Guarantee return value of serve, Pt. 2

axum/src/serve/mod.rs

@@ -80,6 +80,12 @@ pub use self::listener::{Listener, ListenerExt, TapIo};
 /// See also [`HandlerWithoutStateExt::into_make_service_with_connect_info`] and
 /// [`HandlerService::into_make_service_with_connect_info`].
 ///
+/// # Return Value
+///
+/// Although this future resolves to `io::Result<()>`, it will never actually complete or return an
+/// error. Errors on the TCP socket will be handled by sleeping for a short while (currently, one
+/// second).
+///
 /// [`Router`]: crate::Router
 /// [`Router::into_make_service_with_connect_info`]: crate::Router::into_make_service_with_connect_info
 /// [`MethodRouter`]: crate::routing::MethodRouter
@@ -137,6 +143,11 @@ where
     ///     // ...
     /// }
     /// ```
+    ///
+    /// # Return Value
+    ///
+    /// Similarly to [`serve`], although this future resolves to `io::Result<()>`, it will never
+    /// error. It returns `Ok(())` only after the `signal` future completes.
     pub fn with_graceful_shutdown<F>(self, signal: F) -> WithGracefulShutdown<L, M, S, F>
     where
         F: Future<Output = ()> + Send + 'static,
@@ -255,98 +266,113 @@ where
     type IntoFuture = private::ServeFuture;
 
     fn into_future(self) -> Self::IntoFuture {
+        private::ServeFuture(Box::pin(async move {
+            self.run().await;
+            Ok(())
+        }))
+    }
+}
+
+#[cfg(all(feature = "tokio", any(feature = "http1", feature = "http2")))]
+impl<L, M, S, F> WithGracefulShutdown<L, M, S, F>
+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,
+    S: Service<Request, Response = Response, Error = Infallible> + Clone + Send + 'static,
+    S::Future: Send,
+    F: Future<Output = ()> + Send + 'static,
+{
+    async fn run(self) {
         let Self {
             mut listener,
             mut make_service,
             signal,
             _marker: _,
         } = self;
 
-        private::ServeFuture(Box::pin(async move {
-            let (signal_tx, signal_rx) = watch::channel(());
-            let signal_tx = Arc::new(signal_tx);
-            tokio::spawn(async move {
-                signal.await;
-                trace!("received graceful shutdown signal. Telling tasks to shutdown");
-                drop(signal_rx);
-            });
+        let (signal_tx, signal_rx) = watch::channel(());
+        let signal_tx = Arc::new(signal_tx);
+        tokio::spawn(async move {
+            signal.await;
+            trace!("received graceful shutdown signal. Telling tasks to shutdown");
+            drop(signal_rx);
+        });
+
+        let (close_tx, close_rx) = watch::channel(());
+
+        loop {
+            let (io, remote_addr) = tokio::select! {
+                conn = listener.accept() => conn,
+                _ = signal_tx.closed() => {
+                    trace!("signal received, not accepting new connections");
+                    break;
+                }
+            };
 
-            let (close_tx, close_rx) = watch::channel(());
+            let io = TokioIo::new(io);
 
-            loop {
-                let (io, remote_addr) = tokio::select! {
-                    conn = listener.accept() => conn,
-                    _ = signal_tx.closed() => {
-                        trace!("signal received, not accepting new connections");
-                        break;
-                    }
-                };
-
-                let io = TokioIo::new(io);
-
-                trace!("connection {remote_addr:?} accepted");
-
-                poll_fn(|cx| make_service.poll_ready(cx))
-                    .await
-                    .unwrap_or_else(|err| match err {});
-
-                let tower_service = make_service
-                    .call(IncomingStream {
-                        io: &io,
-                        remote_addr,
-                    })
-                    .await
-                    .unwrap_or_else(|err| match err {})
-                    .map_request(|req: Request<Incoming>| req.map(Body::new));
-
-                let hyper_service = TowerToHyperService::new(tower_service);
-
-                let signal_tx = Arc::clone(&signal_tx);
-
-                let close_rx = close_rx.clone();
-
-                tokio::spawn(async move {
-                    #[allow(unused_mut)]
-                    let mut builder = Builder::new(TokioExecutor::new());
-                    // CONNECT protocol needed for HTTP/2 websockets
-                    #[cfg(feature = "http2")]
-                    builder.http2().enable_connect_protocol();
-                    let conn = builder.serve_connection_with_upgrades(io, hyper_service);
-                    pin_mut!(conn);
-
-                    let signal_closed = signal_tx.closed().fuse();
-                    pin_mut!(signal_closed);
-
-                    loop {
-                        tokio::select! {
-                            result = conn.as_mut() => {
-                                if let Err(_err) = result {
-                                    trace!("failed to serve connection: {_err:#}");
-                                }
-                                break;
-                            }
-                            _ = &mut signal_closed => {
-                                trace!("signal received in task, starting graceful shutdown");
-                                conn.as_mut().graceful_shutdown();
+            trace!("connection {remote_addr:?} accepted");
+
+            poll_fn(|cx| make_service.poll_ready(cx))
+                .await
+                .unwrap_or_else(|err| match err {});
+
+            let tower_service = make_service
+                .call(IncomingStream {
+                    io: &io,
+                    remote_addr,
+                })
+                .await
+                .unwrap_or_else(|err| match err {})
+                .map_request(|req: Request<Incoming>| req.map(Body::new));
+
+            let hyper_service = TowerToHyperService::new(tower_service);
+
+            let signal_tx = Arc::clone(&signal_tx);
+
+            let close_rx = close_rx.clone();
+
+            tokio::spawn(async move {
+                #[allow(unused_mut)]
+                let mut builder = Builder::new(TokioExecutor::new());
+                // CONNECT protocol needed for HTTP/2 websockets
+                #[cfg(feature = "http2")]
+                builder.http2().enable_connect_protocol();
+                let conn = builder.serve_connection_with_upgrades(io, hyper_service);
+                pin_mut!(conn);
+
+                let signal_closed = signal_tx.closed().fuse();
+                pin_mut!(signal_closed);
+
+                loop {
+                    tokio::select! {
+                        result = conn.as_mut() => {
+                            if let Err(_err) = result {
+                                trace!("failed to serve connection: {_err:#}");
                             }
+                            break;
+                        }
+                        _ = &mut signal_closed => {
+                            trace!("signal received in task, starting graceful shutdown");
+                            conn.as_mut().graceful_shutdown();
                         }
                     }
+                }
 
-                    drop(close_rx);
-                });
-            }
-
-            drop(close_rx);
-            drop(listener);
+                drop(close_rx);
+            });
+        }
 
-            trace!(
-                "waiting for {} task(s) to finish",
-                close_tx.receiver_count()
-            );
-            close_tx.closed().await;
+        drop(close_rx);
+        drop(listener);
 
-            Ok(())
-        }))
+        trace!(
+            "waiting for {} task(s) to finish",
+            close_tx.receiver_count()
+        );
+        close_tx.closed().await;
     }
 }