Synchronize audio stream teardown

gumble/gumble/handlers.go

@@ -256,6 +256,7 @@ func (c *Client) dispatchAudio(user *User, packet *AudioPacket) {
 	listeners := &c.Config.AudioListeners
 	listeners.mu.Lock()
 	type delivery struct {
+		item     *audioEventItem
 		listener AudioListener
 		ch       chan *AudioPacket
 		new      bool
@@ -272,7 +273,7 @@ func (c *Client) dispatchAudio(user *User, packet *AudioPacket) {
 			ch = make(chan *AudioPacket, bufferSize)
 			item.streams[user] = ch
 		}
-		deliveries = append(deliveries, delivery{item.listener, ch, newStream})
+		deliveries = append(deliveries, delivery{item, item.listener, ch, newStream})
 	}
 	listeners.mu.Unlock()
 
@@ -281,12 +282,20 @@ func (c *Client) dispatchAudio(user *User, packet *AudioPacket) {
 			log.Debug("new audio stream from %s (session=%d)", user.Name, user.Session)
 			delivery.listener.OnAudioStream(&AudioStreamEvent{Client: c, User: user, C: delivery.ch})
 		}
-		select {
-		case delivery.ch <- packet:
-		default:
-			// Never allow a slow listener to block protocol processing.
-			log.Debug("dropping buffered audio for slow listener (session=%d)", user.Session)
+		// User removal can run on a different protocol goroutine. Keep the
+		// listener lock while sending so it cannot close this stream between
+		// the active-stream check and the channel send.
+		listeners.mu.Lock()
+		active := !delivery.item.detached && delivery.item.streams[user] == delivery.ch
+		if active {
+			select {
+			case delivery.ch <- packet:
+			default:
+				// Never allow a slow listener to block protocol processing.
+				log.Debug("dropping buffered audio for slow listener (session=%d)", user.Session)
+			}
 		}
+		listeners.mu.Unlock()
 	}
 }
 
@@ -578,16 +587,18 @@ func (c *Client) handleUserRemove(buffer []byte) error {
 		}
 		delete(c.Users, session)
 
-		// Close audio stream channels for the disconnected user.
-		// This is safe because handleUserRemove and handleUDPTunnel
-		// both run in the serialized readRoutine; no concurrent send
-		// on these channels is possible once the user is removed.
-		for item := c.Config.AudioListeners.head; item != nil; item = item.next {
+		// Close audio stream channels for the disconnected user. UDP audio may
+		// still be dispatched concurrently, so the audio-listener lock also
+		// protects its stream maps and channel sends.
+		listeners := &c.Config.AudioListeners
+		listeners.mu.Lock()
+		for item := listeners.head; item != nil; item = item.next {
 			if ch, ok := item.streams[event.User]; ok {
 				close(ch)
 				delete(item.streams, event.User)
 			}
 		}
+		listeners.mu.Unlock()
 
 		if packet.Reason != nil {
 			event.String = *packet.Reason