transports(websocket): don't send data if websocket closed

CHANGELOG.md

@@ -13,6 +13,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   processing metrics indicate the time a processor needs to generate all its
   output. Note that not all processors generate these kind of metrics.
 
+### Fixed
+
+- Fixed an issue in `FastAPIWebsocketTransport` where it would still try to send
+  data to the websocket after being closed.
+
 ## [0.0.35] - 2024-06-28
 
 ### Changed

src/pipecat/transports/network/fastapi_websocket.py

@@ -12,7 +12,6 @@ import wave
 from typing import Awaitable, Callable
 from pydantic.main import BaseModel
 
-from pipecat.serializers.twilio import TwilioFrameSerializer
 from pipecat.frames.frames import AudioRawFrame, StartFrame
 from pipecat.processors.frame_processor import FrameProcessor
 from pipecat.serializers.base_serializer import FrameSerializer
@@ -114,7 +113,7 @@ class FastAPIWebsocketOutputTransport(BaseOutputTransport):
                 frame = wav_frame
 
             payload = self._params.serializer.serialize(frame)
-            if payload:
+            if payload and self._websocket.client_state == WebSocketState.CONNECTED:
                 await self._websocket.send_text(payload)
 
             self._audio_buffer = self._audio_buffer[self._params.audio_frame_size:]