From 95bec7422ca2f27b7db10de46007bfc4911cad7d Mon Sep 17 00:00:00 2001
From: Simon Wicky <simon@nymtech.net>
Date: Fri, 15 May 2026 12:47:07 +0200
Subject: [PATCH] tweaks and checked arithmetic

---
 common/nym-lp-data/src/clients/traits.rs | 15 ++++++++++++---
 common/nym-lp-data/src/common/traits.rs  | 12 ++++++++++--
 common/nym-lp-data/src/lib.rs            |  2 ++
 nym-mix-sim/README.md                    |  6 +++---
 nym-mix-sim/src/topology/directory.rs    |  2 +-
 5 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/common/nym-lp-data/src/clients/traits.rs b/common/nym-lp-data/src/clients/traits.rs
index 3dea3aad5e..d7cd22499d 100644
--- a/common/nym-lp-data/src/clients/traits.rs
+++ b/common/nym-lp-data/src/clients/traits.rs
@@ -145,12 +145,21 @@ where
         let mut chunk_size = self.frame_size();
 
         if input_options.routing_security() {
-            chunk_size =
-                chunk_size * self.nb_frames() - <Self as RoutingSecurity<_, _, _>>::OVERHEAD_SIZE;
+            // SAFETY : While this CAN technically fail, it means that something is wrong in the code and it's pointless to continue anyway
+            #[allow(clippy::expect_used)]
+            let pre_security_chunk_size = (chunk_size * self.nb_frames())
+                .checked_sub(<Self as RoutingSecurity<_, _, _>>::OVERHEAD_SIZE)
+                .expect("not enough room in a packet for routing security overhead");
+            chunk_size = pre_security_chunk_size;
         }
 
         if input_options.reliability() {
-            chunk_size -= <Self as Reliability<_, _, _>>::OVERHEAD_SIZE;
+            // SAFETY : While this CAN technically fail, it means that something is wrong in the code and it's pointless to continue anyway
+            #[allow(clippy::expect_used)]
+            let pre_reliability_chunk_size = chunk_size
+                .checked_sub(<Self as Reliability<_, _, _>>::OVERHEAD_SIZE)
+                .expect("not enough room in a packet for reliability overhead");
+            chunk_size = pre_reliability_chunk_size;
         }
 
         chunk_size
diff --git a/common/nym-lp-data/src/common/traits.rs b/common/nym-lp-data/src/common/traits.rs
index bbe9e6db90..66b9102d3a 100644
--- a/common/nym-lp-data/src/common/traits.rs
+++ b/common/nym-lp-data/src/common/traits.rs
@@ -121,12 +121,20 @@ where
     Ts: Clone,
     NdId: Clone,
 {
+    // IMPORTANT NOTE : This fn can be not constant to allow e.g. flexible MTU
+    // However, every possible value must be able to accomodate the different overhead.
+    // If it doesn't, the pipeline becomes unusable
     fn packet_size(&self) -> usize;
 
     fn frame_size(&self) -> usize {
+        // SAFETY : While this CAN technically fail, it means that something is wrong in the code and it's pointless to continue anyway
+        #[allow(clippy::expect_used)]
         self.packet_size()
-            - <Self as Transport<Ts, Pkt, NdId>>::OVERHEAD_SIZE
-            - <Self as Framing<Ts, Opts, NdId>>::OVERHEAD_SIZE
+            .checked_sub(
+                <Self as Transport<Ts, Pkt, NdId>>::OVERHEAD_SIZE
+                    + <Self as Framing<Ts, Opts, NdId>>::OVERHEAD_SIZE,
+            )
+            .expect("packet_size smaller than transport + framing overhead")
     }
 
     fn wire_wrap(
diff --git a/common/nym-lp-data/src/lib.rs b/common/nym-lp-data/src/lib.rs
index 3fc0791ded..3ea6a1918a 100644
--- a/common/nym-lp-data/src/lib.rs
+++ b/common/nym-lp-data/src/lib.rs
@@ -38,6 +38,7 @@ pub type PipelinePayload<Ts, Opts, NdId> = PipelineData<Ts, Vec<u8>, Opts, NdId>
 /// pipeline.  It is produced by [`clients::traits::Chunking`] and propagated
 /// unchanged (or with the timestamp transformed) through every subsequent
 /// pipeline stage until the packet is sent on the wire.
+#[derive(Clone)]
 pub struct TimedData<Ts, D> {
     pub timestamp: Ts,
     pub data: D,
@@ -108,6 +109,7 @@ impl<Ts, D> TimedData<Ts, D> {
 /// [`Framing`]: crate::common::traits::Framing
 /// [`Transport`]: crate::common::traits::Transport
 /// [`InputOptions`]: crate::clients::InputOptions
+#[derive(Clone)]
 pub struct PipelineData<Ts, D, Opts, NdId> {
     pub data: TimedData<Ts, D>,
     pub options: Opts,
diff --git a/nym-mix-sim/README.md b/nym-mix-sim/README.md
index c35b38ee6e..cd55f4fb96 100644
--- a/nym-mix-sim/README.md
+++ b/nym-mix-sim/README.md
@@ -33,7 +33,7 @@ cargo run --bin mix-client -- --src 6 --dst 7
 
 Generates a `topology.json` file describing nodes and clients.
 
-```
+```bash
 cargo run --bin nym-mix-sim -- init-topology [OPTIONS]
 ```
 
@@ -49,7 +49,7 @@ Nodes are assigned sequential ports starting at `127.0.0.1:9000`. Clients get tw
 
 Starts the simulation loop.
 
-```
+```bash
 cargo run --bin nym-mix-sim -- run [OPTIONS]
 ```
 
@@ -65,7 +65,7 @@ cargo run --bin nym-mix-sim -- run [OPTIONS]
 
 Injects messages into a running simulation from stdin.
 
-```
+```bash
 cargo run --bin mix-client -- --src <ID> --dst <ID> [--topology <PATH>]
 ```
 
diff --git a/nym-mix-sim/src/topology/directory.rs b/nym-mix-sim/src/topology/directory.rs
index 9eb3b4eefb..69dccd7839 100644
--- a/nym-mix-sim/src/topology/directory.rs
+++ b/nym-mix-sim/src/topology/directory.rs
@@ -48,7 +48,7 @@ impl Directory {
     /// Look up a client by its [`ClientId`].
     ///
     /// Returns `None` when `id` is not present in the directory
-    pub fn client(&self, id: NodeId) -> Option<&SocketAddr> {
+    pub fn client(&self, id: ClientId) -> Option<&SocketAddr> {
         self.clients.get(&id)
     }