From f6008c173c358f87bc814d9cac25fcc5aa1b5208 Mon Sep 17 00:00:00 2001
From: Jonas Platte <jplatte+git@posteo.de>
Date: Sat, 26 Apr 2025 23:21:15 +0200
Subject: [PATCH] serve: Extract prep_serve_connection out of handle_connection

---
 axum/CHANGELOG.md     |  4 ++++
 axum/src/serve/mod.rs | 38 +++++++++++++++++++++++++-------------
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/axum/CHANGELOG.md b/axum/CHANGELOG.md
index 9d4f5d78..7d653677 100644
--- a/axum/CHANGELOG.md
+++ b/axum/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
+- **breaking:** `serve` now requires the listener IO type to be `Sync`
+
+# Unreleased
+
 - **added:** `Router::reset_fallback` ([#3320])
 
 [#3320]: https://github.com/tokio-rs/axum/pull/3320
diff --git a/axum/src/serve/mod.rs b/axum/src/serve/mod.rs
index ca6c39af..ec7ab49a 100644
--- a/axum/src/serve/mod.rs
+++ b/axum/src/serve/mod.rs
@@ -222,6 +222,7 @@ impl<L, M, S> IntoFuture for Serve<L, M, S>
 where
     L: Listener,
     L::Addr: Debug,
+    L::Io: Sync,
     M: for<'a> Service<IncomingStream<'a, L>, Error = Infallible, Response = S> + Send + 'static,
     for<'a> <M as Service<IncomingStream<'a, L>>>::Future: Send,
     S: Service<Request, Response = Response, Error = Infallible> + Clone + Send + 'static,
@@ -336,6 +337,7 @@ impl<L, M, S, F> IntoFuture for WithGracefulShutdown<L, M, S, F>
 where
     L: Listener,
     L::Addr: Debug,
+    L::Io: Sync,
     M: for<'a> Service<IncomingStream<'a, L>, Error = Infallible, Response = S> + Send + 'static,
     for<'a> <M as Service<IncomingStream<'a, L>>>::Future: Send,
     S: Service<Request, Response = Response, Error = Infallible> + Clone + Send + 'static,
@@ -366,6 +368,26 @@ async fn handle_connection<L, M, S>(
 {
     let io = TokioIo::new(io);
 
+    let conn_service = prep_serve_connection(make_service, remote_addr, &io).await;
+    tokio::spawn(serve_connection(
+        io,
+        conn_service,
+        signal_tx.clone(),
+        close_rx.clone(),
+    ));
+}
+
+async fn prep_serve_connection<L, M, S>(
+    make_service: &mut M,
+    remote_addr: <L as Listener>::Addr,
+    io: &TokioIo<<L as Listener>::Io>,
+) -> S
+where
+    L: Listener,
+    L::Addr: Debug,
+    M: for<'a> Service<IncomingStream<'a, L>, Error = Infallible, Response = S> + Send + 'static,
+    for<'a> <M as Service<IncomingStream<'a, L>>>::Future: Send,
+{
     trace!("connection {remote_addr:?} accepted");
 
     make_service
@@ -373,20 +395,10 @@ async fn handle_connection<L, M, S>(
         .await
         .unwrap_or_else(|err| match err {});
 
-    let conn_service = make_service
-        .call(IncomingStream {
-            io: &io,
-            remote_addr,
-        })
+    make_service
+        .call(IncomingStream { io, remote_addr })
         .await
-        .unwrap_or_else(|err| match err {});
-
-    tokio::spawn(serve_connection(
-        io,
-        conn_service,
-        signal_tx.clone(),
-        close_rx.clone(),
-    ));
+        .unwrap_or_else(|err| match err {})
 }
 
 async fn serve_connection<I, S>(