Sanic stops working after trying to open a WS connection

[Cyril Nicodème]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I recently updated my machine to the latest OS (Fedora 39). The codebase was working well before, so I suspect this might be related to the Python version:

Python: 3.12.1

Code snippet

from sanic import Request, Websocket, Sanic
from sanic.response import text

app = Sanic("MyHelloWorldApp")


@app.websocket("/stream")
async def feed(request: Request, ws: Websocket):
    data = "hello!"
    print("Sending: " + data)
    await ws.send(data)
    data = await ws.recv()
    print("Received: " + data)


@app.get('/')
async def hello(request):
    return text("Hello, world.")

if __name__ == "__main__":
    app.run(port=5000, debug=True)

Connecting with Firefox and with the following basic code:

let ws = new WebSocket("ws://127.0.0.1:5000/stream");
ws.onerror = (e) => {
  console.log(e);
}
ws.onopen = () => {
  console.log("connected");
  ws.send("hello");
}

Expected Behavior

Steps to reproduce the issue:

1. Go to http://127.0.0.1:5000/
2. See the "Hello world message"
3. Open the console and paste the above javascript
4. An error is shown in the console: "Firefox can't establish a connection with the server at ws://127.0.0.1:5000/stream" (The message might differ as I have it in French and translated it)
5. Refresh the page : The page hangs, Sanic doesn't answer any requests anymore

How do you run Sanic?

As a script (app.run or Sanic.serve)

Operating System

Linux

Sanic Version

Sanic 23.6.0; Routing 23.12.0

Additional context

From the MOTD:

• mode: debug, single worker
• server: sanic, HTTP/1.1
• platform: Linux-6.6.11-200.fc39.x86_64-x86_64-with-glibc 2.38

[Cyril Nicodème]

For information, I just tried with Python 3.10.13, and it works fine.

Some changes in recent Python's version must impact how Sanic behave, but my lack of deep understanding of the internals of Sanic blocks me for identifying the root cause of the problem.

[Adam Hopkins]

This is not my experience. Granted, I am on the latest main, but I don't think there was anything that would have changed.

Are you still experiencing this?

[Nazrul]

@cnicodeme I've encountered a similar problem using Sanic versions 23.12.1 and Python 3.12.3. I discovered that the issue was related to the protocol configuration. It was resolved by specifying protocol=WebSocketProtocol in the run method. Here’s the necessary import:
from sanic.server.protocols.websocket_protocol import WebSocketProtocol