previous_flush_timestamp FROM status;")
+            .fetch_one(&self.connection_pool)
+            .await
+            .map(|r| r.previous_flush_timestamp)
+    }
+
+    pub(crate) async fn set_flush_status(&self, in_progress: bool) -> Result<(), sqlx::Error> {
+        let in_progress_int = i64::from(in_progress);
+        sqlx::query!("UPDATE status SET flush_in_progress = ?", in_progress_int)
+            .execute(&self.connection_pool)
+            .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn get_client_in_use_status(&self) -> Result<bool, sqlx::Error> {
+        sqlx::query!("SELECT client_in_use FROM status;")
+            .fetch_one(&self.connection_pool)
+            .await
+            .map(|r| r.client_in_use > 0)
+    }
+
+    pub(crate) async fn set_client_in_use_status(&self, in_use: bool) -> Result<(), sqlx::Error> {
+        let in_use_int = i64::from(in_use);
+        sqlx::query!("UPDATE status SET client_in_use = ?", in_use_int)
+            .execute(&self.connection_pool)
+            .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn delete_all_tags(&self) -> Result<(), sqlx::Error> {
+        sqlx::query!("DELETE FROM sender_tag;")
+            .execute(&self.connection_pool)
+            .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn get_tags(&self) -> Result<Vec<StoredSenderTag>, sqlx::Error> {
+        sqlx::query_as!(StoredSenderTag, "SELECT * FROM sender_tag;",)
+            .fetch_all(&self.connection_pool)
+            .await
+    }
+
+    pub(crate) async fn insert_tag(&self, stored_tag: StoredSenderTag) -> Result<(), sqlx::Error> {
+        sqlx::query!(
+            r#"
+                INSERT INTO sender_tag(recipient, tag) VALUES (?, ?);
+            "#,
+            stored_tag.recipient,
+            stored_tag.tag
+        )
+        .execute(&self.connection_pool)
+        .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn delete_all_reply_keys(&self) -> Result<(), sqlx::Error> {
+        sqlx::query!("DELETE FROM reply_key;")
+            .execute(&self.connection_pool)
+            .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn get_reply_keys(&self) -> Result<Vec<StoredReplyKey>, sqlx::Error> {
+        sqlx::query_as!(StoredReplyKey, "SELECT * FROM reply_key;",)
+            .fetch_all(&self.connection_pool)
+            .await
+    }
+
+    pub(crate) async fn insert_reply_key(
+        &self,
+        stored_reply_key: StoredReplyKey,
+    ) -> Result<(), sqlx::Error> {
+        sqlx::query!(
+            r#"
+                INSERT INTO reply_key(key_digest, reply_key, sent_at_timestamp) VALUES (?, ?, ?);
+            "#,
+            stored_reply_key.key_digest,
+            stored_reply_key.reply_key,
+            stored_reply_key.sent_at_timestamp
+        )
+        .execute(&self.connection_pool)
+        .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn get_surb_senders(&self) -> Result<Vec<StoredSurbSender>, sqlx::Error> {
+        sqlx::query_as!(StoredSurbSender, "SELECT * FROM reply_surb_sender;",)
+            .fetch_all(&self.connection_pool)
+            .await
+    }
+
+    pub(crate) async fn insert_surb_sender(
+        &self,
+        stored_surb_sender: StoredSurbSender,
+    ) -> Result<i64, sqlx::Error> {
+        let id = sqlx::query!(
+            r#"
+                INSERT INTO reply_surb_sender(tag, last_sent_timestamp) VALUES (?, ?);
+            "#,
+            stored_surb_sender.tag,
+            stored_surb_sender.last_sent_timestamp
+        )
+        .execute(&self.connection_pool)
+        .await?
+        .last_insert_rowid();
+        Ok(id)
+    }
+
+    pub(crate) async fn get_reply_surbs(
+        &self,
+        sender_id: i64,
+    ) -> Result<Vec<StoredReplySurb>, sqlx::Error> {
+        sqlx::query_as!(
+            StoredReplySurb,
+            "SELECT * FROM reply_surb WHERE reply_surb_sender_id = ?",
+            sender_id
+        )
+        .fetch_all(&self.connection_pool)
+        .await
+    }
+
+    pub(crate) async fn delete_all_reply_surb_data(&self) -> Result<(), sqlx::Error> {
+        sqlx::query!("DELETE FROM reply_surb;")
+            .execute(&self.connection_pool)
+            .await?;
+
+        sqlx::query!("DELETE FROM reply_surb_sender;")
+            .execute(&self.connection_pool)
+            .await?;
+
+        Ok(())
+    }
+
+    pub(crate) async fn insert_reply_surb(
+        &self,
+        stored_reply_surb: StoredReplySurb,
+    ) -> Result<(), sqlx::Error> {
+        sqlx::query!(
+            r#"
+                INSERT INTO reply_surb(reply_surb_sender_id, reply_surb) VALUES (?, ?);
+            "#,
+            stored_reply_surb.reply_surb_sender_id,
+            stored_reply_surb.reply_surb
+        )
+        .execute(&self.connection_pool)
+        .await?;
+        Ok(())
+    }
+
+    pub(crate) async fn get_reply_surb_storage_metadata(
+        &self,
+    ) -> Result<ReplySurbStorageMetadata, sqlx::Error> {
+        sqlx::query_as!(
+            ReplySurbStorageMetadata,
+             r#"
+                SELECT min_reply_surb_threshold as "min_reply_surb_threshold: u32", max_reply_surb_threshold as "max_reply_surb_threshold: u32" FROM reply_surb_storage_metadata;
+             "#,
+        )
+            .fetch_one(&self.connection_pool)
+            .await
+    }
+
+    pub(crate) async fn insert_reply_surb_storage_metadata(
+        &self,
+        metadata: ReplySurbStorageMetadata,
+    ) -> Result<(), sqlx::Error> {
+        sqlx::query!(r#"
+            INSERT INTO reply_surb_storage_metadata(min_reply_surb_threshold, max_reply_surb_threshold)
+            VALUES (?, ?);
+        "#,
+            metadata.min_reply_surb_threshold,
+            metadata.max_reply_surb_threshold,
+        ).execute(&self.connection_pool).await?;
+        Ok(())
+    }
+}
@@ -0,0 +1,336 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+pub use self::error::StorageError;
+use crate::client::replies::reply_storage::backend::fs_backend::manager::StorageManager;
+use crate::client::replies::reply_storage::backend::fs_backend::models::{
+    ReplySurbStorageMetadata, StoredReplyKey, StoredReplySurb, StoredSenderTag, StoredSurbSender,
+};
+use crate::client::replies::reply_storage::surb_storage::ReceivedReplySurbs;
+use crate::client::replies::reply_storage::{
+    CombinedReplyStorage, ReceivedReplySurbsMap, ReplyStorageBackend, SentReplyKeys, UsedSenderTags,
+};
+use async_trait::async_trait;
+use log::{error, info, warn};
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
+use std::fs;
+use std::path::{Path, PathBuf};
+use time::OffsetDateTime;
+
+mod error;
+mod manager;
+mod models;
+
+#[derive(Debug)]
+pub struct Backend {
+    temporary_old_path: Option<PathBuf>,
+    database_path: PathBuf,
+    manager: StorageManager,
+}
+
+impl Backend {
+    const OLD_EXTENSION: &'static str = "old";
+
+    pub async fn init<P: AsRef<Path>>(database_path: P) -> Result<Self, StorageError> {
+        let owned_path: PathBuf = database_path.as_ref().into();
+        if owned_path.file_name().is_none() {
+            return Err(StorageError::DatabasePathWithoutFilename {
+                provided_path: owned_path,
+            });
+        }
+
+        let backend = Backend {
+            temporary_old_path: None,
+            database_path: owned_path,
+            manager: StorageManager::init(database_path, true).await?,
+        };
+
+        backend.manager.create_status_table().await?;
+
+        Ok(backend)
+    }
+
+    pub async fn try_load<P: AsRef<Path>>(database_path: P) -> Result<Self, StorageError> {
+        let owned_path: PathBuf = database_path.as_ref().into();
+        if owned_path.file_name().is_none() {
+            return Err(StorageError::DatabasePathWithoutFilename {
+                provided_path: owned_path,
+            });
+        }
+
+        let manager = StorageManager::init(database_path, false).await?;
+
+        // the database flush wasn't fully finished and thus the data is in inconsistent state
+        // (we don't really know what's properly saved or what's not)
+        if manager.get_flush_status().await? {
+            return Err(StorageError::IncompleteDataFlush);
+        }
+
+        // the process has gone down without full graceful shutdown,
+        // meaning the database doesn't contain valid data anymore
+        // so we have to purge it
+        if manager.get_client_in_use_status().await? {
+            error!("the client hasn't undergone through graceful shutdown the last time it's gone down - we can't trust its reply surbs or stored encryption keys. They shall get purged");
+            manager.delete_all_reply_surb_data().await?;
+            manager.delete_all_reply_keys().await?;
+        }
+
+        let last_flush_timestamp = manager.get_previous_flush_timestamp().await?;
+        let last_flush = match OffsetDateTime::from_unix_timestamp(last_flush_timestamp) {
+            Ok(last_flush) => last_flush,
+            Err(err) => {
+                return Err(StorageError::CorruptedData {
+                    details: format!("failed to parse stored timestamp - {err}"),
+                });
+            }
+        };
+
+        // in theory clients can use our reply surbs whenever they want, even a year in the future
+        // (assuming no key rotation has happened)
+        // but the way it's currently coded, everyone will purge old data
+        let since_last_flush = OffsetDateTime::now_utc() - last_flush;
+        if since_last_flush.whole_days() > 0 {
+            info!("it's been over {} days and {} hours since we last used our data store. our reply surbs are already outdated - we're going to purge them now.", since_last_flush.whole_days(), since_last_flush.whole_hours());
+            manager.delete_all_reply_surb_data().await?;
+        }
+
+        if since_last_flush.whole_days() > 1 {
+            info!("it's been over {} days and {} hours since we last used our data store. our reply keys are already outdated - we're going to purge them now.", since_last_flush.whole_days(), since_last_flush.whole_hours());
+            manager.delete_all_reply_keys().await?;
+        }
+
+        if since_last_flush.whole_days() > 2 {
+            info!("it's been over {} days and {} hours since we last used our data store. our used sender tags are already outdated - we're going to purge them now.", since_last_flush.whole_days(), since_last_flush.whole_hours());
+            manager.delete_all_tags().await?;
+        }
+
+        Ok(Backend {
+            temporary_old_path: None,
+            database_path: owned_path,
+            manager,
+        })
+    }
+
+    async fn close_pool(&mut self) {
+        self.manager.connection_pool.close().await;
+    }
+
+    async fn rotate(&mut self) -> Result<(), StorageError> {
+        self.close_pool().await;
+
+        let new_extension = if let Some(existing_extension) =
+            self.database_path.extension().and_then(|ext| ext.to_str())
+        {
+            format!("{existing_extension}.{}", Self::OLD_EXTENSION)
+        } else {
+            Self::OLD_EXTENSION.to_string()
+        };
+
+        let mut temp_old = self.database_path.clone();
+        temp_old.set_extension(new_extension);
+
+        fs::rename(&self.database_path, &temp_old)
+            .map_err(|err| StorageError::DatabaseRenameError { source: err })?;
+        self.manager = StorageManager::init(&self.database_path, true).await?;
+        self.manager.create_status_table().await?;
+
+        self.temporary_old_path = Some(temp_old);
+        Ok(())
+    }
+
+    fn remove_old(&mut self) -> Result<(), StorageError> {
+        if let Some(old_path) = self.temporary_old_path.take() {
+            fs::remove_file(old_path)
+                .map_err(|err| StorageError::DatabaseOldFileRemoveError { source: err })
+        } else {
+            warn!("the old database file doesn't seem to exist!");
+            Ok(())
+        }
+    }
+
+    async fn start_storage_flush(&self) -> Result<(), StorageError> {
+        Ok(self.manager.set_flush_status(true).await?)
+    }
+
+    async fn end_storage_flush(&self) -> Result<(), StorageError> {
+        self.manager
+            .set_previous_flush_timestamp(OffsetDateTime::now_utc().unix_timestamp())
+            .await?;
+        Ok(self.manager.set_flush_status(false).await?)
+    }
+
+    async fn start_client_use(&self) -> Result<(), StorageError> {
+        Ok(self.manager.set_client_in_use_status(true).await?)
+    }
+
+    async fn stop_client_use(&self) -> Result<(), StorageError> {
+        Ok(self.manager.set_client_in_use_status(false).await?)
+    }
+
+    async fn get_stored_tags(&self) -> Result<UsedSenderTags, StorageError> {
+        let stored = self.manager.get_tags().await?;
+
+        // stop at the first instance of corruption. if even a single entry is malformed,
+        // something weird has happened and we can't trust the rest of the data
+        let raw = stored
+            .into_iter()
+            .map(TryInto::try_into)
+            .collect::<Result<_, _>>()?;
+
+        Ok(UsedSenderTags::from_raw(raw))
+    }
+
+    async fn dump_sender_tags(&self, tags: &UsedSenderTags) -> Result<(), StorageError> {
+        for map_ref in tags.as_raw_iter() {
+            let (recipient, tag) = map_ref.pair();
+            self.manager
+                .insert_tag(StoredSenderTag::new(*recipient, *tag))
+                .await?;
+        }
+        Ok(())
+    }
+
+    async fn get_stored_reply_keys(&self) -> Result<SentReplyKeys, StorageError> {
+        let stored = self.manager.get_reply_keys().await?;
+
+        // stop at the first instance of corruption. if even a single entry is malformed,
+        // something weird has happened and we can't trust the rest of the data
+        let raw = stored
+            .into_iter()
+            .map(TryInto::try_into)
+            .collect::<Result<_, _>>()?;
+
+        Ok(SentReplyKeys::from_raw(raw))
+    }
+
+    async fn dump_sender_reply_keys(&self, reply_keys: &SentReplyKeys) -> Result<(), StorageError> {
+        for map_ref in reply_keys.as_raw_iter() {
+            let (digest, key) = map_ref.pair();
+            self.manager
+                .insert_reply_key(StoredReplyKey::new(*digest, *key))
+                .await?;
+        }
+        Ok(())
+    }
+
+    async fn get_stored_reply_surbs(&self) -> Result<ReceivedReplySurbsMap, StorageError> {
+        let surb_senders = self.manager.get_surb_senders().await?;
+
+        let metadata = self.get_reply_surb_storage_metadata().await?;
+        let mut received_surbs = Vec::with_capacity(surb_senders.len());
+        for sender in surb_senders {
+            let sender_id = sender.id;
+            let (sender_tag, surbs_last_received_at_timestamp): (AnonymousSenderTag, i64) =
+                sender.try_into()?;
+            let stored_surbs = self
+                .manager
+                .get_reply_surbs(sender_id)
+                .await?
+                .into_iter()
+                .map(|raw| raw.try_into())
+                .collect::<Result<_, _>>()?;
+
+            received_surbs.push((
+                sender_tag,
+                ReceivedReplySurbs::new_retrieved(stored_surbs, surbs_last_received_at_timestamp),
+            ))
+        }
+
+        Ok(ReceivedReplySurbsMap::from_raw(
+            metadata.min_reply_surb_threshold as usize,
+            metadata.max_reply_surb_threshold as usize,
+            received_surbs,
+        ))
+    }
+
+    async fn dump_reply_surbs(
+        &self,
+        reply_surbs: &ReceivedReplySurbsMap,
+    ) -> Result<(), StorageError> {
+        for map_ref in reply_surbs.as_raw_iter() {
+            let (tag, received_surbs) = map_ref.pair();
+            let sender_id = self
+                .manager
+                .insert_surb_sender(StoredSurbSender::new(
+                    *tag,
+                    received_surbs.surbs_last_received_at(),
+                ))
+                .await?;
+
+            for reply_surb in received_surbs.surbs_ref() {
+                self.manager
+                    .insert_reply_surb(StoredReplySurb::new(sender_id, reply_surb))
+                    .await?
+            }
+        }
+        Ok(())
+    }
+
+    async fn get_reply_surb_storage_metadata(
+        &self,
+    ) -> Result<ReplySurbStorageMetadata, StorageError> {
+        self.manager
+            .get_reply_surb_storage_metadata()
+            .await
+            .map_err(Into::into)
+    }
+
+    async fn dump_reply_surb_storage_metadata(
+        &self,
+        reply_surbs: &ReceivedReplySurbsMap,
+    ) -> Result<(), StorageError> {
+        self.manager
+            .insert_reply_surb_storage_metadata(ReplySurbStorageMetadata::new(
+                reply_surbs.min_surb_threshold(),
+                reply_surbs.max_surb_threshold(),
+            ))
+            .await
+            .map_err(Into::into)
+    }
+}
+
+#[async_trait]
+impl ReplyStorageBackend for Backend {
+    type StorageError = error::StorageError;
+
+    async fn start_storage_session(&self) -> Result<(), Self::StorageError> {
+        self.start_client_use().await
+    }
+
+    async fn flush_surb_storage(
+        &mut self,
+        storage: &CombinedReplyStorage,
+    ) -> Result<(), Self::StorageError> {
+        // close all connections (there should be none! and rename the file to contain .old extension)
+        self.rotate().await?;
+        self.start_storage_flush().await?;
+
+        self.dump_sender_tags(storage.tags_storage_ref()).await?;
+        self.dump_sender_reply_keys(storage.key_storage_ref())
+            .await?;
+        let surbs_ref = storage.surbs_storage_ref();
+        self.dump_reply_surb_storage_metadata(surbs_ref).await?;
+        self.dump_reply_surbs(surbs_ref).await?;
+
+        self.remove_old()?;
+        self.end_storage_flush().await
+    }
+
+    async fn init_fresh(&mut self, fresh: &CombinedReplyStorage) -> Result<(), Self::StorageError> {
+        // for now nothing more to do apart from dumping the metadata
+        self.dump_reply_surb_storage_metadata(fresh.surbs_storage_ref())
+            .await
+    }
+
+    async fn load_surb_storage(&self) -> Result<CombinedReplyStorage, Self::StorageError> {
+        let reply_keys = self.get_stored_reply_keys().await?;
+        let tags = self.get_stored_tags().await?;
+        let reply_surbs = self.get_stored_reply_surbs().await?;
+
+        Ok(CombinedReplyStorage::load(reply_keys, reply_surbs, tags))
+    }
+
+    async fn stop_storage_session(self) -> Result<(), Self::StorageError> {
+        self.stop_client_use().await
+    }
+}
@@ -0,0 +1,185 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::replies::reply_storage::backend::fs_backend::error::StorageError;
+use crate::client::replies::reply_storage::key_storage::UsedReplyKey;
+use crypto::generic_array::typenum::Unsigned;
+use crypto::Digest;
+use nymsphinx::addressing::clients::{Recipient, RecipientBytes};
+use nymsphinx::anonymous_replies::encryption_key::EncryptionKeyDigest;
+use nymsphinx::anonymous_replies::requests::{AnonymousSenderTag, SENDER_TAG_SIZE};
+use nymsphinx::anonymous_replies::{ReplySurb, SurbEncryptionKey, SurbEncryptionKeySize};
+use nymsphinx::params::ReplySurbKeyDigestAlgorithm;
+
+#[derive(Debug, Clone)]
+pub(crate) struct StoredSenderTag {
+    pub(crate) recipient: Vec<u8>,
+    pub(crate) tag: Vec<u8>,
+}
+
+impl StoredSenderTag {
+    pub(crate) fn new(recipient: RecipientBytes, tag: AnonymousSenderTag) -> StoredSenderTag {
+        StoredSenderTag {
+            recipient: recipient.to_vec(),
+            tag: tag.to_bytes().to_vec(),
+        }
+    }
+}
+
+impl TryFrom<StoredSenderTag> for (RecipientBytes, AnonymousSenderTag) {
+    type Error = StorageError;
+
+    fn try_from(value: StoredSenderTag) -> Result<Self, Self::Error> {
+        let recipient_len = value.recipient.len();
+        let Ok(recipient_bytes) = value.recipient.try_into() else {
+            return Err(StorageError::CorruptedData {
+                details: format!(
+                    "the retrieved recipient has length of {recipient_len} while {} was expected",
+                    Recipient::LEN
+                ),
+            });
+        };
+
+        let tag_len = value.tag.len();
+        let Ok(sender_tag_bytes) = value.tag.try_into() else {
+            return Err(StorageError::CorruptedData {
+                details: format!(
+                    "the retrieved sender tag has length of {tag_len} while {} was expected",
+                    SENDER_TAG_SIZE
+                ),
+            });
+        };
+
+        Ok((
+            recipient_bytes,
+            AnonymousSenderTag::from_bytes(sender_tag_bytes),
+        ))
+    }
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct StoredReplyKey {
+    pub(crate) key_digest: Vec<u8>,
+    pub(crate) reply_key: Vec<u8>,
+    pub(crate) sent_at_timestamp: i64,
+}
+
+impl StoredReplyKey {
+    pub(crate) fn new(key_digest: EncryptionKeyDigest, reply_key: UsedReplyKey) -> StoredReplyKey {
+        StoredReplyKey {
+            key_digest: key_digest.to_vec(),
+            reply_key: (*reply_key).to_bytes(),
+            sent_at_timestamp: reply_key.sent_at_timestamp,
+        }
+    }
+}
+
+impl TryFrom<StoredReplyKey> for (EncryptionKeyDigest, UsedReplyKey) {
+    type Error = StorageError;
+
+    fn try_from(value: StoredReplyKey) -> Result<Self, Self::Error> {
+        let expected_reply_key_digest_size = ReplySurbKeyDigestAlgorithm::output_size();
+        let reply_key_digest_size = value.key_digest.len();
+
+        let Some(digest) = EncryptionKeyDigest::from_exact_iter(value.key_digest) else {
+            return Err(StorageError::CorruptedData {
+                details: format!(
+                    "the reply surb digest has length of {reply_key_digest_size} while {expected_reply_key_digest_size} was expected",
+                ),
+            });
+        };
+
+        let reply_key_len = value.reply_key.len();
+        let Ok(reply_key) = SurbEncryptionKey::try_from_bytes(&value.reply_key) else {
+            return Err(StorageError::CorruptedData {
+                details: format!(
+                    "the reply key has length of {reply_key_len} while {} was expected",
+                    SurbEncryptionKeySize::USIZE
+                ),
+            });
+        };
+
+        Ok((
+            digest,
+            UsedReplyKey::new(reply_key, value.sent_at_timestamp),
+        ))
+    }
+}
+
+pub(crate) struct StoredSurbSender {
+    pub(crate) id: i64,
+    pub(crate) tag: Vec<u8>,
+    pub(crate) last_sent_timestamp: i64,
+}
+
+impl StoredSurbSender {
+    pub(crate) fn new(tag: AnonymousSenderTag, last_sent_timestamp: i64) -> Self {
+        StoredSurbSender {
+            // for the purposes of STORING data,
+            // we ignore that field anyway
+            id: 0,
+            tag: tag.to_bytes().to_vec(),
+            last_sent_timestamp,
+        }
+    }
+}
+
+impl TryFrom<StoredSurbSender> for (AnonymousSenderTag, i64) {
+    type Error = StorageError;
+
+    fn try_from(value: StoredSurbSender) -> Result<Self, Self::Error> {
+        let tag_len = value.tag.len();
+        let Ok(sender_tag_bytes) = value.tag.try_into() else {
+            return Err(StorageError::CorruptedData {
+                details: format!(
+                    "the retrieved sender tag has length of {tag_len} while {} was expected",
+                    SENDER_TAG_SIZE
+                ),
+            });
+        };
+
+        Ok((
+            AnonymousSenderTag::from_bytes(sender_tag_bytes),
+            value.last_sent_timestamp,
+        ))
+    }
+}
+
+pub(crate) struct StoredReplySurb {
+    pub(crate) reply_surb_sender_id: i64,
+    pub(crate) reply_surb: Vec<u8>,
+}
+
+impl StoredReplySurb {
+    pub(crate) fn new(reply_surb_sender_id: i64, reply_surb: &ReplySurb) -> Self {
+        StoredReplySurb {
+            reply_surb_sender_id,
+            reply_surb: reply_surb.to_bytes(),
+        }
+    }
+}
+
+impl TryFrom<StoredReplySurb> for ReplySurb {
+    type Error = StorageError;
+
+    fn try_from(value: StoredReplySurb) -> Result<Self, Self::Error> {
+        ReplySurb::from_bytes(&value.reply_surb).map_err(|err| StorageError::CorruptedData {
+            details: format!("failed to recover the reply surb: {err}"),
+        })
+    }
+}
+
+#[derive(Copy, Clone)]
+pub(crate) struct ReplySurbStorageMetadata {
+    pub(crate) min_reply_surb_threshold: u32,
+    pub(crate) max_reply_surb_threshold: u32,
+}
+
+impl ReplySurbStorageMetadata {
+    pub(crate) fn new(min_reply_surb_threshold: usize, max_reply_surb_threshold: usize) -> Self {
+        Self {
+            min_reply_surb_threshold: min_reply_surb_threshold as u32,
+            max_reply_surb_threshold: max_reply_surb_threshold as u32,
+        }
+    }
+}
@@ -0,0 +1,78 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::replies::reply_storage::CombinedReplyStorage;
+use async_trait::async_trait;
+use std::error::Error;
+use thiserror::Error;
+
+#[cfg(target_arch = "wasm32")]
+pub mod browser_backend;
+
+#[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+pub mod fs_backend;
+
+// #[cfg(all(test, feature = "std"))]
+// third case: node with actual filesystem
+
+#[derive(Debug, Error)]
+#[error("no information provided")]
+pub struct UndefinedError;
+
+pub struct Empty {
+    // we need to keep 'basic' metadata here to "load" the CombinedReplyStorage
+    min_surb_threshold: usize,
+    max_surb_threshold: usize,
+}
+
+#[async_trait]
+impl ReplyStorageBackend for Empty {
+    type StorageError = UndefinedError;
+
+    async fn flush_surb_storage(
+        &mut self,
+        _storage: &CombinedReplyStorage,
+    ) -> Result<(), Self::StorageError> {
+        Ok(())
+    }
+
+    async fn init_fresh(
+        &mut self,
+        _fresh: &CombinedReplyStorage,
+    ) -> Result<(), Self::StorageError> {
+        Ok(())
+    }
+
+    async fn load_surb_storage(&self) -> Result<CombinedReplyStorage, Self::StorageError> {
+        Ok(CombinedReplyStorage::new(
+            self.min_surb_threshold,
+            self.max_surb_threshold,
+        ))
+    }
+}
+
+#[async_trait]
+pub trait ReplyStorageBackend: Sized {
+    type StorageError: Error + 'static;
+
+    async fn start_storage_session(&self) -> Result<(), Self::StorageError> {
+        Ok(())
+    }
+
+    // reply keys and surbs would need additional field set when data is loaded
+    // so if there's some failure, we'd trash it all
+    async fn flush_surb_storage(
+        &mut self,
+        storage: &CombinedReplyStorage,
+    ) -> Result<(), Self::StorageError>;
+
+    /// The purpose of this call is to save any metadata that might be present.
+    /// (such as surb thresholds)
+    async fn init_fresh(&mut self, fresh: &CombinedReplyStorage) -> Result<(), Self::StorageError>;
+
+    async fn load_surb_storage(&self) -> Result<CombinedReplyStorage, Self::StorageError>;
+
+    async fn stop_storage_session(self) -> Result<(), Self::StorageError> {
+        Ok(())
+    }
+}
@@ -0,0 +1,60 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::client::replies::reply_storage::{ReceivedReplySurbsMap, SentReplyKeys, UsedSenderTags};
+
+#[derive(Debug, Clone)]
+pub struct CombinedReplyStorage {
+    sent_reply_keys: SentReplyKeys,
+    received_reply_surbs: ReceivedReplySurbsMap,
+    used_tags: UsedSenderTags,
+}
+
+impl CombinedReplyStorage {
+    pub fn new(min_surb_threshold: usize, max_surb_threshold: usize) -> CombinedReplyStorage {
+        CombinedReplyStorage {
+            sent_reply_keys: SentReplyKeys::new(),
+            received_reply_surbs: ReceivedReplySurbsMap::new(
+                min_surb_threshold,
+                max_surb_threshold,
+            ),
+            used_tags: UsedSenderTags::new(),
+        }
+    }
+
+    pub fn load(
+        sent_reply_keys: SentReplyKeys,
+        received_reply_surbs: ReceivedReplySurbsMap,
+        used_tags: UsedSenderTags,
+    ) -> Self {
+        CombinedReplyStorage {
+            sent_reply_keys,
+            received_reply_surbs,
+            used_tags,
+        }
+    }
+
+    pub fn key_storage(&self) -> SentReplyKeys {
+        self.sent_reply_keys.clone()
+    }
+
+    pub fn surbs_storage(&self) -> ReceivedReplySurbsMap {
+        self.received_reply_surbs.clone()
+    }
+
+    pub fn tags_storage(&self) -> UsedSenderTags {
+        self.used_tags.clone()
+    }
+
+    pub fn key_storage_ref(&self) -> &SentReplyKeys {
+        &self.sent_reply_keys
+    }
+
+    pub fn surbs_storage_ref(&self) -> &ReceivedReplySurbsMap {
+        &self.received_reply_surbs
+    }
+
+    pub fn tags_storage_ref(&self) -> &UsedSenderTags {
+        &self.used_tags
+    }
+}
@@ -0,0 +1,86 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use dashmap::iter::Iter;
+use dashmap::DashMap;
+use nymsphinx::anonymous_replies::encryption_key::EncryptionKeyDigest;
+use nymsphinx::anonymous_replies::SurbEncryptionKey;
+use std::ops::Deref;
+use std::sync::Arc;
+use time::OffsetDateTime;
+
+#[derive(Debug, Clone)]
+pub struct SentReplyKeys {
+    inner: Arc<SentReplyKeysInner>,
+}
+
+#[derive(Debug)]
+struct SentReplyKeysInner {
+    data: DashMap<EncryptionKeyDigest, UsedReplyKey>,
+}
+
+impl SentReplyKeys {
+    pub(crate) fn new() -> SentReplyKeys {
+        SentReplyKeys {
+            inner: Arc::new(SentReplyKeysInner {
+                data: DashMap::new(),
+            }),
+        }
+    }
+
+    #[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+    pub(crate) fn from_raw(raw: Vec<(EncryptionKeyDigest, UsedReplyKey)>) -> SentReplyKeys {
+        SentReplyKeys {
+            inner: Arc::new(SentReplyKeysInner {
+                data: raw.into_iter().collect(),
+            }),
+        }
+    }
+
+    pub(crate) fn as_raw_iter(&self) -> Iter<'_, EncryptionKeyDigest, UsedReplyKey> {
+        self.inner.data.iter()
+    }
+
+    pub(crate) fn insert_multiple(&self, keys: Vec<SurbEncryptionKey>) {
+        let now = OffsetDateTime::now_utc().unix_timestamp();
+        for key in keys {
+            self.insert(UsedReplyKey::new(key, now))
+        }
+    }
+
+    pub(crate) fn insert(&self, key: UsedReplyKey) {
+        self.inner.data.insert(key.compute_digest(), key);
+    }
+
+    pub(crate) fn try_pop(&self, digest: EncryptionKeyDigest) -> Option<UsedReplyKey> {
+        self.inner.data.remove(&digest).map(|(_k, v)| v)
+    }
+
+    pub(crate) fn remove(&self, digest: EncryptionKeyDigest) {
+        self.inner.data.remove(&digest);
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub(crate) struct UsedReplyKey {
+    key: SurbEncryptionKey,
+    // the purpose of this field is to perform invalidation at relatively very long intervals
+    pub(crate) sent_at_timestamp: i64,
+}
+
+impl UsedReplyKey {
+    pub(crate) fn new(key: SurbEncryptionKey, sent_at_timestamp: i64) -> Self {
+        UsedReplyKey {
+            key,
+            sent_at_timestamp,
+        }
+    }
+}
+
+impl Deref for UsedReplyKey {
+    type Target = SurbEncryptionKey;
+
+    fn deref(&self) -> &Self::Target {
+        &self.key
+    }
+}
@@ -0,0 +1,64 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+pub use crate::client::replies::reply_storage::combined::CombinedReplyStorage;
+pub use crate::client::replies::reply_storage::key_storage::SentReplyKeys;
+pub use crate::client::replies::reply_storage::surb_storage::ReceivedReplySurbsMap;
+pub use crate::client::replies::reply_storage::tag_storage::UsedSenderTags;
+pub use backend::*;
+
+mod backend;
+mod combined;
+mod key_storage;
+mod surb_storage;
+mod tag_storage;
+
+// only really exists to get information about shutdown and save data to the backing storage
+pub struct PersistentReplyStorage<T = backend::Empty>
+where
+    T: ReplyStorageBackend,
+{
+    backend: T,
+}
+
+impl<T> PersistentReplyStorage<T>
+where
+    T: ReplyStorageBackend + Send + Sync,
+{
+    pub fn new(backend: T) -> Self {
+        PersistentReplyStorage { backend }
+    }
+
+    pub async fn load_state_from_backend(&self) -> Result<CombinedReplyStorage, T::StorageError> {
+        self.backend.load_surb_storage().await
+    }
+
+    // this will have to get enabled after merging develop
+    pub async fn flush_on_shutdown(
+        mut self,
+        mem_state: CombinedReplyStorage,
+        mut shutdown: task::ShutdownListener,
+    ) {
+        use log::{debug, error, info, warn};
+
+        debug!("Started PersistentReplyStorage");
+        if let Err(err) = self.backend.start_storage_session().await {
+            error!("failed to start the storage session - {err}");
+            return;
+        }
+
+        shutdown.recv().await;
+
+        info!("PersistentReplyStorage is flushing all reply-related data to underlying storage");
+        warn!("you MUST NOT forcefully shutdown now or you risk data corruption!");
+        if let Err(err) = self.backend.flush_surb_storage(&mem_state).await {
+            error!("failed to flush our reply-related data to the persistent storage: {err}")
+        } else {
+            info!("Data flush is complete")
+        }
+
+        if let Err(err) = self.backend.stop_storage_session().await {
+            error!("failed to properly stop the storage session - {err}. We might not be able to smoothly restore it")
+        }
+    }
+}
@@ -0,0 +1,278 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use dashmap::iter::Iter;
+use dashmap::DashMap;
+use log::trace;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
+use nymsphinx::anonymous_replies::ReplySurb;
+use std::collections::VecDeque;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Arc;
+use time::OffsetDateTime;
+
+#[derive(Debug, Clone)]
+pub struct ReceivedReplySurbsMap {
+    inner: Arc<ReceivedReplySurbsMapInner>,
+}
+
+#[derive(Debug)]
+struct ReceivedReplySurbsMapInner {
+    data: DashMap<AnonymousSenderTag, ReceivedReplySurbs>,
+
+    // the minimum amount of surbs that have to be kept in storage for requests for more surbs
+    min_surb_threshold: AtomicUsize,
+
+    // the maximum amount of surbs that we want to keep in storage so that we don't over-request them
+    max_surb_threshold: AtomicUsize,
+}
+
+impl ReceivedReplySurbsMap {
+    pub(crate) fn new(
+        min_surb_threshold: usize,
+        max_surb_threshold: usize,
+    ) -> ReceivedReplySurbsMap {
+        ReceivedReplySurbsMap {
+            inner: Arc::new(ReceivedReplySurbsMapInner {
+                data: DashMap::new(),
+                min_surb_threshold: AtomicUsize::new(min_surb_threshold),
+                max_surb_threshold: AtomicUsize::new(max_surb_threshold),
+            }),
+        }
+    }
+
+    #[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+    pub(crate) fn from_raw(
+        min_surb_threshold: usize,
+        max_surb_threshold: usize,
+        raw: Vec<(AnonymousSenderTag, ReceivedReplySurbs)>,
+    ) -> ReceivedReplySurbsMap {
+        ReceivedReplySurbsMap {
+            inner: Arc::new(ReceivedReplySurbsMapInner {
+                data: raw.into_iter().collect(),
+                min_surb_threshold: AtomicUsize::new(min_surb_threshold),
+                max_surb_threshold: AtomicUsize::new(max_surb_threshold),
+            }),
+        }
+    }
+
+    pub(crate) fn as_raw_iter(&self) -> Iter<'_, AnonymousSenderTag, ReceivedReplySurbs> {
+        self.inner.data.iter()
+    }
+
+    pub(crate) fn remove(&self, target: &AnonymousSenderTag) {
+        self.inner.data.remove(target);
+    }
+
+    pub(crate) fn reset_surbs_last_received_at(&self, target: &AnonymousSenderTag) {
+        if let Some(mut entry) = self.inner.data.get_mut(target) {
+            entry.surbs_last_received_at_timestamp = OffsetDateTime::now_utc().unix_timestamp();
+        }
+    }
+
+    pub(crate) fn surbs_last_received_at(&self, target: &AnonymousSenderTag) -> Option<i64> {
+        self.inner
+            .data
+            .get(target)
+            .map(|e| e.surbs_last_received_at())
+    }
+
+    pub(crate) fn pending_reception(&self, target: &AnonymousSenderTag) -> u32 {
+        self.inner
+            .data
+            .get(target)
+            .map(|e| e.pending_reception())
+            .unwrap_or_default()
+    }
+
+    pub(crate) fn increment_pending_reception(
+        &self,
+        target: &AnonymousSenderTag,
+        amount: u32,
+    ) -> Option<u32> {
+        self.inner
+            .data
+            .get_mut(target)
+            .map(|mut e| e.increment_pending_reception(amount))
+    }
+
+    pub(crate) fn decrement_pending_reception(
+        &self,
+        target: &AnonymousSenderTag,
+        amount: u32,
+    ) -> Option<u32> {
+        self.inner
+            .data
+            .get_mut(target)
+            .map(|mut e| e.decrement_pending_reception(amount))
+    }
+
+    pub(crate) fn reset_pending_reception(&self, target: &AnonymousSenderTag) {
+        if let Some(mut e) = self.inner.data.get_mut(target) {
+            e.reset_pending_reception()
+        }
+    }
+
+    pub(crate) fn min_surb_threshold(&self) -> usize {
+        self.inner.min_surb_threshold.load(Ordering::Relaxed)
+    }
+
+    pub(crate) fn max_surb_threshold(&self) -> usize {
+        self.inner.max_surb_threshold.load(Ordering::Relaxed)
+    }
+
+    pub(crate) fn available_surbs(&self, target: &AnonymousSenderTag) -> usize {
+        self.inner
+            .data
+            .get(target)
+            .map(|entry| entry.items_left())
+            .unwrap_or_default()
+    }
+
+    pub(crate) fn contains_surbs_for(&self, target: &AnonymousSenderTag) -> bool {
+        self.inner.data.contains_key(target)
+    }
+
+    pub(crate) fn get_reply_surbs(
+        &self,
+        target: &AnonymousSenderTag,
+        amount: usize,
+    ) -> (Option<Vec<ReplySurb>>, usize) {
+        if let Some(mut entry) = self.inner.data.get_mut(target) {
+            let surbs_left = entry.items_left();
+            if surbs_left < self.min_surb_threshold() + amount {
+                (None, surbs_left)
+            } else {
+                entry.get_reply_surbs(amount)
+            }
+        } else {
+            (None, 0)
+        }
+    }
+
+    pub(crate) fn get_reply_surb_ignoring_threshold(
+        &self,
+        target: &AnonymousSenderTag,
+    ) -> Option<(Option<ReplySurb>, usize)> {
+        self.inner
+            .data
+            .get_mut(target)
+            .map(|mut s| s.get_reply_surb())
+    }
+
+    pub(crate) fn get_reply_surb(
+        &self,
+        target: &AnonymousSenderTag,
+    ) -> Option<(Option<ReplySurb>, usize)> {
+        self.inner.data.get_mut(target).map(|mut entry| {
+            let surbs_left = entry.items_left();
+            if surbs_left < self.min_surb_threshold() {
+                (None, surbs_left)
+            } else {
+                entry.get_reply_surb()
+            }
+        })
+    }
+
+    pub(crate) fn insert_surbs<I: IntoIterator<Item = ReplySurb>>(
+        &self,
+        target: &AnonymousSenderTag,
+        surbs: I,
+    ) {
+        if let Some(mut existing_data) = self.inner.data.get_mut(target) {
+            existing_data.insert_reply_surbs(surbs)
+        } else {
+            let new_entry = ReceivedReplySurbs::new(surbs.into_iter().collect());
+            self.inner.data.insert(*target, new_entry);
+        }
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct ReceivedReplySurbs {
+    // in the future we'd probably want to put extra data here to indicate when the SURBs got received
+    // so we could invalidate entries from the previous key rotations
+    data: VecDeque<ReplySurb>,
+
+    pending_reception: u32,
+    surbs_last_received_at_timestamp: i64,
+}
+
+impl ReceivedReplySurbs {
+    fn new(initial_surbs: VecDeque<ReplySurb>) -> Self {
+        ReceivedReplySurbs {
+            data: initial_surbs,
+            pending_reception: 0,
+            surbs_last_received_at_timestamp: OffsetDateTime::now_utc().unix_timestamp(),
+        }
+    }
+
+    #[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+    pub(crate) fn new_retrieved(
+        surbs: Vec<ReplySurb>,
+        surbs_last_received_at_timestamp: i64,
+    ) -> ReceivedReplySurbs {
+        ReceivedReplySurbs {
+            data: surbs.into(),
+            pending_reception: 0,
+            surbs_last_received_at_timestamp,
+        }
+    }
+
+    #[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+    pub(crate) fn surbs_ref(&self) -> &VecDeque<ReplySurb> {
+        &self.data
+    }
+
+    pub(crate) fn surbs_last_received_at(&self) -> i64 {
+        self.surbs_last_received_at_timestamp
+    }
+
+    pub(crate) fn pending_reception(&self) -> u32 {
+        self.pending_reception
+    }
+
+    pub(crate) fn increment_pending_reception(&mut self, amount: u32) -> u32 {
+        self.pending_reception += amount;
+        self.pending_reception
+    }
+
+    pub(crate) fn decrement_pending_reception(&mut self, amount: u32) -> u32 {
+        self.pending_reception = self.pending_reception.saturating_sub(amount);
+        self.pending_reception
+    }
+
+    pub(crate) fn reset_pending_reception(&mut self) {
+        self.pending_reception = 0;
+    }
+
+    pub(crate) fn get_reply_surbs(&mut self, amount: usize) -> (Option<Vec<ReplySurb>>, usize) {
+        if self.items_left() < amount {
+            (None, self.items_left())
+        } else {
+            let surbs = self.data.drain(..amount).collect();
+            (Some(surbs), self.items_left())
+        }
+    }
+
+    pub(crate) fn get_reply_surb(&mut self) -> (Option<ReplySurb>, usize) {
+        (self.pop_surb(), self.items_left())
+    }
+
+    fn pop_surb(&mut self) -> Option<ReplySurb> {
+        self.data.pop_front()
+    }
+
+    fn items_left(&self) -> usize {
+        self.data.len()
+    }
+
+    // realistically we're always going to be getting multiple surbs at once
+    pub(crate) fn insert_reply_surbs<I: IntoIterator<Item = ReplySurb>>(&mut self, surbs: I) {
+        let mut v = surbs.into_iter().collect::<VecDeque<_>>();
+        trace!("storing {} surbs in the storage", v.len());
+        self.data.append(&mut v);
+        self.surbs_last_received_at_timestamp = OffsetDateTime::now_utc().unix_timestamp();
+        trace!("we now have {} surbs!", self.data.len());
+    }
+}
@@ -0,0 +1,59 @@
+// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use dashmap::DashMap;
+use nymsphinx::addressing::clients::{Recipient, RecipientBytes};
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
+use std::sync::Arc;
+
+#[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+use dashmap::iter::Iter;
+
+#[derive(Debug, Clone)]
+pub struct UsedSenderTags {
+    inner: Arc<UsedSenderTagsInner>,
+}
+
+#[derive(Debug)]
+struct UsedSenderTagsInner {
+    data: DashMap<RecipientBytes, AnonymousSenderTag>,
+}
+
+impl UsedSenderTags {
+    pub(crate) fn new() -> UsedSenderTags {
+        UsedSenderTags {
+            inner: Arc::new(UsedSenderTagsInner {
+                data: DashMap::new(),
+            }),
+        }
+    }
+
+    #[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+    pub(crate) fn from_raw(raw: Vec<(RecipientBytes, AnonymousSenderTag)>) -> UsedSenderTags {
+        UsedSenderTags {
+            inner: Arc::new(UsedSenderTagsInner {
+                data: raw.into_iter().collect(),
+            }),
+        }
+    }
+
+    #[cfg(all(not(target_arch = "wasm32"), feature = "fs-surb-storage"))]
+    pub(crate) fn as_raw_iter(&self) -> Iter<'_, RecipientBytes, AnonymousSenderTag> {
+        self.inner.data.iter()
+    }
+
+    pub(crate) fn insert_new(&self, recipient: &Recipient, tag: AnonymousSenderTag) {
+        self.inner.data.insert(recipient.to_bytes(), tag);
+    }
+
+    pub(crate) fn try_get_existing(&self, recipient: &Recipient) -> Option<AnonymousSenderTag> {
+        self.inner
+            .data
+            .get(&recipient.to_bytes())
+            .map(|r| *r.value())
+    }
+
+    pub(crate) fn exists(&self, recipient: &Recipient) -> bool {
+        self.inner.data.contains_key(&recipient.to_bytes())
+    }
+}
@@ -1,97 +0,0 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
-// SPDX-License-Identifier: Apache-2.0
-
-use crypto::generic_array::typenum::Unsigned;
-use log::*;
-use nymsphinx::anonymous_replies::{
-    encryption_key::EncryptionKeyDigest, SurbEncryptionKey, SurbEncryptionKeySize,
-};
-use std::path::Path;
-
-#[derive(Debug, thiserror::Error)]
-pub enum ReplyKeyStorageError {
-    #[error("DB Read Error: {0}")]
-    DbReadError(sled::Error),
-    #[error("DB Write Error: {0}")]
-    DbWriteError(sled::Error),
-    #[error("DB Open Error: {0}")]
-    DbOpenError(sled::Error),
-}
-
-/// Permanent storage for keys in all sent [`ReplySURB`]
-///
-/// Each sent out [`ReplySURB`] has a new key associated with it that is going to be used for
-/// payload encryption. In order to -decrypt whatever reply we receive, we need to know which
-/// key to use for that purpose. We do it based on received `H(t)` which has to be included
-/// with each reply.
-/// Moreover, there is no restriction when the [`ReplySURB`] might get used so we need to
-/// have a permanent storage for all the keys that we might ever see in the future.
-#[derive(Debug, Clone)]
-pub struct ReplyKeyStorage {
-    db: sled::Db,
-}
-
-impl ReplyKeyStorage {
-    pub fn load<P: AsRef<Path>>(path: P) -> Result<Self, ReplyKeyStorageError> {
-        let db = match sled::open(path) {
-            Err(e) => return Err(ReplyKeyStorageError::DbOpenError(e)),
-            Ok(db) => db,
-        };
-
-        Ok(ReplyKeyStorage { db })
-    }
-
-    fn read_encryption_key(&self, raw_key: sled::IVec) -> SurbEncryptionKey {
-        let key_bytes_ref = raw_key.as_ref();
-        // if this fails it means we have some database corruption and we
-        // absolutely can't continue
-
-        if key_bytes_ref.len() != SurbEncryptionKeySize::USIZE {
-            error!("REPLY KEY STORAGE DATA CORRUPTION - ENCRYPTION KEY HAS INVALID LENGTH");
-            panic!("REPLY KEY STORAGE DATA CORRUPTION - ENCRYPTION KEY HAS INVALID LENGTH");
-        }
-
-        // this can only fail if the bytes have invalid length but we already asserted it
-        SurbEncryptionKey::try_from_bytes(key_bytes_ref).unwrap()
-    }
-
-    // TOOD: perhaps we could also store some part of original message here too?
-    pub fn insert_encryption_key(
-        &mut self,
-        encryption_key: SurbEncryptionKey,
-    ) -> Result<(), ReplyKeyStorageError> {
-        let digest = encryption_key.compute_digest();
-
-        let insertion_result = match self.db.insert(digest, encryption_key.to_bytes()) {
-            Err(e) => Err(ReplyKeyStorageError::DbWriteError(e)),
-            Ok(existing_key) => {
-                if existing_key.is_some() {
-                    panic!("HASH COLLISION DETECTED")
-                };
-                Ok(())
-            }
-        };
-
-        // TODO: perhaps we could implement some batching mechanism to avoid frequent flushes?
-        self.db.flush().unwrap();
-        insertion_result
-    }
-
-    // Once we use key once, we do not expect to use it again
-    pub fn get_and_remove_encryption_key(
-        &self,
-        key_digest: EncryptionKeyDigest,
-    ) -> Result<Option<SurbEncryptionKey>, ReplyKeyStorageError> {
-        let removal_result = match self.db.remove(key_digest) {
-            Err(e) => Err(ReplyKeyStorageError::DbReadError(e)),
-            Ok(existing_key) => {
-                Ok(existing_key.map(|existing_key| self.read_encryption_key(existing_key)))
-            }
-        };
-
-        // TODO: not sure how to feel about flushing it every single time here...
-        // same with insertion
-        self.db.flush().unwrap();
-        removal_result
-    }
-}
@@ -1,4 +1,4 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

 use crate::spawn_future;
@@ -10,10 +10,9 @@ use rand::seq::SliceRandom;
 use rand::thread_rng;
 use std::ops::Deref;
 use std::sync::Arc;
-use std::time;
 use std::time::Duration;
 use tokio::sync::{RwLock, RwLockReadGuard};
-use topology::{nym_topology_from_detailed, NymTopology};
+use topology::{nym_topology_from_detailed, NymTopology, NymTopologyError};
 use url::Url;

 // I'm extremely curious why compiler NEVER complained about lack of Debug here before
@@ -55,18 +54,36 @@ impl<'a> TopologyReadPermit<'a> {
        &'a self,
        ack_recipient: &Recipient,
        packet_recipient: Option<&Recipient>,
-    ) -> Option<&'a NymTopology> {
-        // Note: implicit deref with Deref for TopologyReadPermit is happening here
-        let topology_ref_option = self.permit.as_ref();
-        topology_ref_option.as_ref().filter(|topology_ref| {
-            !(!topology_ref.can_construct_path_through(DEFAULT_NUM_MIX_HOPS)
-                || !topology_ref.gateway_exists(ack_recipient.gateway())
-                || if let Some(packet_recipient) = packet_recipient {
-                    !topology_ref.gateway_exists(packet_recipient.gateway())
-                } else {
-                    false
-                })
-        })
+    ) -> Result<&'a NymTopology, NymTopologyError> {
+        // 1. Have we managed to get anything from the refresher, i.e. have the nym-api queries gone through?
+        let topology = self
+            .permit
+            .as_ref()
+            .as_ref()
+            .ok_or(NymTopologyError::EmptyNetworkTopology)?;
+
+        // 2. does it have any mixnode at all?
+        // 3. does it have any gateways at all?
+        // 4. does it have a mixnode on each layer?
+        topology.ensure_can_construct_path_through(DEFAULT_NUM_MIX_HOPS)?;
+
+        // 5. does it contain OUR gateway (so that we could create an ack packet)?
+        if !topology.gateway_exists(ack_recipient.gateway()) {
+            return Err(NymTopologyError::NonExistentGatewayError {
+                identity_key: ack_recipient.gateway().to_base58_string(),
+            });
+        }
+
+        // 6. for our target recipient, does it contain THEIR gateway (so that we could create
+        if let Some(recipient) = packet_recipient {
+            if !topology.gateway_exists(recipient.gateway()) {
+                return Err(NymTopologyError::NonExistentGatewayError {
+                    identity_key: recipient.gateway().to_base58_string(),
+                });
+            }
+        }
+
+        Ok(topology)
    }
 }

@@ -104,10 +121,10 @@ impl TopologyAccessor {

    // only used by the client at startup to get a slightly more reasonable error message
    // (currently displays as unused because health checker is disabled due to required changes)
-    pub async fn is_routable(&self) -> bool {
+    pub async fn ensure_is_routable(&self) -> Result<(), NymTopologyError> {
        match &self.inner.read().await.0 {
-            None => false,
-            Some(ref topology) => topology.can_construct_path_through(DEFAULT_NUM_MIX_HOPS),
+            None => Err(NymTopologyError::EmptyNetworkTopology),
+            Some(ref topology) => topology.ensure_can_construct_path_through(DEFAULT_NUM_MIX_HOPS),
        }
    }
 }
@@ -120,14 +137,14 @@ impl Default for TopologyAccessor {

 pub struct TopologyRefresherConfig {
    validator_api_urls: Vec<Url>,
-    refresh_rate: time::Duration,
+    refresh_rate: Duration,
    client_version: String,
 }

 impl TopologyRefresherConfig {
    pub fn new(
        validator_api_urls: Vec<Url>,
-        refresh_rate: time::Duration,
+        refresh_rate: Duration,
        client_version: String,
    ) -> Self {
        TopologyRefresherConfig {
@@ -241,7 +258,7 @@ impl TopologyRefresher {

        let mixnodes = match self.validator_client.get_cached_active_mixnodes().await {
            Err(err) => {
-                error!("failed to get network mixnodes - {}", err);
+                error!("failed to get network mixnodes - {err}");
                return None;
            }
            Ok(mixes) => mixes,
@@ -249,7 +266,7 @@ impl TopologyRefresher {

        let gateways = match self.validator_client.get_cached_gateways().await {
            Err(err) => {
-                error!("failed to get network gateways - {}", err);
+                error!("failed to get network gateways - {err}");
                return None;
            }
            Ok(gateways) => gateways,
@@ -289,8 +306,8 @@ impl TopologyRefresher {
            .await;
    }

-    pub async fn is_topology_routable(&self) -> bool {
-        self.topology_accessor.is_routable().await
+    pub async fn ensure_topology_is_routable(&self) -> Result<(), NymTopologyError> {
+        self.topology_accessor.ensure_is_routable().await
    }

    pub fn start_with_shutdown(mut self, mut shutdown: task::ShutdownListener) {
@@ -320,21 +337,4 @@ impl TopologyRefresher {
            log::debug!("TopologyRefresher: Exiting");
        })
    }
-
-    pub fn start(mut self) {
-        spawn_future(async move {
-            #[cfg(not(target_arch = "wasm32"))]
-            let mut interval = tokio_stream::wrappers::IntervalStream::new(tokio::time::interval(
-                self.refresh_rate,
-            ));
-
-            #[cfg(target_arch = "wasm32")]
-            let mut interval =
-                gloo_timers::future::IntervalStream::new(self.refresh_rate.as_millis() as u32);
-
-            while (interval.next().await).is_some() {
-                self.refresh().await;
-            }
-        })
-    }
 }
@@ -30,6 +30,28 @@ const DEFAULT_TOPOLOGY_RESOLUTION_TIMEOUT: Duration = Duration::from_millis(5_00
 // bandwidth bridging protocol, we can come back to a smaller timeout value
 const DEFAULT_GATEWAY_RESPONSE_TIMEOUT: Duration = Duration::from_secs(5 * 60);

+// reply-surbs related:
+
+// define when to request
+// clients/client-core/src/client/replies/reply_storage/surb_storage.rs
+const DEFAULT_MINIMUM_REPLY_SURB_STORAGE_THRESHOLD: usize = 10;
+const DEFAULT_MAXIMUM_REPLY_SURB_STORAGE_THRESHOLD: usize = 200;
+
+// define how much to request at once
+// clients/client-core/src/client/replies/reply_controller.rs
+const DEFAULT_MINIMUM_REPLY_SURB_REQUEST_SIZE: u32 = 10;
+const DEFAULT_MAXIMUM_REPLY_SURB_REQUEST_SIZE: u32 = 100;
+
+const DEFAULT_MAXIMUM_ALLOWED_SURB_REQUEST_SIZE: u32 = 500;
+
+const DEFAULT_MAXIMUM_REPLY_SURB_WAITING_PERIOD: Duration = Duration::from_secs(10);
+
+// 12 hours
+const DEFAULT_MAXIMUM_REPLY_SURB_AGE: Duration = Duration::from_secs(12 * 60 * 60);
+
+// 24 hours
+const DEFAULT_MAXIMUM_REPLY_KEY_AGE: Duration = Duration::from_secs(24 * 60 * 60);
+
 pub fn missing_string_value() -> String {
    MISSING_VALUE.to_string()
 }
@@ -48,7 +70,6 @@ pub struct Config<T> {
    #[serde(default)]
    debug: DebugConfig,
 }
-
 impl<T> ClientCoreConfigTrait for Config<T> {
    fn get_gateway_endpoint(&self) -> &GatewayEndpointConfig {
        &self.client.gateway_endpoint
@@ -60,12 +81,10 @@ impl<T> Config<T> {
    where
        T: NymConfig,
    {
-        let mut cfg = Config::default();
-        cfg.with_id(id);
-        cfg
+        Config::default().with_id(id)
    }

-    pub fn with_id<S: Into<String>>(&mut self, id: S)
+    pub fn with_id<S: Into<String>>(mut self, id: S) -> Self
    where
        T: NymConfig,
    {
@@ -112,14 +131,9 @@ impl<T> Config<T> {
            self.client.ack_key_file = self::Client::<T>::default_ack_key_file(&id);
        }

-        if self
-            .client
-            .reply_encryption_key_store_path
-            .as_os_str()
-            .is_empty()
-        {
-            self.client.reply_encryption_key_store_path =
-                self::Client::<T>::default_reply_encryption_key_store_path(&id);
+        if self.client.reply_surb_database_path.as_os_str().is_empty() {
+            self.client.reply_surb_database_path =
+                self::Client::<T>::default_reply_surb_database_path(&id);
        }

        if self.client.database_path.as_os_str().is_empty() {
@@ -127,6 +141,7 @@ impl<T> Config<T> {
        }

        self.client.id = id;
+        self
    }

    pub fn with_disabled_credentials(&mut self, disabled_credentials_mode: bool) {
@@ -198,10 +213,6 @@ impl<T> Config<T> {
        self.client.gateway_shared_key_file.clone()
    }

-    pub fn get_reply_encryption_key_store_path(&self) -> PathBuf {
-        self.client.reply_encryption_key_store_path.clone()
-    }
-
    pub fn get_ack_key_file(&self) -> PathBuf {
        self.client.ack_key_file.clone()
    }
@@ -234,6 +245,14 @@ impl<T> Config<T> {
        self.client.database_path.clone()
    }

+    pub fn get_reply_surb_database_path(&self) -> PathBuf {
+        self.client.reply_surb_database_path.clone()
+    }
+
+    pub fn get_version(&self) -> &str {
+        &self.client.version
+    }
+
    // Debug getters
    pub fn get_debug_config(&self) -> &DebugConfig {
        &self.debug
@@ -287,8 +306,36 @@ impl<T> Config<T> {
        self.debug.use_extended_packet_size
    }

-    pub fn get_version(&self) -> &str {
-        &self.client.version
+    pub fn get_minimum_reply_surb_storage_threshold(&self) -> usize {
+        self.debug.minimum_reply_surb_storage_threshold
+    }
+
+    pub fn get_maximum_reply_surb_storage_threshold(&self) -> usize {
+        self.debug.maximum_reply_surb_storage_threshold
+    }
+
+    pub fn get_minimum_reply_surb_request_size(&self) -> u32 {
+        self.debug.minimum_reply_surb_request_size
+    }
+
+    pub fn get_maximum_reply_surb_request_size(&self) -> u32 {
+        self.debug.maximum_reply_surb_request_size
+    }
+
+    pub fn get_maximum_allowed_reply_surb_request_size(&self) -> u32 {
+        self.debug.maximum_allowed_reply_surb_request_size
+    }
+
+    pub fn get_maximum_reply_surb_waiting_period(&self) -> Duration {
+        self.debug.maximum_reply_surb_waiting_period
+    }
+
+    pub fn get_maximum_reply_surb_age(&self) -> Duration {
+        self.debug.maximum_reply_surb_age
+    }
+
+    pub fn get_maximum_reply_key_age(&self) -> Duration {
+        self.debug.maximum_reply_key_age
    }
 }

@@ -316,6 +363,22 @@ pub struct GatewayEndpointConfig {
    pub gateway_listener: String,
 }

+#[cfg_attr(target_arch = "wasm32", wasm_bindgen)]
+impl GatewayEndpointConfig {
+    #[cfg_attr(target_arch = "wasm32", wasm_bindgen(constructor))]
+    pub fn new(
+        gateway_id: String,
+        gateway_owner: String,
+        gateway_listener: String,
+    ) -> GatewayEndpointConfig {
+        GatewayEndpointConfig {
+            gateway_id,
+            gateway_owner,
+            gateway_listener,
+        }
+    }
+}
+
 impl From<topology::gateway::Node> for GatewayEndpointConfig {
    fn from(node: topology::gateway::Node) -> GatewayEndpointConfig {
        let gateway_listener = node.clients_address();
@@ -368,16 +431,15 @@ pub struct Client<T> {
    /// acknowledgement so that nobody besides the client knows which packet it refers to.
    ack_key_file: PathBuf,

-    /// Full path to file containing reply encryption keys of all reply-SURBs we have ever
-    /// sent but not received back.
-    reply_encryption_key_store_path: PathBuf,
-
    /// Information regarding how the client should send data to gateway.
    gateway_endpoint: GatewayEndpointConfig,

    /// Path to the database containing bandwidth credentials of this client.
    database_path: PathBuf,

+    /// Path to the persistent store for received reply surbs, unused encryption keys and used sender tags.
+    reply_surb_database_path: PathBuf,
+
    /// nym_home_directory specifies absolute path to the home nym Clients directory.
    /// It is expected to use default value and hence .toml file should not redefine this field.
    nym_root_directory: PathBuf,
@@ -401,9 +463,9 @@ impl<T: NymConfig> Default for Client<T> {
            public_encryption_key_file: Default::default(),
            gateway_shared_key_file: Default::default(),
            ack_key_file: Default::default(),
-            reply_encryption_key_store_path: Default::default(),
            gateway_endpoint: Default::default(),
            database_path: Default::default(),
+            reply_surb_database_path: Default::default(),
            nym_root_directory: T::default_root_directory(),
            super_struct: Default::default(),
        }
@@ -435,9 +497,10 @@ impl<T: NymConfig> Client<T> {
        T::default_data_directory(Some(id)).join("ack_key.pem")
    }

-    fn default_reply_encryption_key_store_path(id: &str) -> PathBuf {
-        T::default_data_directory(Some(id)).join("reply_key_store")
+    fn default_reply_surb_database_path(id: &str) -> PathBuf {
+        T::default_data_directory(Some(id)).join("persistent_reply_store.sqlite")
    }
+
    fn default_database_path(id: &str) -> PathBuf {
        T::default_data_directory(Some(id)).join(DB_FILE_NAME)
    }
@@ -513,6 +576,37 @@ pub struct DebugConfig {

    /// Controls whether the sent sphinx packet use a NON-DEFAULT bigger size.
    pub use_extended_packet_size: Option<ExtendedPacketSize>,
+
+    /// Defines the minimum number of reply surbs the client wants to keep in its storage at all times.
+    /// It can only allow to go below that value if its to request additional reply surbs.
+    pub minimum_reply_surb_storage_threshold: usize,
+
+    /// Defines the maximum number of reply surbs the client wants to keep in its storage at any times.
+    pub maximum_reply_surb_storage_threshold: usize,
+
+    /// Defines the minimum number of reply surbs the client would request.
+    pub minimum_reply_surb_request_size: u32,
+
+    /// Defines the maximum number of reply surbs the client would request.
+    pub maximum_reply_surb_request_size: u32,
+
+    /// Defines the maximum number of reply surbs a remote party is allowed to request from this client at once.
+    pub maximum_allowed_reply_surb_request_size: u32,
+
+    /// Defines maximum amount of time the client is going to wait for reply surbs before explicitly asking
+    /// for more even though in theory they wouldn't need to.
+    #[serde(with = "humantime_serde")]
+    pub maximum_reply_surb_waiting_period: Duration,
+
+    /// Defines maximum amount of time given reply surb is going to be valid for.
+    /// This is going to be superseded by key rotation once implemented.
+    #[serde(with = "humantime_serde")]
+    pub maximum_reply_surb_age: Duration,
+
+    /// Defines maximum amount of time given reply key is going to be valid for.
+    /// This is going to be superseded by key rotation once implemented.
+    #[serde(with = "humantime_serde")]
+    pub maximum_reply_key_age: Duration,
 }

 #[derive(Clone, Copy, Debug, Serialize, Deserialize, PartialEq, Eq)]
@@ -538,6 +632,14 @@ impl Default for DebugConfig {
            disable_loop_cover_traffic_stream: false,
            disable_main_poisson_packet_distribution: false,
            use_extended_packet_size: None,
+            minimum_reply_surb_storage_threshold: DEFAULT_MINIMUM_REPLY_SURB_STORAGE_THRESHOLD,
+            maximum_reply_surb_storage_threshold: DEFAULT_MAXIMUM_REPLY_SURB_STORAGE_THRESHOLD,
+            minimum_reply_surb_request_size: DEFAULT_MINIMUM_REPLY_SURB_REQUEST_SIZE,
+            maximum_reply_surb_request_size: DEFAULT_MAXIMUM_REPLY_SURB_REQUEST_SIZE,
+            maximum_allowed_reply_surb_request_size: DEFAULT_MAXIMUM_ALLOWED_SURB_REQUEST_SIZE,
+            maximum_reply_surb_waiting_period: DEFAULT_MAXIMUM_REPLY_SURB_WAITING_PERIOD,
+            maximum_reply_surb_age: DEFAULT_MAXIMUM_REPLY_SURB_AGE,
+            maximum_reply_key_age: DEFAULT_MAXIMUM_REPLY_KEY_AGE,
        }
    }
 }
@@ -1,47 +1,56 @@
 // Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-#[cfg(feature = "reply-surb")]
-use crate::client::reply_key_storage::ReplyKeyStorageError;
+use crate::client::replies::reply_storage::ReplyStorageBackend;
 use crypto::asymmetric::identity::Ed25519RecoveryError;
 use gateway_client::error::GatewayClientError;
+use topology::NymTopologyError;
 use validator_client::ValidatorClientError;

 #[derive(thiserror::Error, Debug)]
-pub enum ClientCoreError {
+pub enum ClientCoreError<B: ReplyStorageBackend> {
    #[error("I/O error: {0}")]
    IoError(#[from] std::io::Error),
+
    #[error("Gateway client error: {0}")]
    GatewayClientError(#[from] GatewayClientError),
+
    #[error("Ed25519 error: {0}")]
    Ed25519RecoveryError(#[from] Ed25519RecoveryError),
+
    #[error("Validator client error: {0}")]
    ValidatorClientError(#[from] ValidatorClientError),

-    #[cfg(feature = "reply-surb")]
-    #[error("Reply key storage error: {0}")]
-    ReplyKeyStorageError(#[from] ReplyKeyStorageError),
-
    #[error("No gateway with id: {0}")]
    NoGatewayWithId(String),
+
    #[error("No gateways on network")]
    NoGatewaysOnNetwork,
+
    #[error("Failed to setup gateway")]
    FailedToSetupGateway,
+
    #[error("List of validator apis is empty")]
    ListOfValidatorApisIsEmpty,
+
    #[error("Could not load existing gateway configuration: {0}")]
    CouldNotLoadExistingGatewayConfiguration(std::io::Error),
+
    #[error("The current network topology seem to be insufficient to route any packets through")]
-    InsufficientNetworkTopology,
+    InsufficientNetworkTopology(#[from] NymTopologyError),
+
+    #[error("experienced a failure with our reply surb persistent storage: {source}")]
+    SurbStorageError { source: B::StorageError },

    #[error("The gateway id is invalid - {0}")]
    UnableToCreatePublicKeyFromGatewayId(Ed25519RecoveryError),

    #[error("The identity of the gateway is unknwown - did you run init?")]
    GatewayIdUnknown,
+
    #[error("The owner of the gateway is unknown - did you run init?")]
    GatewayOwnerUnknown,
+
    #[error("The address of the gateway is unknown - did you run init?")]
    GatwayAddressUnknown,

@@ -1,25 +1,29 @@
-use std::{sync::Arc, time::Duration};
-
-use rand::{rngs::OsRng, seq::SliceRandom, thread_rng};
-use tap::TapFallible;
-use url::Url;
-
-use config::NymConfig;
-use crypto::asymmetric::identity;
-use gateway_client::GatewayClient;
-use gateway_requests::registration::handshake::SharedKeys;
-use topology::{filter::VersionFilterable, gateway};
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0

+use crate::client::replies::reply_storage::ReplyStorageBackend;
 use crate::{
    client::key_manager::KeyManager,
    config::{persistence::key_pathfinder::ClientKeyPathfinder, Config},
    error::ClientCoreError,
 };
+use config::NymConfig;
+use crypto::asymmetric::identity;
+use gateway_client::GatewayClient;
+use gateway_requests::registration::handshake::SharedKeys;
+use rand::{rngs::OsRng, seq::SliceRandom, thread_rng};
+use std::{sync::Arc, time::Duration};
+use tap::TapFallible;
+use topology::{filter::VersionFilterable, gateway};
+use url::Url;

-pub(super) async fn query_gateway_details(
+pub(super) async fn query_gateway_details<B>(
    validator_servers: Vec<Url>,
    chosen_gateway_id: Option<String>,
-) -> Result<gateway::Node, ClientCoreError> {
+) -> Result<gateway::Node, ClientCoreError<B>>
+where
+    B: ReplyStorageBackend,
+{
    let validator_api = validator_servers
        .choose(&mut thread_rng())
        .ok_or(ClientCoreError::ListOfValidatorApisIsEmpty)?;
@@ -51,10 +55,13 @@ pub(super) async fn query_gateway_details(
    }
 }

-async fn register_with_gateway(
+async fn register_with_gateway<B>(
    gateway: &gateway::Node,
    our_identity: Arc<identity::KeyPair>,
-) -> Result<Arc<SharedKeys>, ClientCoreError> {
+) -> Result<Arc<SharedKeys>, ClientCoreError<B>>
+where
+    B: ReplyStorageBackend,
+{
    let timeout = Duration::from_millis(1500);
    let mut gateway_client = GatewayClient::new_init(
        gateway.clients_address(),
@@ -74,12 +81,13 @@ async fn register_with_gateway(
    Ok(shared_keys)
 }

-pub(super) async fn register_with_gateway_and_store_keys<T>(
+pub(super) async fn register_with_gateway_and_store_keys<T, B>(
    gateway_details: gateway::Node,
    config: &Config<T>,
-) -> Result<(), ClientCoreError>
+) -> Result<(), ClientCoreError<B>>
 where
    T: NymConfig,
+    B: ReplyStorageBackend,
 {
    let mut rng = OsRng;
    let mut key_manager = KeyManager::new(&mut rng);
@@ -12,6 +12,7 @@ use tap::TapFallible;
 use config::NymConfig;
 use crypto::asymmetric::{encryption, identity};

+use crate::client::replies::reply_storage::ReplyStorageBackend;
 use crate::{
    config::{
        persistence::key_pathfinder::ClientKeyPathfinder, ClientCoreConfigTrait, Config,
@@ -62,28 +63,37 @@ impl Display for InitResults {

 /// Convenience function for setting up the gateway for a client. Depending on the arguments given
 /// it will do the sensible thing.
-pub async fn setup_gateway<C: NymConfig + ClientCoreConfigTrait, T: NymConfig>(
+pub async fn setup_gateway<B, C, T>(
    register_gateway: bool,
    user_chosen_gateway_id: Option<String>,
    config: &Config<T>,
-) -> Result<GatewayEndpointConfig, ClientCoreError> {
+) -> Result<GatewayEndpointConfig, ClientCoreError<B>>
+where
+    B: ReplyStorageBackend,
+    C: NymConfig + ClientCoreConfigTrait,
+    T: NymConfig,
+{
    let id = config.get_id();
    if register_gateway {
        register_with_gateway(user_chosen_gateway_id, config).await
    } else if let Some(user_chosen_gateway_id) = user_chosen_gateway_id {
        config_gateway_with_existing_keys(user_chosen_gateway_id, config).await
    } else {
-        reuse_existing_gateway_config::<C>(&id)
+        reuse_existing_gateway_config::<B, C>(&id)
    }
 }

 /// Get the gateway details by querying the validator-api. Either pick one at random or use
 /// the chosen one if it's among the available ones.
 /// Saves keys to disk, specified by the paths in `config`.
-pub async fn register_with_gateway<T: NymConfig>(
+pub async fn register_with_gateway<B, T>(
    user_chosen_gateway_id: Option<String>,
    config: &Config<T>,
-) -> Result<GatewayEndpointConfig, ClientCoreError> {
+) -> Result<GatewayEndpointConfig, ClientCoreError<B>>
+where
+    B: ReplyStorageBackend,
+    T: NymConfig,
+{
    println!("Configuring gateway");
    let gateway =
        query_gateway_details(config.get_validator_api_endpoints(), user_chosen_gateway_id).await?;
@@ -101,10 +111,14 @@ pub async fn register_with_gateway<T: NymConfig>(
 /// create any keys.
 /// This assumes that the user knows what they are doing, and that the existing keys are valid for
 /// the gateway being used
-pub async fn config_gateway_with_existing_keys<T: NymConfig>(
+pub async fn config_gateway_with_existing_keys<B, T>(
    user_chosen_gateway_id: String,
    config: &Config<T>,
-) -> Result<GatewayEndpointConfig, ClientCoreError> {
+) -> Result<GatewayEndpointConfig, ClientCoreError<B>>
+where
+    B: ReplyStorageBackend,
+    T: NymConfig,
+{
    println!("Using gateway provided by user, keeping existing keys");
    let gateway = query_gateway_details(
        config.get_validator_api_endpoints(),
@@ -116,9 +130,13 @@ pub async fn config_gateway_with_existing_keys<T: NymConfig>(
 }

 /// Read and reuse the existing gateway configuration from a file that was generate earlier.
-pub fn reuse_existing_gateway_config<T: NymConfig + ClientCoreConfigTrait>(
+pub fn reuse_existing_gateway_config<B, T>(
    id: &str,
-) -> Result<GatewayEndpointConfig, ClientCoreError> {
+) -> Result<GatewayEndpointConfig, ClientCoreError<B>>
+where
+    B: ReplyStorageBackend,
+    T: NymConfig + ClientCoreConfigTrait,
+{
    println!("Not registering gateway, will reuse existing config and keys");
    T::load_from_file(Some(id))
        .map(|existing_config| existing_config.get_gateway_endpoint().clone())
@@ -135,15 +153,19 @@ pub fn reuse_existing_gateway_config<T: NymConfig + ClientCoreConfigTrait>(
 }

 /// Get the client address by loading the keys from stored files.
-pub fn get_client_address_from_stored_keys<T>(
+pub fn get_client_address_from_stored_keys<B, T>(
    config: &Config<T>,
-) -> Result<Recipient, ClientCoreError>
+) -> Result<Recipient, ClientCoreError<B>>
 where
    T: config::NymConfig,
+    B: ReplyStorageBackend,
 {
-    fn load_identity_keys(
+    fn load_identity_keys<B>(
        pathfinder: &ClientKeyPathfinder,
-    ) -> Result<identity::KeyPair, ClientCoreError> {
+    ) -> Result<identity::KeyPair, ClientCoreError<B>>
+    where
+        B: ReplyStorageBackend,
+    {
        let identity_keypair: identity::KeyPair =
            pemstore::load_keypair(&pemstore::KeyPairPath::new(
                pathfinder.private_identity_key().to_owned(),
@@ -153,9 +175,12 @@ where
        Ok(identity_keypair)
    }

-    fn load_sphinx_keys(
+    fn load_sphinx_keys<B>(
        pathfinder: &ClientKeyPathfinder,
-    ) -> Result<encryption::KeyPair, ClientCoreError> {
+    ) -> Result<encryption::KeyPair, ClientCoreError<B>>
+    where
+        B: ReplyStorageBackend,
+    {
        let sphinx_keypair: encryption::KeyPair =
            pemstore::load_keypair(&pemstore::KeyPairPath::new(
                pathfinder.private_encryption_key().to_owned(),
@@ -27,14 +27,13 @@ pretty_env_logger = "0.4" # for formatting log messages
 rand = { version = "0.7.3", features = ["wasm-bindgen"] } # rng-related traits + some rng implementation to use
 serde = { version = "1.0.104", features = ["derive"] } # for config serialization/deserialization
 serde_json = "1.0"
-sled = "0.34" # for storage of replySURB decryption keys
-tap = "1.0.1"
 thiserror = "1.0.34"
+tap = "1.0.1"
 tokio = { version = "1.21.2", features = ["rt-multi-thread", "net", "signal"] } # async runtime
 tokio-tungstenite = "0.14" # websocket

 ## internal
-client-core = { path = "../client-core" }
+client-core = { path = "../client-core", features = ["fs-surb-storage"] }
 client-connections = { path = "../../common/client-connections" }
 coconut-interface = { path = "../../common/coconut-interface", optional = true }
 config = { path = "../../common/config" }
@@ -25,58 +25,59 @@ async fn get_self_address(ws_stream: &mut WebSocketStream<MaybeTlsStream<TcpStre
    let response = send_message_and_get_response(ws_stream, self_address_request).await;

    match response {
-        ServerResponse::SelfAddress(recipient) => recipient,
+        ServerResponse::SelfAddress(recipient) => *recipient,
        _ => panic!("received an unexpected response!"),
    }
 }

 async fn send_file_with_reply() {
-    let uri = "ws://localhost:1977";
-    let (mut ws_stream, _) = connect_async(uri).await.unwrap();
-
-    let recipient = get_self_address(&mut ws_stream).await;
-    println!("our full address is: {}", recipient);
-
-    let read_data = std::fs::read("examples/dummy_file").unwrap();
-
-    let send_request = ClientRequest::Send {
-        recipient,
-        message: read_data,
-        with_reply_surb: true,
-        connection_id: Some(0),
-    };
-
-    println!("sending content of 'dummy_file' over the mix network...");
-    let response = send_message_and_get_response(&mut ws_stream, send_request.serialize()).await;
-
-    let received = match response {
-        ServerResponse::Received(received) => received,
-        _ => panic!("received an unexpected response!"),
-    };
-
-    println!("writing the file back to the disk!");
-    std::fs::write("examples/received_file_withreply", received.message).unwrap();
-
-    let reply_message = b"hello from reply SURB! - thanks for sending me the file!".to_vec();
-    let reply_request = ClientRequest::Reply {
-        message: reply_message.clone(),
-        reply_surb: received.reply_surb.unwrap(),
-    };
-
-    println!(
-        "sending {:?} (using reply SURB!) over the mix network...",
-        String::from_utf8(reply_message).unwrap()
-    );
-    let response = send_message_and_get_response(&mut ws_stream, reply_request.serialize()).await;
-    let received = match response {
-        ServerResponse::Received(received) => received,
-        _ => panic!("received an unexpected response!"),
-    };
-
-    println!(
-        "received {:#?} from the mix network!",
-        String::from_utf8(received.message).unwrap()
-    );
+    todo!("reimplement surb usage here : )")
+    // let uri = "ws://localhost:1977";
+    // let (mut ws_stream, _) = connect_async(uri).await.unwrap();
+    //
+    // let recipient = get_self_address(&mut ws_stream).await;
+    // println!("our full address is: {}", recipient);
+    //
+    // let read_data = std::fs::read("examples/dummy_file").unwrap();
+    //
+    // let send_request = ClientRequest::Send {
+    //     recipient,
+    //     message: read_data,
+    //     with_reply_surb: true,
+    //     connection_id: Some(0),
+    // };
+    //
+    // println!("sending content of 'dummy_file' over the mix network...");
+    // let response = send_message_and_get_response(&mut ws_stream, send_request.serialize()).await;
+    //
+    // let received = match response {
+    //     ServerResponse::Received(received) => received,
+    //     _ => panic!("received an unexpected response!"),
+    // };
+    //
+    // println!("writing the file back to the disk!");
+    // std::fs::write("examples/received_file_withreply", received.message).unwrap();
+    //
+    // let reply_message = b"hello from reply SURB! - thanks for sending me the file!".to_vec();
+    // let reply_request = ClientRequest::Reply {
+    //     message: reply_message.clone(),
+    //     reply_surb: received.reply_surb.unwrap(),
+    // };
+    //
+    // println!(
+    //     "sending {:?} (using reply SURB!) over the mix network...",
+    //     String::from_utf8(reply_message).unwrap()
+    // );
+    // let response = send_message_and_get_response(&mut ws_stream, reply_request.serialize()).await;
+    // let received = match response {
+    //     ServerResponse::Received(received) => received,
+    //     _ => panic!("received an unexpected response!"),
+    // };
+    //
+    // println!(
+    //     "received {:#?} from the mix network!",
+    //     String::from_utf8(received.message).unwrap()
+    // );
 }

 async fn send_file_without_reply() {
@@ -91,7 +92,6 @@ async fn send_file_without_reply() {
    let send_request = ClientRequest::Send {
        recipient,
        message: read_data,
-        with_reply_surb: false,
        connection_id: Some(0),
    };

@@ -3,7 +3,7 @@

 use crate::client::config::template::config_template;
 pub use client_core::config::MISSING_VALUE;
-use client_core::config::{ClientCoreConfigTrait, Config as BaseConfig};
+use client_core::config::{ClientCoreConfigTrait, Config as BaseConfig, DebugConfig};
 use config::defaults::DEFAULT_WEBSOCKET_LISTENING_PORT;
 use config::NymConfig;
 use serde::{Deserialize, Serialize};
@@ -28,7 +28,7 @@ impl SocketType {
        }
    }

-    pub fn is_websocket(self) -> bool {
+    pub fn is_websocket(&self) -> bool {
        matches!(self, SocketType::WebSocket)
    }
 }
@@ -110,6 +110,10 @@ impl Config {
        &mut self.base
    }

+    pub fn get_debug_settings(&self) -> &DebugConfig {
+        self.get_base().get_debug_config()
+    }
+
    pub fn get_socket_type(&self) -> SocketType {
        self.socket.socket_type
    }
@@ -49,13 +49,12 @@ private_encryption_key_file = '{{ client.private_encryption_key_file }}'
 # Path to file containing public encryption key.
 public_encryption_key_file = '{{ client.public_encryption_key_file }}'

-# Full path to file containing reply encryption keys of all reply-SURBs we have ever
-# sent but not received back.
-reply_encryption_key_store_path = '{{ client.reply_encryption_key_store_path }}'
-
 # Path to the database containing bandwidth credentials
 database_path = '{{ client.database_path }}'

+# Path to the persistent store for received reply surbs, unused encryption keys and used sender tags.
+reply_surb_database_path = '{{ client.reply_surb_database_path }}'
+
 ##### additional client config options #####

 # A gateway specific, optional, base58 stringified shared key used for
@@ -1,11 +1,13 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

 use crate::client::config::Config;
 use crate::error::ClientError;
 use crate::websocket;
 use client_connections::TransmissionLane;
-use client_core::client::base_client::{BaseClientBuilder, ClientInput, ClientOutput};
+use client_core::client::base_client::{
+    non_wasm_helpers, BaseClientBuilder, ClientInput, ClientOutput,
+};
 use client_core::client::inbound_messages::InputMessage;
 use client_core::client::key_manager::KeyManager;
 use client_core::client::received_buffer::{ReceivedBufferMessage, ReconstructedMessagesReceiver};
@@ -14,7 +16,7 @@ use futures::channel::mpsc;
 use gateway_client::bandwidth::BandwidthController;
 use log::*;
 use nymsphinx::addressing::clients::Recipient;
-use nymsphinx::anonymous_replies::ReplySurb;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
 use nymsphinx::receiver::ReconstructedMessage;
 use task::{wait_for_signal, ShutdownNotifier};

@@ -107,7 +109,7 @@ impl SocketClient {

    /// blocking version of `start_socket` method. Will run forever (or until SIGINT is sent)
    pub async fn run_socket_forever(self) -> Result<(), ClientError> {
-        let shutdown = self.start_socket().await?;
+        let mut shutdown = self.start_socket().await?;
        wait_for_signal().await;

        println!(
@@ -120,8 +122,8 @@ impl SocketClient {
        // Some of these components have shutdown signalling implemented as part of socks5 work,
        // but since it's not fully implemented (yet) for all the components of the native client,
        // we don't try to wait and instead just stop immediately.
-        //log::info!("Waiting for tasks to finish... (Press ctrl-c to force)");
-        //shutdown.wait_for_shutdown().await;
+        log::info!("Waiting for tasks to finish... (Press ctrl-c to force)");
+        shutdown.wait_for_shutdown().await;

        log::info!("Stopping nym-client");
        Ok(())
@@ -136,6 +138,11 @@ impl SocketClient {
            self.config.get_base(),
            self.key_manager,
            Some(Self::create_bandwidth_controller(&self.config).await),
+            non_wasm_helpers::setup_fs_reply_surb_backend(
+                self.config.get_base().get_reply_surb_database_path(),
+                self.config.get_debug_settings(),
+            )
+            .await?,
        );

        let self_address = base_builder.as_mix_recipient();
@@ -160,6 +167,11 @@ impl SocketClient {
            self.config.get_base(),
            self.key_manager,
            Some(Self::create_bandwidth_controller(&self.config).await),
+            non_wasm_helpers::setup_fs_reply_surb_backend(
+                self.config.get_base().get_reply_surb_database_path(),
+                self.config.get_debug_settings(),
+            )
+            .await?,
        );

        let mut started_client = base_client.start_base().await?;
@@ -197,14 +209,9 @@ impl DirectClient {
    /// EXPERIMENTAL DIRECT RUST API
    /// It's untested and there are absolutely no guarantees about it (but seems to have worked
    /// well enough in local tests)
-    pub async fn send_message(
-        &mut self,
-        recipient: Recipient,
-        message: Vec<u8>,
-        with_reply_surb: bool,
-    ) {
+    pub async fn send_regular_message(&mut self, recipient: Recipient, message: Vec<u8>) {
        let lane = TransmissionLane::General;
-        let input_msg = InputMessage::new_fresh(recipient, message, with_reply_surb, lane);
+        let input_msg = InputMessage::new_regular(recipient, message, lane);

        self.client_input
            .input_sender
@@ -216,8 +223,28 @@ impl DirectClient {
    /// EXPERIMENTAL DIRECT RUST API
    /// It's untested and there are absolutely no guarantees about it (but seems to have worked
    /// well enough in local tests)
-    pub async fn send_reply(&mut self, reply_surb: ReplySurb, message: Vec<u8>) {
-        let input_msg = InputMessage::new_reply(reply_surb, message);
+    pub async fn send_anonymous_message(
+        &mut self,
+        recipient: Recipient,
+        message: Vec<u8>,
+        reply_surbs: u32,
+    ) {
+        let lane = TransmissionLane::General;
+        let input_msg = InputMessage::new_anonymous(recipient, message, reply_surbs, lane);
+
+        self.client_input
+            .input_sender
+            .send(input_msg)
+            .await
+            .expect("InputMessageReceiver has stopped receiving!");
+    }
+
+    /// EXPERIMENTAL DIRECT RUST API
+    /// It's untested and there are absolutely no guarantees about it (but seems to have worked
+    /// well enough in local tests)
+    pub async fn send_reply(&mut self, recipient_tag: AnonymousSenderTag, message: Vec<u8>) {
+        let lane = TransmissionLane::General;
+        let input_msg = InputMessage::new_reply(recipient_tag, message, lane);

        self.client_input
            .input_sender
@@ -1,19 +1,17 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-use std::fmt::Display;
-
-use clap::Args;
-use config::NymConfig;
-use nymsphinx::addressing::clients::Recipient;
-use serde::Serialize;
-use tap::TapFallible;
-
 use crate::{
    client::config::Config,
    commands::{override_config, OverrideConfig},
    error::ClientError,
 };
+use clap::Args;
+use config::NymConfig;
+use nymsphinx::addressing::clients::Recipient;
+use serde::Serialize;
+use std::fmt::Display;
+use tap::TapFallible;

 #[derive(Args, Clone)]
 pub(crate) struct Init {
@@ -136,7 +134,7 @@ pub(crate) async fn execute(args: &Init) -> Result<(), ClientError> {

    // Setup gateway by either registering a new one, or creating a new config from the selected
    // one but with keys kept, or reusing the gateway configuration.
-    let gateway = client_core::init::setup_gateway::<Config, _>(
+    let gateway = client_core::init::setup_gateway::<_, Config, _>(
        register_gateway,
        user_chosen_gateway_id,
        config.get_base(),
@@ -1,14 +1,17 @@
+use client_core::client::replies::reply_storage::fs_backend;
 use client_core::error::ClientCoreError;

 #[derive(thiserror::Error, Debug)]
 pub enum ClientError {
    #[error("I/O error: {0}")]
    IoError(#[from] std::io::Error),
+
    #[error("client-core error: {0}")]
-    ClientCoreError(#[from] ClientCoreError),
+    ClientCoreError(#[from] ClientCoreError<fs_backend::Backend>),

    #[error("Failed to load config for: {0}")]
    FailedToLoadConfig(String),
+
    #[error("Failed local version check, client and config mismatch")]
    FailedLocalVersionCheck,

@@ -14,7 +14,7 @@ use futures::channel::mpsc;
 use futures::{SinkExt, StreamExt};
 use log::*;
 use nymsphinx::addressing::clients::Recipient;
-use nymsphinx::anonymous_replies::ReplySurb;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
 use nymsphinx::receiver::ReconstructedMessage;
 use tokio::net::TcpStream;
 use tokio_tungstenite::{
@@ -62,9 +62,13 @@ impl Clone for Handler {

 impl Drop for Handler {
    fn drop(&mut self) {
-        self.buffer_requester
+        if self
+            .buffer_requester
            .unbounded_send(ReceivedBufferMessage::ReceiverDisconnect)
-            .expect("the buffer request failed!")
+            .is_err()
+        {
+            error!("we failed to disconnect the receiver from the buffer! presumably the shutdown procedure has been initiated!")
+        }
    }
 }

@@ -89,18 +93,22 @@ impl Handler {

    async fn handle_send(
        &mut self,
-        recipient: &Recipient,
+        recipient: Recipient,
        message: Vec<u8>,
-        with_reply_surb: bool,
        connection_id: Option<u64>,
    ) -> Option<ServerResponse> {
+        info!(
+            "Attempting to send {:.2} kiB message to {recipient} on connection_id {connection_id:?}",
+            message.len() as f64 / 1024.0
+        );
+
        // We map the absence of a connection id as going into the general lane.
        let lane = connection_id.map_or(TransmissionLane::General, |id| {
            TransmissionLane::ConnectionId(id)
        });

        // the ack control is now responsible for chunking, etc.
-        let input_msg = InputMessage::new_fresh(*recipient, message, with_reply_surb, lane);
+        let input_msg = InputMessage::new_regular(recipient, message, lane);
        self.msg_input
            .send(input_msg)
            .await
@@ -109,53 +117,119 @@ impl Handler {
        // Only reply back with a `LaneQueueLength` if the sender providided a connection id
        let connection_id = match lane {
            TransmissionLane::General
-            | TransmissionLane::Reply
+            | TransmissionLane::ReplySurbRequest
            | TransmissionLane::Retransmission
-            | TransmissionLane::Control => return None,
+            | TransmissionLane::AdditionalReplySurbs => return None,
            TransmissionLane::ConnectionId(id) => id,
        };

        // on receiving a send, we reply back the current lane queue length for that connection id.
        // Note that this does _NOT_ take into account the packets that have been received but not
        // yet reach `OutQueueControl`, so it might be a tad low.
-        let Ok(lane_queue_lengths) = self.lane_queue_lengths.lock() else {
-            log::warn!(
-                "Failed to get the lane queue length lock, \
-                not responding back with the current queue length"
-            );
-            return None;
-        };
-
-        let queue_length = lane_queue_lengths.get(&lane).unwrap_or(0);
-        Some(ServerResponse::LaneQueueLength(connection_id, queue_length))
-    }
-
-    async fn handle_reply(
-        &mut self,
-        reply_surb: ReplySurb,
-        message: Vec<u8>,
-    ) -> Option<ServerResponse> {
-        if message.len() > ReplySurb::max_msg_len(Default::default()) {
-            return Some(
-                ServerResponse::new_error(
-                    format!(
-                        "too long message to put inside a reply SURB. Received: {} bytes and maximum is {} bytes",
-                        message.len(), ReplySurb::max_msg_len(Default::default()))
-                    )
-                );
+        if let Ok(lane_queue_lengths) = self.lane_queue_lengths.lock() {
+            let queue_length = lane_queue_lengths.get(&lane).unwrap_or(0);
+            return Some(ServerResponse::LaneQueueLength {
+                lane: connection_id,
+                queue_length,
+            });
        }

-        let input_msg = InputMessage::new_reply(reply_surb, message);
+        log::warn!("Failed to get the lane queue length lock, not responding back with the current queue length");
+        None
+    }
+
+    async fn handle_send_anonymous(
+        &mut self,
+        recipient: Recipient,
+        message: Vec<u8>,
+        reply_surbs: u32,
+        connection_id: Option<u64>,
+    ) -> Option<ServerResponse> {
+        info!(
+            "Attempting to anonymously send {:.2} kiB message to {recipient} on connection_id {connection_id:?} while attaching {reply_surbs} replySURBs.",
+            message.len() as f64 / 1024.0
+        );
+
+        // We map the absence of a connection id as going into the general lane.
+        let lane = connection_id.map_or(TransmissionLane::General, |id| {
+            TransmissionLane::ConnectionId(id)
+        });
+
+        let input_msg = InputMessage::new_anonymous(recipient, message, reply_surbs, lane);
        self.msg_input
            .send(input_msg)
            .await
            .expect("InputMessageReceiver has stopped receiving!");

+        // Only reply back with a `LaneQueueLength` if the sender providided a connection id
+        let connection_id = match lane {
+            TransmissionLane::General
+            | TransmissionLane::ReplySurbRequest
+            | TransmissionLane::Retransmission
+            | TransmissionLane::AdditionalReplySurbs => return None,
+            TransmissionLane::ConnectionId(id) => id,
+        };
+
+        // on receiving a send, we reply back the current lane queue length for that connection id.
+        // Note that this does _NOT_ take into account the packets that have been received but not
+        // yet reach `OutQueueControl`, so it might be a tad low.
+        if let Ok(lane_queue_lengths) = self.lane_queue_lengths.lock() {
+            let queue_length = lane_queue_lengths.get(&lane).unwrap_or(0);
+            return Some(ServerResponse::LaneQueueLength {
+                lane: connection_id,
+                queue_length,
+            });
+        }
+
+        log::warn!("Failed to get the lane queue length lock, not responding back with the current queue length");
+        None
+    }
+
+    async fn handle_reply(
+        &mut self,
+        recipient_tag: AnonymousSenderTag,
+        message: Vec<u8>,
+        connection_id: Option<u64>,
+    ) -> Option<ServerResponse> {
+        info!("Attempting to send {:.2} kiB reply message to {recipient_tag} on connection_id {connection_id:?}", message.len() as f64 / 1024.0);
+
+        // We map the absence of a connection id as going into the general lane.
+        let lane = connection_id.map_or(TransmissionLane::General, |id| {
+            TransmissionLane::ConnectionId(id)
+        });
+
+        let input_msg = InputMessage::new_reply(recipient_tag, message, lane);
+        self.msg_input
+            .send(input_msg)
+            .await
+            .expect("InputMessageReceiver has stopped receiving!");
+
+        // Only reply back with a `LaneQueueLength` if the sender providided a connection id
+        let connection_id = match lane {
+            TransmissionLane::General
+            | TransmissionLane::ReplySurbRequest
+            | TransmissionLane::Retransmission
+            | TransmissionLane::AdditionalReplySurbs => return None,
+            TransmissionLane::ConnectionId(id) => id,
+        };
+
+        // on receiving a send, we reply back the current lane queue length for that connection id.
+        // Note that this does _NOT_ take into account the packets that have been received but not
+        // yet reach `OutQueueControl`, so it might be a tad low.
+        if let Ok(lane_queue_lengths) = self.lane_queue_lengths.lock() {
+            let queue_length = lane_queue_lengths.get(&lane).unwrap_or(0);
+            return Some(ServerResponse::LaneQueueLength {
+                lane: connection_id,
+                queue_length,
+            });
+        }
+
+        log::warn!("Failed to get the lane queue length lock, not responding back with the current queue length");
        None
    }

    fn handle_self_address(&self) -> ServerResponse {
-        ServerResponse::SelfAddress(self.self_full_address)
+        ServerResponse::SelfAddress(Box::new(self.self_full_address))
    }

    fn handle_closed_connection(&self, connection_id: u64) -> Option<ServerResponse> {
@@ -175,7 +249,10 @@ impl Handler {

        let lane = TransmissionLane::ConnectionId(connection_id);
        let queue_length = lane_queue_lengths.get(&lane).unwrap_or(0);
-        Some(ServerResponse::LaneQueueLength(connection_id, queue_length))
+        Some(ServerResponse::LaneQueueLength {
+            lane: connection_id,
+            queue_length,
+        })
    }

    async fn handle_request(&mut self, request: ClientRequest) -> Option<ServerResponse> {
@@ -183,16 +260,25 @@ impl Handler {
            ClientRequest::Send {
                recipient,
                message,
-                with_reply_surb,
+                connection_id,
+            } => self.handle_send(recipient, message, connection_id).await,
+
+            ClientRequest::SendAnonymous {
+                recipient,
+                message,
+                reply_surbs,
                connection_id,
            } => {
-                self.handle_send(&recipient, message, with_reply_surb, connection_id)
+                self.handle_send_anonymous(recipient, message, reply_surbs, connection_id)
                    .await
            }
+
            ClientRequest::Reply {
                message,
-                reply_surb,
-            } => self.handle_reply(reply_surb, message).await,
+                sender_tag,
+                connection_id,
+            } => self.handle_reply(sender_tag, message, connection_id).await,
+
            ClientRequest::SelfAddress => Some(self.handle_self_address()),
            ClientRequest::ClosedConnection(id) => self.handle_closed_connection(id),
            ClientRequest::GetLaneQueueLength(id) => self.handle_get_lane_queue_length(id),
@@ -299,8 +385,7 @@ impl Handler {
                    if let Some(response) = self.handle_ws_request(socket_msg).await {
                        if let Err(err) = self.send_websocket_response(response).await {
                            warn!(
-                                "Failed to send message over websocket: {}. Assuming the connection is dead.",
-                                err
+                                "Failed to send message over websocket: {err}. Assuming the connection is dead.",
                            );
                            break;
                        }
@@ -308,9 +393,10 @@ impl Handler {
                }
                // or a reconstructed mix message that we need to push back to the client
                mix_messages = msg_receiver.next() => {
-                    let mix_messages = mix_messages.expect(
-                        "mix messages sender was unexpectedly closed! this shouldn't have ever happened!",
-                    );
+                    let Some(mix_messages) = mix_messages else {
+                        error!("mix messages sender was unexpectedly closed! this shouldn't have ever happened! (unless we're shutting down - TODO: implement proper graceful shutdown handler)");
+                        return
+                    };
                    if let Err(e) = self.push_websocket_received_plaintexts(mix_messages).await {
                        warn!("failed to send sphinx packets back to the client - {:?}, assuming the connection is dead", e);
                        break;
@@ -54,9 +54,8 @@ impl Listener {
                        Ok((mut socket, remote_addr)) => {
                            debug!("Received connection from {:?}", remote_addr);
                            if self.state.is_connected() {
-                                warn!("tried to duplicate!");
+                                warn!("Tried to open a duplicate websocket connection. The request came from {}", remote_addr);
                                // if we've already got a connection, don't allow another one
-                                debug!("but there was already a connection present!");
                                // while we only ever want to accept a single connection, we don't want
                                // to leave clients hanging (and also allow for reconnection if it somehow
                                // was dropped)
@@ -24,8 +24,11 @@ impl fmt::Debug for Error {
 }

 impl Error {
-    pub fn new(kind: ErrorKind, message: String) -> Self {
-        Error { kind, message }
+    pub fn new<S: Into<String>>(kind: ErrorKind, message: S) -> Self {
+        Error {
+            kind,
+            message: message.into(),
+        }
    }
 }

@@ -62,6 +65,31 @@ pub enum ErrorKind {
    Other = 0xFF,
 }

+impl TryFrom<u8> for ErrorKind {
+    type Error = Error;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            _ if value == (ErrorKind::EmptyRequest as u8) => Ok(ErrorKind::EmptyRequest),
+            _ if value == (ErrorKind::TooShortRequest as u8) => Ok(ErrorKind::TooShortRequest),
+            _ if value == (ErrorKind::UnknownRequest as u8) => Ok(ErrorKind::UnknownRequest),
+            _ if value == (ErrorKind::MalformedRequest as u8) => Ok(ErrorKind::MalformedRequest),
+
+            _ if value == (ErrorKind::EmptyResponse as u8) => Ok(ErrorKind::EmptyResponse),
+            _ if value == (ErrorKind::TooShortResponse as u8) => Ok(ErrorKind::TooShortResponse),
+            _ if value == (ErrorKind::UnknownResponse as u8) => Ok(ErrorKind::UnknownResponse),
+            _ if value == (ErrorKind::MalformedResponse as u8) => Ok(ErrorKind::MalformedResponse),
+
+            _ if value == (ErrorKind::Other as u8) => Ok(ErrorKind::Other),
+
+            n => Err(Error::new(
+                ErrorKind::MalformedResponse,
+                format!("invalid error code {}", n),
+            )),
+        }
+    }
+}
+
 impl ErrorKind {
    pub(crate) fn as_str(&self) -> &'static str {
        match *self {
@@ -1,4 +1,4 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

 // all variable size data is always prefixed with u64 length
@@ -7,69 +7,115 @@
 use crate::error::{self, ErrorKind};
 use crate::text::ClientRequestText;
 use nymsphinx::addressing::clients::Recipient;
-use nymsphinx::anonymous_replies::ReplySurb;
+use nymsphinx::anonymous_replies::requests::{AnonymousSenderTag, SENDER_TAG_SIZE};
 use std::convert::{TryFrom, TryInto};
 use std::mem::size_of;

-/// Value tag representing [`Send`] variant of the [`ClientRequest`]
-pub const SEND_REQUEST_TAG: u8 = 0x00;
+#[repr(u8)]
+enum ClientRequestTag {
+    /// Value tag representing [`Send`] variant of the [`ClientRequest`]
+    Send = 0x00,

-/// Value tag representing [`Reply`] variant of the [`ClientRequest`]
-pub const REPLY_REQUEST_TAG: u8 = 0x01;
+    /// Value tag representing [`SendAnonymous`] variant of the [`ClientRequest`]
+    SendAnonymous = 0x01,

-/// Value tag representing [`SelfAddress`] variant of the [`ClientRequest`]
-pub const SELF_ADDRESS_REQUEST_TAG: u8 = 0x02;
+    /// Value tag representing [`Reply`] variant of the [`ClientRequest`]
+    Reply = 0x02,

-/// Value tag representing [`ClosedConnection`] variant of the [`ClientRequest`]
-pub const CLOSED_CONNECTION_REQUEST_TAG: u8 = 0x03;
+    /// Value tag representing [`SelfAddress`] variant of the [`ClientRequest`]
+    SelfAddress = 0x03,

-/// Value tag representing [`GetLaneQueueLength`] variant of the [`ClientRequest`]
-pub const GET_LANE_QUEUE_LENGHT_TAG: u8 = 0x04;
+    /// Value tag representing [`ClosedConnection`] variant of the [`ClientRequest`]
+    ClosedConnection = 0x04,
+
+    /// Value tag representing [`GetLaneQueueLength`] variant of the [`ClientRequest`]
+    GetLaneQueueLength = 0x05,
+}
+
+impl TryFrom<u8> for ClientRequestTag {
+    type Error = error::Error;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            _ if value == (Self::Send as u8) => Ok(Self::Send),
+            _ if value == (Self::SendAnonymous as u8) => Ok(Self::SendAnonymous),
+            _ if value == (Self::Reply as u8) => Ok(Self::Reply),
+            _ if value == (Self::SelfAddress as u8) => Ok(Self::SelfAddress),
+            _ if value == (Self::ClosedConnection as u8) => Ok(Self::ClosedConnection),
+            _ if value == (Self::GetLaneQueueLength as u8) => Ok(Self::GetLaneQueueLength),
+            n => Err(error::Error::new(
+                ErrorKind::UnknownRequest,
+                format!("{n} does not correspond to any valid request tag"),
+            )),
+        }
+    }
+}

 #[allow(non_snake_case)]
 #[derive(Debug)]
 pub enum ClientRequest {
+    /// The simplest message variant where no additional information is attached.
+    /// You're simply sending your `data` to specified `recipient` without any tagging.
+    ///
+    /// Ends up with `NymMessage::Plain` variant
    Send {
        recipient: Recipient,
        message: Vec<u8>,
-        // Perhaps we could change it to a number to indicate how many reply_SURBs we want to include?
-        with_reply_surb: bool,
        connection_id: Option<u64>,
    },
-    Reply {
+
+    /// Create a message used for a duplex anonymous communication where the recipient
+    /// will never learn of our true identity. This is achieved by carefully sending `reply_surbs`.
+    ///
+    /// Note that if reply_surbs is set to zero then
+    /// this variant requires the client having sent some reply_surbs in the past
+    /// (and thus the recipient also knowing our sender tag).
+    ///
+    /// Ends up with `NymMessage::Repliable` variant
+    SendAnonymous {
+        recipient: Recipient,
        message: Vec<u8>,
-        reply_surb: ReplySurb,
+        reply_surbs: u32,
+        connection_id: Option<u64>,
    },
+
+    /// Attempt to use our internally received and stored `ReplySurb` to send the message back
+    /// to specified recipient whilst not knowing its full identity (or even gateway).
+    ///
+    /// Ends up with `NymMessage::Reply` variant
+    Reply {
+        sender_tag: AnonymousSenderTag,
+        message: Vec<u8>,
+        connection_id: Option<u64>,
+    },
+
    SelfAddress,
+
    ClosedConnection(u64),
+
    GetLaneQueueLength(u64),
 }

 // we could have been parsing it directly TryFrom<WsMessage>, but we want to retain
 // information about whether it came from binary or text to send appropriate response back
 impl ClientRequest {
-    // SEND_REQUEST_TAG || with_surb || recipient || conn_id || data_len || data
-    fn serialize_send(
-        recipient: Recipient,
-        data: Vec<u8>,
-        with_reply_surb: bool,
-        connection_id: Option<u64>,
-    ) -> Vec<u8> {
+    // SEND_REQUEST_TAG || recipient || conn_id || data_len || data
+    fn serialize_send(recipient: Recipient, data: Vec<u8>, connection_id: Option<u64>) -> Vec<u8> {
        let data_len_bytes = (data.len() as u64).to_be_bytes();
        let conn_id_bytes = connection_id.unwrap_or(0).to_be_bytes();
-        std::iter::once(SEND_REQUEST_TAG)
-            .chain(std::iter::once(with_reply_surb as u8))
-            .chain(recipient.to_bytes().iter().cloned()) // will not be length prefixed because the length is constant
-            .chain(conn_id_bytes.iter().cloned())
-            .chain(data_len_bytes.iter().cloned())
+
+        std::iter::once(ClientRequestTag::Send as u8)
+            .chain(recipient.to_bytes().into_iter()) // will not be length prefixed because the length is constant
+            .chain(conn_id_bytes.into_iter())
+            .chain(data_len_bytes.into_iter())
            .chain(data.into_iter())
            .collect()
    }

-    // SEND_REQUEST_TAG || with_reply || recipient || conn_id || data_len || data
+    // SEND_REQUEST_TAG || recipient || conn_id || data_len || data
    fn deserialize_send(b: &[u8]) -> Result<Self, error::Error> {
-        // we need to have at least 1 (tag) + 1 (reply flag) + Recipient::LEN + 2*sizeof<u64> bytes
-        if b.len() < 2 + Recipient::LEN + 2 * size_of::<u64>() {
+        // we need to have at least 1 (tag) + Recipient::LEN + 2*sizeof<u64> bytes
+        if b.len() < 1 + Recipient::LEN + 2 * size_of::<u64>() {
            return Err(error::Error::new(
                ErrorKind::TooShortRequest,
                "not enough data provided to recover 'send'".to_string(),
@@ -77,21 +123,10 @@ impl ClientRequest {
        }

        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], SEND_REQUEST_TAG);
-
-        let with_reply_surb = match b[1] {
-            0 => false,
-            1 => true,
-            n => {
-                return Err(error::Error::new(
-                    ErrorKind::MalformedRequest,
-                    format!("invalid reply surb flag {}", n),
-                ))
-            }
-        };
+        debug_assert_eq!(b[0], ClientRequestTag::Send as u8);

        let mut recipient_bytes = [0u8; Recipient::LEN];
-        recipient_bytes.copy_from_slice(&b[2..2 + Recipient::LEN]);
+        recipient_bytes.copy_from_slice(&b[1..1 + Recipient::LEN]);
        let recipient = match Recipient::try_from_bytes(recipient_bytes) {
            Ok(recipient) => recipient,
            Err(err) => {
@@ -104,7 +139,7 @@ impl ClientRequest {

        let mut connection_id_bytes = [0u8; size_of::<u64>()];
        connection_id_bytes
-            .copy_from_slice(&b[2 + Recipient::LEN..2 + Recipient::LEN + size_of::<u64>()]);
+            .copy_from_slice(&b[1 + Recipient::LEN..1 + Recipient::LEN + size_of::<u64>()]);
        let connection_id = u64::from_be_bytes(connection_id_bytes);
        let connection_id = if connection_id == 0 {
            None
@@ -113,9 +148,9 @@ impl ClientRequest {
        };

        let data_len_bytes =
-            &b[2 + Recipient::LEN + size_of::<u64>()..2 + Recipient::LEN + 2 * size_of::<u64>()];
+            &b[1 + Recipient::LEN + size_of::<u64>()..1 + Recipient::LEN + 2 * size_of::<u64>()];
        let data_len = u64::from_be_bytes(data_len_bytes.try_into().unwrap());
-        let data = &b[2 + Recipient::LEN + 2 * size_of::<u64>()..];
+        let data = &b[1 + Recipient::LEN + 2 * size_of::<u64>()..];
        if data.len() as u64 != data_len {
            return Err(error::Error::new(
                ErrorKind::MalformedRequest,
@@ -128,33 +163,111 @@ impl ClientRequest {
        }

        Ok(ClientRequest::Send {
-            with_reply_surb,
            recipient,
            message: data.to_vec(),
            connection_id,
        })
    }

-    // REPLY_REQUEST_TAG || surb_len || surb || message_len || message
-    fn serialize_reply(message: Vec<u8>, reply_surb: &ReplySurb) -> Vec<u8> {
-        let reply_surb_bytes = reply_surb.to_bytes();
-        let surb_len_bytes = (reply_surb_bytes.len() as u64).to_be_bytes();
-        let message_len_bytes = (message.len() as u64).to_be_bytes();
+    // SEND_ANONYMOUS_REQUEST_TAG || reply_surbs || recipient || conn_id || data_len || data
+    fn serialize_send_anonymous(
+        recipient: Recipient,
+        data: Vec<u8>,
+        reply_surbs: u32,
+        connection_id: Option<u64>,
+    ) -> Vec<u8> {
+        let data_len_bytes = (data.len() as u64).to_be_bytes();
+        let conn_id_bytes = connection_id.unwrap_or(0).to_be_bytes();

-        std::iter::once(REPLY_REQUEST_TAG)
-            .chain(surb_len_bytes.iter().cloned())
-            .chain(reply_surb_bytes.into_iter())
-            .chain(message_len_bytes.iter().cloned())
+        std::iter::once(ClientRequestTag::SendAnonymous as u8)
+            .chain(reply_surbs.to_be_bytes().into_iter())
+            .chain(recipient.to_bytes().into_iter()) // will not be length prefixed because the length is constant
+            .chain(conn_id_bytes.into_iter())
+            .chain(data_len_bytes.into_iter())
+            .chain(data.into_iter())
+            .collect()
+    }
+
+    // SEND_ANONYMOUS_REQUEST_TAG || reply_surbs || recipient || data_len || data
+    fn deserialize_send_anonymous(b: &[u8]) -> Result<Self, error::Error> {
+        // we need to have at least 1 (tag) + sizeof<u32> (num surbs) + Recipient::LEN + 2 *sizeof<u64> bytes
+        if b.len() < 1 + size_of::<u32>() + Recipient::LEN + 2 * size_of::<u64>() {
+            return Err(error::Error::new(
+                ErrorKind::TooShortRequest,
+                "not enough data provided to recover 'send_anonymous'".to_string(),
+            ));
+        }
+
+        // this MUST match because it was called by 'deserialize'
+        debug_assert_eq!(b[0], ClientRequestTag::SendAnonymous as u8);
+
+        let reply_surbs = u32::from_be_bytes([b[1], b[2], b[3], b[4]]);
+
+        let mut recipient_bytes = [0u8; Recipient::LEN];
+        recipient_bytes.copy_from_slice(&b[5..5 + Recipient::LEN]);
+        let recipient = match Recipient::try_from_bytes(recipient_bytes) {
+            Ok(recipient) => recipient,
+            Err(err) => {
+                return Err(error::Error::new(
+                    ErrorKind::MalformedRequest,
+                    format!("malformed recipient: {:?}", err),
+                ))
+            }
+        };
+
+        let mut connection_id_bytes = [0u8; size_of::<u64>()];
+        connection_id_bytes
+            .copy_from_slice(&b[5 + Recipient::LEN..5 + Recipient::LEN + size_of::<u64>()]);
+        let connection_id = u64::from_be_bytes(connection_id_bytes);
+        let connection_id = if connection_id == 0 {
+            None
+        } else {
+            Some(connection_id)
+        };
+
+        let data_len_bytes =
+            &b[5 + Recipient::LEN + size_of::<u64>()..5 + Recipient::LEN + 2 * size_of::<u64>()];
+        let data_len = u64::from_be_bytes(data_len_bytes.try_into().unwrap());
+        let data = &b[5 + Recipient::LEN + 2 * size_of::<u64>()..];
+        if data.len() as u64 != data_len {
+            return Err(error::Error::new(
+                ErrorKind::MalformedRequest,
+                format!(
+                    "data len has inconsistent length. specified: {} got: {}",
+                    data_len,
+                    data.len()
+                ),
+            ));
+        }
+
+        Ok(ClientRequest::SendAnonymous {
+            reply_surbs,
+            recipient,
+            message: data.to_vec(),
+            connection_id,
+        })
+    }
+
+    // REPLY_REQUEST_TAG || SENDER_TAG || conn_id || message_len || message
+    fn serialize_reply(
+        message: Vec<u8>,
+        sender_tag: AnonymousSenderTag,
+        connection_id: Option<u64>,
+    ) -> Vec<u8> {
+        let message_len_bytes = (message.len() as u64).to_be_bytes();
+        let conn_id_bytes = connection_id.unwrap_or(0).to_be_bytes();
+
+        std::iter::once(ClientRequestTag::Reply as u8)
+            .chain(sender_tag.to_bytes().into_iter())
+            .chain(conn_id_bytes.into_iter())
+            .chain(message_len_bytes.into_iter())
            .chain(message.into_iter())
            .collect()
    }

-    // REPLY_REQUEST_TAG || surb_len || surb || message_len || message
+    // REPLY_REQUEST_TAG || SENDER_TAG || conn_id || message_len || message
    fn deserialize_reply(b: &[u8]) -> Result<Self, error::Error> {
-        // we need to have at the very least 2 * sizeof<u64> bytes (in case, for some peculiar reason
-        // message and reply surb were 0 len - the request would still be malformed, but would in theory
-        // be parse'able)
-        if b.len() < 1 + 2 * size_of::<u64>() {
+        if b.len() < 1 + SENDER_TAG_SIZE + 2 * size_of::<u64>() {
            return Err(error::Error::new(
                ErrorKind::TooShortRequest,
                "not enough data provided to recover 'reply'".to_string(),
@@ -162,42 +275,28 @@ impl ClientRequest {
        }

        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], REPLY_REQUEST_TAG);
+        debug_assert_eq!(b[0], ClientRequestTag::Reply as u8);

-        let reply_surb_len =
-            u64::from_be_bytes(b[1..1 + size_of::<u64>()].as_ref().try_into().unwrap());
+        // the unwrap here is fine as we're definitely using exactly SENDER_TAG_SIZE bytes
+        let sender_tag =
+            AnonymousSenderTag::from_bytes(b[1..1 + SENDER_TAG_SIZE].try_into().unwrap());

-        // make sure we won't go out of bounds here
-        if reply_surb_len > (b.len() - 1 + 2 * size_of::<u64>()) as u64 {
-            return Err(error::Error::new(
-                ErrorKind::MalformedRequest,
-                format!(
-                    "not enough data to recover reply surb with specified length {}",
-                    reply_surb_len
-                ),
-            ));
-        }
-
-        let surb_bound = 1 + size_of::<u64>() + reply_surb_len as usize;
-
-        let reply_surb_bytes = &b[1 + size_of::<u64>()..surb_bound];
-        let reply_surb = match ReplySurb::from_bytes(reply_surb_bytes) {
-            Ok(reply_surb) => reply_surb,
-            Err(err) => {
-                return Err(error::Error::new(
-                    ErrorKind::MalformedRequest,
-                    format!("malformed reply surb: {:?}", err),
-                ))
-            }
+        let mut connection_id_bytes = [0u8; size_of::<u64>()];
+        connection_id_bytes
+            .copy_from_slice(&b[1 + SENDER_TAG_SIZE..1 + SENDER_TAG_SIZE + size_of::<u64>()]);
+        let connection_id = u64::from_be_bytes(connection_id_bytes);
+        let connection_id = if connection_id == 0 {
+            None
+        } else {
+            Some(connection_id)
        };

        let message_len = u64::from_be_bytes(
-            b[surb_bound..surb_bound + size_of::<u64>()]
-                .as_ref()
+            b[1 + SENDER_TAG_SIZE + size_of::<u64>()..1 + SENDER_TAG_SIZE + 2 * size_of::<u64>()]
                .try_into()
                .unwrap(),
        );
-        let message = &b[surb_bound + size_of::<u64>()..];
+        let message = &b[1 + SENDER_TAG_SIZE + 2 * size_of::<u64>()..];
        if message.len() as u64 != message_len {
            return Err(error::Error::new(
                ErrorKind::MalformedRequest,
@@ -208,33 +307,32 @@ impl ClientRequest {
                ),
            ));
        }
-        // TODO: should this blow HERE, i.e. during deserialization that the data you're trying
-        // to send via reply is too long?

        Ok(ClientRequest::Reply {
-            reply_surb,
            message: message.to_vec(),
+            sender_tag,
+            connection_id,
        })
    }

    // SELF_ADDRESS_REQUEST_TAG
    fn serialize_self_address() -> Vec<u8> {
-        std::iter::once(SELF_ADDRESS_REQUEST_TAG).collect()
+        vec![ClientRequestTag::SelfAddress as u8]
    }

    // SELF_ADDRESS_REQUEST_TAG
-    fn deserialize_self_address(b: &[u8]) -> Self {
+    fn deserialize_self_address(b: &[u8]) -> Result<Self, error::Error> {
        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], SELF_ADDRESS_REQUEST_TAG);
+        debug_assert_eq!(b[0], ClientRequestTag::SelfAddress as u8);

-        ClientRequest::SelfAddress
+        Ok(ClientRequest::SelfAddress)
    }

    // CLOSED_CONNECTION_REQUEST_TAG
    fn serialize_closed_connection(connection_id: u64) -> Vec<u8> {
        let conn_id_bytes = connection_id.to_be_bytes();
-        std::iter::once(CLOSED_CONNECTION_REQUEST_TAG)
-            .chain(conn_id_bytes.iter().copied())
+        std::iter::once(ClientRequestTag::ClosedConnection as u8)
+            .chain(conn_id_bytes.into_iter())
            .collect()
    }

@@ -243,12 +341,12 @@ impl ClientRequest {
        if b.len() != 1 + size_of::<u64>() {
            return Err(error::Error::new(
                ErrorKind::MalformedRequest,
-                "the received closed connection has invalid length".to_string(),
+                "The received closed connection has invalid length",
            ));
        }

        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], CLOSED_CONNECTION_REQUEST_TAG);
+        debug_assert_eq!(b[0], ClientRequestTag::ClosedConnection as u8);

        let mut connection_id_bytes = [0u8; size_of::<u64>()];
        connection_id_bytes.copy_from_slice(&b[1..=size_of::<u64>()]);
@@ -260,8 +358,8 @@ impl ClientRequest {
    // GET_LANE_QUEUE_LENGHT_TAG
    fn serialize_get_lane_queue_lengths(connection_id: u64) -> Vec<u8> {
        let conn_id_bytes = connection_id.to_be_bytes();
-        std::iter::once(GET_LANE_QUEUE_LENGHT_TAG)
-            .chain(conn_id_bytes.iter().copied())
+        std::iter::once(ClientRequestTag::GetLaneQueueLength as u8)
+            .chain(conn_id_bytes.into_iter())
            .collect()
    }

@@ -270,12 +368,12 @@ impl ClientRequest {
        if b.len() != 1 + size_of::<u64>() {
            return Err(error::Error::new(
                ErrorKind::MalformedRequest,
-                "the received get lane queue length has invalid length".to_string(),
+                "The received get lane queue lengths has invalid length",
            ));
        }

        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], GET_LANE_QUEUE_LENGHT_TAG);
+        debug_assert_eq!(b[0], ClientRequestTag::GetLaneQueueLength as u8);

        let mut connection_id_bytes = [0u8; size_of::<u64>()];
        connection_id_bytes.copy_from_slice(&b[1..=size_of::<u64>()]);
@@ -289,14 +387,21 @@ impl ClientRequest {
            ClientRequest::Send {
                recipient,
                message,
-                with_reply_surb,
                connection_id,
-            } => Self::serialize_send(recipient, message, with_reply_surb, connection_id),
+            } => Self::serialize_send(recipient, message, connection_id),
+
+            ClientRequest::SendAnonymous {
+                recipient,
+                message,
+                reply_surbs,
+                connection_id,
+            } => Self::serialize_send_anonymous(recipient, message, reply_surbs, connection_id),

            ClientRequest::Reply {
                message,
-                reply_surb,
-            } => Self::serialize_reply(message, &reply_surb),
+                sender_tag,
+                connection_id,
+            } => Self::serialize_reply(message, sender_tag, connection_id),

            ClientRequest::SelfAddress => Self::serialize_self_address(),

@@ -316,28 +421,16 @@ impl ClientRequest {
            ));
        }

-        if b.len() < size_of::<u8>() {
-            return Err(error::Error::new(
-                ErrorKind::TooShortRequest,
-                format!(
-                    "not enough data provided to recover request tag. Provided only {} bytes",
-                    b.len()
-                ),
-            ));
-        }
-        let request_tag = b[0];
+        let request_tag = ClientRequestTag::try_from(b[0])?;

        // determine what kind of request that is and try to deserialize it
        match request_tag {
-            SEND_REQUEST_TAG => Self::deserialize_send(b),
-            REPLY_REQUEST_TAG => Self::deserialize_reply(b),
-            SELF_ADDRESS_REQUEST_TAG => Ok(Self::deserialize_self_address(b)),
-            CLOSED_CONNECTION_REQUEST_TAG => Self::deserialize_closed_connection(b),
-            GET_LANE_QUEUE_LENGHT_TAG => Self::deserialize_get_lane_queue_length(b),
-            n => Err(error::Error::new(
-                ErrorKind::UnknownRequest,
-                format!("type {n}"),
-            )),
+            ClientRequestTag::Send => Self::deserialize_send(b),
+            ClientRequestTag::SendAnonymous => Self::deserialize_send_anonymous(b),
+            ClientRequestTag::Reply => Self::deserialize_reply(b),
+            ClientRequestTag::SelfAddress => Self::deserialize_self_address(b),
+            ClientRequestTag::ClosedConnection => Self::deserialize_closed_connection(b),
+            ClientRequestTag::GetLaneQueueLength => Self::deserialize_get_lane_queue_length(b),
        }
    }

@@ -365,50 +458,52 @@ mod tests {
        let recipient = Recipient::try_from_base58_string("CytBseW6yFXUMzz4SGAKdNLGR7q3sJLLYxyBGvutNEQV.4QXYyEVc5fUDjmmi8PrHN9tdUFV4PCvSJE1278cHyvoe@4sBbL1ngf1vtNqykydQKTFh26sQCw888GpUqvPvyNB4f").unwrap();
        let recipient_string = recipient.to_string();

-        let send_request_no_surb = ClientRequest::Send {
+        let send_request = ClientRequest::Send {
            recipient,
            message: b"foomp".to_vec(),
-            with_reply_surb: false,
            connection_id: Some(42),
        };

-        let bytes = send_request_no_surb.serialize();
+        let bytes = send_request.serialize();
        let recovered = ClientRequest::deserialize(&bytes).unwrap();
        match recovered {
            ClientRequest::Send {
                recipient,
                message,
-                with_reply_surb,
                connection_id,
            } => {
                assert_eq!(recipient.to_string(), recipient_string);
                assert_eq!(message, b"foomp".to_vec());
-                assert!(!with_reply_surb);
                assert_eq!(connection_id, Some(42))
            }
            _ => unreachable!(),
        }
+    }

-        let send_request_surb = ClientRequest::Send {
-            recipient,
+    #[test]
+    fn send_anonymous_request_serialization_works() {
+        let original_recipient = Recipient::try_from_base58_string("CytBseW6yFXUMzz4SGAKdNLGR7q3sJLLYxyBGvutNEQV.4QXYyEVc5fUDjmmi8PrHN9tdUFV4PCvSJE1278cHyvoe@4sBbL1ngf1vtNqykydQKTFh26sQCw888GpUqvPvyNB4f").unwrap();
+
+        let send_anonymous_request = ClientRequest::SendAnonymous {
+            recipient: original_recipient,
            message: b"foomp".to_vec(),
-            with_reply_surb: true,
-            connection_id: None,
+            reply_surbs: 666,
+            connection_id: Some(42),
        };

-        let bytes = send_request_surb.serialize();
+        let bytes = send_anonymous_request.serialize();
        let recovered = ClientRequest::deserialize(&bytes).unwrap();
        match recovered {
-            ClientRequest::Send {
+            ClientRequest::SendAnonymous {
                recipient,
                message,
-                with_reply_surb,
+                reply_surbs,
                connection_id,
            } => {
-                assert_eq!(recipient.to_string(), recipient_string);
+                assert_eq!(recipient, original_recipient);
                assert_eq!(message, b"foomp".to_vec());
-                assert!(with_reply_surb);
-                assert_eq!(connection_id, None)
+                assert_eq!(connection_id, Some(42));
+                assert_eq!(reply_surbs, 666)
            }
            _ => unreachable!(),
        }
@@ -416,22 +511,23 @@ mod tests {

    #[test]
    fn reply_request_serialization_works() {
-        let reply_surb_string = "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";
-        let reply_surb = ReplySurb::from_base58_string(reply_surb_string).unwrap();
        let reply_request = ClientRequest::Reply {
+            sender_tag: [8u8; SENDER_TAG_SIZE].into(),
            message: b"foomp".to_vec(),
-            reply_surb,
+            connection_id: Some(42),
        };

        let bytes = reply_request.serialize();
        let recovered = ClientRequest::deserialize(&bytes).unwrap();
        match recovered {
            ClientRequest::Reply {
-                reply_surb,
+                sender_tag,
                message,
+                connection_id,
            } => {
-                assert_eq!(reply_surb.to_base58_string(), reply_surb_string);
+                assert_eq!(sender_tag, [8u8; SENDER_TAG_SIZE].into());
                assert_eq!(message, b"foomp".to_vec());
+                assert_eq!(connection_id, Some(42));
            }
            _ => unreachable!(),
        }
@@ -458,4 +554,15 @@ mod tests {
            _ => unreachable!(),
        }
    }
+
+    #[test]
+    fn get_lane_queue_length_request_serialization_works() {
+        let close_connection_request = ClientRequest::GetLaneQueueLength(42);
+        let bytes = close_connection_request.serialize();
+        let recovered = ClientRequest::deserialize(&bytes).unwrap();
+        match recovered {
+            ClientRequest::GetLaneQueueLength(id) => assert_eq!(id, 42),
+            _ => unreachable!(),
+        }
+    }
 }
@@ -1,36 +1,54 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

 // all variable size data is always prefixed with u64 length
 // tags are u8

-#![allow(unknown_lints)] // due to using `clippy::branches_sharing_code` which does not exist on `stable` just yet
-
 use crate::error::{self, ErrorKind};
 use crate::text::ServerResponseText;
 use nymsphinx::addressing::clients::Recipient;
-use nymsphinx::anonymous_replies::ReplySurb;
+use nymsphinx::anonymous_replies::requests::{AnonymousSenderTag, SENDER_TAG_SIZE};
 use nymsphinx::receiver::ReconstructedMessage;
 use std::convert::TryInto;
 use std::mem::size_of;

-/// Value tag representing [`Error`] variant of the [`ServerResponse`]
-pub const ERROR_RESPONSE_TAG: u8 = 0x00;
+#[repr(u8)]
+enum ServerResponseTag {
+    /// Value tag representing [`Error`] variant of the [`ServerResponse`]
+    Error = 0x00,

-/// Value tag representing [`Received`] variant of the [`ServerResponse`]
-pub const RECEIVED_RESPONSE_TAG: u8 = 0x01;
+    /// Value tag representing [`Received`] variant of the [`ServerResponse`]
+    Received = 0x01,

-/// Value tag representing [`SelfAddress`] variant of the [`ServerResponse`]
-pub const SELF_ADDRESS_RESPONSE_TAG: u8 = 0x02;
+    /// Value tag representing [`SelfAddress`] variant of the [`ServerResponse`]
+    SelfAddress = 0x02,

-/// Value tag representing [`LaneQueueLength`] variant of the [`ServerResponse`]
-pub const LANE_QUEUE_LENGTH_RESPONSE_TAG: u8 = 0x03;
+    /// Value tag representing [`LaneQueueLength`] variant of the [`ServerResponse`]
+    LaneQueueLength = 0x03,
+}
+
+impl TryFrom<u8> for ServerResponseTag {
+    type Error = error::Error;
+
+    fn try_from(value: u8) -> Result<Self, error::Error> {
+        match value {
+            _ if value == (Self::Error as u8) => Ok(Self::Error),
+            _ if value == (Self::Received as u8) => Ok(Self::Received),
+            _ if value == (Self::SelfAddress as u8) => Ok(Self::SelfAddress),
+            _ if value == (Self::LaneQueueLength as u8) => Ok(Self::LaneQueueLength),
+            n => Err(error::Error::new(
+                ErrorKind::UnknownResponse,
+                format!("{n} does not correspond to any valid response tag"),
+            )),
+        }
+    }
+}

 #[derive(Debug)]
 pub enum ServerResponse {
    Received(ReconstructedMessage),
-    SelfAddress(Recipient),
-    LaneQueueLength(u64, usize),
+    SelfAddress(Box<Recipient>),
+    LaneQueueLength { lane: u64, queue_length: usize },
    Error(error::Error),
 }

@@ -42,24 +60,19 @@ impl ServerResponse {
        })
    }

-    // RECEIVED_RESPONSE_TAG || with_reply || (surb_len || surb) || msg_len || msg
+    // RECEIVED_RESPONSE_TAG || 1 | 0 indicating sender_tag || Option<sender_tag> || msg_len || msg
    fn serialize_received(reconstructed_message: ReconstructedMessage) -> Vec<u8> {
        let message_len_bytes = (reconstructed_message.message.len() as u64).to_be_bytes();
-        if let Some(reply_surb) = reconstructed_message.reply_surb {
-            let reply_surb_bytes = reply_surb.to_bytes();
-            let surb_len_bytes = (reply_surb_bytes.len() as u64).to_be_bytes();

-            // with_reply || surb_len || surb || msg_len || msg
-            std::iter::once(RECEIVED_RESPONSE_TAG)
+        if let Some(sender_tag) = reconstructed_message.sender_tag {
+            std::iter::once(ServerResponseTag::Received as u8)
                .chain(std::iter::once(true as u8))
-                .chain(surb_len_bytes.iter().cloned())
-                .chain(reply_surb_bytes.iter().cloned())
+                .chain(sender_tag.to_bytes().into_iter())
                .chain(message_len_bytes.iter().cloned())
                .chain(reconstructed_message.message.into_iter())
                .collect()
        } else {
-            // without_reply || msg_len || msg
-            std::iter::once(RECEIVED_RESPONSE_TAG)
+            std::iter::once(ServerResponseTag::Received as u8)
                .chain(std::iter::once(false as u8))
                .chain(message_len_bytes.iter().cloned())
                .chain(reconstructed_message.message.into_iter())
@@ -67,10 +80,9 @@ impl ServerResponse {
        }
    }

-    // RECEIVED_RESPONSE_TAG || with_reply || (surb_len || surb) || msg_len || msg
+    // RECEIVED_RESPONSE_TAG || 1 | 0 indicating sender_tag || Option<sender_tag> || msg_len || msg
    fn deserialize_received(b: &[u8]) -> Result<Self, error::Error> {
        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], RECEIVED_RESPONSE_TAG);

        // we must be able to read at the very least if it has a reply_surb and length of some field
        if b.len() < 2 + size_of::<u64>() {
@@ -79,101 +91,70 @@ impl ServerResponse {
                "not enough data provided to recover 'received'".to_string(),
            ));
        }
+        debug_assert_eq!(b[0], ServerResponseTag::Received as u8);

-        let with_reply_surb = match b[1] {
+        let has_sender_tag = match b[1] {
            0 => false,
            1 => true,
            n => {
                return Err(error::Error::new(
                    ErrorKind::MalformedResponse,
-                    format!("invalid reply flag {}", n),
+                    format!("invalid sender tag flag {n}"),
                ))
            }
        };

-        // this is a false positive as even though the code is the same, it refers to different things
-        #[allow(clippy::branches_sharing_code)]
-        if with_reply_surb {
-            let reply_surb_len =
-                u64::from_be_bytes(b[2..2 + size_of::<u64>()].as_ref().try_into().unwrap());
-
-            // make sure we won't go out of bounds here
-            if reply_surb_len > (b.len() - 2 + 2 * size_of::<u64>()) as u64 {
+        let mut i = 2;
+        let sender_tag = if has_sender_tag {
+            if b[2..].len() < SENDER_TAG_SIZE {
                return Err(error::Error::new(
-                    ErrorKind::MalformedResponse,
-                    "not enough bytes to read reply_surb bytes!".to_string(),
+                    ErrorKind::TooShortResponse,
+                    "not enough data provided to recover 'received'".to_string(),
                ));
            }
-
-            let surb_bound = 2 + size_of::<u64>() + reply_surb_len as usize;
-
-            let reply_surb_bytes = &b[2 + size_of::<u64>()..surb_bound];
-            let reply_surb = match ReplySurb::from_bytes(reply_surb_bytes) {
-                Ok(reply_surb) => reply_surb,
-                Err(err) => {
-                    return Err(error::Error::new(
-                        ErrorKind::MalformedResponse,
-                        format!("malformed reply SURB: {:?}", err),
-                    ))
-                }
-            };
-
-            let message_len = u64::from_be_bytes(
-                b[surb_bound..surb_bound + size_of::<u64>()]
-                    .as_ref()
-                    .try_into()
-                    .unwrap(),
-            );
-            let message = &b[surb_bound + size_of::<u64>()..];
-            if message.len() as u64 != message_len {
-                return Err(error::Error::new(
-                    ErrorKind::MalformedResponse,
-                    format!(
-                        "message len has inconsistent length. specified: {} got: {}",
-                        message_len,
-                        message.len()
-                    ),
-                ));
-            }
-
-            Ok(ServerResponse::Received(ReconstructedMessage {
-                message: message.to_vec(),
-                reply_surb: Some(reply_surb),
-            }))
+            i += SENDER_TAG_SIZE;
+            Some(AnonymousSenderTag::from_bytes(
+                b[2..2 + SENDER_TAG_SIZE].try_into().unwrap(),
+            ))
        } else {
-            let message_len =
-                u64::from_be_bytes(b[2..2 + size_of::<u64>()].as_ref().try_into().unwrap());
-            let message = &b[2 + size_of::<u64>()..];
-            if message.len() as u64 != message_len {
-                return Err(error::Error::new(
-                    ErrorKind::MalformedResponse,
-                    format!(
-                        "message len has inconsistent length. specified: {} got: {}",
-                        message_len,
-                        message.len()
-                    ),
-                ));
-            }
+            None
+        };

-            Ok(ServerResponse::Received(ReconstructedMessage {
-                message: message.to_vec(),
-                reply_surb: None,
-            }))
+        if b[i..].len() < size_of::<u64>() {
+            return Err(error::Error::new(
+                ErrorKind::TooShortResponse,
+                "not enough data provided to recover 'received'".to_string(),
+            ));
        }
+
+        let message_len = u64::from_be_bytes(b[i..i + size_of::<u64>()].try_into().unwrap());
+        let message = &b[i + size_of::<u64>()..];
+        if message.len() as u64 != message_len {
+            return Err(error::Error::new(
+                ErrorKind::MalformedResponse,
+                format!(
+                    "message len has inconsistent length. specified: {} got: {}",
+                    message_len,
+                    message.len()
+                ),
+            ));
+        }
+
+        Ok(ServerResponse::Received(ReconstructedMessage {
+            message: message.to_vec(),
+            sender_tag,
+        }))
    }

    // SELF_ADDRESS_RESPONSE_TAG || self_address
    fn serialize_self_address(address: Recipient) -> Vec<u8> {
-        std::iter::once(SELF_ADDRESS_RESPONSE_TAG)
-            .chain(address.to_bytes().iter().cloned())
+        std::iter::once(ServerResponseTag::SelfAddress as u8)
+            .chain(address.to_bytes().into_iter())
            .collect()
    }

    // SELF_ADDRESS_RESPONSE_TAG || self_address
    fn deserialize_self_address(b: &[u8]) -> Result<Self, error::Error> {
-        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], SELF_ADDRESS_RESPONSE_TAG);
-
        if b.len() != 1 + Recipient::LEN {
            return Err(error::Error::new(
                ErrorKind::TooShortResponse,
@@ -181,6 +162,9 @@ impl ServerResponse {
            ));
        }

+        // this MUST match because it was called by 'deserialize'
+        debug_assert_eq!(b[0], ServerResponseTag::SelfAddress as u8);
+
        let mut recipient_bytes = [0u8; Recipient::LEN];
        recipient_bytes.copy_from_slice(&b[1..1 + Recipient::LEN]);

@@ -194,12 +178,12 @@ impl ServerResponse {
            }
        };

-        Ok(ServerResponse::SelfAddress(recipient))
+        Ok(ServerResponse::SelfAddress(Box::new(recipient)))
    }

    // LANE_QUEUE_LENGTH_RESPONSE_TAG || lane || queue_length
    fn serialize_lane_queue_length(lane: u64, queue_length: usize) -> Vec<u8> {
-        std::iter::once(LANE_QUEUE_LENGTH_RESPONSE_TAG)
+        std::iter::once(ServerResponseTag::LaneQueueLength as u8)
            .chain(lane.to_be_bytes().iter().cloned())
            .chain(queue_length.to_be_bytes().iter().cloned())
            .collect()
@@ -208,7 +192,7 @@ impl ServerResponse {
    // LANE_QUEUE_LENGTH_RESPONSE_TAG || lane || queue_length
    fn deserialize_lane_queue_length(b: &[u8]) -> Result<Self, error::Error> {
        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], LANE_QUEUE_LENGTH_RESPONSE_TAG);
+        debug_assert_eq!(b[0], ServerResponseTag::LaneQueueLength as u8);

        let mut lane_bytes = [0u8; size_of::<u64>()];
        lane_bytes.copy_from_slice(&b[1..=size_of::<u64>()]);
@@ -219,15 +203,15 @@ impl ServerResponse {
            .copy_from_slice(&b[1 + size_of::<u64>()..1 + size_of::<u64>() + size_of::<usize>()]);
        let queue_length = usize::from_be_bytes(queue_length_bytes);

-        Ok(ServerResponse::LaneQueueLength(lane, queue_length))
+        Ok(ServerResponse::LaneQueueLength { lane, queue_length })
    }

    // ERROR_RESPONSE_TAG || err_code || msg_len || msg
    fn serialize_error(error: error::Error) -> Vec<u8> {
        let message_len_bytes = (error.message.len() as u64).to_be_bytes();
-        std::iter::once(ERROR_RESPONSE_TAG)
+        std::iter::once(ServerResponseTag::Error as u8)
            .chain(std::iter::once(error.kind as u8))
-            .chain(message_len_bytes.iter().cloned())
+            .chain(message_len_bytes.into_iter())
            .chain(error.message.into_bytes().into_iter())
            .collect()
    }
@@ -235,7 +219,7 @@ impl ServerResponse {
    // ERROR_RESPONSE_TAG || err_code || msg_len || msg
    fn deserialize_error(b: &[u8]) -> Result<Self, error::Error> {
        // this MUST match because it was called by 'deserialize'
-        debug_assert_eq!(b[0], ERROR_RESPONSE_TAG);
+        debug_assert_eq!(b[0], ServerResponseTag::Error as u8);

        if b.len() < size_of::<u8>() + size_of::<u64>() {
            return Err(error::Error::new(
@@ -244,26 +228,7 @@ impl ServerResponse {
            ));
        }

-        let error_kind = match b[1] {
-            _ if b[1] == (ErrorKind::EmptyRequest as u8) => ErrorKind::EmptyRequest,
-            _ if b[1] == (ErrorKind::TooShortRequest as u8) => ErrorKind::TooShortRequest,
-            _ if b[1] == (ErrorKind::UnknownRequest as u8) => ErrorKind::UnknownRequest,
-            _ if b[1] == (ErrorKind::MalformedRequest as u8) => ErrorKind::MalformedRequest,
-
-            _ if b[1] == (ErrorKind::EmptyResponse as u8) => ErrorKind::EmptyResponse,
-            _ if b[1] == (ErrorKind::TooShortResponse as u8) => ErrorKind::TooShortResponse,
-            _ if b[1] == (ErrorKind::UnknownResponse as u8) => ErrorKind::UnknownResponse,
-            _ if b[1] == (ErrorKind::MalformedResponse as u8) => ErrorKind::MalformedResponse,
-
-            _ if b[1] == (ErrorKind::Other as u8) => ErrorKind::Other,
-
-            n => {
-                return Err(error::Error::new(
-                    ErrorKind::MalformedResponse,
-                    format!("invalid error code {}", n),
-                ))
-            }
-        };
+        let error_kind = ErrorKind::try_from(b[1])?;

        let message_len =
            u64::from_be_bytes(b[2..2 + size_of::<u64>()].as_ref().try_into().unwrap());
@@ -300,8 +265,8 @@ impl ServerResponse {
            ServerResponse::Received(reconstructed_message) => {
                Self::serialize_received(reconstructed_message)
            }
-            ServerResponse::SelfAddress(address) => Self::serialize_self_address(address),
-            ServerResponse::LaneQueueLength(lane, queue_length) => {
+            ServerResponse::SelfAddress(address) => Self::serialize_self_address(*address),
+            ServerResponse::LaneQueueLength { lane, queue_length } => {
                Self::serialize_lane_queue_length(lane, queue_length)
            }
            ServerResponse::Error(err) => Self::serialize_error(err),
@@ -328,18 +293,14 @@ impl ServerResponse {
            ));
        }

-        let response_tag = b[0];
+        let response_tag = ServerResponseTag::try_from(b[0])?;

        // determine what kind of response that is and try to deserialize it
        match response_tag {
-            RECEIVED_RESPONSE_TAG => Self::deserialize_received(b),
-            SELF_ADDRESS_RESPONSE_TAG => Self::deserialize_self_address(b),
-            LANE_QUEUE_LENGTH_RESPONSE_TAG => Self::deserialize_lane_queue_length(b),
-            ERROR_RESPONSE_TAG => Self::deserialize_error(b),
-            n => Err(error::Error::new(
-                ErrorKind::UnknownResponse,
-                format!("type {}", n),
-            )),
+            ServerResponseTag::Received => Self::deserialize_received(b),
+            ServerResponseTag::SelfAddress => Self::deserialize_self_address(b),
+            ServerResponseTag::LaneQueueLength => Self::deserialize_lane_queue_length(b),
+            ServerResponseTag::Error => Self::deserialize_error(b),
        }
    }

@@ -361,35 +322,33 @@ mod tests {

    #[test]
    fn received_response_serialization_works() {
-        let reply_surb_string = "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";
-
-        let received_with_surb = ServerResponse::Received(ReconstructedMessage {
+        let received_with_sender_tag = ServerResponse::Received(ReconstructedMessage {
            message: b"foomp".to_vec(),
-            reply_surb: Some(ReplySurb::from_base58_string(reply_surb_string).unwrap()),
+            sender_tag: Some([42u8; SENDER_TAG_SIZE].into()),
        });
-        let bytes = received_with_surb.serialize();
+        let bytes = received_with_sender_tag.serialize();
        let recovered = ServerResponse::deserialize(&bytes).unwrap();
        match recovered {
            ServerResponse::Received(reconstructed) => {
                assert_eq!(reconstructed.message, b"foomp".to_vec());
                assert_eq!(
-                    reconstructed.reply_surb.unwrap().to_base58_string(),
-                    reply_surb_string
+                    reconstructed.sender_tag,
+                    Some([42u8; SENDER_TAG_SIZE].into())
                )
            }
            _ => unreachable!(),
        }

-        let received_without_surb = ServerResponse::Received(ReconstructedMessage {
+        let received_without_sender_tag = ServerResponse::Received(ReconstructedMessage {
            message: b"foomp".to_vec(),
-            reply_surb: None,
+            sender_tag: None,
        });
-        let bytes = received_without_surb.serialize();
+        let bytes = received_without_sender_tag.serialize();
        let recovered = ServerResponse::deserialize(&bytes).unwrap();
        match recovered {
            ServerResponse::Received(reconstructed) => {
                assert_eq!(reconstructed.message, b"foomp".to_vec());
-                assert!(reconstructed.reply_surb.is_none())
+                assert!(reconstructed.sender_tag.is_none())
            }
            _ => unreachable!(),
        }
@@ -400,7 +359,7 @@ mod tests {
        let recipient = Recipient::try_from_base58_string("CytBseW6yFXUMzz4SGAKdNLGR7q3sJLLYxyBGvutNEQV.4QXYyEVc5fUDjmmi8PrHN9tdUFV4PCvSJE1278cHyvoe@4sBbL1ngf1vtNqykydQKTFh26sQCw888GpUqvPvyNB4f").unwrap();
        let recipient_string = recipient.to_string();

-        let self_address_response = ServerResponse::SelfAddress(recipient);
+        let self_address_response = ServerResponse::SelfAddress(Box::new(recipient));
        let bytes = self_address_response.serialize();
        let recovered = ServerResponse::deserialize(&bytes).unwrap();
        match recovered {
@@ -413,11 +372,14 @@ mod tests {

    #[test]
    fn lane_queue_length_response_serialization_works() {
-        let lane_queue_length_response = ServerResponse::LaneQueueLength(13, 42);
+        let lane_queue_length_response = ServerResponse::LaneQueueLength {
+            lane: 13,
+            queue_length: 42,
+        };
        let bytes = lane_queue_length_response.serialize();
        let recovered = ServerResponse::deserialize(&bytes).unwrap();
        match recovered {
-            ServerResponse::LaneQueueLength(lane, queue_length) => {
+            ServerResponse::LaneQueueLength { lane, queue_length } => {
                assert_eq!(lane, 13);
                assert_eq!(queue_length, 42)
            }
@@ -1,11 +1,11 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

 use crate::error::ErrorKind;
 use crate::requests::ClientRequest;
 use crate::responses::ServerResponse;
 use nymsphinx::addressing::clients::Recipient;
-use nymsphinx::anonymous_replies::ReplySurb;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
 use serde::{Deserialize, Serialize};
 use std::convert::{TryFrom, TryInto};

@@ -19,15 +19,22 @@ pub(super) enum ClientRequestText {
    Send {
        message: String,
        recipient: String,
-        with_reply_surb: bool,
+        connection_id: Option<u64>,
+    },
+    #[serde(rename_all = "camelCase")]
+    SendAnonymous {
+        recipient: String,
+        message: String,
+        reply_surbs: u32,
+        connection_id: Option<u64>,
+    },
+    #[serde(rename_all = "camelCase")]
+    Reply {
+        sender_tag: String,
+        message: String,
        connection_id: Option<u64>,
    },
    SelfAddress,
-    #[serde(rename_all = "camelCase")]
-    Reply {
-        message: String,
-        reply_surb: String,
-    },
 }

 impl TryFrom<String> for ClientRequestText {
@@ -46,7 +53,6 @@ impl TryInto<ClientRequest> for ClientRequestText {
            ClientRequestText::Send {
                message,
                recipient,
-                with_reply_surb,
                connection_id,
            } => {
                let message_bytes = message.into_bytes();
@@ -57,23 +63,42 @@ impl TryInto<ClientRequest> for ClientRequestText {
                Ok(ClientRequest::Send {
                    message: message_bytes,
                    recipient,
-                    with_reply_surb,
+                    connection_id,
+                })
+            }
+            ClientRequestText::SendAnonymous {
+                recipient,
+                message,
+                reply_surbs,
+                connection_id,
+            } => {
+                let message_bytes = message.into_bytes();
+                let recipient = Recipient::try_from_base58_string(recipient).map_err(|err| {
+                    Self::Error::new(ErrorKind::MalformedRequest, err.to_string())
+                })?;
+                Ok(ClientRequest::SendAnonymous {
+                    recipient,
+                    message: message_bytes,
+                    reply_surbs,
                    connection_id,
                })
            }
            ClientRequestText::SelfAddress => Ok(ClientRequest::SelfAddress),
            ClientRequestText::Reply {
+                sender_tag,
                message,
-                reply_surb,
+                connection_id,
            } => {
                let message_bytes = message.into_bytes();
-                let reply_surb = ReplySurb::from_base58_string(reply_surb).map_err(|err| {
-                    Self::Error::new(ErrorKind::MalformedRequest, err.to_string())
-                })?;
+                let sender_tag =
+                    AnonymousSenderTag::try_from_base58_string(sender_tag).map_err(|err| {
+                        Self::Error::new(ErrorKind::MalformedRequest, err.to_string())
+                    })?;

                Ok(ClientRequest::Reply {
+                    sender_tag,
                    message: message_bytes,
-                    reply_surb,
+                    connection_id,
                })
            }
        }
@@ -89,7 +114,7 @@ pub(super) enum ServerResponseText {
    #[serde(rename_all = "camelCase")]
    Received {
        message: String,
-        reply_surb: Option<String>,
+        sender_tag: Option<String>,
    },
    SelfAddress {
        address: String,
@@ -131,15 +156,13 @@ impl From<ServerResponse> for ServerResponseText {
                    // TODO: ask DH what is more appropriate, lossy utf8 conversion or returning error and then
                    // pure binary later
                    message: String::from_utf8_lossy(&reconstructed.message).into_owned(),
-                    reply_surb: reconstructed
-                        .reply_surb
-                        .map(|reply_surb| reply_surb.to_base58_string()),
+                    sender_tag: reconstructed.sender_tag.map(|tag| tag.to_base58_string()),
                }
            }
            ServerResponse::SelfAddress(recipient) => ServerResponseText::SelfAddress {
                address: recipient.to_string(),
            },
-            ServerResponse::LaneQueueLength(lane, queue_length) => {
+            ServerResponse::LaneQueueLength { lane, queue_length } => {
                ServerResponseText::LaneQueueLength { lane, queue_length }
            }
            ServerResponse::Error(err) => ServerResponseText::Error {
@@ -26,7 +26,7 @@ tokio = { version = "1.21.2", features = ["rt-multi-thread", "net", "signal"] }
 url = "2.2"

 # internal
-client-core = { path = "../client-core" }
+client-core = { path = "../client-core", features = ["fs-surb-storage"] }
 client-connections = { path = "../../common/client-connections" }
 coconut-interface = { path = "../../common/coconut-interface", optional = true }
 config = { path = "../../common/config" }
@@ -3,7 +3,7 @@

 use crate::client::config::template::config_template;
 pub use client_core::config::MISSING_VALUE;
-use client_core::config::{ClientCoreConfigTrait, Config as BaseConfig};
+use client_core::config::{ClientCoreConfigTrait, Config as BaseConfig, DebugConfig};
 use config::defaults::DEFAULT_SOCKS5_LISTENING_PORT;
 use config::NymConfig;
 use nymsphinx::addressing::clients::Recipient;
@@ -12,6 +12,9 @@ use std::path::PathBuf;

 mod template;

+const DEFAULT_CONNECTION_START_SURBS: u32 = 20;
+const DEFAULT_PER_REQUEST_SURBS: u32 = 3;
+
 #[derive(Debug, Default, Deserialize, PartialEq, Serialize)]
 #[serde(deny_unknown_fields)]
 pub struct Config {
@@ -19,6 +22,9 @@ pub struct Config {
    base: BaseConfig<Config>,

    socks5: Socks5,
+
+    #[serde(default)]
+    socks5_debug: Socks5Debug,
 }

 impl NymConfig for Config {
@@ -63,6 +69,7 @@ impl Config {
        Config {
            base: BaseConfig::new(id),
            socks5: Socks5::new(provider_mix_address),
+            socks5_debug: Socks5Debug::default(),
        }
    }

@@ -78,7 +85,24 @@ impl Config {
        self
    }

+    pub fn with_anonymous_replies(mut self, anonymous_replies: bool) -> Self {
+        self.socks5.send_anonymously = anonymous_replies;
+        self
+    }
+
    // getters
+    pub fn get_base(&self) -> &BaseConfig<Self> {
+        &self.base
+    }
+
+    pub fn get_base_mut(&mut self) -> &mut BaseConfig<Self> {
+        &mut self.base
+    }
+
+    pub fn get_debug_settings(&self) -> &DebugConfig {
+        self.get_base().get_debug_config()
+    }
+
    pub fn get_config_file_save_location(&self) -> PathBuf {
        self.config_directory().join(Self::config_file_name())
    }
@@ -88,17 +112,21 @@ impl Config {
            .expect("malformed provider address")
    }

-    pub fn get_base(&self) -> &BaseConfig<Self> {
-        &self.base
-    }
-
-    pub fn get_base_mut(&mut self) -> &mut BaseConfig<Self> {
-        &mut self.base
+    pub fn get_send_anonymously(&self) -> bool {
+        self.socks5.send_anonymously
    }

    pub fn get_listening_port(&self) -> u16 {
        self.socks5.listening_port
    }
+
+    pub fn get_connection_start_surbs(&self) -> u32 {
+        self.socks5_debug.connection_start_surbs
+    }
+
+    pub fn get_per_request_surbs(&self) -> u32 {
+        self.socks5_debug.per_request_surbs
+    }
 }

 #[derive(Debug, Deserialize, PartialEq, Eq, Serialize)]
@@ -109,6 +137,13 @@ pub struct Socks5 {

    /// The mix address of the provider to which all requests are going to be sent.
    provider_mix_address: String,
+
+    /// Specifies whether this client is going to use an anonymous sender tag for communication with the service provider.
+    /// While this is going to hide its actual address information, it will make the actual communication
+    /// slower and consume nearly double the bandwidth as it will require sending reply SURBs.
+    ///
+    /// Note that some service providers might not support this.
+    send_anonymously: bool,
 }

 impl Socks5 {
@@ -116,6 +151,7 @@ impl Socks5 {
        Socks5 {
            listening_port: DEFAULT_SOCKS5_LISTENING_PORT,
            provider_mix_address: provider_mix_address.into(),
+            send_anonymously: false,
        }
    }
 }
@@ -125,6 +161,26 @@ impl Default for Socks5 {
        Socks5 {
            listening_port: DEFAULT_SOCKS5_LISTENING_PORT,
            provider_mix_address: "".into(),
+            send_anonymously: false,
+        }
+    }
+}
+
+#[derive(Debug, Deserialize, PartialEq, Eq, Serialize)]
+#[serde(deny_unknown_fields)]
+pub struct Socks5Debug {
+    /// Number of reply SURBs attached to each `Request::Connect` message.
+    connection_start_surbs: u32,
+
+    /// Number of reply SURBs attached to each `Request::Send` message.
+    per_request_surbs: u32,
+}
+
+impl Default for Socks5Debug {
+    fn default() -> Self {
+        Socks5Debug {
+            connection_start_surbs: DEFAULT_CONNECTION_START_SURBS,
+            per_request_surbs: DEFAULT_PER_REQUEST_SURBS,
        }
    }
 }
@@ -49,13 +49,12 @@ private_encryption_key_file = '{{ client.private_encryption_key_file }}'
 # Path to file containing public encryption key.
 public_encryption_key_file = '{{ client.public_encryption_key_file }}'

-# Full path to file containing reply encryption keys of all reply-SURBs we have ever
-# sent but not received back.
-reply_encryption_key_store_path = '{{ client.reply_encryption_key_store_path }}'
-
 # Path to the database containing bandwidth credentials
 database_path = '{{ client.database_path }}'

+# Path to the persistent store for received reply surbs, unused encryption keys and used sender tags.
+reply_surb_database_path = '{{ client.reply_surb_database_path }}'
+
 ##### additional client config options #####

 # A gateway specific, optional, base58 stringified shared key used for
@@ -92,6 +91,12 @@ provider_mix_address = '{{ socks5.provider_mix_address }}'
 # The port on which the client will be listening for incoming requests
 listening_port = {{ socks5.listening_port }}

+# Specifies whether this client is going to use an anonymous sender tag for communication with the service provider.
+# While this is going to hide its actual address information, it will make the actual communication
+# slower and consume nearly double the bandwidth as it will require sending reply SURBs.
+#
+# Note that some service providers might not support this.
+send_anonymously = {{ socks5.send_anonymously }}

 ##### logging configuration options #####

@@ -104,6 +109,9 @@ listening_port = {{ socks5.listening_port }}
 # The following options should not be modified unless you know EXACTLY what you are doing
 # as if set incorrectly, they may impact your anonymity.

+# [socks5_debug]
+
+
 [debug]

 average_packet_delay = '{{ debug.average_packet_delay }}'
@@ -3,11 +3,14 @@

 use crate::client::config::Config;
 use crate::error::Socks5ClientError;
+use crate::socks;
 use crate::socks::{
    authentication::{AuthenticationMethods, Authenticator, User},
    server::SphinxSocksServer,
 };
-use client_core::client::base_client::{BaseClientBuilder, ClientInput, ClientOutput};
+use client_core::client::base_client::{
+    non_wasm_helpers, BaseClientBuilder, ClientInput, ClientOutput,
+};
 use client_core::client::key_manager::KeyManager;
 use client_core::config::persistence::key_pathfinder::ClientKeyPathfinder;
 use futures::channel::mpsc;
@@ -17,6 +20,7 @@ use log::*;
 use nymsphinx::addressing::clients::Recipient;
 use std::error::Error;
 use task::{wait_for_signal_and_error, ShutdownListener, ShutdownNotifier};
+use url::Url;

 pub mod config;

@@ -52,23 +56,23 @@ impl NymClient {

    async fn create_bandwidth_controller(config: &Config) -> BandwidthController {
        #[cfg(feature = "coconut")]
+        //temp hard code these values for testing
+        let qwerty_validator: Url =
+            Url::from_str("http://qwerty-validator.qa.nymte.ch:26657/").unwrap();
+        let val_api: Url =
+            Url::from_str("https://qwerty-coconut-one-validator-api.qa.nymte.ch/api").unwrap();
+
        let bandwidth_controller = {
            let details = network_defaults::NymNetworkDetails::new_from_env();
            let mut client_config =
                validator_client::Config::try_from_nym_network_details(&details)
                    .expect("failed to construct validator client config");
-            let nymd_url = config
-                .get_base()
-                .get_validator_endpoints()
-                .pop()
-                .expect("No nymd validator endpoint provided");
-            let api_url = config
-                .get_base()
-                .get_validator_api_endpoints()
-                .pop()
-                .expect("No validator api endpoint provided");
+
            // overwrite env configuration with config URLs
-            client_config = client_config.with_urls(nymd_url, api_url);
+            client_config = client_config.with_urls(qwerty_validator, val_api);
+
+            println!("{:?}", client_config);
+
            let client = validator_client::Client::new_query(client_config)
                .expect("Could not construct query client");
            let coconut_api_clients =
@@ -114,6 +118,11 @@ impl NymClient {
            config.get_provider_mix_address(),
            self_address,
            shared_lane_queue_lengths,
+            socks::client::Config::new(
+                config.get_send_anonymously(),
+                config.get_connection_start_surbs(),
+                config.get_per_request_surbs(),
+            ),
            shutdown.clone(),
        );
        task::spawn_with_report_error(
@@ -193,6 +202,11 @@ impl NymClient {
            self.config.get_base(),
            self.key_manager,
            Some(Self::create_bandwidth_controller(&self.config).await),
+            non_wasm_helpers::setup_fs_reply_surb_backend(
+                self.config.get_base().get_reply_surb_database_path(),
+                self.config.get_debug_settings(),
+            )
+            .await?,
        );

        let self_address = base_builder.as_mix_recipient();
@@ -1,19 +1,17 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-use std::fmt::Display;
-
-use clap::Args;
-use config::NymConfig;
-use nymsphinx::addressing::clients::Recipient;
-use serde::Serialize;
-use tap::TapFallible;
-
 use crate::{
    client::config::Config,
    commands::{override_config, OverrideConfig},
    error::Socks5ClientError,
 };
+use clap::Args;
+use config::NymConfig;
+use nymsphinx::addressing::clients::Recipient;
+use serde::Serialize;
+use std::fmt::Display;
+use tap::TapFallible;

 #[derive(Args, Clone)]
 pub(crate) struct Init {
@@ -25,6 +23,14 @@ pub(crate) struct Init {
    #[clap(long)]
    provider: String,

+    /// Specifies whether this client is going to use an anonymous sender tag for communication with the service provider.
+    /// While this is going to hide its actual address information, it will make the actual communication
+    /// slower and consume nearly double the bandwidth as it will require sending reply SURBs.
+    ///
+    /// Note that some service providers might not support this.
+    #[clap(long)]
+    use_anonymous_sender_tag: bool,
+
    /// Id of the gateway we are going to connect to.
    #[clap(long)]
    gateway: Option<String>,
@@ -72,6 +78,7 @@ impl From<Init> for OverrideConfig {
            nymd_validators: init_config.nymd_validators,
            api_validators: init_config.api_validators,
            port: init_config.port,
+            use_anonymous_sender_tag: init_config.use_anonymous_sender_tag,
            fastmode: init_config.fastmode,
            no_cover: init_config.no_cover,
            #[cfg(feature = "coconut")]
@@ -138,7 +145,7 @@ pub(crate) async fn execute(args: &Init) -> Result<(), Socks5ClientError> {

    // Setup gateway by either registering a new one, or creating a new config from the selected
    // one but with keys kept, or reusing the gateway configuration.
-    let gateway = client_core::init::setup_gateway::<Config, _>(
+    let gateway = client_core::init::setup_gateway::<_, Config, _>(
        register_gateway,
        user_chosen_gateway_id,
        config.get_base(),
@@ -82,6 +82,7 @@ pub(crate) struct OverrideConfig {
    nymd_validators: Option<String>,
    api_validators: Option<String>,
    port: Option<u16>,
+    use_anonymous_sender_tag: bool,
    fastmode: bool,
    no_cover: bool,

@@ -122,6 +123,10 @@ pub(crate) fn override_config(mut config: Config, args: OverrideConfig) -> Confi
            .set_custom_validator_apis(parse_validators(&raw_validators));
    }

+    if args.use_anonymous_sender_tag {
+        config = config.with_anonymous_replies(true)
+    }
+
    if let Some(port) = args.port {
        config = config.with_port(port);
    }
@@ -22,6 +22,14 @@ pub(crate) struct Run {
    #[clap(long)]
    config: Option<String>,

+    /// Specifies whether this client is going to use an anonymous sender tag for communication with the service provider.
+    /// While this is going to hide its actual address information, it will make the actual communication
+    /// slower and consume nearly double the bandwidth as it will require sending reply SURBs.
+    ///
+    /// Note that some service providers might not support this.
+    #[clap(long)]
+    use_anonymous_sender_tag: bool,
+
    /// Address of the socks5 provider to send messages to.
    #[clap(long)]
    provider: Option<String>,
@@ -65,6 +73,7 @@ impl From<Run> for OverrideConfig {
            nymd_validators: run_config.nymd_validators,
            api_validators: run_config.api_validators,
            port: run_config.port,
+            use_anonymous_sender_tag: run_config.use_anonymous_sender_tag,
            fastmode: run_config.fastmode,
            no_cover: run_config.no_cover,
            #[cfg(feature = "coconut")]
@@ -1,21 +1,24 @@
-use client_core::error::ClientCoreError;
-
 use crate::socks::types::SocksProxyError;
+use client_core::client::replies::reply_storage::fs_backend;
+use client_core::error::ClientCoreError;

 #[derive(thiserror::Error, Debug)]
 pub enum Socks5ClientError {
    #[error("I/O error: {0}")]
    IoError(#[from] std::io::Error),
+
    #[error("client-core error: {0}")]
-    ClientCoreError(#[from] ClientCoreError),
+    ClientCoreError(#[from] ClientCoreError<fs_backend::Backend>),

    #[error("SOCKS proxy error")]
    SocksProxyError(SocksProxyError),

    #[error("Failed to load config for: {0}")]
    FailedToLoadConfig(String),
+
    #[error("Failed local version check, client and config mismatch")]
    FailedLocalVersionCheck,
+
    #[error("Fail to bind address")]
    FailToBindAddress,
 }
@@ -126,11 +126,33 @@ impl AsyncWrite for StreamState {
    }
 }

+#[derive(Debug, Copy, Clone)]
+pub(crate) struct Config {
+    use_surbs_for_responses: bool,
+    connection_start_surbs: u32,
+    per_request_surbs: u32,
+}
+
+impl Config {
+    pub(crate) fn new(
+        use_surbs_for_responses: bool,
+        connection_start_surbs: u32,
+        per_request_surbs: u32,
+    ) -> Self {
+        Self {
+            use_surbs_for_responses,
+            connection_start_surbs,
+            per_request_surbs,
+        }
+    }
+}
+
 /// A client connecting to the Socks proxy server, because
 /// it wants to make a Nym-protected outbound request. Typically, this is
 /// something like e.g. a wallet app running on your laptop connecting to
 /// `SphinxSocksServer`.
 pub(crate) struct SocksClient {
+    config: Config,
    controller_sender: ControllerSender,
    stream: StreamState,
    auth_nmethods: u8,
@@ -160,6 +182,7 @@ impl Drop for SocksClient {
 impl SocksClient {
    #[allow(clippy::too_many_arguments)]
    pub fn new(
+        config: Config,
        stream: TcpStream,
        authenticator: Authenticator,
        input_sender: InputMessageSender,
@@ -175,6 +198,7 @@ impl SocksClient {
        let connection_id = Self::generate_random();

        SocksClient {
+            config,
            controller_sender,
            connection_id,
            stream: StreamState::Available(stream),
@@ -268,14 +292,14 @@ impl SocksClient {
        self.handle_request().await
    }

-    async fn send_connect_to_mixnet(&mut self, remote_address: RemoteAddress) {
-        let req = Request::new_connect(self.connection_id, remote_address, self.self_address);
+    async fn send_anonymous_connect_to_mixnet(&mut self, remote_address: RemoteAddress) {
+        let req = Request::new_connect(self.connection_id, remote_address, None);
        let msg = Message::Request(req);

-        let input_message = InputMessage::new_fresh(
+        let input_message = InputMessage::new_anonymous(
            self.service_provider,
            msg.into_bytes(),
-            false,
+            self.config.connection_start_surbs,
            TransmissionLane::ConnectionId(self.connection_id),
        );
        self.input_sender
@@ -284,6 +308,30 @@ impl SocksClient {
            .expect("InputMessageReceiver has stopped receiving!");
    }

+    async fn send_connect_to_mixnet_with_return_address(&mut self, remote_address: RemoteAddress) {
+        let req = Request::new_connect(self.connection_id, remote_address, Some(self.self_address));
+        let msg = Message::Request(req);
+
+        let input_message = InputMessage::new_regular(
+            self.service_provider,
+            msg.into_bytes(),
+            TransmissionLane::ConnectionId(self.connection_id),
+        );
+        self.input_sender
+            .send(input_message)
+            .await
+            .expect("InputMessageReceiver has stopped receiving!");
+    }
+
+    async fn send_connect_to_mixnet(&mut self, remote_address: RemoteAddress) {
+        if self.config.use_surbs_for_responses {
+            self.send_anonymous_connect_to_mixnet(remote_address).await
+        } else {
+            self.send_connect_to_mixnet_with_return_address(remote_address)
+                .await
+        }
+    }
+
    async fn run_proxy(&mut self, conn_receiver: ConnectionReceiver, remote_proxy_target: String) {
        self.send_connect_to_mixnet(remote_proxy_target.clone())
            .await;
@@ -300,6 +348,8 @@ impl SocksClient {

        let connection_id = self.connection_id;
        let input_sender = self.input_sender.clone();
+        let anonymous = self.config.use_surbs_for_responses;
+        let per_request_surbs = self.config.per_request_surbs;

        let recipient = self.service_provider;
        let (stream, _) = ProxyRunner::new(
@@ -316,7 +366,16 @@ impl SocksClient {
            let provider_request = Request::new_send(conn_id, read_data, socket_closed);
            let provider_message = Message::Request(provider_request);
            let lane = TransmissionLane::ConnectionId(conn_id);
-            InputMessage::new_fresh(recipient, provider_message.into_bytes(), false, lane)
+            if anonymous {
+                InputMessage::new_anonymous(
+                    recipient,
+                    provider_message.into_bytes(),
+                    per_request_surbs,
+                    lane,
+                )
+            } else {
+                InputMessage::new_regular(recipient, provider_message.into_bytes(), lane)
+            }
        })
        .await
        .into_inner();
@@ -54,8 +54,8 @@ impl MixnetResponseListener {

    async fn on_message(&self, reconstructed_message: ReconstructedMessage) {
        let raw_message = reconstructed_message.message;
-        if reconstructed_message.reply_surb.is_some() {
-            warn!("this message had a surb - we didn't do anything with it");
+        if reconstructed_message.sender_tag.is_some() {
+            warn!("this message was sent anonymously - it couldn't have come from the service provider");
        }

        let response = match Message::try_from_bytes(&raw_message) {
@@ -5,7 +5,7 @@ use std::convert::TryFrom;
 use self::types::SocksProxyError;

 pub mod authentication;
-mod client;
+pub(crate) mod client;
 pub(crate) mod mixnet_responses;
 mod request;
 pub mod server;
@@ -3,6 +3,7 @@ use crate::error::Socks5ClientError;
 use super::{
    authentication::Authenticator, client::SocksClient, mixnet_responses::MixnetResponseListener,
 };
+use crate::socks::client;
 use client_connections::{ConnectionCommandSender, LaneQueueLengths};
 use client_core::client::{
    inbound_messages::InputMessageSender, received_buffer::ReceivedBufferRequestSender,
@@ -21,6 +22,7 @@ pub struct SphinxSocksServer {
    listening_address: SocketAddr,
    service_provider: Recipient,
    self_address: Recipient,
+    client_config: client::Config,
    lane_queue_lengths: LaneQueueLengths,
    shutdown: ShutdownListener,
 }
@@ -33,6 +35,7 @@ impl SphinxSocksServer {
        service_provider: Recipient,
        self_address: Recipient,
        lane_queue_lengths: LaneQueueLengths,
+        client_config: client::Config,
        shutdown: ShutdownListener,
    ) -> Self {
        // hardcode ip as we (presumably) ONLY want to listen locally. If we change it, we can
@@ -44,6 +47,7 @@ impl SphinxSocksServer {
            listening_address: format!("{}:{}", ip, port).parse().unwrap(),
            service_provider,
            self_address,
+            client_config,
            lane_queue_lengths,
            shutdown,
        }
@@ -86,6 +90,7 @@ impl SphinxSocksServer {
            tokio::select! {
                Ok((stream, _remote)) = listener.accept() => {
                    let mut client = SocksClient::new(
+                        self.client_config,
                        stream,
                        self.authenticator.clone(),
                        input_sender.clone(),
@@ -65,7 +65,6 @@ async function main() {
 *
 * Message and recipient are taken from the values in the user interface.
 *
- * @param {Client} nymClient the nym client to use for message sending
 */
 async function sendMessageTo() {
  const message = document.getElementById('message').value;
@@ -96,10 +95,13 @@ function displaySend(message) {
 /**
 * Display received text messages in the browser. Colour them green.
 *
- * @param {string} message
+ * @param {Uint8Array} raw
 */
-function displayReceived(message) {
-  const content = message;
+function displayReceived(raw, sender_tag) {
+  const content = new TextDecoder().decode(raw);
+  if (sender_tag !== undefined) {
+    console.log("this message also contained some surbs from", sender_tag)
+  }

  let timestamp = new Date().toISOString().substr(11, 12);
  let receivedDiv = document.createElement('div');
@@ -116,7 +118,7 @@ function displayReceived(message) {
 /**
 * Display the nymClient's sender address in the user interface
 *
- * @param {Client} nymClient
+ * @param {String} address
 */
 function displaySenderAddress(address) {
  document.getElementById('sender').value = address;
@@ -17,38 +17,7 @@ importScripts('nym_client_wasm.js');
 console.log('Initializing worker');

 // wasm_bindgen creates a global variable (with the exports attached) that is in scope after `importScripts`
-const { default_debug, get_gateway, NymClient, set_panic_hook, Config } = wasm_bindgen;
-
-class ClientWrapper {
-  constructor(config, onMessageHandler) {
-    this.rustClient = new NymClient(config);
-    this.rustClient.set_on_message(onMessageHandler);
-    this.rustClient.set_on_gateway_connect(this.onConnect);
-  }
-
-  selfAddress = () => {
-    return this.rustClient.self_address();
-  };
-
-  onConnect = () => {
-    console.log('Established (and authenticated) gateway connection!');
-  };
-
-  start = async () => {
-    // this is current limitation of wasm in rust - for async methods you can't take self by reference...
-    // I'm trying to figure out if I can somehow hack my way around it, but for time being you have to re-assign
-    // the object (it's the same one)
-    this.rustClient = await this.rustClient.start();
-  };
-
-  sendMessage = async (recipient, message) => {
-    this.rustClient = await this.rustClient.send_message(recipient, message);
-  };
-
-  sendBinaryMessage = async (recipient, message) => {
-    this.rustClient = await this.rustClient.send_binary_message(recipient, message);
-  };
-}
+const { default_debug, NymClientBuilder, set_panic_hook, Config, GatewayEndpointConfig } = wasm_bindgen;

 let client = null;

@@ -62,11 +31,12 @@ async function main() {
  set_panic_hook();

  // validator server we will use to get topology from
-  const validator = 'https://validator.nymtech.net/api'; //"http://localhost:8081";
-  const preferredGateway = 'E3mvZTHQCdBvhfr178Swx9g4QG3kkRUun7YnToLMcMbM';
-
-  const gatewayEndpoint = await get_gateway(validator, preferredGateway);
-  gatewayEndpoint.gateway_listener = "wss://gateway1.nymtech.net:443"; // this is needed if we want it to work on the web. However this gateway is a v1 gateway, we will need to change for v2 once we get there
+  const validator = 'https://qwerty-validator-api.qa.nymte.ch/api';
+  
+  const gatewayId = 'EVupP2tRUeZo5Y6RpBHAbm8kSntpgNyZNL6yCr7BDEoG';
+  const gatewayOwner = 'n1rmlew3euapuq7rs4s4j9apv00whrsazr764kl7';
+  const gatewayListener = 'ws://176.58.120.72:9000';
+  const gatewayEndpoint = new GatewayEndpointConfig(gatewayId, gatewayOwner, gatewayListener)

  // only really useful if you want to adjust some settings like traffic rate
  // (if not needed you can just pass a null)
@@ -94,12 +64,17 @@ async function main() {
  };

  console.log('Instantiating WASM client...');
-  client = new ClientWrapper(config, onMessageHandler);
+  
+  let clientBuilder = new NymClientBuilder(config, onMessageHandler)
  console.log('Web worker creating WASM client...');
-  await client.start();
+  let local_client = await clientBuilder.start_client();
  console.log('WASM client running!');
-
-  const selfAddress = client.rustClient.self_address();
+  
+  const selfAddress = local_client.self_address();
+  
+  // set the global (I guess we don't have to anymore?)
+  client = local_client;
+  
  console.log(`Client address is ${selfAddress}`);
  self.postMessage({
    kind: 'Ready',
@@ -114,7 +89,8 @@ async function main() {
      switch (event.data.kind) {
        case 'SendMessage': {
          const { message, recipient } = event.data.args;
-          await client.sendMessage(message, recipient);
+          let uint8Array = new TextEncoder().encode(message);
+          await client.send_regular_message(uint8Array, recipient);
        }
      }
    }
@@ -106,6 +106,34 @@ pub struct Debug {

    /// Controls whether the sent sphinx packet use the NON-DEFAULT bigger size.
    pub use_extended_packet_size: bool,
+
+    /// Defines the minimum number of reply surbs the client wants to keep in its storage at all times.
+    /// It can only allow to go below that value if its to request additional reply surbs.
+    pub minimum_reply_surb_storage_threshold: usize,
+
+    /// Defines the maximum number of reply surbs the client wants to keep in its storage at any times.
+    pub maximum_reply_surb_storage_threshold: usize,
+
+    /// Defines the minimum number of reply surbs the client would request.
+    pub minimum_reply_surb_request_size: u32,
+
+    /// Defines the maximum number of reply surbs the client would request.
+    pub maximum_reply_surb_request_size: u32,
+
+    /// Defines the maximum number of reply surbs a remote party is allowed to request from this client at once.
+    pub maximum_allowed_reply_surb_request_size: u32,
+
+    /// Defines maximum amount of time the client is going to wait for reply surbs before explicitly asking
+    /// for more even though in theory they wouldn't need to.
+    pub maximum_reply_surb_waiting_period_ms: u64,
+
+    /// Defines maximum amount of time given reply surb is going to be valid for.
+    /// This is going to be superseded by key rotation once implemented.
+    pub maximum_reply_surb_age_ms: u64,
+
+    /// Defines maximum amount of time given reply key is going to be valid for.
+    /// This is going to be superseded by key rotation once implemented.
+    pub maximum_reply_key_age_ms: u64,
 }

 impl From<Debug> for ConfigDebug {
@@ -135,6 +163,16 @@ impl From<Debug> for ConfigDebug {
            disable_main_poisson_packet_distribution: debug
                .disable_main_poisson_packet_distribution,
            use_extended_packet_size,
+            minimum_reply_surb_storage_threshold: debug.minimum_reply_surb_storage_threshold,
+            maximum_reply_surb_storage_threshold: debug.maximum_reply_surb_storage_threshold,
+            minimum_reply_surb_request_size: debug.minimum_reply_surb_request_size,
+            maximum_reply_surb_request_size: debug.maximum_reply_surb_request_size,
+            maximum_allowed_reply_surb_request_size: debug.maximum_allowed_reply_surb_request_size,
+            maximum_reply_surb_waiting_period: Duration::from_millis(
+                debug.maximum_reply_surb_waiting_period_ms,
+            ),
+            maximum_reply_surb_age: Duration::from_millis(debug.maximum_reply_surb_age_ms),
+            maximum_reply_key_age: Duration::from_millis(debug.maximum_reply_key_age_ms),
        }
    }
 }
@@ -157,6 +195,16 @@ impl From<ConfigDebug> for Debug {
            disable_main_poisson_packet_distribution: debug
                .disable_main_poisson_packet_distribution,
            use_extended_packet_size: debug.use_extended_packet_size.is_some(),
+            minimum_reply_surb_storage_threshold: debug.minimum_reply_surb_storage_threshold,
+            maximum_reply_surb_storage_threshold: debug.maximum_reply_surb_storage_threshold,
+            minimum_reply_surb_request_size: debug.minimum_reply_surb_request_size,
+            maximum_reply_surb_request_size: debug.maximum_reply_surb_request_size,
+            maximum_allowed_reply_surb_request_size: debug.maximum_allowed_reply_surb_request_size,
+            maximum_reply_surb_waiting_period_ms: debug
+                .maximum_reply_surb_waiting_period
+                .as_millis() as u64,
+            maximum_reply_surb_age_ms: debug.maximum_reply_surb_age.as_millis() as u64,
+            maximum_reply_key_age_ms: debug.maximum_reply_key_age.as_millis() as u64,
        }
    }
 }
@@ -0,0 +1,30 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use client_core::client::base_client::ClientInput;
+use client_core::client::inbound_messages::InputMessage;
+use js_sys::Promise;
+use std::sync::Arc;
+use wasm_bindgen::JsValue;
+use wasm_bindgen_futures::future_to_promise;
+
+// defining helper trait as we could directly call the method on the wrapper
+pub(crate) trait InputSender {
+    fn send_message(&self, message: InputMessage) -> Promise;
+}
+
+impl InputSender for Arc<ClientInput> {
+    fn send_message(&self, message: InputMessage) -> Promise {
+        let this = Arc::clone(self);
+        future_to_promise(async move {
+            match this.input_sender.send(message).await {
+                Ok(_) => Ok(JsValue::null()),
+                Err(_) => {
+                    let js_error =
+                        js_sys::Error::new("InputMessageReceiver has stopped receiving!");
+                    Err(JsValue::from(js_error))
+                }
+            }
+        })
+    }
+}
@@ -2,59 +2,65 @@
 // SPDX-License-Identifier: Apache-2.0

 use self::config::Config;
+use crate::client::helpers::InputSender;
 use crate::client::response_pusher::ResponsePusher;
 use client_connections::TransmissionLane;
 use client_core::client::base_client::{BaseClientBuilder, ClientInput, ClientOutput};
+use client_core::client::replies::reply_storage::browser_backend;
 use client_core::client::{inbound_messages::InputMessage, key_manager::KeyManager};
-use crypto::asymmetric::identity;
+use gateway_client::bandwidth::BandwidthController;
+use js_sys::Promise;
 use nymsphinx::addressing::clients::Recipient;
+use nymsphinx::anonymous_replies::requests::AnonymousSenderTag;
 use rand::rngs::OsRng;
+use std::sync::Arc;
 use task::ShutdownNotifier;
 use wasm_bindgen::prelude::*;
+use wasm_bindgen_futures::future_to_promise;
 use wasm_utils::{console_error, console_log};

 pub mod config;
+mod helpers;
 mod response_pusher;

 #[wasm_bindgen]
 pub struct NymClient {
-    config: Config,
-
-    /// KeyManager object containing smart pointers to all relevant keys used by the client.
-    // due to disgusting workaround I had to wrap the key_manager in an Option
-    // so that the interface wouldn't change (i.e. both `start` and `new` would still return a `NymClient`)
-    key_manager: Option<KeyManager>,
-    self_address: Option<String>,
-
-    // TODO: this should be stored somewhere persistently
-    // received_keys: HashSet<SURBEncryptionKey>,
-    /// Channel used for transforming 'raw' messages into sphinx packets and sending them
-    /// through the mix network.
-    client_input: Option<ClientInput>,
-
-    // callbacks
-    on_message: Option<js_sys::Function>,
-    on_binary_message: Option<js_sys::Function>,
-    on_gateway_connect: Option<js_sys::Function>,
+    self_address: String,
+    client_input: Arc<ClientInput>,

    // even though we don't use graceful shutdowns, other components rely on existence of this struct
    // and if it's dropped, everything will start going offline
-    _shutdown: Option<ShutdownNotifier>,
+    _shutdown: ShutdownNotifier,
 }

 #[wasm_bindgen]
-impl NymClient {
+pub struct NymClientBuilder {
+    config: Config,
+
+    /// KeyManager object containing smart pointers to all relevant keys used by the client.
+    key_manager: KeyManager,
+
+    reply_surb_storage_backend: browser_backend::Backend,
+
+    on_message: js_sys::Function,
+
+    // unimplemented:
+    bandwidth_controller: Option<BandwidthController>,
+    disabled_credentials: bool,
+}
+
+#[wasm_bindgen]
+impl NymClientBuilder {
    #[wasm_bindgen(constructor)]
-    pub fn new(config: Config) -> Self {
-        Self {
+    pub fn new(config: Config, on_message: js_sys::Function) -> Self {
+        //, key_manager: Option<KeyManager>) {
+        NymClientBuilder {
+            reply_surb_storage_backend: Self::setup_reply_surb_storage_backend(&config),
            config,
-            key_manager: Some(Self::setup_key_manager()),
-            on_message: None,
-            on_binary_message: None,
-            on_gateway_connect: None,
-            client_input: None,
-            self_address: None,
-            _shutdown: None,
+            key_manager: Self::setup_key_manager(),
+            on_message,
+            bandwidth_controller: None,
+            disabled_credentials: true,
        }
    }

@@ -69,117 +75,154 @@ impl NymClient {
        KeyManager::new(&mut rng)
    }

-    pub fn set_on_message(&mut self, on_message: js_sys::Function) {
-        self.on_message = Some(on_message);
-    }
-
-    pub fn set_on_binary_message(&mut self, on_binary_message: js_sys::Function) {
-        self.on_binary_message = Some(on_binary_message);
-    }
-
-    pub fn set_on_gateway_connect(&mut self, on_connect: js_sys::Function) {
-        self.on_gateway_connect = Some(on_connect)
-    }
-
-    fn as_mix_recipient(&self) -> Recipient {
-        // another disgusting (and hopefully temporary) workaround
-        let key_manager_ref = self
-            .key_manager
-            .as_ref()
-            .expect("attempting to call 'as_mix_recipient' after 'start'");
-
-        Recipient::new(
-            *key_manager_ref.identity_keypair().public_key(),
-            *key_manager_ref.encryption_keypair().public_key(),
-            identity::PublicKey::from_base58_string(&self.config.gateway_endpoint.gateway_id)
-                .expect("no gateway has been selected"),
+    // don't get too excited about the name, under the hood it's just a big fat placeholder
+    // with no persistence
+    fn setup_reply_surb_storage_backend(config: &Config) -> browser_backend::Backend {
+        browser_backend::Backend::new(
+            config.debug.minimum_reply_surb_storage_threshold,
+            config.debug.maximum_reply_surb_storage_threshold,
        )
    }

+    fn start_reconstructed_pusher(client_output: ClientOutput, on_message: js_sys::Function) {
+        ResponsePusher::new(client_output, on_message).start()
+    }
+
+    pub async fn start_client(self) -> Promise {
+        future_to_promise(async move {
+            console_log!("Starting the wasm client");
+
+            let base_builder = BaseClientBuilder::new(
+                &self.config.gateway_endpoint,
+                &self.config.debug,
+                self.key_manager,
+                self.bandwidth_controller,
+                self.reply_surb_storage_backend,
+                self.disabled_credentials,
+                vec![self.config.validator_api_url.clone()],
+            );
+
+            let self_address = base_builder.as_mix_recipient().to_string();
+            let mut started_client = match base_builder.start_base().await {
+                Ok(base_client) => base_client,
+                Err(err) => {
+                    let error_msg = format!("failed to start the base client components - {err}");
+                    console_error!("{}", error_msg);
+                    let js_error = js_sys::Error::new(&error_msg);
+                    return Err(JsValue::from(js_error));
+                }
+            };
+
+            let client_input = started_client.client_input.register_producer();
+            let client_output = started_client.client_output.register_consumer();
+
+            Self::start_reconstructed_pusher(client_output, self.on_message);
+
+            Ok(JsValue::from(NymClient {
+                self_address,
+                client_input: Arc::new(client_input),
+                _shutdown: started_client.shutdown_notifier,
+            }))
+        })
+    }
+}
+
+#[wasm_bindgen]
+impl NymClient {
    pub fn self_address(&self) -> String {
-        if let Some(address) = &self.self_address {
-            address.clone()
-        } else {
-            self.as_mix_recipient().to_string()
+        self.self_address.clone()
+    }
+
+    fn parse_recipient(recipient: &str) -> Result<Recipient, JsValue> {
+        match Recipient::try_from_base58_string(recipient) {
+            Ok(recipient) => Ok(recipient),
+            Err(err) => {
+                let error_msg = format!("{recipient} is not a valid Nym network recipient - {err}");
+                console_error!("{}", error_msg);
+                let js_error = js_sys::Error::new(&error_msg);
+                Err(JsValue::from(js_error))
+            }
        }
    }

-    // Right now it's impossible to have async exported functions to take `&mut self` rather than mut self
-    // TODO: try Rc<RefCell<Self>> approach?
-    pub async fn send_message(self, message: String, recipient: String) -> Self {
-        console_log!("Sending {} to {}", message, recipient);
-
-        let message_bytes = message.into_bytes();
-        self.send_binary_message(message_bytes, recipient).await
+    fn parse_sender_tag(tag: &str) -> Result<AnonymousSenderTag, JsValue> {
+        match AnonymousSenderTag::try_from_base58_string(tag) {
+            Ok(tag) => Ok(tag),
+            Err(err) => {
+                let error_msg = format!("{tag} is not a valid Nym AnonymousSenderTag - {err}");
+                console_error!("{}", error_msg);
+                let js_error = js_sys::Error::new(&error_msg);
+                Err(JsValue::from(js_error))
+            }
+        }
    }

-    pub async fn send_binary_message(self, message: Vec<u8>, recipient: String) -> Self {
-        console_log!("Sending {} bytes to {}", message.len(), recipient);
-
-        let recipient = Recipient::try_from_base58_string(recipient).unwrap();
-        let lane = TransmissionLane::General;
-
-        let input_msg = InputMessage::new_fresh(recipient, message, false, lane);
-
-        self.client_input
-            .as_ref()
-            .expect("start method was not called before!")
-            .input_sender
-            .send(input_msg)
-            .await
-            .expect("InputMessageReceiver has stopped receiving!");
-
-        self
-    }
-
-    fn start_reconstructed_pusher(
-        client_output: ClientOutput,
-        on_message: Option<js_sys::Function>,
-        on_binary_message: Option<js_sys::Function>,
-    ) {
-        ResponsePusher::new(client_output, on_message, on_binary_message).start()
-    }
-
-    pub async fn start(mut self) -> NymClient {
-        console_log!("Starting the wasm client");
-
-        let base_builder = BaseClientBuilder::new(
-            &self.config.gateway_endpoint,
-            &self.config.debug,
-            self.key_manager.take().unwrap(),
-            None,
-            true,
-            vec![self.config.validator_api_url.clone()],
+    /// The simplest message variant where no additional information is attached.
+    /// You're simply sending your `data` to specified `recipient` without any tagging.
+    ///
+    /// Ends up with `NymMessage::Plain` variant
+    pub fn send_regular_message(&self, message: Vec<u8>, recipient: String) -> Promise {
+        console_log!(
+            "Attempting to send {:.2} kiB message to {recipient}",
+            message.len() as f64 / 1024.0
        );

-        self.self_address = Some(base_builder.as_mix_recipient().to_string());
-        let mut started_client = match base_builder.start_base().await {
-            Ok(base_client) => base_client,
-            Err(err) => {
-                console_error!("failed to start base client components - {}", err);
-                // proper error handling is left here as an exercise for the reader (hi Mark : ))
-                panic!("failed to start base client components - {err}")
-            }
+        let recipient = match Self::parse_recipient(&recipient) {
+            Ok(recipient) => recipient,
+            Err(err) => return Promise::reject(&err),
        };
-        match self.on_gateway_connect.as_ref() {
-            Some(callback) => {
-                callback
-                    .call0(&JsValue::null())
-                    .expect("on connect callback failed!");
-            }
-            None => console_log!("Gateway connection established - no callback specified"),
+        let lane = TransmissionLane::General;
+
+        let input_msg = InputMessage::new_regular(recipient, message, lane);
+        self.client_input.send_message(input_msg)
+    }
+
+    /// Creates a message used for a duplex anonymous communication where the recipient
+    /// will never learn of our true identity. This is achieved by carefully sending `reply_surbs`.
+    ///
+    /// Note that if reply_surbs is set to zero then
+    /// this variant requires the client having sent some reply_surbs in the past
+    /// (and thus the recipient also knowing our sender tag).
+    ///
+    /// Ends up with `NymMessage::Repliable` variant
+    pub fn send_anonymous_message(
+        &self,
+        message: Vec<u8>,
+        recipient: String,
+        reply_surbs: u32,
+    ) -> Promise {
+        console_log!(
+            "Attempting to anonymously send {:.2} kiB message to {recipient} while attaching {reply_surbs} replySURBs.",
+            message.len() as f64 / 1024.0
+        );
+
+        let recipient = match Self::parse_recipient(&recipient) {
+            Ok(recipient) => recipient,
+            Err(err) => return Promise::reject(&err),
        };
+        let lane = TransmissionLane::General;

-        // those should be moved to a completely different struct, but I don't want to break compatibility for now
-        let client_input = started_client.client_input.register_producer();
-        let client_output = started_client.client_output.register_consumer();
+        let input_msg = InputMessage::new_anonymous(recipient, message, reply_surbs, lane);
+        self.client_input.send_message(input_msg)
+    }

-        let on_message = self.on_message.take();
-        let on_binary_message = self.on_binary_message.take();
-        Self::start_reconstructed_pusher(client_output, on_message, on_binary_message);
-        self.client_input = Some(client_input);
-        self._shutdown = Some(started_client.shutdown_notifier);
+    /// Attempt to use our internally received and stored `ReplySurb` to send the message back
+    /// to specified recipient whilst not knowing its full identity (or even gateway).
+    ///
+    /// Ends up with `NymMessage::Reply` variant
+    pub fn send_reply(&self, message: Vec<u8>, recipient_tag: String) -> Promise {
+        console_log!(
+            "Attempting to send {:.2} kiB reply message to {recipient_tag}",
+            message.len() as f64 / 1024.0
+        );

-        self
+        let sender_tag = match Self::parse_sender_tag(&recipient_tag) {
+            Ok(recipient) => recipient,
+            Err(err) => return Promise::reject(&err),
+        };
+        let lane = TransmissionLane::General;
+
+        let input_msg = InputMessage::new_reply(sender_tag, message, lane);
+        self.client_input.send_message(input_msg)
    }
 }
@@ -5,27 +5,18 @@ use client_core::client::base_client::ClientOutput;
 use client_core::client::received_buffer::{ReceivedBufferMessage, ReconstructedMessagesReceiver};
 use futures::channel::mpsc;
 use futures::StreamExt;
+use js_sys::Uint8Array;
 use wasm_bindgen::JsValue;
 use wasm_bindgen_futures::spawn_local;
-use wasm_utils::console_log;
+use wasm_utils::console_error;

 pub(crate) struct ResponsePusher {
    reconstructed_receiver: ReconstructedMessagesReceiver,
-    on_message: Option<js_sys::Function>,
-    on_binary_message: Option<js_sys::Function>,
+    on_message: js_sys::Function,
 }

 impl ResponsePusher {
-    pub(crate) fn new(
-        client_output: ClientOutput,
-        on_message: Option<js_sys::Function>,
-        on_binary_message: Option<js_sys::Function>,
-    ) -> Self {
-        if on_message.is_none() && on_binary_message.is_none() {
-            // exercise for the reader : )
-            panic!("neither 'on_message' nor 'on_binary_message' was set!")
-        }
-
+    pub(crate) fn new(client_output: ClientOutput, on_message: js_sys::Function) -> Self {
        // register our output
        let (reconstructed_sender, reconstructed_receiver) = mpsc::unbounded();

@@ -40,7 +31,6 @@ impl ResponsePusher {
        ResponsePusher {
            reconstructed_receiver,
            on_message,
-            on_binary_message,
        }
    }

@@ -49,23 +39,20 @@ impl ResponsePusher {
            let this = JsValue::null();

            while let Some(reconstructed) = self.reconstructed_receiver.next().await {
-                for msg in reconstructed {
-                    if let Some(ref callback_binary) = self.on_binary_message {
-                        let arg1 = serde_wasm_bindgen::to_value(&msg.message).unwrap();
-                        callback_binary
-                            .call1(&this, &arg1)
-                            .expect("on binary message failed!");
-                    }
-                    if let Some(ref callback) = self.on_message {
-                        if msg.reply_surb.is_some() {
-                            console_log!("the received message contained a reply-surb that we do not know how to handle (yet)")
-                        }
-                        let stringified = String::from_utf8_lossy(&msg.message).into_owned();
-                        let arg1 = serde_wasm_bindgen::to_value(&stringified).unwrap();
-                        callback.call1(&this, &arg1).expect("on message failed!");
-                    }
+                for reconstructed_msg in reconstructed {
+                    let (msg, tag) = reconstructed_msg.into_inner();
+
+                    let msg_slice: &[u8] = &msg;
+                    let array = Uint8Array::from(msg_slice);
+                    let arg1 = JsValue::from(array);
+                    let arg2 = JsValue::from(tag);
+                    self.on_message
+                        .call2(&this, &arg1, &arg2)
+                        .expect("on binary message failed!");
                }
            }
+
+            console_error!("we stopped receiving reconstructed messages!")
        })
    }
 }
@@ -10,9 +10,11 @@ pub type ConnectionId = u64;
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
 pub enum TransmissionLane {
    General,
-    Reply,
+    // we need to treat surb-related requests and responses at higher priority
+    // so that the rest of underlying communication could actually continue
+    ReplySurbRequest,
+    AdditionalReplySurbs,
    Retransmission,
-    Control,
    ConnectionId(ConnectionId),
 }

@@ -57,6 +57,7 @@ version = "0.4"

 [target."cfg(target_arch = \"wasm32\")".dependencies.wasm-utils]
 path = "../../wasm-utils"
+features = ["websocket"]

 # only import it in wasm. Prefer proper tokio timer in non-wasm
 [target."cfg(target_arch = \"wasm32\")".dependencies.wasm-timer]
@@ -410,7 +410,7 @@ impl GatewayClient {
        match gateway_protocol {
            None => {
                warn!("the gateway we're connected to has not specified its protocol version. It's probably running version < 1.1.X, but that's still fine for now. It will become a hard error in 1.2.0");
-                // note: in 1.2.0 we will have to return a hard error here
+                // note: in +1.2.0 we will have to return a hard error here
                Ok(())
            }
            Some(v) if v != PROTOCOL_VERSION => {
@@ -16,7 +16,7 @@ pub mod client;
 pub mod error;
 pub mod packet_router;
 pub mod socket_state;
-#[cfg(feature = "wasm")]
+#[cfg(target_arch = "wasm32")]
 mod wasm_storage;

 /// Helper method for reading from websocket stream. Helps to flatten the structure.
@@ -1,20 +1,12 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
+
 use crate::{validator_api, ValidatorClientError};
 use coconut_dkg_common::types::NodeIndex;
-#[cfg(feature = "nymd-client")]
-use coconut_dkg_common::{
-    dealer::ContractDealing, types::DealerDetails, verification_key::ContractVKShare,
-};
-#[cfg(feature = "nymd-client")]
-use coconut_interface::Base58;
 use coconut_interface::VerificationKey;
-use mixnet_contract_common::families::{Family, FamilyHead};
 use mixnet_contract_common::mixnode::MixNodeDetails;
+use mixnet_contract_common::MixId;
 use mixnet_contract_common::{GatewayBond, IdentityKeyRef};
-use mixnet_contract_common::{IdentityKey, MixId};
-#[cfg(feature = "nymd-client")]
-use std::str::FromStr;
 use validator_api_requests::coconut::{
    BlindSignRequestBody, BlindedSignatureResponse, VerifyCredentialBody, VerifyCredentialResponse,
 };
@@ -28,15 +20,24 @@ use crate::nymd::traits::{DkgQueryClient, MixnetQueryClient, MultisigQueryClient
 #[cfg(feature = "nymd-client")]
 use crate::nymd::{self, CosmWasmClient, NymdClient, QueryNymdClient, SigningNymdClient};
 #[cfg(feature = "nymd-client")]
+use coconut_dkg_common::{
+    dealer::ContractDealing, types::DealerDetails, verification_key::ContractVKShare,
+};
+#[cfg(feature = "nymd-client")]
+use coconut_interface::Base58;
+#[cfg(feature = "nymd-client")]
 use cw3::ProposalResponse;
 #[cfg(feature = "nymd-client")]
 use mixnet_contract_common::{
+    families::{Family, FamilyHead},
    mixnode::MixNodeBond,
    pending_events::{PendingEpochEvent, PendingIntervalEvent},
-    Delegation, RewardedSetNodeStatus, UnbondedMixnode,
+    Delegation, IdentityKey, RewardedSetNodeStatus, UnbondedMixnode,
 };
 #[cfg(feature = "nymd-client")]
 use network_defaults::NymNetworkDetails;
+#[cfg(feature = "nymd-client")]
+use std::str::FromStr;
 use url::Url;
 #[cfg(feature = "nymd-client")]
 use validator_api_requests::models::MixNodeBondAnnotated;
@@ -161,7 +161,7 @@ impl SphinxPacketProcessor {
    ) -> Result<MixProcessingResult, MixProcessingError> {
        match packet {
            ProcessedPacket::ForwardHop(packet, address, delay) => {
-                self.process_forward_hop(packet, address, delay, packet_mode)
+                self.process_forward_hop(*packet, address, delay, packet_mode)
            }
            // right now there's no use for the surb_id included in the header - probably it should get removed from the
            // sphinx all together?
@@ -9,6 +9,7 @@ edition = "2021"
 [dependencies]
 rand = { version = "0.7.3", features = ["wasm-bindgen"] }
 rand_distr = "0.3"
+thiserror = "1.0.37"

 nymsphinx-acknowledgements = { path = "acknowledgements" }
 nymsphinx-addressing = { path = "addressing" }
@@ -72,6 +72,10 @@ impl SurbAck {
        PacketSize::AckPacket.size() + MAX_NODE_ADDRESS_UNPADDED_LEN
    }

+    pub fn expected_total_delay(&self) -> Delay {
+        self.expected_total_delay
+    }
+
    pub fn prepare_for_sending(self) -> (Delay, Vec<u8>) {
        // SURB_FIRST_HOP || SURB_ACK
        let surb_bytes: Vec<_> = self
@@ -10,6 +10,7 @@ edition = "2021"
 crypto = { path = "../../crypto", features = ["asymmetric"] } # all addresses are expressed in terms on their crypto keys
 nymsphinx-types = { path = "../types" } # we need to be able to refer to some types defined inside sphinx crate
 serde = "1.0" # implementing serialization/deserialization for some types, like `Recipient`
+thiserror = "1.0.37"

 [dev-dependencies]
 rand = "0.7"
@@ -10,6 +10,7 @@ use nymsphinx_types::Destination;
 use serde::de::{Error as SerdeError, Unexpected, Visitor};
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use std::fmt::{self, Formatter};
+use thiserror::Error;

 // Not entirely sure whether this is the correct place for those, but let's see how it's going
 // to work out
@@ -19,46 +20,25 @@ const CLIENT_ENCRYPTION_KEY_SIZE: usize = encryption::PUBLIC_KEY_SIZE;
 pub type ClientIdentity = identity::PublicKey;
 const CLIENT_IDENTITY_SIZE: usize = identity::PUBLIC_KEY_LENGTH;

-#[derive(Debug)]
+pub type RecipientBytes = [u8; Recipient::LEN];
+
+#[derive(Debug, Error)]
 pub enum RecipientFormattingError {
-    MalformedRecipientError,
+    #[error("recipient is malformed - {reason} ")]
+    MalformedRecipientError { reason: String },
+
+    #[error("recipient's identity key is malformed: {0}")]
    MalformedIdentityError(identity::Ed25519RecoveryError),
-    MalformedEncryptionKeyError(encryption::KeyRecoveryError),
+
+    #[error("recipient's encryption key is malformed: {0}")]
+    MalformedEncryptionKeyError(#[from] encryption::KeyRecoveryError),
+
+    #[error("recipient gateway's identity key is malformed: {0}")]
    MalformedGatewayError(identity::Ed25519RecoveryError),
 }

-impl fmt::Display for RecipientFormattingError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            RecipientFormattingError::MalformedRecipientError => {
-                write!(f, "recipient is malformed")
-            }
-            RecipientFormattingError::MalformedIdentityError(id_err) => {
-                write!(f, "recipient's identity key is malformed: {}", id_err)
-            }
-            RecipientFormattingError::MalformedEncryptionKeyError(enc_err) => {
-                write!(f, "recipient's encryption key is malformed: {}", enc_err)
-            }
-            RecipientFormattingError::MalformedGatewayError(id_err) => write!(
-                f,
-                "recipient gateway's identity key is malformed: {}",
-                id_err
-            ),
-        }
-    }
-}
-
-// since we have Debug and Display might as well slap Error on top of it too
-impl std::error::Error for RecipientFormattingError {}
-
-impl From<encryption::KeyRecoveryError> for RecipientFormattingError {
-    fn from(err: encryption::KeyRecoveryError) -> Self {
-        RecipientFormattingError::MalformedEncryptionKeyError(err)
-    }
-}
-
 // TODO: this should a different home... somewhere, but where?
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct Recipient {
    client_identity: ClientIdentity,
    client_encryption_key: ClientEncryptionKey,
@@ -154,7 +134,7 @@ impl Recipient {
        &self.gateway
    }

-    pub fn to_bytes(self) -> [u8; Self::LEN] {
+    pub fn to_bytes(self) -> RecipientBytes {
        let mut out = [0u8; Self::LEN];
        out[..CLIENT_IDENTITY_SIZE].copy_from_slice(&self.client_identity.to_bytes());
        out[CLIENT_IDENTITY_SIZE..CLIENT_IDENTITY_SIZE + CLIENT_ENCRYPTION_KEY_SIZE]
@@ -165,7 +145,7 @@ impl Recipient {
        out
    }

-    pub fn try_from_bytes(bytes: [u8; Self::LEN]) -> Result<Self, RecipientFormattingError> {
+    pub fn try_from_bytes(bytes: RecipientBytes) -> Result<Self, RecipientFormattingError> {
        let identity_bytes = &bytes[..CLIENT_IDENTITY_SIZE];
        let enc_key_bytes =
            &bytes[CLIENT_IDENTITY_SIZE..CLIENT_IDENTITY_SIZE + CLIENT_ENCRYPTION_KEY_SIZE];
@@ -196,14 +176,20 @@ impl Recipient {
        let string_address = full_address.into();
        let split: Vec<_> = string_address.split('@').collect();
        if split.len() != 2 {
-            return Err(RecipientFormattingError::MalformedRecipientError);
+            return Err(RecipientFormattingError::MalformedRecipientError {
+                reason: "the string address does not contain exactly a single '@' character"
+                    .to_string(),
+            });
        }
        let client_half = split[0];
        let gateway_half = split[1];

        let split_client: Vec<_> = client_half.split('.').collect();
        if split_client.len() != 2 {
-            return Err(RecipientFormattingError::MalformedRecipientError);
+            return Err(RecipientFormattingError::MalformedRecipientError {
+                reason: "the string address does not contain exactly a single '.' character"
+                    .to_string(),
+            });
        }

        let client_identity = match ClientIdentity::from_base58_string(split_client[0]) {
@@ -5,6 +5,7 @@ use crypto::asymmetric::identity;
 use nymsphinx_types::{NodeAddressBytes, NODE_ADDRESS_LENGTH};
 use std::convert::{TryFrom, TryInto};
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
+use thiserror::Error;

 // Not entirely sure whether this is the correct place for those, but let's see how it's going
 // to work out
@@ -20,10 +21,23 @@ pub const NODE_IDENTITY_SIZE: usize = identity::PUBLIC_KEY_LENGTH;
 /// In this case it's an ipv6 socket address (with version prefix)
 pub const MAX_NODE_ADDRESS_UNPADDED_LEN: usize = 19;

-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum NymNodeRoutingAddressError {
-    InsufficientNumberOfBytesAvailableError,
-    InvalidIpVersion,
+    #[error("Attempted to deserialize NymNodeRoutingAddress without providing any bytes")]
+    NoBytesProvided,
+
+    #[error("Provided insufficient amount of few bytes to deserialize a valid NymNodeRoutingAddress for IPv{protocol_version} variant. Received {received} and required {required}")]
+    TooFewBytesProvided {
+        protocol_version: u8,
+        received: usize,
+        required: usize,
+    },
+
+    #[error("{received} is not a valid version of the Internet Protocol (IP). Expected either '4' or '6'")]
+    InvalidIpVersion { received: u8 },
+
+    #[error("Could not serialize NymNodeRoutingAddress into NodeAddressBytes as that requires using at least {required} bytes and only {NODE_ADDRESS_LENGTH} are available")]
+    TooSmallBytesRepresentation { required: usize },
 }

 /// Current representation of Node routing information used in Nym system.
@@ -84,28 +98,39 @@ impl NymNodeRoutingAddress {
    /// Tries to recover `Self` from a bytes slice.
    /// Does not care if it's zero-padded or not.
    pub fn try_from_bytes(b: &[u8]) -> Result<Self, NymNodeRoutingAddressError> {
-        // the bare minimum to represent `Self` is 7 bytes (for the shorter V4 version)
-        if b.len() < 7 {
-            return Err(NymNodeRoutingAddressError::InsufficientNumberOfBytesAvailableError);
+        if b.is_empty() {
+            return Err(NymNodeRoutingAddressError::NoBytesProvided);
        }

        let ip_version = b[0];
-        let port: u16 = u16::from_be_bytes([b[1], b[2]]);
        let ip = match ip_version {
-            4 => IpAddr::V4(Ipv4Addr::new(b[3], b[4], b[5], b[6])),
+            4 => {
+                if b.len() < 7 {
+                    return Err(NymNodeRoutingAddressError::TooFewBytesProvided {
+                        protocol_version: 4,
+                        received: b.len(),
+                        required: 7,
+                    });
+                }
+                IpAddr::V4(Ipv4Addr::new(b[3], b[4], b[5], b[6]))
+            }
            6 => {
                if b.len() < 19 {
-                    return Err(
-                        NymNodeRoutingAddressError::InsufficientNumberOfBytesAvailableError,
-                    );
+                    return Err(NymNodeRoutingAddressError::TooFewBytesProvided {
+                        protocol_version: 6,
+                        received: b.len(),
+                        required: 19,
+                    });
                }
                let mut address_octets = [0u8; 16];
                address_octets.copy_from_slice(&b[3..19]);
                IpAddr::V6(Ipv6Addr::from(address_octets))
            }
-            _ => return Err(NymNodeRoutingAddressError::InvalidIpVersion),
+            v => return Err(NymNodeRoutingAddressError::InvalidIpVersion { received: v }),
        };

+        let port: u16 = u16::from_be_bytes([b[1], b[2]]);
+
        Ok(Self(SocketAddr::new(ip, port)))
    }

@@ -148,7 +173,9 @@ impl TryInto<NodeAddressBytes> for NymNodeRoutingAddress {
    fn try_into(self) -> Result<NodeAddressBytes, Self::Error> {
        // first check if we have enough bytes to represent `self`:
        if self.bytes_min_len() > NODE_ADDRESS_LENGTH {
-            return Err(NymNodeRoutingAddressError::InsufficientNumberOfBytesAvailableError);
+            return Err(NymNodeRoutingAddressError::TooSmallBytesRepresentation {
+                required: self.bytes_min_len(),
+            });
        }

        let padded_address = self.as_zero_padded_bytes(NODE_ADDRESS_LENGTH);
@@ -7,12 +7,16 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

 [dependencies]
-rand = {version = "0.7.3", features = ["wasm-bindgen"]}
+rand = { version = "0.7.3", features = ["wasm-bindgen"] }
 bs58 = "0.4"
 serde = "1.0"
+thiserror = "1"

 crypto = { path = "../../crypto" }
 nymsphinx-addressing = { path = "../addressing" }
 nymsphinx-params = { path = "../params" }
 nymsphinx-types = { path = "../types" }
 topology = { path = "../../topology" }
+
+[target."cfg(target_arch = \"wasm32\")".dependencies.wasm-bindgen]
+version = "0.2.83"
@@ -16,7 +16,7 @@ pub type EncryptionKeyDigest =

 pub type SurbEncryptionKeySize = <ReplySurbEncryptionAlgorithm as KeySizeUser>::KeySize;

-#[derive(Clone, Debug)]
+#[derive(Clone, Copy, Debug)]
 pub struct SurbEncryptionKey(CipherKey<ReplySurbEncryptionAlgorithm>);

 #[derive(Debug)]
@@ -3,6 +3,7 @@

 pub mod encryption_key;
 pub mod reply_surb;
+pub mod requests;

 pub use encryption_key::{SurbEncryptionKey, SurbEncryptionKeySize};
 pub use reply_surb::{ReplySurb, ReplySurbError};
@@ -1,4 +1,4 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

 use crate::encryption_key::{SurbEncryptionKey, SurbEncryptionKeyError, SurbEncryptionKeySize};
@@ -14,44 +14,22 @@ use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use std::convert::TryFrom;
 use std::fmt::{self, Formatter};
 use std::time;
+use thiserror::Error;
 use topology::{NymTopology, NymTopologyError};

-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum ReplySurbError {
+    #[error("tried to use reply SURB with an unpadded message")]
    UnpaddedMessageError,
-    MalformedStringError(bs58::decode::Error),
-    RecoveryError(SphinxError),
-    InvalidEncryptionKeyData(SurbEncryptionKeyError),
-}

-impl fmt::Display for ReplySurbError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            ReplySurbError::UnpaddedMessageError => {
-                write!(f, "tried to use reply SURB with an unpadded message")
-            }
-            ReplySurbError::MalformedStringError(decode_err) => {
-                write!(f, "reply SURB is incorrectly formatted: {}", decode_err)
-            }
-            ReplySurbError::RecoveryError(sphinx_err) => {
-                write!(f, "failed to recover reply SURB from bytes: {}", sphinx_err)
-            }
-            ReplySurbError::InvalidEncryptionKeyData(surb_key_err) => write!(
-                f,
-                "failed to recover reply SURB encryption key from bytes: {}",
-                surb_key_err
-            ),
-        }
-    }
-}
+    #[error("reply SURB is incorrectly formatted: {0}")]
+    MalformedStringError(#[from] bs58::decode::Error),

-// since we have Debug and Display might as well slap Error on top of it too
-impl std::error::Error for ReplySurbError {}
+    #[error("failed to recover reply SURB from bytes: {0}")]
+    RecoveryError(#[from] SphinxError),

-impl From<SurbEncryptionKeyError> for ReplySurbError {
-    fn from(err: SurbEncryptionKeyError) -> Self {
-        ReplySurbError::InvalidEncryptionKeyData(err)
-    }
+    #[error("failed to recover reply SURB encryption key from bytes: {0}")]
+    InvalidEncryptionKeyData(#[from] SurbEncryptionKeyError),
 }

 #[derive(Debug)]
@@ -157,6 +135,8 @@ impl ReplySurb {
    }

    pub fn from_bytes(bytes: &[u8]) -> Result<Self, ReplySurbError> {
+        // TODO: introduce bound checks to guard us against out of bound reads
+
        let encryption_key =
            SurbEncryptionKey::try_from_bytes(&bytes[..SurbEncryptionKeySize::USIZE])?;

@@ -189,21 +169,22 @@ impl ReplySurb {
    // - surb-ack
    // - key digest
    // - encrypted plaintext with padding to constant length
-    pub fn apply_surb(
+    pub fn apply_surb<M: AsRef<[u8]>>(
        self,
-        message: &[u8],
+        message: M,
        packet_size: Option<PacketSize>,
    ) -> Result<(SphinxPacket, NymNodeRoutingAddress), ReplySurbError> {
        let packet_size = packet_size.unwrap_or_default();

-        if message.len() != packet_size.plaintext_size() {
+        let message_bytes = message.as_ref();
+        if message_bytes.len() != packet_size.plaintext_size() {
            return Err(ReplySurbError::UnpaddedMessageError);
        }

        // this can realistically only fail on too long messages and we just checked for that
        let (packet, first_hop) = self
            .surb
-            .use_surb(message, packet_size.payload_size())
+            .use_surb(message_bytes, packet_size.payload_size())
            .expect("this error indicates inconsistent message length checking - it shouldn't have happened!");

        let first_hop_address = NymNodeRoutingAddress::try_from(first_hop).unwrap();
@@ -0,0 +1,476 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::{ReplySurb, ReplySurbError};
+use nymsphinx_addressing::clients::{Recipient, RecipientFormattingError};
+use rand::{CryptoRng, RngCore};
+use std::fmt::{Display, Formatter};
+use std::mem;
+use thiserror::Error;
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen::prelude::*;
+
+pub const SENDER_TAG_SIZE: usize = 16;
+
+#[derive(Debug, Error)]
+pub enum InvalidAnonymousSenderTagRepresentation {
+    #[error("Failed to decode the base58-encoded string - {0}")]
+    MalformedString(#[from] bs58::decode::Error),
+
+    #[error(
+        "Decoded AnonymousSenderTag has invalid length. Expected {expected}, but got {received}"
+    )]
+    InvalidLength { received: usize, expected: usize },
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+#[cfg_attr(target_arch = "wasm32", wasm_bindgen)]
+pub struct AnonymousSenderTag([u8; SENDER_TAG_SIZE]);
+
+impl From<[u8; SENDER_TAG_SIZE]> for AnonymousSenderTag {
+    fn from(bytes: [u8; SENDER_TAG_SIZE]) -> Self {
+        AnonymousSenderTag(bytes)
+    }
+}
+
+impl Display for AnonymousSenderTag {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.to_base58_string())
+    }
+}
+
+impl AnonymousSenderTag {
+    pub fn new_random<R: RngCore + CryptoRng>(rng: &mut R) -> Self {
+        let mut bytes = [0u8; SENDER_TAG_SIZE];
+        rng.fill_bytes(&mut bytes);
+        AnonymousSenderTag(bytes)
+    }
+
+    pub fn to_bytes(&self) -> [u8; SENDER_TAG_SIZE] {
+        self.0
+    }
+
+    pub fn from_bytes(bytes: [u8; SENDER_TAG_SIZE]) -> Self {
+        AnonymousSenderTag(bytes)
+    }
+
+    pub fn to_base58_string(self) -> String {
+        bs58::encode(self.to_bytes()).into_string()
+    }
+
+    pub fn try_from_base58_string<I: AsRef<[u8]>>(
+        val: I,
+    ) -> Result<Self, InvalidAnonymousSenderTagRepresentation> {
+        let bytes = bs58::decode(val).into_vec()?;
+        if bytes.len() != SENDER_TAG_SIZE {
+            return Err(InvalidAnonymousSenderTagRepresentation::InvalidLength {
+                received: bytes.len(),
+                expected: SENDER_TAG_SIZE,
+            });
+        }
+
+        // the unwrap here is fine as we just asserted the bytes are of exactly SENDER_TAG_SIZE length
+        let byte_array: [u8; SENDER_TAG_SIZE] = bytes.try_into().unwrap();
+        Ok(AnonymousSenderTag::from_bytes(byte_array))
+    }
+}
+
+#[derive(Debug, Error)]
+pub enum InvalidReplyRequestError {
+    #[error("Did not provide sufficient number of bytes to deserialize a valid request")]
+    RequestTooShortToDeserialize,
+
+    #[error("{received} is not a valid content tag for a repliable message")]
+    InvalidRepliableContentTag { received: u8 },
+
+    #[error("{received} is not a valid content tag for a reply message")]
+    InvalidReplyContentTag { received: u8 },
+
+    #[error("failed to deserialize recipient information - {0}")]
+    MalformedRecipient(#[from] RecipientFormattingError),
+
+    #[error("failed to deserialize replySURB - {0}")]
+    MalformedReplySurb(#[from] ReplySurbError),
+}
+
+#[derive(Debug)]
+pub struct RepliableMessage {
+    pub sender_tag: AnonymousSenderTag,
+    pub content: RepliableMessageContent,
+}
+
+impl Display for RepliableMessage {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match &self.content {
+            RepliableMessageContent::Data {
+                message,
+                reply_surbs,
+            } => write!(
+                f,
+                "repliable {:.2} kiB data message with {} reply surbs attached from {}",
+                message.len() as f64 / 1024.0,
+                reply_surbs.len(),
+                self.sender_tag,
+            ),
+            RepliableMessageContent::AdditionalSurbs { reply_surbs } => write!(
+                f,
+                "repliable additional surbs message ({} reply surbs attached) from {}",
+                reply_surbs.len(),
+                self.sender_tag,
+            ),
+            RepliableMessageContent::Heartbeat {
+                additional_reply_surbs,
+            } => {
+                write!(
+                    f,
+                    "repliable heartbeat message ({} reply surbs attached) from {}",
+                    additional_reply_surbs.len(),
+                    self.sender_tag,
+                )
+            }
+        }
+    }
+}
+
+impl RepliableMessage {
+    pub fn new_data(
+        data: Vec<u8>,
+        sender_tag: AnonymousSenderTag,
+        reply_surbs: Vec<ReplySurb>,
+    ) -> Self {
+        RepliableMessage {
+            sender_tag,
+            content: RepliableMessageContent::Data {
+                message: data,
+                reply_surbs,
+            },
+        }
+    }
+
+    pub fn new_additional_surbs(
+        sender_tag: AnonymousSenderTag,
+        reply_surbs: Vec<ReplySurb>,
+    ) -> Self {
+        RepliableMessage {
+            sender_tag,
+            content: RepliableMessageContent::AdditionalSurbs { reply_surbs },
+        }
+    }
+
+    pub fn into_bytes(self) -> Vec<u8> {
+        let content_tag = self.content.tag();
+
+        self.sender_tag
+            .to_bytes()
+            .into_iter()
+            .chain(std::iter::once(content_tag as u8))
+            .chain(self.content.into_bytes())
+            .collect()
+    }
+
+    pub fn try_from_bytes(
+        bytes: &[u8],
+        num_mix_hops: u8,
+    ) -> Result<Self, InvalidReplyRequestError> {
+        if bytes.len() < SENDER_TAG_SIZE + 1 {
+            return Err(InvalidReplyRequestError::RequestTooShortToDeserialize);
+        }
+        let sender_tag =
+            AnonymousSenderTag::from_bytes(bytes[..SENDER_TAG_SIZE].try_into().unwrap());
+        let content_tag = RepliableMessageContentTag::try_from(bytes[SENDER_TAG_SIZE])?;
+
+        let content = RepliableMessageContent::try_from_bytes(
+            &bytes[SENDER_TAG_SIZE + 1..],
+            num_mix_hops,
+            content_tag,
+        )?;
+
+        Ok(RepliableMessage {
+            sender_tag,
+            content,
+        })
+    }
+}
+
+// this recovery code is shared between all variants containing reply surbs
+fn recover_reply_surbs(
+    bytes: &[u8],
+    num_mix_hops: u8,
+) -> Result<(Vec<ReplySurb>, usize), InvalidReplyRequestError> {
+    let mut consumed = mem::size_of::<u32>();
+    if bytes.len() < consumed {
+        return Err(InvalidReplyRequestError::RequestTooShortToDeserialize);
+    }
+    let num_surbs = u32::from_be_bytes([bytes[0], bytes[1], bytes[2], bytes[3]]);
+    let surb_size = ReplySurb::serialized_len(num_mix_hops);
+    if bytes[consumed..].len() < num_surbs as usize * surb_size {
+        return Err(InvalidReplyRequestError::RequestTooShortToDeserialize);
+    }
+
+    let mut reply_surbs = Vec::with_capacity(num_surbs as usize);
+    for _ in 0..num_surbs as usize {
+        let surb_bytes = &bytes[consumed..consumed + surb_size];
+        let reply_surb = ReplySurb::from_bytes(surb_bytes)?;
+        reply_surbs.push(reply_surb);
+
+        consumed += surb_size;
+    }
+
+    Ok((reply_surbs, consumed))
+}
+
+#[repr(u8)]
+enum RepliableMessageContentTag {
+    Data = 0,
+    AdditionalSurbs = 1,
+    Heartbeat = 2,
+}
+
+impl TryFrom<u8> for RepliableMessageContentTag {
+    type Error = InvalidReplyRequestError;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            _ if value == (RepliableMessageContentTag::Data as u8) => Ok(Self::Data),
+            _ if value == (RepliableMessageContentTag::AdditionalSurbs as u8) => {
+                Ok(Self::AdditionalSurbs)
+            }
+            _ if value == (RepliableMessageContentTag::Heartbeat as u8) => Ok(Self::Heartbeat),
+            val => Err(InvalidReplyRequestError::InvalidRepliableContentTag { received: val }),
+        }
+    }
+}
+
+// sent by original sender that initialised the communication that knows address of the remote
+#[derive(Debug)]
+pub enum RepliableMessageContent {
+    Data {
+        message: Vec<u8>,
+        reply_surbs: Vec<ReplySurb>,
+    },
+    AdditionalSurbs {
+        reply_surbs: Vec<ReplySurb>,
+    },
+    Heartbeat {
+        additional_reply_surbs: Vec<ReplySurb>,
+    },
+}
+
+impl RepliableMessageContent {
+    pub fn into_bytes(self) -> Vec<u8> {
+        match self {
+            RepliableMessageContent::Data {
+                message,
+                reply_surbs,
+            } => {
+                let num_surbs = reply_surbs.len() as u32;
+
+                num_surbs
+                    .to_be_bytes()
+                    .into_iter()
+                    .chain(reply_surbs.into_iter().flat_map(|s| s.to_bytes()))
+                    .chain(message.into_iter())
+                    .collect()
+            }
+            RepliableMessageContent::AdditionalSurbs { reply_surbs } => {
+                let num_surbs = reply_surbs.len() as u32;
+
+                num_surbs
+                    .to_be_bytes()
+                    .into_iter()
+                    .chain(reply_surbs.into_iter().flat_map(|s| s.to_bytes()))
+                    .collect()
+            }
+            RepliableMessageContent::Heartbeat {
+                additional_reply_surbs,
+            } => {
+                let num_surbs = additional_reply_surbs.len() as u32;
+
+                num_surbs
+                    .to_be_bytes()
+                    .into_iter()
+                    .chain(
+                        additional_reply_surbs
+                            .into_iter()
+                            .flat_map(|s| s.to_bytes()),
+                    )
+                    .collect()
+            }
+        }
+    }
+
+    fn try_from_bytes(
+        bytes: &[u8],
+        num_mix_hops: u8,
+        tag: RepliableMessageContentTag,
+    ) -> Result<Self, InvalidReplyRequestError> {
+        if bytes.is_empty() {
+            return Err(InvalidReplyRequestError::RequestTooShortToDeserialize);
+        }
+
+        let (reply_surbs, n) = recover_reply_surbs(bytes, num_mix_hops)?;
+
+        match tag {
+            RepliableMessageContentTag::Data => Ok(RepliableMessageContent::Data {
+                message: bytes[n..].to_vec(),
+                reply_surbs,
+            }),
+            RepliableMessageContentTag::AdditionalSurbs => {
+                Ok(RepliableMessageContent::AdditionalSurbs { reply_surbs })
+            }
+            RepliableMessageContentTag::Heartbeat => Ok(RepliableMessageContent::Heartbeat {
+                additional_reply_surbs: reply_surbs,
+            }),
+        }
+    }
+
+    fn tag(&self) -> RepliableMessageContentTag {
+        match self {
+            RepliableMessageContent::Data { .. } => RepliableMessageContentTag::Data,
+            RepliableMessageContent::AdditionalSurbs { .. } => {
+                RepliableMessageContentTag::AdditionalSurbs
+            }
+            RepliableMessageContent::Heartbeat { .. } => RepliableMessageContentTag::Heartbeat,
+        }
+    }
+}
+
+// sent by the remote party who does **NOT** know the original sender's identity
+#[derive(Debug)]
+pub struct ReplyMessage {
+    pub content: ReplyMessageContent,
+}
+
+impl Display for ReplyMessage {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match &self.content {
+            ReplyMessageContent::Data { message } => write!(
+                f,
+                "{:.2} kiB reply data message",
+                message.len() as f64 / 1024.0
+            ),
+            ReplyMessageContent::SurbRequest { recipient, amount } => write!(
+                f,
+                "request for {amount} additional reply SURBs from {recipient}",
+            ),
+        }
+    }
+}
+
+impl ReplyMessage {
+    pub fn new_data_message(message: Vec<u8>) -> Self {
+        ReplyMessage {
+            content: ReplyMessageContent::Data { message },
+        }
+    }
+
+    pub fn new_surb_request_message(recipient: Recipient, amount: u32) -> Self {
+        ReplyMessage {
+            content: ReplyMessageContent::SurbRequest {
+                recipient: Box::new(recipient),
+                amount,
+            },
+        }
+    }
+
+    pub fn into_bytes(self) -> Vec<u8> {
+        let content_tag = self.content.tag();
+
+        std::iter::once(content_tag as u8)
+            .chain(self.content.into_bytes())
+            .collect()
+    }
+
+    pub fn try_from_bytes(bytes: &[u8]) -> Result<Self, InvalidReplyRequestError> {
+        if bytes.is_empty() {
+            return Err(InvalidReplyRequestError::RequestTooShortToDeserialize);
+        }
+        let tag = ReplyMessageContentTag::try_from(bytes[0])?;
+        let content = ReplyMessageContent::try_from_bytes(&bytes[1..], tag)?;
+
+        Ok(ReplyMessage { content })
+    }
+}
+
+#[repr(u8)]
+enum ReplyMessageContentTag {
+    Data = 0,
+    SurbRequest = 1,
+}
+
+impl TryFrom<u8> for ReplyMessageContentTag {
+    type Error = InvalidReplyRequestError;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            _ if value == (ReplyMessageContentTag::Data as u8) => Ok(Self::Data),
+            _ if value == (ReplyMessageContentTag::SurbRequest as u8) => Ok(Self::SurbRequest),
+            val => Err(InvalidReplyRequestError::InvalidReplyContentTag { received: val }),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum ReplyMessageContent {
+    // TODO: later allow to request surbs whilst sending data
+    Data {
+        message: Vec<u8>,
+    },
+    SurbRequest {
+        recipient: Box<Recipient>,
+        amount: u32,
+    },
+}
+
+impl ReplyMessageContent {
+    pub fn into_bytes(self) -> Vec<u8> {
+        match self {
+            ReplyMessageContent::Data { message } => message,
+            ReplyMessageContent::SurbRequest { recipient, amount } => recipient
+                .to_bytes()
+                .into_iter()
+                .chain(amount.to_be_bytes().into_iter())
+                .collect(),
+        }
+    }
+
+    fn try_from_bytes(
+        bytes: &[u8],
+        tag: ReplyMessageContentTag,
+    ) -> Result<Self, InvalidReplyRequestError> {
+        if bytes.is_empty() {
+            return Err(InvalidReplyRequestError::RequestTooShortToDeserialize);
+        }
+
+        match tag {
+            ReplyMessageContentTag::Data => Ok(ReplyMessageContent::Data {
+                message: bytes.to_vec(),
+            }),
+            ReplyMessageContentTag::SurbRequest => {
+                if bytes.len() != Recipient::LEN + std::mem::size_of::<u32>() {
+                    return Err(InvalidReplyRequestError::RequestTooShortToDeserialize);
+                }
+                let mut recipient_bytes = [0u8; Recipient::LEN];
+                recipient_bytes.copy_from_slice(&bytes[..Recipient::LEN]);
+
+                Ok(ReplyMessageContent::SurbRequest {
+                    recipient: Box::new(Recipient::try_from_bytes(recipient_bytes)?),
+                    amount: u32::from_be_bytes([
+                        bytes[Recipient::LEN],
+                        bytes[Recipient::LEN + 1],
+                        bytes[Recipient::LEN + 2],
+                        bytes[Recipient::LEN + 3],
+                    ]),
+                })
+            }
+        }
+    }
+
+    fn tag(&self) -> ReplyMessageContentTag {
+        match self {
+            ReplyMessageContent::Data { .. } => ReplyMessageContentTag::Data,
+            ReplyMessageContent::SurbRequest { .. } => ReplyMessageContentTag::SurbRequest,
+        }
+    }
+}
@@ -9,6 +9,7 @@ edition = "2021"
 [dependencies]
 log = "0.4.8"
 rand = { version = "0.7.3", features = ["wasm-bindgen"] }
+thiserror = "1.0.37"

 nymsphinx-addressing = { path = "../addressing" }
 nymsphinx-params = { path = "../params" }
@@ -1,12 +1,10 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-use crate::set::generate_set_id;
 use crate::ChunkingError;
 use nymsphinx_params::{SerializedFragmentIdentifier, FRAG_ID_LEN};
-use rand::Rng;
 use std::convert::TryInto;
-use std::fmt::{self, Formatter};
+use std::fmt::{self, Debug, Formatter};

 // Personal reflection: In hindsight I've spent too much time on relatively too little
 // gain here, as even though I might have saved couple of bytes per packet, the gain
@@ -60,7 +58,7 @@ pub const COVER_FRAG_ID: FragmentIdentifier = FragmentIdentifier {
 /// and u8 position of the `Fragment` in the set.
 // TODO: this should really be redesigned, especially how cover and reply messages are really
 // "abusing" this. They should work with it natively instead.
-#[derive(Debug, Clone, Copy, Hash, Eq, PartialEq)]
+#[derive(Debug, Clone, Copy, Hash, Eq, PartialEq, Ord, PartialOrd)]
 pub struct FragmentIdentifier {
    set_id: i32,
    fragment_position: u8,
@@ -77,20 +75,6 @@ impl fmt::Display for FragmentIdentifier {
 }

 impl FragmentIdentifier {
-    // I really dislike how 'hacky' this function seems
-    // refer to: https://github.com/nymtech/nym/issues/294 for further discussion
-    pub fn new_reply<R: Rng>(rng: &mut R) -> Self {
-        FragmentIdentifier {
-            set_id: generate_set_id(rng),
-            fragment_position: 0,
-        }
-    }
-
-    // and this one
-    pub fn is_reply(self) -> bool {
-        self.set_id > 0 && self.fragment_position == 0
-    }
-
    pub fn to_bytes(self) -> SerializedFragmentIdentifier {
        debug_assert_eq!(FRAG_ID_LEN, 5);

@@ -110,7 +94,7 @@ impl FragmentIdentifier {
        let set_id = i32::from_be_bytes([b[0], b[1], b[2], b[3]]);
        // set_id == 0 is valid for COVER_FRAG_ID and replies
        if set_id < 0 {
-            return Err(ChunkingError::MalformedFragmentIdentifier);
+            return Err(ChunkingError::MalformedFragmentIdentifier { received: set_id });
        }

        Ok(FragmentIdentifier {
@@ -124,12 +108,22 @@ impl FragmentIdentifier {
 /// Each `Fragment` after being marshaled is guaranteed to fit into a single sphinx packet.
 /// The `Fragment` itself consists of part, or whole of, message to be sent as well as additional
 /// header used to reconstruct the message after being received.
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Clone)]
 pub struct Fragment {
    header: FragmentHeader,
    payload: Vec<u8>,
 }

+// manual implementation to hide detailed payload that we don't care about
+impl Debug for Fragment {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Fragment")
+            .field("header", &self.header)
+            .field("payload length", &self.payload.len())
+            .finish()
+    }
+}
+
 impl Fragment {
    /// Tries to encapsulate provided payload slice and metadata into a `Fragment`.
    /// It can fail if payload would not fully fit in a single `Fragment` or some of the metadata
@@ -153,24 +147,42 @@ impl Fragment {

        // check for whether payload has expected length, which depend on whether fragment is linked
        // and if it's the only one or the last one in the set (then lower bound is removed)
+        let max_linked_len = linked_fragment_payload_max_len(max_plaintext_size);
+        let max_unlinked_len = unlinked_fragment_payload_max_len(max_plaintext_size);
+
        if previous_fragments_set_id.is_some() {
            if total_fragments > 1 {
-                if payload.len() != linked_fragment_payload_max_len(max_plaintext_size) {
-                    return Err(ChunkingError::InvalidPayloadLengthError);
+                if payload.len() != max_linked_len {
+                    return Err(ChunkingError::InvalidPayloadLengthError {
+                        received: payload.len(),
+                        expected: max_linked_len,
+                    });
                }
-            } else if payload.len() > linked_fragment_payload_max_len(max_plaintext_size) {
-                return Err(ChunkingError::InvalidPayloadLengthError);
+            } else if payload.len() > max_linked_len {
+                return Err(ChunkingError::TooLongPayloadLengthError {
+                    received: payload.len(),
+                    expected_at_most: max_linked_len,
+                });
            }
        } else if next_fragments_set_id.is_some() {
-            if payload.len() != linked_fragment_payload_max_len(max_plaintext_size) {
-                return Err(ChunkingError::InvalidPayloadLengthError);
+            if payload.len() != max_linked_len {
+                return Err(ChunkingError::InvalidPayloadLengthError {
+                    received: payload.len(),
+                    expected: max_linked_len,
+                });
            }
        } else if total_fragments != current_fragment {
-            if payload.len() != unlinked_fragment_payload_max_len(max_plaintext_size) {
-                return Err(ChunkingError::InvalidPayloadLengthError);
+            if payload.len() != max_unlinked_len {
+                return Err(ChunkingError::InvalidPayloadLengthError {
+                    received: payload.len(),
+                    expected: max_unlinked_len,
+                });
            }
-        } else if payload.len() > unlinked_fragment_payload_max_len(max_plaintext_size) {
-            return Err(ChunkingError::InvalidPayloadLengthError);
+        } else if payload.len() > max_unlinked_len {
+            return Err(ChunkingError::TooLongPayloadLengthError {
+                received: payload.len(),
+                expected_at_most: max_unlinked_len,
+            });
        }

        Ok(Fragment {
@@ -347,7 +359,10 @@ impl FragmentHeader {
    fn try_from_bytes(b: &[u8]) -> Result<(Self, usize), ChunkingError> {
        // header needs to be at least 7 bytes long
        if b.len() < UNLINKED_FRAGMENTED_HEADER_LEN {
-            return Err(ChunkingError::TooShortFragmentData);
+            return Err(ChunkingError::TooShortFragmentHeader {
+                received: b.len(),
+                expected: UNLINKED_FRAGMENTED_HEADER_LEN,
+            });
        }
        let frag_id = i32::from_be_bytes(b[0..4].try_into().unwrap());
        // sanity check for the fragmentation flag
@@ -370,7 +385,10 @@ impl FragmentHeader {
        let read_bytes = if b[6] != 0 {
            // there's linking ID supposedly attached, make sure we have enough bytes to parse
            if b.len() < LINKED_FRAGMENTED_HEADER_LEN {
-                return Err(ChunkingError::TooShortFragmentData);
+                return Err(ChunkingError::TooShortFragmentHeader {
+                    received: b.len(),
+                    expected: LINKED_FRAGMENTED_HEADER_LEN,
+                });
            }
            let flagged_linked_id = i32::from_be_bytes(b[6..10].try_into().unwrap());

@@ -3,6 +3,7 @@

 use crate::fragment::{linked_fragment_payload_max_len, unlinked_fragment_payload_max_len};
 pub use set::split_into_sets;
+use thiserror::Error;

 // Future consideration: currently in a lot of places, the payloads have randomised content
 // which is not a perfect testing strategy as it might not detect some edge cases I never would
@@ -45,18 +46,26 @@ pub mod set;
 /// Both of those concepts as well as their structures, i.e. `Set` and `Fragment`
 /// are further explained in the respective files.

-#[derive(PartialEq, Eq, Debug)]
+#[derive(PartialEq, Eq, Debug, Error)]
 pub enum ChunkingError {
-    InvalidPayloadLengthError,
-    TooBigMessageToSplit,
+    #[error("Received payload is too long. Got {received}, expected {expected}")]
+    InvalidPayloadLengthError { received: usize, expected: usize },
+
+    #[error("Received payload is too long. Got {received}, expected at most {expected_at_most}")]
+    TooLongPayloadLengthError {
+        received: usize,
+        expected_at_most: usize,
+    },
+
+    // this should really be split into multiple variants to provide better error information
+    #[error("Provided header was malformed or contained self-contradicting fields")]
    MalformedHeaderError,
-    NoValidProvidersError,
-    NoValidRoutesAvailableError,
-    InvalidTopologyError,
-    TooShortFragmentData,
-    MalformedFragmentData,
-    UnexpectedFragmentCount,
-    MalformedFragmentIdentifier,
+
+    #[error("Received too few bytes to deserialize fragment header. Got {received}, expected {expected}")]
+    TooShortFragmentHeader { received: usize, expected: usize },
+
+    #[error("Received fragment identifier ({received}) is not a valid value!")]
+    MalformedFragmentIdentifier { received: i32 },
 }

 /// Returns number of fragments the message will be split to as well as number of available
@@ -94,7 +103,7 @@ pub fn number_of_required_fragments(

            // we know for sure that all fragments in all but last set are definitely full
            // (last one has single 'linked' fragment)
-            let without_last = (n - 1) * (u8::max_value() as usize);
+            let without_last = (n - 1) * (u8::MAX as usize);
            let linked_fragments_without_last = (2 * n - 2) - 1;
            let unlinked_fragments_without_last = without_last - linked_fragments_without_last;

@@ -8,6 +8,7 @@ edition = "2021"

 [dependencies]
 rand = { version = "0.7.3", features = ["wasm-bindgen"] }
+thiserror = "1.0.37"

 crypto = { path = "../../crypto" }
 nymsphinx-acknowledgements = { path = "../acknowledgements" }
@@ -6,7 +6,7 @@ use crypto::symmetric::stream_cipher;
 use nymsphinx_acknowledgements::surb_ack::SurbAck;
 use nymsphinx_acknowledgements::AckKey;
 use nymsphinx_addressing::clients::Recipient;
-use nymsphinx_addressing::nodes::{NymNodeRoutingAddress, NymNodeRoutingAddressError};
+use nymsphinx_addressing::nodes::NymNodeRoutingAddress;
 use nymsphinx_chunking::fragment::COVER_FRAG_ID;
 use nymsphinx_forwarding::packet::MixPacket;
 use nymsphinx_params::packet_sizes::PacketSize;
@@ -18,35 +18,18 @@ use nymsphinx_types::{delays, Error as SphinxError};
 use rand::{CryptoRng, RngCore};
 use std::convert::TryFrom;
 use std::time;
+use thiserror::Error;
 use topology::{NymTopology, NymTopologyError};

 pub const LOOP_COVER_MESSAGE_PAYLOAD: &[u8] = b"The cake is a lie!";

-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum CoverMessageError {
-    NoValidProvidersError,
-    InvalidTopologyError,
-    SphinxError(SphinxError),
-    InvalidFirstMixAddress,
-}
+    #[error("Could not construct cover message due to invalid topology - {0}")]
+    InvalidTopologyError(#[from] NymTopologyError),

-impl From<SphinxError> for CoverMessageError {
-    fn from(err: SphinxError) -> Self {
-        CoverMessageError::SphinxError(err)
-    }
-}
-
-impl From<NymNodeRoutingAddressError> for CoverMessageError {
-    fn from(_: NymNodeRoutingAddressError) -> Self {
-        use CoverMessageError::*;
-        InvalidFirstMixAddress
-    }
-}
-
-impl From<NymTopologyError> for CoverMessageError {
-    fn from(_: NymTopologyError) -> Self {
-        CoverMessageError::InvalidTopologyError
-    }
+    #[error("Could not construct a valid sphinx packet - {0}")]
+    SphinxError(#[from] SphinxError),
 }

 pub fn generate_loop_cover_surb_ack<R>(
@@ -178,7 +178,7 @@ mod packet_encoding {
        ];
        SphinxPacketBuilder::new()
            .with_payload_size(size.payload_size())
-            .build_packet(b"foomp".to_vec(), &route, &destination, &delays)
+            .build_packet(b"foomp", &route, &destination, &delays)
            .unwrap()
    }

@@ -1,6 +1,7 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

+pub mod message;
 pub mod preparer;
 pub mod receiver;
 pub mod utils;
@@ -16,3 +17,6 @@ pub use nymsphinx_forwarding as forwarding;
 pub use nymsphinx_framing as framing;
 pub use nymsphinx_params as params;
 pub use nymsphinx_types::*;
+
+// TEMP UNTIL FURTHER REFACTORING
+pub use preparer::payload::NymsphinxPayloadBuilder;
@@ -0,0 +1,238 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::chunking;
+use crypto::asymmetric::encryption;
+use crypto::Digest;
+use nymsphinx_addressing::clients::Recipient;
+use nymsphinx_addressing::nodes::MAX_NODE_ADDRESS_UNPADDED_LEN;
+use nymsphinx_anonymous_replies::requests::{
+    InvalidReplyRequestError, RepliableMessage, RepliableMessageContent, ReplyMessage,
+    ReplyMessageContent,
+};
+use nymsphinx_chunking::fragment::Fragment;
+use nymsphinx_params::{PacketSize, ReplySurbKeyDigestAlgorithm};
+use rand::Rng;
+use std::fmt::{Display, Formatter};
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum NymMessageError {
+    #[error("{received} is not a valid type tag for a NymMessage")]
+    InvalidMessageType { received: u8 },
+
+    #[error(transparent)]
+    InvalidReplyRequest(#[from] InvalidReplyRequestError),
+
+    #[error("The received message seems to have incorrect zero padding (no '1' byte found)")]
+    InvalidMessagePadding,
+
+    #[error("Received empty message for deserialization")]
+    EmptyMessage,
+}
+
+#[repr(u8)]
+enum NymMessageType {
+    Plain = 0,
+    Repliable = 1,
+    Reply = 2,
+}
+
+impl TryFrom<u8> for NymMessageType {
+    type Error = NymMessageError;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            _ if value == (NymMessageType::Plain as u8) => Ok(Self::Plain),
+            _ if value == (NymMessageType::Repliable as u8) => Ok(Self::Repliable),
+            _ if value == (NymMessageType::Reply as u8) => Ok(Self::Reply),
+            val => Err(NymMessageError::InvalidMessageType { received: val }),
+        }
+    }
+}
+
+pub type PlainMessage = Vec<u8>;
+
+#[derive(Debug)]
+pub enum NymMessage {
+    Plain(PlainMessage),
+    Repliable(RepliableMessage),
+    Reply(ReplyMessage),
+}
+
+impl Display for NymMessage {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            NymMessage::Plain(plain_message) => write!(
+                f,
+                "plain {:.2} kiB message",
+                plain_message.len() as f64 / 1024.0
+            ),
+            NymMessage::Repliable(repliable_message) => repliable_message.fmt(f),
+            NymMessage::Reply(reply_message) => reply_message.fmt(f),
+        }
+    }
+}
+
+impl NymMessage {
+    pub fn new_additional_surbs_request(recipient: Recipient, amount: u32) -> Self {
+        NymMessage::Reply(ReplyMessage {
+            content: ReplyMessageContent::SurbRequest {
+                recipient: Box::new(recipient),
+                amount,
+            },
+        })
+    }
+
+    pub fn new_plain(msg: Vec<u8>) -> Self {
+        NymMessage::Plain(msg)
+    }
+
+    pub fn new_repliable(msg: RepliableMessage) -> Self {
+        NymMessage::Repliable(msg)
+    }
+
+    pub fn new_reply(msg: ReplyMessage) -> Self {
+        NymMessage::Reply(msg)
+    }
+
+    pub fn is_reply_surb_request(&self) -> bool {
+        match self {
+            NymMessage::Reply(reply_msg) => {
+                matches!(reply_msg.content, ReplyMessageContent::SurbRequest { .. })
+            }
+            _ => false,
+        }
+    }
+
+    pub fn into_inner_data(self) -> Vec<u8> {
+        match self {
+            NymMessage::Plain(data) => data,
+            NymMessage::Repliable(repliable) => match repliable.content {
+                RepliableMessageContent::Data { message, .. } => message,
+                _ => Vec::new(),
+            },
+            NymMessage::Reply(reply) => match reply.content {
+                ReplyMessageContent::Data { message } => message,
+                _ => Vec::new(),
+            },
+        }
+    }
+
+    fn typ(&self) -> NymMessageType {
+        match self {
+            NymMessage::Plain(_) => NymMessageType::Plain,
+            NymMessage::Repliable(_) => NymMessageType::Repliable,
+            NymMessage::Reply(_) => NymMessageType::Reply,
+        }
+    }
+
+    fn inner_bytes(self) -> Vec<u8> {
+        match self {
+            NymMessage::Plain(msg) => msg,
+            NymMessage::Repliable(msg) => msg.into_bytes(),
+            NymMessage::Reply(msg) => msg.into_bytes(),
+        }
+    }
+
+    // the message is in the format of:
+    // typ || msg
+    fn into_bytes(self) -> Vec<u8> {
+        let typ = self.typ();
+
+        std::iter::once(typ as u8)
+            .chain(self.inner_bytes())
+            .collect()
+    }
+
+    fn try_from_bytes(bytes: &[u8], num_mix_hops: u8) -> Result<Self, NymMessageError> {
+        if bytes.is_empty() {
+            return Err(NymMessageError::EmptyMessage);
+        }
+
+        let typ_tag = NymMessageType::try_from(bytes[0])?;
+        match typ_tag {
+            NymMessageType::Plain => Ok(NymMessage::Plain(bytes[1..].to_vec())),
+            NymMessageType::Repliable => Ok(NymMessage::Repliable(
+                RepliableMessage::try_from_bytes(&bytes[1..], num_mix_hops)?,
+            )),
+            NymMessageType::Reply => Ok(NymMessage::Reply(ReplyMessage::try_from_bytes(
+                &bytes[1..],
+            )?)),
+        }
+    }
+
+    /// Length of plaintext (from the sphinx point of view) data that is available per sphinx
+    /// packet.
+    pub fn available_plaintext_per_packet(&self, packet_size: PacketSize) -> usize {
+        let ack_overhead = MAX_NODE_ADDRESS_UNPADDED_LEN + PacketSize::AckPacket.size();
+
+        let variant_overhead = match self {
+            // each plain or repliable packet attaches an ephemeral public key so that the recipient
+            // could perform diffie-hellman with its own keys followed by a kdf to re-derive
+            // the packet encryption key
+            NymMessage::Plain(_) | NymMessage::Repliable(_) => encryption::PUBLIC_KEY_SIZE,
+            // each reply attaches the digest of the encryption key so that the recipient could
+            // lookup correct key for decryption,
+            NymMessage::Reply(_) => ReplySurbKeyDigestAlgorithm::output_size(),
+        };
+
+        packet_size.plaintext_size() - ack_overhead - variant_overhead
+    }
+
+    /// Pads the message so that after it gets chunked, it will occupy exactly N sphinx packets.
+    /// Produces new_message = message || 1 || 0000....
+    pub fn pad_to_full_packet_lengths(self, plaintext_per_packet: usize) -> PaddedMessage {
+        let bytes = self.into_bytes();
+
+        // 1 is added as there will always have to be at least a single byte of padding (1) added
+        // to be able to later distinguish the actual padding from the underlying message
+        let (_, space_left) =
+            chunking::number_of_required_fragments(bytes.len() + 1, plaintext_per_packet);
+
+        bytes
+            .into_iter()
+            .chain(std::iter::once(1u8))
+            .chain(std::iter::repeat(0u8).take(space_left))
+            .collect::<Vec<_>>()
+            .into()
+    }
+}
+
+pub struct PaddedMessage(Vec<u8>);
+
+impl PaddedMessage {
+    pub fn new_reconstructed(bytes: Vec<u8>) -> Self {
+        PaddedMessage(bytes)
+    }
+
+    /// Splits the padded message into [`Fragment`] that when serialized are going to become
+    /// sphinx packet payloads.
+    pub fn split_into_fragments<R: Rng>(
+        self,
+        rng: &mut R,
+        plaintext_per_packet: usize,
+    ) -> Vec<Fragment> {
+        chunking::split_into_sets(rng, &self.0, plaintext_per_packet)
+            .into_iter()
+            .flat_map(|fragment_set| fragment_set.into_iter())
+            .collect()
+    }
+
+    // reverse of NymMessage::pad_to_full_packet_lengths
+    pub fn remove_padding(self, num_mix_hops: u8) -> Result<NymMessage, NymMessageError> {
+        // we are looking for first occurrence of 1 in the tail and we get its index
+        if let Some(padding_end) = self.0.iter().rposition(|b| *b == 1) {
+            // and now we only take bytes until that point (but not including it)
+            NymMessage::try_from_bytes(&self.0[..padding_end], num_mix_hops)
+        } else {
+            Err(NymMessageError::InvalidMessagePadding)
+        }
+    }
+}
+
+impl From<Vec<u8>> for PaddedMessage {
+    fn from(bytes: Vec<u8>) -> Self {
+        PaddedMessage(bytes)
+    }
+}
@@ -1,24 +1,17 @@
-// Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
+// Copyright 2021-2022 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

-use crate::chunking;
-use crypto::asymmetric::encryption;
-use crypto::shared_key::new_ephemeral_shared_key;
-use crypto::symmetric::stream_cipher;
-use crypto::Digest;
+use crate::message::NymMessage;
+use crate::NymsphinxPayloadBuilder;
 use nymsphinx_acknowledgements::surb_ack::SurbAck;
 use nymsphinx_acknowledgements::AckKey;
 use nymsphinx_addressing::clients::Recipient;
-use nymsphinx_addressing::nodes::{NymNodeRoutingAddress, MAX_NODE_ADDRESS_UNPADDED_LEN};
-use nymsphinx_anonymous_replies::encryption_key::SurbEncryptionKey;
+use nymsphinx_addressing::nodes::NymNodeRoutingAddress;
 use nymsphinx_anonymous_replies::reply_surb::ReplySurb;
 use nymsphinx_chunking::fragment::{Fragment, FragmentIdentifier};
 use nymsphinx_forwarding::packet::MixPacket;
 use nymsphinx_params::packet_sizes::PacketSize;
-use nymsphinx_params::{
-    PacketEncryptionAlgorithm, PacketHkdfAlgorithm, ReplySurbEncryptionAlgorithm,
-    ReplySurbKeyDigestAlgorithm, DEFAULT_NUM_MIX_HOPS,
-};
+use nymsphinx_params::DEFAULT_NUM_MIX_HOPS;
 use nymsphinx_types::builder::SphinxPacketBuilder;
 use nymsphinx_types::{delays, Delay};
 use rand::{CryptoRng, Rng};
@@ -26,6 +19,8 @@ use std::convert::TryFrom;
 use std::time::Duration;
 use topology::{NymTopology, NymTopologyError};

+pub(crate) mod payload;
+
 /// Represents fully packed and prepared [`Fragment`] that can be sent through the mix network.
 pub struct PreparedFragment {
    /// Indicates the total expected round-trip time, i.e. delay from the sending of this message
@@ -36,27 +31,17 @@ pub struct PreparedFragment {
    /// address of the node to which the message should be sent, the actual 'chunk' of the message
    /// going through the mix network and also the 'mode' of the packet, i.e. VPN or Mix.
    pub mix_packet: MixPacket,
-}

-#[derive(Debug)]
-pub enum PreparationError {
-    TopologyError(NymTopologyError),
-    TooLongReplyMessageError,
-}
-
-impl From<NymTopologyError> for PreparationError {
-    fn from(err: NymTopologyError) -> Self {
-        PreparationError::TopologyError(err)
-    }
+    /// Identifier to uniquely identify a fragment.
+    pub fragment_identifier: FragmentIdentifier,
 }

 /// Prepares the message that is to be sent through the mix network by attaching
 /// an optional reply-SURB, padding it to appropriate length, encrypting its content,
 /// and chunking into appropriate size [`Fragment`]s.
-// #[cfg_attr(not(target_arch = "wasm32"), derive(Clone))]
 #[derive(Clone)]
 #[must_use]
-pub struct MessagePreparer<R: CryptoRng + Rng> {
+pub struct MessagePreparer<R> {
    /// Instance of a cryptographically secure random number generator.
    rng: R,

@@ -115,86 +100,70 @@ where
        self.sender_address = sender_address;
    }

-    /// Length of plaintext (from the sphinx point of view) data that is available per sphinx
-    /// packet.
-    fn available_plaintext_per_packet(&self) -> usize {
-        // we need to put first hop's destination alongside the actual ack data
-        // TODO: a possible optimization way down the line: currently we're always assuming that
-        // the addresses will have `MAX_NODE_ADDRESS_UNPADDED_LEN`, i.e. be ipv6. In most cases
-        // they're actually going to be ipv4 hence wasting few bytes every packet.
-        // To fully utilise all available space, I guess first we'd need to generate routes for ACKs
-        // and only then perform the chunking with `available_plaintext_size` being called per chunk.
-        // However this will probably introduce bunch of complexity
-        // for relatively not a lot of gain, so it shouldn't be done just yet.
-        let ack_overhead = MAX_NODE_ADDRESS_UNPADDED_LEN + PacketSize::AckPacket.size();
-        let ephemeral_public_key_overhead = encryption::PUBLIC_KEY_SIZE;
-
-        self.packet_size.plaintext_size() - ack_overhead - ephemeral_public_key_overhead
-    }
-
-    /// Pads the message so that after it gets chunked, it will occupy exactly N sphinx packets.
-    /// Produces new_message = message || 1 || 0000....
-    fn pad_message(&self, message: Vec<u8>) -> Vec<u8> {
-        // 1 is added as there will always have to be at least a single byte of padding (1) added
-        // to be able to later distinguish the actual padding from the underlying message
-        let (_, space_left) = chunking::number_of_required_fragments(
-            message.len() + 1,
-            self.available_plaintext_per_packet(),
-        );
-
-        message
-            .into_iter()
-            .chain(std::iter::once(1u8))
-            .chain(std::iter::repeat(0u8).take(space_left))
-            .collect()
-    }
-
-    /// Attaches reply-SURB to the message alongside the reply key.
-    /// Results in:
-    /// new_message = 0 || message
-    /// OR
-    /// new_message = 1 || REPLY_KEY || REPLY_SURB || message
-    fn optionally_attach_reply_surb(
+    pub fn generate_reply_surbs(
        &mut self,
-        message: Vec<u8>,
-        should_attach: bool,
+        amount: usize,
        topology: &NymTopology,
-    ) -> Result<(Vec<u8>, Option<SurbEncryptionKey>), PreparationError> {
-        if should_attach {
+    ) -> Result<Vec<ReplySurb>, NymTopologyError> {
+        let mut reply_surbs = Vec::with_capacity(amount);
+        for _ in 0..amount {
            let reply_surb = ReplySurb::construct(
                &mut self.rng,
                &self.sender_address,
                self.average_packet_delay,
                topology,
            )?;
-
-            let reply_key = reply_surb.encryption_key();
-            // if there's a reply surb, the message takes form of `1 || REPLY_KEY || REPLY_SURB || MSG`
-            Ok((
-                std::iter::once(true as u8)
-                    .chain(reply_surb.to_bytes().iter().cloned())
-                    .chain(message.into_iter())
-                    .collect(),
-                Some(reply_key.clone()),
-            ))
-        } else {
-            // but if there's no reply surb, the message takes form of `0 || MSG`
-            Ok((
-                std::iter::once(false as u8)
-                    .chain(message.into_iter())
-                    .collect(),
-                None,
-            ))
+            reply_surbs.push(reply_surb)
        }
+
+        Ok(reply_surbs)
    }

-    /// Splits the message into [`Fragment`] that are going to be put later put into sphinx packets.
-    fn split_message(&mut self, message: Vec<u8>) -> Vec<Fragment> {
-        let plaintext_per_packet = self.available_plaintext_per_packet();
-        chunking::split_into_sets(&mut self.rng, &message, plaintext_per_packet)
-            .into_iter()
-            .flat_map(|fragment_set| fragment_set.into_iter())
-            .collect()
+    /// The procedure is as follows:
+    /// For each fragment:
+    /// - compute SURB_ACK
+    /// - generate (x, g^x)
+    /// - obtain key k from the reply-surb which was computed as follows:
+    ///     k = KDF(remote encryption key ^ x) this is equivalent to KDF( dh(remote, x) )
+    /// - compute v_b = AES-128-CTR(k, serialized_fragment)
+    /// - compute vk_b = H(k) || v_b
+    /// - compute sphinx_plaintext = SURB_ACK || H(k) || v_b
+    /// - compute sphinx_packet by applying the reply surb on the sphinx_plaintext
+    pub fn prepare_reply_chunk_for_sending(
+        &mut self,
+        fragment: Fragment,
+        topology: &NymTopology,
+        ack_key: &AckKey,
+        reply_surb: ReplySurb,
+    ) -> Result<PreparedFragment, NymTopologyError> {
+        // this is not going to be accurate by any means. but that's the best estimation we can do
+        let expected_forward_delay = Delay::new_from_millis(
+            (self.average_packet_delay.as_millis() * self.num_mix_hops as u128) as u64,
+        );
+
+        let fragment_identifier = fragment.fragment_identifier();
+
+        // create an ack
+        let surb_ack = self.generate_surb_ack(fragment_identifier, topology, ack_key)?;
+        let ack_delay = surb_ack.expected_total_delay();
+
+        let packet_payload = NymsphinxPayloadBuilder::new(fragment, surb_ack)
+            .build_reply(reply_surb.encryption_key());
+
+        // the unwrap here is fine as the failures can only originate from attempting to use invalid payload lenghts
+        // and we just very carefully constructed a (presumably) valid one
+        let (sphinx_packet, first_hop_address) = reply_surb
+            .apply_surb(packet_payload, Some(self.packet_size))
+            .unwrap();
+
+        Ok(PreparedFragment {
+            // the round-trip delay is the sum of delays of all hops on the forward route as
+            // well as the total delay of the ack packet.
+            // we don't know the delays inside the reply surbs so we use best-effort estimation from our poisson distribution
+            total_delay: expected_forward_delay + ack_delay,
+            mix_packet: MixPacket::new(first_hop_address, sphinx_packet, Default::default()),
+            fragment_identifier,
+        })
    }

    /// Tries to convert this [`Fragment`] into a [`SphinxPacket`] that can be sent through the Nym mix-network,
@@ -221,46 +190,14 @@ where
        ack_key: &AckKey,
        packet_recipient: &Recipient,
    ) -> Result<PreparedFragment, NymTopologyError> {
+        let fragment_identifier = fragment.fragment_identifier();
+
        // create an ack
-        let (ack_delay, surb_ack_bytes) = self
-            .generate_surb_ack(fragment.fragment_identifier(), topology, ack_key)?
-            .prepare_for_sending();
+        let surb_ack = self.generate_surb_ack(fragment_identifier, topology, ack_key)?;
+        let ack_delay = surb_ack.expected_total_delay();

-        // TODO:
-        // TODO:
-        // TODO:
-        // TODO:
-        // TODO: ASK @AP AND @DH WHETHER THOSE KEYS CAN/SHOULD ALSO BE REUSED IN VPN MODE!!
-        // TODO:
-        // TODO:
-        // TODO:
-        // TODO:
-
-        // create keys for 'payload' encryption
-        let (ephemeral_keypair, shared_key) =
-            new_ephemeral_shared_key::<PacketEncryptionAlgorithm, PacketHkdfAlgorithm, _>(
-                &mut self.rng,
-                packet_recipient.encryption_key(),
-            );
-
-        // serialize fragment and encrypt its content
-        let mut chunk_data = fragment.into_bytes();
-
-        let zero_iv = stream_cipher::zero_iv::<PacketEncryptionAlgorithm>();
-        stream_cipher::encrypt_in_place::<PacketEncryptionAlgorithm>(
-            &shared_key,
-            &zero_iv,
-            &mut chunk_data,
-        );
-
-        // combine it together as follows:
-        // SURB_ACK_FIRST_HOP || SURB_ACK_DATA || EPHEMERAL_KEY || CHUNK_DATA
-        // (note: surb_ack_bytes contains SURB_ACK_FIRST_HOP || SURB_ACK_DATA )
-        let packet_payload: Vec<_> = surb_ack_bytes
-            .into_iter()
-            .chain(ephemeral_keypair.public_key().to_bytes().iter().cloned())
-            .chain(chunk_data.into_iter())
-            .collect();
+        let packet_payload = NymsphinxPayloadBuilder::new(fragment, surb_ack)
+            .build_regular(&mut self.rng, packet_recipient.encryption_key());

        // generate pseudorandom route for the packet
        let route = topology.random_route_to_gateway(
@@ -290,6 +227,7 @@ where
            // note that the last hop of the packet is a gateway that does not do any delays
            total_delay: delays.iter().take(delays.len() - 1).sum::<Delay>() + ack_delay,
            mix_packet: MixPacket::new(first_hop_address, sphinx_packet, Default::default()),
+            fragment_identifier,
        })
    }

@@ -310,113 +248,12 @@ where
        )
    }

-    /// Attaches an optional reply-surb and correct padding to the underlying message
-    /// and splits it into [`Fragment`] that can be later packed into sphinx packets to be
-    /// sent through the mix network.
-    pub fn prepare_and_split_message(
-        &mut self,
-        message: Vec<u8>,
-        with_reply_surb: bool,
-        topology: &NymTopology,
-    ) -> Result<(Vec<Fragment>, Option<SurbEncryptionKey>), PreparationError> {
-        let (message, reply_key) =
-            self.optionally_attach_reply_surb(message, with_reply_surb, topology)?;
+    pub fn pad_and_split_message(&mut self, message: NymMessage) -> Vec<Fragment> {
+        let plaintext_per_packet = message.available_plaintext_per_packet(self.packet_size);

-        let message = self.pad_message(message);
-
-        Ok((self.split_message(message), reply_key))
-    }
-
-    // TODO: perhaps the return type could somehow be combined with [`PreparedFragment`] ?
-    pub async fn prepare_reply_for_use(
-        &mut self,
-        message: Vec<u8>,
-        reply_surb: ReplySurb,
-        topology: &NymTopology,
-        ack_key: &AckKey,
-    ) -> Result<(MixPacket, FragmentIdentifier), PreparationError> {
-        // there's no chunking in reply-surbs so there's a hard limit on message,
-        // we also need to put the key digest into the message (same size as ephemeral key)
-        // and need 1 byte to indicate padding length (this is not the case for 'normal' messages
-        // as there the padding is added for the whole message)
-        // so before doing any processing, let's see if we have enough space for it all
-        let ack_overhead = MAX_NODE_ADDRESS_UNPADDED_LEN + PacketSize::AckPacket.size();
-        if message.len()
-            > self.packet_size.plaintext_size()
-                - ack_overhead
-                - ReplySurbKeyDigestAlgorithm::output_size()
-                - 1
-        {
-            return Err(PreparationError::TooLongReplyMessageError);
-        }
-
-        let reply_id = FragmentIdentifier::new_reply(&mut self.rng);
-
-        // create an ack
-        // even though it won't be used for retransmission, it must be present so that
-        // gateways could not distinguish reply packets from normal messages due to lack of said acks
-        // note: the ack delay is irrelevant since we do not know the delay of actual surb
-        let (_, surb_ack_bytes) = self
-            .generate_surb_ack(reply_id, topology, ack_key)?
-            .prepare_for_sending();
-
-        let zero_pad_len = self.packet_size.plaintext_size()
-            - message.len()
-            - ack_overhead
-            - ReplySurbKeyDigestAlgorithm::output_size()
-            - 1;
-
-        // create reply message that will reach the recipient:
-        let mut reply_content: Vec<_> = message
-            .into_iter()
-            .chain(std::iter::once(1))
-            .chain(std::iter::repeat(0).take(zero_pad_len))
-            .collect();
-
-        // encrypt the reply message
-        let zero_iv = stream_cipher::zero_iv::<ReplySurbEncryptionAlgorithm>();
-        stream_cipher::encrypt_in_place::<ReplySurbEncryptionAlgorithm>(
-            reply_surb.encryption_key().inner(),
-            &zero_iv,
-            &mut reply_content,
-        );
-
-        // combine it together as follows:
-        // SURB_ACK_FIRST_HOP || SURB_ACK_DATA || KEY_DIGEST || E (REPLY_MESSAGE || 1 || 0*)
-        // (note: surb_ack_bytes contains SURB_ACK_FIRST_HOP || SURB_ACK_DATA )
-        let packet_payload: Vec<_> = surb_ack_bytes
-            .into_iter()
-            .chain(reply_surb.encryption_key().compute_digest().iter().copied())
-            .chain(reply_content.into_iter())
-            .collect();
-
-        // finally put it all inside a sphinx packet
-        // this can only fail if packet payload has incorrect size, but if it does, it means
-        // there's a bug in the above code
-        let (packet, first_hop) = reply_surb
-            .apply_surb(&packet_payload, Some(self.packet_size))
-            .unwrap();
-
-        Ok((
-            MixPacket::new(first_hop, packet, Default::default()),
-            reply_id,
-        ))
-    }
-
-    #[allow(dead_code)]
-    #[cfg(test)]
-    pub(crate) fn test_fixture() -> MessagePreparer<rand::rngs::OsRng> {
-        let rng = rand::rngs::OsRng;
-        let dummy_address = Recipient::try_from_base58_string("CytBseW6yFXUMzz4SGAKdNLGR7q3sJLLYxyBGvutNEQV.4QXYyEVc5fUDjmmi8PrHN9tdUFV4PCvSJE1278cHyvoe@4sBbL1ngf1vtNqykydQKTFh26sQCw888GpUqvPvyNB4f").unwrap();
-
-        MessagePreparer {
-            rng,
-            packet_size: Default::default(),
-            sender_address: dummy_address,
-            average_packet_delay: Default::default(),
-            average_ack_delay: Default::default(),
-            num_mix_hops: DEFAULT_NUM_MIX_HOPS,
-        }
+        message
+            .pad_to_full_packet_lengths(plaintext_per_packet)
+            .split_into_fragments(&mut self.rng, plaintext_per_packet)
    }
 }

@@ -0,0 +1,97 @@
+// Copyright 2022 - Nym Technologies SA <contact@nymtech.net>
+// SPDX-License-Identifier: Apache-2.0
+
+use crypto::aes::cipher::{KeyIvInit, StreamCipher};
+use crypto::asymmetric::encryption;
+use crypto::shared_key::new_ephemeral_shared_key;
+use crypto::symmetric::stream_cipher;
+use crypto::symmetric::stream_cipher::CipherKey;
+use nymsphinx_acknowledgements::surb_ack::SurbAck;
+use nymsphinx_anonymous_replies::SurbEncryptionKey;
+use nymsphinx_chunking::fragment::Fragment;
+use nymsphinx_params::{
+    PacketEncryptionAlgorithm, PacketHkdfAlgorithm, ReplySurbEncryptionAlgorithm,
+};
+use rand::{CryptoRng, RngCore};
+
+pub struct NymsphinxPayloadBuilder {
+    fragment: Fragment,
+    surb_ack: SurbAck,
+}
+
+impl NymsphinxPayloadBuilder {
+    pub fn new(fragment: Fragment, surb_ack: SurbAck) -> Self {
+        NymsphinxPayloadBuilder { fragment, surb_ack }
+    }
+
+    fn build<C>(
+        self,
+        packet_encryption_key: &CipherKey<C>,
+        variant_data: impl IntoIterator<Item = u8>,
+    ) -> NymsphinxPayload
+    where
+        C: StreamCipher + KeyIvInit,
+    {
+        let (_, surb_ack_bytes) = self.surb_ack.prepare_for_sending();
+
+        let mut fragment_data = self.fragment.into_bytes();
+        stream_cipher::encrypt_in_place::<C>(
+            packet_encryption_key,
+            &stream_cipher::zero_iv::<C>(),
+            &mut fragment_data,
+        );
+
+        // combines all the data as follows:
+        // SURB_ACK || VARIANT_SPECIFIC_DATA || CHUNK_DATA
+        // where variant-specific data is as follows:
+        // for replies it would be the digest of the encryption key used
+        // for 'regular' messages it would be the public component used in DH later used in the KDF
+        NymsphinxPayload(
+            surb_ack_bytes
+                .into_iter()
+                .chain(variant_data.into_iter())
+                .chain(fragment_data.into_iter())
+                .collect(),
+        )
+    }
+
+    pub fn build_reply(self, packet_encryption_key: &SurbEncryptionKey) -> NymsphinxPayload {
+        let key_digest = packet_encryption_key.compute_digest();
+        self.build::<ReplySurbEncryptionAlgorithm>(
+            packet_encryption_key.inner(),
+            key_digest.into_iter(),
+        )
+    }
+
+    pub fn build_regular<R>(
+        self,
+        rng: &mut R,
+        recipient_encryption_key: &encryption::PublicKey,
+    ) -> NymsphinxPayload
+    where
+        R: RngCore + CryptoRng,
+    {
+        // create keys for 'payload' encryption
+        let (ephemeral_keypair, shared_key) = new_ephemeral_shared_key::<
+            PacketEncryptionAlgorithm,
+            PacketHkdfAlgorithm,
+            _,
+        >(rng, recipient_encryption_key);
+
+        self.build::<PacketEncryptionAlgorithm>(
+            &shared_key,
+            ephemeral_keypair.public_key().to_bytes(),
+        )
+    }
+}
+
+// the actual byte data that will be put into the sphinx packet paylaod.
+// no more transformations are going to happen to it
+// TODO: use that fact for some better compile time assertions
+pub struct NymsphinxPayload(Vec<u8>);
+
+impl AsRef<[u8]> for NymsphinxPayload {
+    fn as_ref(&self) -> &[u8] {
+        &self.0
+    }
+}
@@ -1,13 +1,22 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0

+use crate::message::{NymMessage, NymMessageError, PaddedMessage, PlainMessage};
+use crypto::aes::cipher::{KeyIvInit, StreamCipher};
 use crypto::asymmetric::encryption;
 use crypto::shared_key::recompute_shared_key;
 use crypto::symmetric::stream_cipher;
-use nymsphinx_anonymous_replies::reply_surb::{ReplySurb, ReplySurbError};
+use crypto::symmetric::stream_cipher::CipherKey;
+use nymsphinx_anonymous_replies::requests::AnonymousSenderTag;
+use nymsphinx_anonymous_replies::SurbEncryptionKey;
 use nymsphinx_chunking::fragment::Fragment;
 use nymsphinx_chunking::reconstruction::MessageReconstructor;
-use nymsphinx_params::{PacketEncryptionAlgorithm, PacketHkdfAlgorithm, DEFAULT_NUM_MIX_HOPS};
+use nymsphinx_chunking::ChunkingError;
+use nymsphinx_params::{
+    PacketEncryptionAlgorithm, PacketHkdfAlgorithm, ReplySurbEncryptionAlgorithm,
+    DEFAULT_NUM_MIX_HOPS,
+};
+use thiserror::Error;

 // TODO: should this live in this file?
 #[derive(Debug)]
@@ -15,31 +24,53 @@ pub struct ReconstructedMessage {
    /// The actual plaintext message that was received.
    pub message: Vec<u8>,

-    /// Optional ReplySURB to allow for an anonymous reply to the sender.
-    pub reply_surb: Option<ReplySurb>,
+    /// Optional ephemeral sender tag indicating pseudo-identity of the party who sent us the message
+    /// (alongside any reply SURBs)
+    pub sender_tag: Option<AnonymousSenderTag>,
 }

-#[derive(Debug)]
+impl From<ReconstructedMessage> for (Vec<u8>, Option<AnonymousSenderTag>) {
+    fn from(msg: ReconstructedMessage) -> Self {
+        (msg.message, msg.sender_tag)
+    }
+}
+
+impl ReconstructedMessage {
+    pub fn new(message: Vec<u8>, sender_tag: AnonymousSenderTag) -> Self {
+        Self {
+            message,
+            sender_tag: Some(sender_tag),
+        }
+    }
+
+    pub fn into_inner(self) -> (Vec<u8>, Option<AnonymousSenderTag>) {
+        self.into()
+    }
+}
+
+impl From<PlainMessage> for ReconstructedMessage {
+    fn from(message: PlainMessage) -> Self {
+        ReconstructedMessage {
+            message,
+            sender_tag: None,
+        }
+    }
+}
+
+#[derive(Debug, Error)]
 pub enum MessageRecoveryError {
-    InvalidSurbPrefixError,
-    MalformedSurbError(ReplySurbError),
-    InvalidRemoteEphemeralKey(encryption::KeyRecoveryError),
-    MalformedFragmentError,
-    InvalidMessagePaddingError,
-    MalformedReconstructedMessage(Vec<i32>),
-    TooShortMessageError,
-}
+    #[error("Recovered remote x25519 public key is invalid - {0}")]
+    InvalidRemoteEphemeralKey(#[from] encryption::KeyRecoveryError),

-impl From<ReplySurbError> for MessageRecoveryError {
-    fn from(err: ReplySurbError) -> Self {
-        MessageRecoveryError::MalformedSurbError(err)
-    }
-}
+    #[error("The reconstructed message was malformed - {source}")]
+    MalformedReconstructedMessage {
+        #[source]
+        source: NymMessageError,
+        used_sets: Vec<i32>,
+    },

-impl From<encryption::KeyRecoveryError> for MessageRecoveryError {
-    fn from(err: encryption::KeyRecoveryError) -> Self {
-        MessageRecoveryError::InvalidRemoteEphemeralKey(err)
-    }
+    #[error("Failed to recover message fragment - {0}")]
+    FragmentRecoveryError(#[from] ChunkingError),
 }

 pub struct MessageReceiver {
@@ -64,36 +95,34 @@ impl MessageReceiver {
        self
    }

-    /// Parses the message to strip and optionally recover reply SURB.
-    fn recover_reply_surb_from_message(
-        &self,
-        message: &mut Vec<u8>,
-    ) -> Result<Option<ReplySurb>, MessageRecoveryError> {
-        match message[0] {
-            n if n == false as u8 => {
-                message.remove(0);
-                Ok(None)
-            }
-            n if n == true as u8 => {
-                let surb_len: usize = ReplySurb::serialized_len(self.num_mix_hops);
-                // note the extra +1 (due to 0/1 message prefix)
-                let surb_bytes = &message[1..1 + surb_len];
-                let reply_surb = ReplySurb::from_bytes(surb_bytes)?;
+    fn decrypt_raw_message<C>(&self, message: &mut [u8], key: &CipherKey<C>)
+    where
+        C: StreamCipher + KeyIvInit,
+    {
+        let zero_iv = stream_cipher::zero_iv::<C>();
+        stream_cipher::decrypt_in_place::<C>(key, &zero_iv, message)
+    }

-                *message = message.drain(1 + surb_len..).collect();
-                Ok(Some(reply_surb))
-            }
-            _ => Err(MessageRecoveryError::InvalidSurbPrefixError),
-        }
+    /// Given raw fragment data, **WITH KEY DIGEST PREFIX ALREADY REMOVED!!**, uses looked up
+    /// key to decrypt fragment data
+    pub fn recover_plaintext_from_reply(
+        &self,
+        reply_ciphertext: &mut [u8],
+        reply_key: SurbEncryptionKey,
+    ) {
+        self.decrypt_raw_message::<ReplySurbEncryptionAlgorithm>(
+            reply_ciphertext,
+            reply_key.inner(),
+        )
    }

    /// Given raw fragment data, recovers the remote ephemeral key, recomputes shared secret,
    /// uses it to decrypt fragment data
-    pub fn recover_plaintext(
+    pub fn recover_plaintext_from_regular_packet<'a>(
        &self,
        local_key: &encryption::PrivateKey,
-        mut raw_enc_frag: Vec<u8>,
-    ) -> Result<Vec<u8>, MessageRecoveryError> {
+        raw_enc_frag: &'a mut [u8],
+    ) -> Result<&'a mut [u8], MessageRecoveryError> {
        // 1. recover remote encryption key
        let remote_key_bytes = &raw_enc_frag[..encryption::PUBLIC_KEY_SIZE];
        let remote_ephemeral_key = encryption::PublicKey::from_bytes(remote_key_bytes)?;
@@ -105,33 +134,17 @@ impl MessageReceiver {
        );

        // 3. decrypt fragment data
-        let fragment_bytes = &mut raw_enc_frag[encryption::PUBLIC_KEY_SIZE..];
+        let fragment_ciphertext = &mut raw_enc_frag[encryption::PUBLIC_KEY_SIZE..];

-        let zero_iv = stream_cipher::zero_iv::<PacketEncryptionAlgorithm>();
-        Ok(stream_cipher::decrypt::<PacketEncryptionAlgorithm>(
-            &encryption_key,
-            &zero_iv,
-            fragment_bytes,
-        ))
+        self.decrypt_raw_message::<PacketEncryptionAlgorithm>(fragment_ciphertext, &encryption_key);
+        let fragment_data = fragment_ciphertext;
+
+        Ok(fragment_data)
    }

    /// Given fragment data recovers [`Fragment`] itself.
    pub fn recover_fragment(&self, frag_data: &[u8]) -> Result<Fragment, MessageRecoveryError> {
-        Fragment::try_from_bytes(frag_data)
-            .map_err(|_| MessageRecoveryError::MalformedFragmentError)
-    }
-
-    /// Removes the zero padding from the message that was initially included to ensure same length
-    /// sphinx payloads.
-    pub fn remove_padding(message: &mut Vec<u8>) -> Result<(), MessageRecoveryError> {
-        // we are looking for first occurrence of 1 in the tail and we get its index
-        if let Some(i) = message.iter().rposition(|b| *b == 1) {
-            // and now we only take bytes until that point (but not including it)
-            *message = message.drain(..i).collect();
-            Ok(())
-        } else {
-            Err(MessageRecoveryError::InvalidMessagePaddingError)
-        }
+        Ok(Fragment::try_from_bytes(frag_data)?)
    }

    /// Inserts given [`Fragment`] into the reconstructor.
@@ -144,30 +157,15 @@ impl MessageReceiver {
    pub fn insert_new_fragment(
        &mut self,
        fragment: Fragment,
-    ) -> Result<Option<(ReconstructedMessage, Vec<i32>)>, MessageRecoveryError> {
-        if let Some((mut message, used_sets)) = self.reconstructor.insert_new_fragment(fragment) {
-            // Split message into plaintext and reply-SURB
-            let reply_surb = match self.recover_reply_surb_from_message(&mut message) {
-                Ok(reply_surb) => reply_surb,
-                Err(_) => {
-                    return Err(MessageRecoveryError::MalformedReconstructedMessage(
-                        used_sets,
-                    ));
-                }
-            };
-
-            // Finally, remove the zero padding from the message
-            Self::remove_padding(&mut message).map_err(|_| {
-                MessageRecoveryError::MalformedReconstructedMessage(used_sets.clone())
-            })?;
-
-            Ok(Some((
-                ReconstructedMessage {
-                    message,
-                    reply_surb,
-                },
-                used_sets,
-            )))
+    ) -> Result<Option<(NymMessage, Vec<i32>)>, MessageRecoveryError> {
+        if let Some((message, used_sets)) = self.reconstructor.insert_new_fragment(fragment) {
+            match PaddedMessage::new_reconstructed(message).remove_padding(self.num_mix_hops) {
+                Ok(message) => Ok(Some((message, used_sets))),
+                Err(err) => Err(MessageRecoveryError::MalformedReconstructedMessage {
+                    source: err,
+                    used_sets,
+                }),
+            }
        } else {
            Ok(None)
        }
@@ -188,16 +186,14 @@ mod message_receiver {
    use super::*;
    use crypto::asymmetric::identity;
    use mixnet_contract_common::Layer;
-    use nymsphinx_addressing::clients::Recipient;
-    use rand::rngs::OsRng;
    use std::collections::HashMap;
-    use std::time::Duration;
    use topology::{gateway, mix, NymTopology};

    // TODO: is it somehow maybe possible to move it to `topology` and have if conditionally
    // available to other modules?
    /// Returns a hardcoded, valid instance of [`NymTopology`] that is to be used in
    /// tests requiring instance of topology.
+    #[allow(dead_code)]
    fn topology_fixture() -> NymTopology {
        let mut mixes = HashMap::new();
        mixes.insert(
@@ -282,41 +278,4 @@ mod message_receiver {
            }],
        )
    }
-
-    #[test]
-    fn correctly_splits_message_into_plaintext_and_surb() {
-        let message_receiver: MessageReceiver = Default::default();
-
-        // the actual 'correctness' of the underlying message doesn't matter for this test
-        let message = vec![42; 100];
-        let dummy_recipient = Recipient::try_from_base58_string("CytBseW6yFXUMzz4SGAKdNLGR7q3sJLLYxyBGvutNEQV.4QXYyEVc5fUDjmmi8PrHN9tdUFV4PCvSJE1278cHyvoe@FioFa8nMmPpQnYi7JyojoTuwGLeyNS8BF4ChPr29zUML").unwrap();
-        let average_delay = Duration::from_millis(500);
-        let topology = topology_fixture();
-
-        let reply_surb =
-            ReplySurb::construct(&mut OsRng, &dummy_recipient, average_delay, &topology).unwrap();
-
-        let reply_surb_bytes = reply_surb.to_bytes();
-
-        // this is not exactly what is 'received' but rather after "some" processing, however,
-        // this is the expected argument to the function
-        let mut received_without_surb: Vec<_> =
-            std::iter::once(0).chain(message.iter().cloned()).collect();
-
-        let reply_surb = message_receiver
-            .recover_reply_surb_from_message(&mut received_without_surb)
-            .unwrap();
-        assert_eq!(received_without_surb, message);
-        assert!(reply_surb.is_none());
-
-        let mut received_with_surb: Vec<_> = std::iter::once(1)
-            .chain(reply_surb_bytes.iter().cloned())
-            .chain(message.iter().cloned())
-            .collect();
-        let reply_surb = message_receiver
-            .recover_reply_surb_from_message(&mut received_with_surb)
-            .unwrap();
-        assert_eq!(received_with_surb, message);
-        assert_eq!(reply_surb_bytes, reply_surb.unwrap().to_bytes());
-    }
 }
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
Tommy Verrall	691ccb1306	merge in latest release	2022-12-13 12:32:40 +01:00
Jędrzej Stuczyński	c7c6ff0389	Merge branch 'develop' into release/v1.2.0	2022-12-13 11:21:05 +00:00
Jędrzej Stuczyński	8622142c3d	Feature/prioritise surb retransmission (#1883 ) * Improved error messages + removed redundant variants * Improved estimation of 'expected_forward_delay' * Removed old wasm-specific startup code * Removed old unused reply-related code * hacky and temporary way of buffering retransmission data * offloading retransmission reply handling to ReplyController * fixed linter errors + rebuffering retransmission data on failure * Removed unused fields from wasm client debug config	2022-12-12 13:27:20 +00:00
Jędrzej Stuczyński	1b7c048c96	Reverted hard requirement for gateway protocol presence (#1875 )	2022-12-09 11:09:57 +00:00
Jędrzej Stuczyński	825791f2c7	Feature/multi surbs basic wasm interface (#1846 ) * Added builder to wasm client * missing wasm_bindgen macros * Added constructor macro on GatewayEndpointConfig * Attempting to use updated wasm client api * Removing dead code * Exposed other messages types in wasm client * cleanup in js-example * Changed 'self_address' to be a method call * Removed needless borrow when cloning an Arc * Improving arguments in 'on_message' callback * fixed wasm-client dependency/features	2022-12-08 17:10:42 +00:00
Jędrzej Stuczyński	83af0d4d76	Remove panic if ReconstructedMessagesReceiver is closed (#1868 ) Instead log error and return because presumably the shutdown procedure has started	2022-12-08 14:01:07 +00:00
Jędrzej Stuczyński	75b7b12c46	Saving reply key timestamp on data flush (#1867 )	2022-12-08 11:52:15 +00:00
Jędrzej Stuczyński	6286c6e2fd	Fixed clippy warning in test code	2022-12-08 09:55:36 +00:00
Jędrzej Stuczyński	68142e7535	logging created tag details	2022-12-07 15:06:34 +00:00
Jędrzej Stuczyński	2c4611044c	Feature/multi surbs invalidation (#1858 ) * Cleaned up RealMessagesController constructor * introduced config field for maximum_reply_surb_age * Handling edge-case reply-surb failures * invalidating old reply surbs * Removing old reply keys from cache * Invalidating old reply keys * missing config changes	2022-12-07 14:19:41 +00:00
Jędrzej Stuczyński	11fe5cfbf8	Marking dead test code	2022-12-06 14:15:29 +00:00
Jędrzej Stuczyński	793fac514a	Making native client wait for shutdown	2022-12-06 13:00:11 +00:00
Jędrzej Stuczyński	4578cda0ae	Feature/develop resync (#1844 ) * Network-requester: throttle inbound connections (#1789) * Return and handle ClientRequest::LaneQueueLenghts * Pass lane queue lengths to inbound future * Remove unused self reference * Request lane queue lengths periodically for all open connections * Add timeouts * Rename to ConnectionCommandSender and Receiver * Rename to client_connection_tx/rx * Fix wasm build * Replace bool with enum * rust: bump required version to 1.65 in some crates that need it * Add step to release GH actions (#1792) * feat: add a release step to nym contracts GH action * feat: add shrinking the size of wasm * Possibilty to change gateway ws listener (#1779) * add: set gatewayListener * Update types.ts * Update worker.ts * Update contracts-build.yml * real_traffic_stream: reduce frequency of status print (#1794) * Update wallet and connect lock files (#1793) * client-core: add warning when delay multiplier is larger than 1 * Fix decrypting stored received msg (#1786) * Fix decrypting stored received msg * rustfmt * Moving binary message recovery to separate function Co-authored-by: Jędrzej Stuczyński <jedrzej.stuczynski@gmail.com> * Feature/use expect instead of panicking (#1797) * Implementation of 'Debug' on 'RealMessage' * expect with failed channel name instead of throwing empty panics * Introduced Debug trait constraint in ProxyRunner * Derive Debug for socks5_requests::Message * Make connection_id optional in ClientRequest::Send (#1798) * changelog: add missing entry for fixing message decrypt in gateway-client * websocket-requests: fix length check before deserialize (#1799) * Fix export dkg contract addr (#1800) * Export dkg contract for mainnet when no config file present * Remove redundant env files * nym-cli: improve error reporting/handling and changed `vesting-schedule` queries to use query client instead of signing client * Feature/gateway client protocol version (#1795) * Introducing concept of gateway protocol version * Remove version-based gateway filtering * Fixed the unit test * grammar * Set build on latest release on schedule event * Added nightly build workflow on second latest release * socks5: if any task panics, signal all other tasks to shutdown (#1805) * socks5: signal shutdown on error * Mark as success * Tidy * Reduce wait to 5 sec * Replace unwrap with expect * Two more unwraps * Update changelog * client-core: less frequent status logging (#1806) * Feature/nym connect UI updates (#1784) * create custom titlebar * create help page * create generic modal component * create separate connection time component * link to shipyard docs * move timer to separate component and update connection status component usage * use separate component for copying ip and port details * only show infomodal once after connection * set service provider on tauri side * Emit events when stopped * listen and unlisten for tauri events * connect: add trace log to get_services * Add back CI notifications * Update README Co-authored-by: Jon Häggblad <jon.haggblad@gmail.com> Co-authored-by: Mark Sinclair <14054343+mmsinclair@users.noreply.github.com> * Use default serde value for upgrade (#1807) * fix ui overflow bug (#1808) * update nym connect error text (#1809) * set flag to false * Fix wait_for_signal_and_error on win (#1811) * Add socks5-client changes to nym-connect changelog * Fix links in nym-connect changelog * More entries in nym-connect CHANGELOG * Fix typo in changelog * Update CHANGELOG.md * Experiment/client refactoring (#1814) * experimenting with extracting more common client code * drying up the wasm client * allowing some dead code for the time being * fixed formatting in nym-connect * made socks5 client inside nym-connect immutable * made clippy a bit happier * hidden away target locking for recv timeout * New transactions for increasing amount of pledged tokens * unit tests * Added an option to pledge extra tokens through the vesting contract * Introduced wallet endpoints for new operations * Using updated pledge cap in the vesting contract * Bumping version numbers * Changelog for v1.1.1 * Bumping final version numbers for 1.1.1 * Bumping nym-cli version, missed it last time * socks5-client: SOCKS4a support (#1822) * socks5-client: SOCKS4a support * Tidy * Fix a few errors in socks5 client and network-requester (#1823) * Fix two unwraps in socks5 and network-requester * Make sure client task never sends shutdown signal * Fix panic on getting socks version * wip * connecting to the back and making the requests work * display details modal * logs removal * Feature/pledge more (#1679) * New transactions for increasing amount of pledged tokens * unit tests * Added an option to pledge extra tokens through the vesting contract * Introduced wallet endpoints for new operations * Using updated pledge cap in the vesting contract * Changelog update * nym-connect: update lock file * avoid mix tokens pools * amount error * envs/mainnet: update to latest mixnet contract and nymd validator url * validator-api: add missing shortform for --config-env-file (#1830) * gateway-client: handle shutdown listener (#1829) * WIP * WIP: try another approach * WIP * Reworked * Tidy * fix * validator-api: remove storage dependency in contract cache (#1685) * validator-api: remove storage dependency in contract cache * validator-client: update detailed routes * contract_cache: forward to new endpoints for compat * Move reward_estimate * client: add --no-cover and update --fastmode (#1831) * adding a oversaturaded bonding more modal * common/task: extract out spawn_with_report_error (#1837) * stop panic on failed buffer request * Compilable wasm client * Enabled hard error on lack of gateway-client protocol version * Missing generic parameter for ClientCoreError in BackendError * Removed unused imports * Additional wasm feature locking Co-authored-by: Jon Häggblad <jon.haggblad@gmail.com> Co-authored-by: Fran Arbanas <arbanasfran@gmail.com> Co-authored-by: cgi-bin/ <6095048+sven-hash@users.noreply.github.com> Co-authored-by: Mark Sinclair <14054343+mmsinclair@users.noreply.github.com> Co-authored-by: Bogdan-Ștefan Neacşu <bogdan@nymtech.net> Co-authored-by: Mark Sinclair <mmsinclair@users.noreply.github.com> Co-authored-by: Raphaël Walther <raphael@nymtech.net> Co-authored-by: Fouad <fmtabbara@hotmail.co.uk> Co-authored-by: Gala <calero.vg@gmail.com> Co-authored-by: Dave Hrycyszyn <futurechimp@users.noreply.github.com>	2022-12-05 18:27:44 +00:00
Tommy Verrall	2f726d73ca	merge in binary changes	2022-12-05 15:55:53 +01:00
Jędrzej Stuczyński	758ba5593c	Feature/persistent surbs data (#1835 ) * prototyping wip * Implemented ReplyStorageBackend trait for the sql-backed storage * Storing correct surb threshold * using correct database path * Starting surb persistent storage in native and socks5 clients * loading or creating fresh surb storage in socks5 and native clients * making clippy happier + fixing config templates * Creating status table on database rotation * Completed the 'Empty' ReplyStorageBackend * feature locking wasm-incompatible bits and pieces	2022-12-05 14:38:30 +00:00
Bogdan-Ștefan Neacșu	dca3217a0e	Use one command instead of two	2022-12-05 16:32:39 +02:00
Bogdan-Ștefan Neacșu	27e35f6931	Expose name of standard directories	2022-12-05 16:32:39 +02:00
Tommy Verrall	a74c3885bb	merge	2022-12-02 10:47:22 +01:00
Tommy Verrall	cf1cf06feb	coconut qa-testing - after setting the features to coconut in the socks5 config - we then set enabled credentials - after configuration is tinkered, we still need to buy bandwidth - POC	2022-12-01 19:46:56 +01:00
Jędrzej Stuczyński	0cc67b1c77	Defined socks5 client startup flag to enable reply-surb communication (#1804 )	2022-11-25 16:52:31 +00:00
Jędrzej Stuczyński	ee80e7faaf	Using Display implementation of MessageRecoveryError when logging (#1803 ) * Using Display implementation of MessageRecoveryError when logging * Updated changelog	2022-11-25 16:17:12 +00:00
Jędrzej Stuczyński	e695813d24	Making anonymous sender tag human readable (#1801 ) * Created wrapper with string serialization for AnonymousSenderTag * Using Display implementation of AnonymousSenderTag for logs	2022-11-25 15:38:24 +00:00
Jędrzej Stuczyński	a5c6b31384	Missing changelog entry for multi-surbs (#1802 )	2022-11-25 15:27:16 +00:00
Jędrzej Stuczyński	4cbfa9c0fa	Feature/multi surbs (#1796 ) * bunch of wip with focus on serialization * Being able to send normal data (NO SURBS yet) to yourself again * Fixed RepliableMessage deserialization * Recovering data from surb messages * Extracted common code in sphinx payload construction * Cleanup within received buffer * requesting, sending and using additional reply surbs * Following discussion with @simonwicky, removing sender proof and decreasing size of sender tag * Made sender tag more easily configurable * Refactoring of message creation * Propagating reply surb acks but not retransmitting them yet * Surb retransmissions * requesting additional surbs from the retransmission flow * correctly determining the point of requesting additional surbs * Ability to use socks5 (and network requester) with surbs * Improved surbs retranmsission reliability * naive way of not over-requesting surbs * wip on tag storage * Improved error propagation for message construction * Requesting more surbs for stale entries * Better controlling the point of having to request additional surbs * Using pseudorandom sender tag instead of a hardcoded one * First cleanup round in MessageHandler * Error cleanup and if simplification * Assigned a more permanent name to the ReplyController * Removed PendingReply redundant type * Made socks5 client less eager to over-send reply surbs * 'anonymous' field on socks5 client to decide whether to use surbs or attach address * Dead code and import removal in client-core * Updating ClientRequest variants * Adjusted decision threshold for requesting more surbs * Native client cleanup * Made socks5 client usage of surbs configurable * Restored statistics in network requester * Validator-api compiles once again * Further improved surb request logic * boxing the recipient in controller requests * Removal of hardcoded values in favour of propagating them from the config * more validation during surb requests * Fixed ClientRequest::Send deserialization * Added length checks for request deserialization * post-merge formatting * Unit tests once again compile and pass * controlling retransmission_reply_surb_request_size from config * More Recipient boxing action * Requesting additional reply surbs for retransmission BEFORE dipping below the threshold * Making clippy generally happier * Wasm client compiles (but might not yet work correctly) * Feature/use expect instead of panicking (#1797) * Implementation of 'Debug' on 'RealMessage' * expect with failed channel name instead of throwing empty panics * Introduced Debug trait constraint in ProxyRunner * Derive Debug for socks5_requests::Message * Fix decrypting stored received msg (#1786) * Fix decrypting stored received msg * rustfmt * Moving binary message recovery to separate function Co-authored-by: Jędrzej Stuczyński <jedrzej.stuczynski@gmail.com> * real_traffic_stream: reduce frequency of status print (#1794) * Properly defined unnamed errors * Dealing with previously ignored errors * logging improvements * Removed old example code Co-authored-by: Jon Häggblad <jon.haggblad@gmail.com>	2022-11-25 14:16:01 +00:00