add preconnect audio buffer API to LocalAudioTrack - #648
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Adds start_preconnect_buffer/stop_preconnect_buffer/send_preconnect_buffer to LocalAudioTrack, backed by a zero-allocation circular bytearray ring buffer. Sends buffered audio via byte stream data channels using the existing lk.agent.pre-connect-audio-buffer protocol.
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| if self._preconnect_buffer is None: | ||
| raise RuntimeError("preconnect buffer is not active") | ||
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| async with self._send_lock: | ||
| data = self._preconnect_buffer.capture() |
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🟡 TOCTOU race: _preconnect_buffer checked before lock but accessed inside lock
In send_preconnect_buffer, self._preconnect_buffer is checked for None at line 121 before acquiring self._send_lock at line 124. If the lock is contended (another send_preconnect_buffer call is in-flight), the async with self._send_lock: line yields control. During this yield, stop_preconnect_buffer() (which is synchronous) can be called from another callback—setting self._preconnect_buffer = None at livekit-rtc/livekit/rtc/track.py:116. When the lock is finally acquired, self._preconnect_buffer.capture() at line 125 will raise AttributeError: 'NoneType' object has no attribute 'capture'. The fix is to move the None-check inside the lock.
| if self._preconnect_buffer is None: | |
| raise RuntimeError("preconnect buffer is not active") | |
| async with self._send_lock: | |
| data = self._preconnect_buffer.capture() | |
| async with self._send_lock: | |
| if self._preconnect_buffer is None: | |
| raise RuntimeError("preconnect buffer is not active") | |
| data = self._preconnect_buffer.capture() |
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| def _on_participant_active(participant: RemoteParticipant) -> None: | ||
| if participant.identity != target_identity: | ||
| return | ||
| if not track.has_preconnect_buffer: | ||
| return | ||
| room.off("participant_active", _on_participant_active) | ||
| _send_buffer(participant) |
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🟡 Event listener leak in _setup_preconnect_auto_send when preconnect buffer is stopped before target becomes active
In _on_participant_active, when the target identity matches but track.has_preconnect_buffer returns False, the handler returns early without calling room.off("participant_active", _on_participant_active) to unregister itself. This means the handler stays registered on the room indefinitely, holding references to track, room, and other closure variables. Worse, if start_preconnect_buffer() is called again later and the same identity fires participant_active again (e.g. after a reconnect), the stale handler will unexpectedly trigger and send the buffer.
The fix is to unregister the handler whenever the target identity matches, regardless of the buffer state — _send_buffer already checks has_preconnect_buffer internally.
| def _on_participant_active(participant: RemoteParticipant) -> None: | |
| if participant.identity != target_identity: | |
| return | |
| if not track.has_preconnect_buffer: | |
| return | |
| room.off("participant_active", _on_participant_active) | |
| _send_buffer(participant) | |
| def _on_participant_active(participant: RemoteParticipant) -> None: | |
| if participant.identity != target_identity: | |
| return | |
| room.off("participant_active", _on_participant_active) | |
| _send_buffer(participant) |
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