fix(tunnel): data race in CloseOnIdle and goroutine leak in sniffingWebsocketFrame

- Use write lock (Lock) instead of read lock (RLock) in CloseOnIdle since
  it modifies the close channel, preventing a race with Close() that could
  panic on double-close of channel.
- Buffer sniffingWebsocketFrame errc to capacity 2 and close both
  connections on first error to ensure the remaining copy goroutine
  unblocks and exits cleanly.

handler/tunnel/entrypoint.go

@@ -440,8 +440,8 @@ func (ep *entrypoint) handleUpgradeResponse(ctx context.Context, rw io.ReadWrite
 	return xnet.Pipe(ctx, rw, backConn)
 }
 
-func (ep *entrypoint) sniffingWebsocketFrame(ctx context.Context, rw, cc io.ReadWriter, ro *xrecorder.HandlerRecorderObject, log logger.Logger) error {
-	errc := make(chan error, 1)
+func (ep *entrypoint) sniffingWebsocketFrame(ctx context.Context, rw, cc io.ReadWriteCloser, ro *xrecorder.HandlerRecorderObject, log logger.Logger) error {
+	errc := make(chan error, 2)
 
 	sampleRate := ep.websocketSampleRate
 	if sampleRate == 0 {
@@ -503,6 +503,9 @@ func (ep *entrypoint) sniffingWebsocketFrame(ctx context.Context, rw, cc io.Read
 		}
 	}()
 
+	<-errc
+	rw.Close()
+	cc.Close()
 	<-errc
 	return nil
 }

handler/tunnel/tunnel.go

@@ -230,8 +230,8 @@ func (t *Tunnel) Close() error {
 }
 
 func (t *Tunnel) CloseOnIdle() bool {
-	t.mu.RLock()
-	defer t.mu.RUnlock()
+	t.mu.Lock()
+	defer t.mu.Unlock()
 
 	select {
 	case <-t.close: