From 41b145dd04b2655796b9e55ff6e2043dec090fd1 Mon Sep 17 00:00:00 2001
From: Tin Lai <tin@tinyiu.com>
Date: Fri, 9 Oct 2026 13:11:10 +1100
Subject: [PATCH] fix(webtransport): cancel pending handshakes when frontend
 closes

---
 Cargo.lock                                    |  1 +
 crates/aeronet_webtransport/Cargo.toml        |  3 +
 .../src/client/backend.rs                     | 75 +++++++++++++++++--
 3 files changed, 73 insertions(+), 6 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index bd24ba31..470d0604 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -298,6 +298,7 @@ dependencies = [
  "futures",
  "js-sys",
  "spki",
+ "tokio",
  "tracing",
  "wasm-bindgen",
  "wtransport",
diff --git a/crates/aeronet_webtransport/Cargo.toml b/crates/aeronet_webtransport/Cargo.toml
index 1031b81b..6cfb9e33 100644
--- a/crates/aeronet_webtransport/Cargo.toml
+++ b/crates/aeronet_webtransport/Cargo.toml
@@ -59,6 +59,9 @@ wtransport = { workspace = true }
 x509-cert = { workspace = true }
 xwt-wtransport = { workspace = true }
 
+[target.'cfg(not(target_family = "wasm"))'.dev-dependencies]
+tokio = { workspace = true, features = ["rt", "net", "time"] }
+
 [target.'cfg(target_family = "wasm")'.dependencies]
 js-sys = { workspace = true }
 wasm-bindgen = { workspace = true }
diff --git a/crates/aeronet_webtransport/src/client/backend.rs b/crates/aeronet_webtransport/src/client/backend.rs
index 97e7117a..0538b049 100644
--- a/crates/aeronet_webtransport/src/client/backend.rs
+++ b/crates/aeronet_webtransport/src/client/backend.rs
@@ -11,10 +11,24 @@ use {
     xwt_core::prelude::*,
 };
 
+// Dropping a Rust future does not cancel a JavaScript `ready` promise.
+// Explicitly close the browser transport unless ownership reaches Session.
+#[cfg(target_family = "wasm")]
+struct PendingWebTransport(Option<xwt_web::web_wt_sys::WebTransport>);
+
+#[cfg(target_family = "wasm")]
+impl Drop for PendingWebTransport {
+    fn drop(&mut self) {
+        if let Some(transport) = self.0.take() {
+            transport.close();
+        }
+    }
+}
+
 pub async fn start(
     config: ClientConfig,
     target: ConnectTarget,
-    tx_next: oneshot::Sender<ToConnected>,
+    mut tx_next: oneshot::Sender<ToConnected>,
 ) -> Result<Never, DisconnectReason> {
     let endpoint = {
         #[cfg(target_family = "wasm")]
@@ -35,16 +49,20 @@ pub async fn start(
     };
     debug!("Created endpoint");
 
-    let conn = {
+    let connecting = async {
         #[cfg(target_family = "wasm")]
         {
-            endpoint
+            let connecting = endpoint
                 .connect(&target)
                 .await
-                .map_err(|err| ClientError::Connect(err.into()))?
+                .map_err(|err| ClientError::Connect(err.into()))?;
+            let mut pending = PendingWebTransport(Some(connecting.transport.clone()));
+            let session = connecting
                 .wait_connect()
                 .await
-                .map_err(|err| ClientError::AwaitConnect(err.into()))?
+                .map_err(|err| ClientError::AwaitConnect(err.into()))?;
+            pending.0 = None;
+            Ok::<_, ClientError>(session)
         }
 
         #[cfg(not(target_family = "wasm"))]
@@ -54,7 +72,18 @@ pub async fn start(
                 .connect(target)
                 .await
                 .map(xwt_wtransport::Connection)
-                .map_err(ClientError::Connect)?
+                .map_err(ClientError::Connect)
+        }
+    };
+    // Cancellation must also cover the handshake, before SessionBackend has
+    // a disconnect channel. Dropping the frontend's receiver cancels this
+    // future and drops the native endpoint rather than leaving a retired task.
+    let conn = {
+        let cancelled = tx_next.cancellation();
+        futures::pin_mut!(connecting, cancelled);
+        match futures::future::select(cancelled, connecting).await {
+            futures::future::Either::Left(_) => return Err(SessionError::FrontendClosed.into()),
+            futures::future::Either::Right((result, _)) => result?,
         }
     };
     debug!("Connected");
@@ -92,3 +121,37 @@ pub async fn start(
     debug!("Starting session loop");
     Err(backend.start().await)
 }
+
+#[cfg(all(test, not(target_family = "wasm")))]
+mod tests {
+    use {super::*, core::time::Duration, wtransport::endpoint::IntoConnectOptions};
+
+    #[test]
+    fn dropping_frontend_cancels_pending_handshake_without_waiting_for_network_timeout() {
+        let runtime = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+        runtime.block_on(async {
+            // Bound but silent UDP peer: no connection-refused shortcut.
+            let peer = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
+            let config = ClientConfig::builder()
+                .with_bind_default()
+                .with_native_certs()
+                .max_idle_timeout(Some(Duration::from_secs(5)))
+                .unwrap()
+                .build();
+            let (tx, rx) = oneshot::channel();
+            let target = format!("https://{}/", peer.local_addr().unwrap()).into_options();
+            let task = tokio::spawn(start(config, target, tx));
+            tokio::task::yield_now().await;
+            drop(rx);
+            let result = tokio::time::timeout(Duration::from_millis(500), task).await;
+            assert!(
+                result.is_ok(),
+                "abandoned handshake continued running after fallback"
+            );
+            assert!(result.unwrap().unwrap().is_err());
+        });
+    }
+}