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Fix: Ensure on_client_disconnected event always fires in FastAPIWebsocketTransport #2762

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Fix: Ensure on_client_disconnected event always fires in FastAPIWebsocketTransport #2762

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20 changes: 15 additions & 5 deletions src/pipecat/transports/websocket/fastapi.py
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Original file line number Diff line number Diff line change
Expand Up @@ -278,6 +278,13 @@ async def cleanup(self):

async def _receive_messages(self):
"""Main message receiving loop for WebSocket messages."""

async def trigger_disconnect_if_needed():
# Trigger `on_client_disconnected` if the client actually disconnects,
# that is, we are not the ones disconnecting.
if not self._client.is_closing:
await self._client.trigger_client_disconnected()

try:
async for message in self._client.receive():
if not self._params.serializer:
Expand All @@ -294,11 +301,14 @@ async def _receive_messages(self):
await self.push_frame(frame)
except Exception as e:
logger.error(f"{self} exception receiving data: {e.__class__.__name__} ({e})")

# Trigger `on_client_disconnected` if the client actually disconnects,
# that is, we are not the ones disconnecting.
if not self._client.is_closing:
await self._client.trigger_client_disconnected()
Comment on lines -300 to -301
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@filipi87 filipi87 Oct 1, 2025

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I guess that reaching this point means the client has closed the socket, which will trigger on_client_disconnected.

Usually, the task is cancelled(stop) inside the user’s code at that point. Like, inside the on_client_disconnected callback.

I’m not sure how the race condition you mentioned would specifically impact this case. Like who is invoking stop at the same time ?

Have you been able to reproduce the issue locally ? Do you have the steps we should follow ?

Also tagging @aconchillo here for thoughts.

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@aconchillo aconchillo Oct 1, 2025

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I feel the same. Also. we only want to trigger on_client_disconnected when the client really disconnects.

finally:
# Use shield to prevent cancellation from stopping the disconnect callback
try:
await asyncio.shield(trigger_disconnect_if_needed())
except asyncio.CancelledError:
# Even if we're cancelled, try to trigger the disconnect
await trigger_disconnect_if_needed()
raise

async def _monitor_websocket(self):
"""Wait for self._params.session_timeout seconds, if the websocket is still open, trigger timeout event."""
Expand Down