Duplicate WebSocketException class in starlette and websockets

[ukalwa]

Hello,

It looks like there is a websocket exception base class in both starlette and websockets. Should they be treated as separate. I ran into an issue where I am catching all websocket exceptions (including ConnectionClosedError) raised in a fastapi endpoint and using startlette.exceptions.WebSocketException didn't work. I had to use websockets.exceptions.WebSocketException to catch them.

Should I be using websockets.exceptions or starlette.exceptions? FastAPI exports starlette.exceptions but they don't seem to work in this case.

---

Here is a simple contrived example:

from fastapi import FastAPI, WebSocket, WebSocketException, WebSocketDisconnect
import websockets.exceptions as ex
from traceback import print_exc
import asyncio

app = FastAPI()

@app.websocket("/ws/test")
async def test_ws_endpoint(websocket: WebSocket):
    await websocket.accept()
    try:
        while True:
             await websocket.send_json("test")
             await asyncio.sleep(10)
    except (WebSocketDisconnect, WebSocketException) as e:
        # Should get the trace here but it doesn't
        print_exc()
    except (ex.WebSocketException) as e:
        # Instead, the trace is printed here
        print_exc()
    finally:
        await websocket.close()

Here is the stack trace:

Traceback (most recent call last):
  File "/home/test/app.py", line 11, in test_ws_endpoint
    await websocket.send_json(None)
  File "/home/test/.venv/lib/python3.10/site-packages/starlette/websockets.py", line 173, in send_json
    await self.send({"type": "websocket.send", "text": text})
  File "/home/test/.venv/lib/python3.10/site-packages/starlette/websockets.py", line 85, in send
    await self._send(message)
  File "/home/test/.venv/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 65, in sender
    await send(message)
  File "/home/test/.venv/lib/python3.10/site-packages/uvicorn/protocols/websockets/websockets_impl.py", line 311, in asgi_send
    await self.send(data)  # type: ignore[arg-type]
  File "/home/test/.venv/lib/python3.10/site-packages/websockets/legacy/protocol.py", line 635, in send
    await self.ensure_open()
  File "/home/test/.venv/lib/python3.10/site-packages/websockets/legacy/protocol.py", line 944, in ensure_open
    raise self.connection_closed_exc()
websockets.exceptions.ConnectionClosedError: received 1005 (no status code [internal]); then sent 1005 (no status code [internal])

To reproduce, the client connects to the socket and then disconnects.

[Kludex]

What uvicorn version are you using?

[ukalwa]

Yes, I just checked and it also happens on 0.19.0

[ukalwa]

FWIW, I think changing the base ws exception to inherit from base exception of wsproto or websockets instead of Exception might fix the issue?

[ukalwa]

Base exception in websockets is defined as:

# websockets/exceptions.py#68
class WebSocketException(Exception):
    """
    Base class for all exceptions defined by websockets.

    """

And in wsproto:

# wsproto/utilities.py#21
class ProtocolError(Exception):
    pass

[Kludex]

Yes, I just checked and it also happens on 0.19.0

Yeah, but I thought I had fixed this on 0.20.0 for wsproto.

The issue is not on starlette, it's on uvicorn.

[ukalwa]

Maybe it's a different error(?) In my case, it is a SSE (server sent event), the api sends logs from the server side to connected clients periodically until the client disconnects.