fix: stop drain_proxy on subscriber arrival to prevent relay queue leak

blackhole.stop() alone doesn't remove the drain_proxy from
relay.__proxies. Relay continues putting frames into the dead
proxy's queue, causing unbounded memory growth.

Now add_track_subscriber calls drain_proxy.stop() (removes from
relay) + blackhole.stop() (cancels internal recv task) + drain_task.cancel()
(safety net).

Author: aliev

getstream/video/rtc/pc.py

@@ -142,7 +142,9 @@ def __init__(
 
         self.track_map = {}  # track_id -> (MediaRelay, original_track)
         self.video_frame_trackers = {}  # track_id -> VideoFrameTracker
-        self._video_blackholes: dict[str, tuple[MediaBlackhole, asyncio.Task]] = {}
+        self._video_drains: dict[
+            str, tuple[MediaBlackhole, asyncio.Task, MediaStreamTrack]
+        ] = {}
         self._background_tasks: set[asyncio.Task] = set()
 
         @self.on("track")
@@ -168,6 +170,15 @@ async def on_track(track: aiortc.mediastreams.MediaStreamTrack):
                 tracked_track = VideoFrameTracker(track)
                 self.video_frame_trackers[track.id] = tracked_track
 
+                # Drain unconsumed video frames to prevent unbounded queue growth
+                # in RTCRtpReceiver (aiortc issue #554)
+                if self._drain_video_frames:
+                    drain_proxy = relay.subscribe(tracked_track)
+                    blackhole = MediaBlackhole()
+                    blackhole.addTrack(drain_proxy)
+                    drain_task = asyncio.create_task(blackhole.start())
+                    self._video_drains[track.id] = (blackhole, drain_task, drain_proxy)
+
             self.track_map[track.id] = (relay, tracked_track)
 
             if track.kind == "audio":
@@ -183,14 +194,6 @@ def _emit_pcm(pcm: PcmData):
 
             proxy = relay.subscribe(tracked_track)
 
-            # Drain unconsumed video frames to prevent unbounded queue growth
-            # in RTCRtpReceiver (aiortc issue #554)
-            if track.kind == "video" and self._drain_video_frames:
-                drain_proxy = relay.subscribe(tracked_track)
-                blackhole = MediaBlackhole()
-                blackhole.addTrack(drain_proxy)
-                drain_task = asyncio.create_task(blackhole.start())
-                self._video_blackholes[track.id] = (blackhole, drain_task)
             self.emit("track_added", proxy, user)
 
         @self.on("icegatheringstatechange")
@@ -205,10 +208,13 @@ def add_track_subscriber(
         """Add a new subscriber to an existing track's MediaRelay."""
         track_data = self.track_map.get(track_id)
 
-        blackhole, drain_task = self._video_blackholes.pop(track_id, (None, None))
+        blackhole, drain_task, drain_proxy = self._video_drains.pop(
+            track_id, (None, None, None)
+        )
 
-        if blackhole and drain_task:
+        if blackhole and drain_task and drain_proxy:
             task = asyncio.create_task(blackhole.stop())
+            drain_proxy.stop()
             drain_task.cancel()  # safety net if start() becomes long-lived in future aiortc
             self._background_tasks.add(task)
             task.add_done_callback(self._background_tasks.discard)

tests/rtc/test_subscriber_drain.py

@@ -16,7 +16,7 @@ def subscriber_pc():
     pc._drain_video_frames = True
     pc.track_map = {}
     pc.video_frame_trackers = {}
-    pc._video_blackholes = {}
+    pc._video_drains = {}
     pc._background_tasks = set()
     pc._listeners = {}
     return pc
@@ -32,12 +32,14 @@ async def test_blackhole_stopped_when_subscriber_added(self, subscriber_pc):
 
         blackhole = Mock()
         blackhole.stop = AsyncMock()
-        subscriber_pc._video_blackholes[track_id] = (blackhole, Mock())
+        drain_proxy = Mock()
+        subscriber_pc._video_drains[track_id] = (blackhole, Mock(), drain_proxy)
 
         subscriber_pc.add_track_subscriber(track_id)
 
         blackhole.stop.assert_called_once()
-        assert track_id not in subscriber_pc._video_blackholes
+        drain_proxy.stop.assert_called_once()
+        assert track_id not in subscriber_pc._video_drains
 
     def test_no_error_when_no_drain_exists(self, subscriber_pc):
         track_id = "user123:video:0"