Fix FastAPIWebsocketTransport to handle both binary and text messages

src/pipecat/transports/websocket/fastapi.py

@@ -33,7 +33,7 @@ from pipecat.frames.frames import (
     StartFrame,
 )
 from pipecat.processors.frame_processor import FrameDirection
-from pipecat.serializers.base_serializer import FrameSerializer, FrameSerializerType
+from pipecat.serializers.base_serializer import FrameSerializer
 from pipecat.transports.base_input import BaseInputTransport
 from pipecat.transports.base_output import BaseOutputTransport
 from pipecat.transports.base_transport import BaseTransport, TransportParams
@@ -77,6 +77,26 @@ class FastAPIWebsocketCallbacks(BaseModel):
     on_session_timeout: Callable[[WebSocket], Awaitable[None]]
 
 
+class _WebSocketMessageIterator:
+    """Async iterator for WebSocket messages that yields both binary and text."""
+
+    def __init__(self, websocket: WebSocket):
+        self._websocket = websocket
+
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self) -> bytes | str:
+        message = await self._websocket.receive()
+        if message["type"] == "websocket.disconnect":
+            raise StopAsyncIteration
+        if "bytes" in message and message["bytes"] is not None:
+            return message["bytes"]
+        if "text" in message and message["text"] is not None:
+            return message["text"]
+        raise StopAsyncIteration
+
+
 class FastAPIWebsocketClient:
     """WebSocket client wrapper for handling connections and message passing.
 
@@ -84,17 +104,15 @@ class FastAPIWebsocketClient:
     with support for both binary and text message types.
     """
 
-    def __init__(self, websocket: WebSocket, is_binary: bool, callbacks: FastAPIWebsocketCallbacks):
+    def __init__(self, websocket: WebSocket, callbacks: FastAPIWebsocketCallbacks):
         """Initialize the WebSocket client.
 
         Args:
             websocket: The FastAPI WebSocket connection.
-            is_binary: Whether to use binary message format.
             callbacks: Event callback functions.
         """
         self._websocket = websocket
         self._closing = False
-        self._is_binary = is_binary
         self._callbacks = callbacks
         self._leave_counter = 0
 
@@ -110,9 +128,9 @@ class FastAPIWebsocketClient:
         """Get an async iterator for receiving WebSocket messages.
 
         Returns:
-            An async iterator yielding bytes or strings based on message type.
+            An async iterator yielding bytes or strings.
         """
-        return self._websocket.iter_bytes() if self._is_binary else self._websocket.iter_text()
+        return _WebSocketMessageIterator(self._websocket)
 
     async def send(self, data: str | bytes):
         """Send data through the WebSocket connection.
@@ -122,7 +140,7 @@ class FastAPIWebsocketClient:
         """
         try:
             if self._can_send():
-                if self._is_binary:
+                if isinstance(data, bytes):
                     await self._websocket.send_bytes(data)
                 else:
                     await self._websocket.send_text(data)
@@ -510,10 +528,7 @@ class FastAPIWebsocketTransport(BaseTransport):
             on_session_timeout=self._on_session_timeout,
         )
 
-        is_binary = False
-        if self._params.serializer:
-            is_binary = self._params.serializer.type == FrameSerializerType.BINARY
-        self._client = FastAPIWebsocketClient(websocket, is_binary, self._callbacks)
+        self._client = FastAPIWebsocketClient(websocket, self._callbacks)
 
         self._input = FastAPIWebsocketInputTransport(
             self, self._client, self._params, name=self._input_name

tests/test_fastapi_websocket.py

@@ -0,0 +1,70 @@
+#
+# Copyright (c) 2024-2026, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
+import unittest
+from unittest.mock import AsyncMock
+
+from pipecat.transports.websocket.fastapi import _WebSocketMessageIterator
+
+
+class TestWebSocketMessageIterator(unittest.IsolatedAsyncioTestCase):
+    async def test_yields_binary_message(self):
+        mock_websocket = AsyncMock()
+        mock_websocket.receive.side_effect = [
+            {"type": "websocket.receive", "bytes": b"binary data", "text": None},
+            {"type": "websocket.disconnect"},
+        ]
+
+        iterator = _WebSocketMessageIterator(mock_websocket)
+        messages = [msg async for msg in iterator]
+
+        self.assertEqual(len(messages), 1)
+        self.assertEqual(messages[0], b"binary data")
+
+    async def test_yields_text_message(self):
+        mock_websocket = AsyncMock()
+        mock_websocket.receive.side_effect = [
+            {"type": "websocket.receive", "bytes": None, "text": "text data"},
+            {"type": "websocket.disconnect"},
+        ]
+
+        iterator = _WebSocketMessageIterator(mock_websocket)
+        messages = [msg async for msg in iterator]
+
+        self.assertEqual(len(messages), 1)
+        self.assertEqual(messages[0], "text data")
+
+    async def test_yields_mixed_messages(self):
+        mock_websocket = AsyncMock()
+        mock_websocket.receive.side_effect = [
+            {"type": "websocket.receive", "bytes": b"binary", "text": None},
+            {"type": "websocket.receive", "bytes": None, "text": "text"},
+            {"type": "websocket.receive", "bytes": b"more binary", "text": None},
+            {"type": "websocket.disconnect"},
+        ]
+
+        iterator = _WebSocketMessageIterator(mock_websocket)
+        messages = [msg async for msg in iterator]
+
+        self.assertEqual(len(messages), 3)
+        self.assertEqual(messages[0], b"binary")
+        self.assertEqual(messages[1], "text")
+        self.assertEqual(messages[2], b"more binary")
+
+    async def test_stops_on_disconnect(self):
+        mock_websocket = AsyncMock()
+        mock_websocket.receive.side_effect = [
+            {"type": "websocket.disconnect"},
+        ]
+
+        iterator = _WebSocketMessageIterator(mock_websocket)
+        messages = [msg async for msg in iterator]
+
+        self.assertEqual(len(messages), 0)
+
+
+if __name__ == "__main__":
+    unittest.main()