chore: add test

actix-web/CHANGES.md

@@ -2,7 +2,7 @@
 
 ## Unreleased
 
-- Enable dual-stack IPv6 sockets on Windows so that binding to `[::]` also accepts IPv4 connections.
+- Enable dual-stack IPv6 sockets on Windows when possible so that Actix-created listeners bound to `[::]` also accept IPv4 connections.
 - Panic when calling `Route::to()` or `Route::service()` after `Route::wrap()` to prevent silently dropping route middleware. [#3944]
 - Fix `HttpRequest::{match_pattern,match_name}` reporting path-only matches when route guards disambiguate overlapping resources. [#3346]
 - Fix `Readlines` handling of lines split across payload chunks so combined line limits are enforced and complete lines are yielded.

actix-web/src/server.rs

@@ -447,10 +447,11 @@ where
     ///
     /// # Dual-Stack IPv6
     ///
-    /// On Windows, binding to an IPv6 address (e.g., `[::]:8080`) automatically enables dual-stack
-    /// mode, allowing the socket to accept both IPv4 and IPv6 connections. On Linux and macOS,
-    /// dual-stack is typically already the OS default. If you need IPv6-only behavior on Windows,
-    /// create the listener manually and pass it to [`listen()`](Self::listen()).
+    /// On Windows, when this method creates an IPv6 listener (e.g., for `[::]:8080`), this
+    /// attempts to enable dual-stack mode so the socket can accept both IPv4 and IPv6
+    /// connections. On Linux and macOS, dual-stack is typically already the OS default. If you
+    /// need IPv6-only behavior on Windows, create the listener manually and pass it to
+    /// [`listen()`](Self::listen()).
     ///
     /// # Typical Usage
     ///

actix-web/tests/test_httpserver.rs

@@ -217,3 +217,48 @@ async fn test_tcp_nodelay_enabled() {
 async fn test_tcp_nodelay_disabled() {
     assert_tcp_nodelay_config(false).await;
 }
+
+#[actix_rt::test]
+#[cfg(windows)]
+async fn test_dual_stack_ipv6_on_windows() {
+    let (tx, rx) = mpsc::channel();
+
+    thread::spawn(move || {
+        actix_rt::System::new()
+            .block_on(async {
+                let srv = HttpServer::new(|| {
+                    App::new().service(
+                        web::resource("/")
+                            .route(web::to(|| async { HttpResponse::Ok().body("test") })),
+                    )
+                })
+                .workers(1)
+                .disable_signals()
+                .bind("[::]:0")
+                .unwrap();
+
+                let port = srv.addrs()[0].port();
+                let srv = srv.run();
+
+                tx.send((srv.handle(), port)).unwrap();
+                srv.await
+            })
+            .unwrap();
+    });
+
+    let (srv, port) = rx.recv().unwrap();
+
+    let client = awc::Client::builder()
+        .connector(awc::Connector::new().timeout(Duration::from_secs(1)))
+        .finish();
+
+    let response = client
+        .get(format!("http://127.0.0.1:{port}"))
+        .send()
+        .await
+        .unwrap();
+
+    assert!(response.status().is_success());
+
+    srv.stop(false).await;
+}