WebSocket Server Breaks After Installing gevent-websocket

[mglst]

I am encountering an issue where the WebSocket server functions correctly without gevent-websocket installed, but breaks once the library is added.

• Without gevent-websocket: WebSocket connections to ws://127.0.0.1:5001/ws work as expected. I can successfully connect using:
  • My browser’s JS console.
  • An iOS app I'm developing.
    However, the following warning appears in the server console:
    WARNING in __init__: WebSocket transport not available. Install gevent-websocket for improved performance.
• With gevent-websocket installed: The server accepts WebSocket connections but immediately closes them. I see a 101 Switching Protocols response in the network logs, followed by errors and a closed connection on the client side. The server does not report any anomalies

Here is the code in question. It's a minimal Flask app using both flask-sock and Flask-SocketIO, with gevent:

from gevent import monkey

monkey.patch_all(thread=True, time=True)

from flask import Flask
from flask_sock import Sock
from flask_socketio import SocketIO

app = Flask(__name__)
app.config["SECRET_KEY"] = "secret!"
socketio = SocketIO(app)
sock = Sock(app)


@sock.route("/ws")
def echo(ws):
    ws.send("Hello, World!")
    while True:
        data = ws.receive()
        ws.send(data)


if __name__ == "__main__":
    socketio.run(app, host="0.0.0.0", port=5001)

The above works with gevent-websocket if I remove socketio.

Here's the result of my pip freeze. These are all the latest versions I can install. I'm using python 3.12.8.

bidict==0.23.1
blinker==1.9.0
click==8.1.7
Flask==3.1.0
flask-sock==0.7.0
Flask-SocketIO==5.4.1
gevent==24.11.1
gevent-websocket==0.10.1
greenlet==3.1.1
h11==0.14.0
itsdangerous==2.2.0
Jinja2==3.1.4
MarkupSafe==3.0.2
python-engineio==4.10.1
python-socketio==5.11.4
setuptools==75.6.0
simple-websocket==1.1.0
Werkzeug==3.1.3
wsproto==1.2.0
zope.event==5.0
zope.interface==7.2

[miguelgrinberg]

gevent-websocket was released last in 2017. Why do you need it?

[mglst]

I need both WebSockets and Socketio, I don't specifically need gevent-websocket, I just happen to be using gevent. I'll just ignore the warning and move on. The warning tripped me up though, since I installed gevent-websocket long before running into this issue, and it took me a while to realise that it wasn't client side. Presumably the warning isn't coming from flask-sock?

[miguelgrinberg]

In the current version of Flask-SocketIO the gevent-websocket package is not required, in fact, it is best not to use it since it is unmaintained and has been for many years. I now realize that there is a warning in this package that is outdated. I'll remove it. WebSocket works fine without gevent-websocket in current versions, the simple-websocket package is used instead, so if you have that one installed you are good to go.

Also, you referenced Flask-Sock and initially wrote this issue on that project, but Flask-Sock has no connection to Flask-SocketIO. None at all, they are different solution, both use WebSocket, but that is as far as the connection goes.

[miguelgrinberg]

The warning has been removed, since it does not apply anymore.