From 4aac7d35b69a5d0906a6f2acd5d1d0beb52dcbb8 Mon Sep 17 00:00:00 2001
From: Chris O'Neil <chriso83@protonmail.com>
Date: Mon, 11 May 2026 22:57:41 +0100
Subject: [PATCH] perf(chunk): hold ChunkPutRequest content as Bytes for
 zero-copy fan-out
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Replace `content: Vec<u8>` with `content: bytes::Bytes` on
ChunkPutRequest. Wire format is unchanged — Bytes serialises as a byte
sequence under postcard/serde, identical to Vec<u8> — but the in-memory
representation is now refcounted, so callers that send the same chunk
to multiple peers (notably close-group replication) share a single
backing buffer instead of deep-copying the 4 MB payload per peer.

Heaptrack against a 20 MB upload on a release ant binary showed the
client's peak heap dominated by RawVecInner::finish_grow calls in
ChunkPutRequest construction, with 168 MB consumed via
ChunkMessage::encode → chunk_put_to_close_group. The fan-out path was
running `content.to_vec()` once per recipient at chunk.rs:173, which
the new Bytes-typed field eliminates from the caller side.

This commit is the protocol-side half of the fix; the ant-client side
drops the `to_vec()` in a follow-up PR.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 Cargo.toml   |  2 +-
 src/chunk.rs | 17 ++++++++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 510e822..3390d67 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -37,7 +37,7 @@ postcard = { version = "1.1.3", features = ["use-std"] }
 rmp-serde = "1"
 
 # Byte utilities
-bytes = "1"
+bytes = { version = "1", features = ["serde"] }
 hex = "0.4"
 
 # Logging (optional — behind `logging` feature flag, mirroring ant-node)
diff --git a/src/chunk.rs b/src/chunk.rs
index d2d838d..351b574 100644
--- a/src/chunk.rs
+++ b/src/chunk.rs
@@ -6,6 +6,7 @@
 //! This module defines the wire protocol messages for chunk operations
 //! using postcard serialization for compact, fast encoding.
 
+use bytes::Bytes;
 use serde::{Deserialize, Serialize};
 
 /// Protocol identifier for chunk operations.
@@ -121,12 +122,18 @@ impl ChunkMessage {
 // =============================================================================
 
 /// Request to store a chunk.
+///
+/// `content` is held as `bytes::Bytes` so that callers fanning the same
+/// chunk out to multiple recipients (e.g. close-group replication) share a
+/// single backing buffer via refcount instead of deep-copying the 4 MB
+/// payload per peer. Wire format is unchanged: `Bytes` serializes as a
+/// byte sequence, identical to `Vec<u8>` under postcard/serde.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ChunkPutRequest {
     /// The content-addressed identifier (BLAKE3 of content).
     pub address: XorName,
     /// The chunk data.
-    pub content: Vec<u8>,
+    pub content: Bytes,
     /// Optional payment proof (serialized `ProofOfPayment`).
     /// Required for new chunks unless already verified.
     pub payment_proof: Option<Vec<u8>>,
@@ -135,7 +142,7 @@ pub struct ChunkPutRequest {
 impl ChunkPutRequest {
     /// Create a new PUT request.
     #[must_use]
-    pub fn new(address: XorName, content: Vec<u8>) -> Self {
+    pub fn new(address: XorName, content: Bytes) -> Self {
         Self {
             address,
             content,
@@ -145,7 +152,7 @@ impl ChunkPutRequest {
 
     /// Create a new PUT request with payment proof.
     #[must_use]
-    pub fn with_payment(address: XorName, content: Vec<u8>, payment_proof: Vec<u8>) -> Self {
+    pub fn with_payment(address: XorName, content: Bytes, payment_proof: Vec<u8>) -> Self {
         Self {
             address,
             content,
@@ -386,7 +393,7 @@ mod tests {
     #[test]
     fn test_put_request_encode_decode() {
         let address = [0xAB; 32];
-        let content = vec![1, 2, 3, 4, 5];
+        let content = Bytes::from_static(&[1, 2, 3, 4, 5]);
         let request = ChunkPutRequest::new(address, content.clone());
         let msg = ChunkMessage {
             request_id: 42,
@@ -409,7 +416,7 @@ mod tests {
     #[test]
     fn test_put_request_with_payment() {
         let address = [0xAB; 32];
-        let content = vec![1, 2, 3, 4, 5];
+        let content = Bytes::from_static(&[1, 2, 3, 4, 5]);
         let payment = vec![10, 20, 30];
         let request = ChunkPutRequest::with_payment(address, content.clone(), payment.clone());