From e32783bced33abfad03561477260be5cef91c684 Mon Sep 17 00:00:00 2001
From: mfahampshire <maxhampshire@pm.me>
Date: Fri, 30 Jan 2026 15:39:16 +0000
Subject: [PATCH] Remove serde requirement for MixPacket

---
 .../src/client/inbound_messages.rs            | 10 +++---
 .../input_message_listener.rs                 | 28 ++++++++++++---
 common/nymsphinx/forwarding/src/packet.rs     | 34 -------------------
 3 files changed, 30 insertions(+), 42 deletions(-)

diff --git a/common/client-core/src/client/inbound_messages.rs b/common/client-core/src/client/inbound_messages.rs
index f01ba54749..7e81ea6570 100644
--- a/common/client-core/src/client/inbound_messages.rs
+++ b/common/client-core/src/client/inbound_messages.rs
@@ -5,7 +5,6 @@ use crate::make_bincode_serializer;
 use bincode::Options;
 use nym_sphinx::addressing::clients::Recipient;
 use nym_sphinx::anonymous_replies::requests::AnonymousSenderTag;
-use nym_sphinx::forwarding::packet::MixPacket;
 use nym_sphinx::params::PacketType;
 use nym_task::connections::TransmissionLane;
 use serde::{Deserialize, Serialize};
@@ -26,8 +25,11 @@ pub enum InputMessage {
     /// Fire an already prepared mix packets into the network.
     /// No guarantees are made about it. For example no retransmssion
     /// will be attempted if it gets dropped.
+    ///
+    /// Packets are stored as pre-serialized bytes, which avoids
+    /// requiring Serde on MixPacket.
     Premade {
-        msgs: Vec<MixPacket>,
+        packet_bytes: Vec<Vec<u8>>,
         lane: TransmissionLane,
     },
 
@@ -81,11 +83,11 @@ impl InputMessage {
     }
 
     pub fn new_premade(
-        msgs: Vec<MixPacket>,
+        packet_bytes: Vec<Vec<u8>>,
         lane: TransmissionLane,
         packet_type: PacketType,
     ) -> Self {
-        let message = InputMessage::Premade { msgs, lane };
+        let message = InputMessage::Premade { packet_bytes, lane };
         if packet_type == PacketType::Mix {
             message
         } else {
diff --git a/common/client-core/src/client/real_messages_control/acknowledgement_control/input_message_listener.rs b/common/client-core/src/client/real_messages_control/acknowledgement_control/input_message_listener.rs
index 69ca92709f..90ced22a6d 100644
--- a/common/client-core/src/client/real_messages_control/acknowledgement_control/input_message_listener.rs
+++ b/common/client-core/src/client/real_messages_control/acknowledgement_control/input_message_listener.rs
@@ -45,7 +45,25 @@ where
         }
     }
 
-    async fn handle_premade_packets(&mut self, packets: Vec<MixPacket>, lane: TransmissionLane) {
+    async fn handle_premade_packets(&mut self, packet_bytes: Vec<Vec<u8>>, lane: TransmissionLane) {
+        // Deserialize packet bytes back to MixPacket
+        let packets: Vec<MixPacket> = packet_bytes
+            .into_iter()
+            .filter_map(|bytes| {
+                MixPacket::try_from_v2_bytes(&bytes)
+                    .map_err(|e| {
+                        warn!("Failed to deserialize premade packet: {}", e);
+                        e
+                    })
+                    .ok()
+            })
+            .collect();
+
+        if packets.is_empty() {
+            warn!("No valid premade packets to send");
+            return;
+        }
+
         self.message_handler
             .send_premade_mix_packets(
                 packets
@@ -156,7 +174,9 @@ where
                 self.handle_reply(recipient_tag, data, lane, max_retransmissions)
                     .await;
             }
-            InputMessage::Premade { msgs, lane } => self.handle_premade_packets(msgs, lane).await,
+            InputMessage::Premade { packet_bytes, lane } => {
+                self.handle_premade_packets(packet_bytes, lane).await
+            }
             InputMessage::MessageWrapper {
                 message,
                 packet_type,
@@ -202,8 +222,8 @@ where
                     self.handle_reply(recipient_tag, data, lane, max_retransmissions)
                         .await;
                 }
-                InputMessage::Premade { msgs, lane } => {
-                    self.handle_premade_packets(msgs, lane).await
+                InputMessage::Premade { packet_bytes, lane } => {
+                    self.handle_premade_packets(packet_bytes, lane).await
                 }
                 // MessageWrappers can't be nested
                 InputMessage::MessageWrapper { .. } => {
diff --git a/common/nymsphinx/forwarding/src/packet.rs b/common/nymsphinx/forwarding/src/packet.rs
index 32b8c893ee..907d2c1cde 100644
--- a/common/nymsphinx/forwarding/src/packet.rs
+++ b/common/nymsphinx/forwarding/src/packet.rs
@@ -4,11 +4,6 @@
 use nym_sphinx_addressing::nodes::{NymNodeRoutingAddress, NymNodeRoutingAddressError};
 use nym_sphinx_params::{PacketSize, PacketType, SphinxKeyRotation};
 use nym_sphinx_types::{NymPacket, NymPacketError};
-use serde::{
-    Deserialize, Deserializer, Serialize, Serializer,
-    de::{self, Visitor},
-};
-use std::fmt;
 
 use nym_sphinx_anonymous_replies::reply_surb::AppliedReplySurb;
 use nym_sphinx_params::key_rotation::InvalidSphinxKeyRotation;
@@ -187,32 +182,3 @@ impl MixPacket {
             .collect())
     }
 }
-
-// MAX TODO implement for v1 as well for back compat? - this was added in the original asyncread/write work when we only had one v
-impl Serialize for MixPacket {
-    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
-        serializer.serialize_bytes(&self.to_v2_bytes().map_err(serde::ser::Error::custom)?)
-    }
-}
-
-struct MixPacketVisitor;
-
-impl<'de> Visitor<'de> for MixPacketVisitor {
-    type Value = MixPacket;
-
-    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        formatter.write_str("a byte array representing a mix packet")
-    }
-
-    fn visit_bytes<E: de::Error>(self, v: &[u8]) -> Result<Self::Value, E> {
-        MixPacket::try_from_v2_bytes(v).map_err(serde::de::Error::custom)
-    }
-}
-
-impl<'de> Deserialize<'de> for MixPacket {
-    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
-        deserializer.deserialize_bytes(MixPacketVisitor)
-    }
-}
-
-// TODO: test for serialization and errors!