Recieving messages does not work.

[michael-brennan2005]

from flask import Flask
from flask_cors import CORS
from flask_socketio import SocketIO, send, emit

app = Flask(__name__)
socketio = SocketIO(app, cors_allowed_origins='*')
CORS(app)

@socketio.on('ping')
def ping(json):
    emit('ping', {})

if __name__ == '__main__':
    socketio.run(app)

Here is my app. I know that the messages are being sent successfully from the client because I am getting an error. The client code looks like this:

   const socket = io('localhost:5000')
    let pingMs: string = ""
    let lastTime: number = 0

    const ping = () => {
        lastTime = Date.now()
        pingMs = "Pinging..."
        socket.emit('ping')
    }

    socket.on('ping', () => {
        const currentTime = Date.now()
        pingMs = `${currentTime - lastTime}ms`
    })

As you can see I'm making a ping feature just to evaluate this software.

When I send a message on the client, I get this error in the python code:

Traceback (most recent call last):
  File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.8/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/home/michaelb/.local/lib/python3.8/site-packages/socketio/server.py", line 730, in _handle_event_internal
    r = server._trigger_event(data[0], namespace, sid, *data[1:])
  File "/home/michaelb/.local/lib/python3.8/site-packages/socketio/server.py", line 755, in _trigger_event
    return self.handlers[namespace][event](*args)
  File "/home/michaelb/.local/lib/python3.8/site-packages/flask_socketio/__init__.py", line 282, in _handler
    return self._handle_event(handler, message, namespace, sid,
  File "/home/michaelb/.local/lib/python3.8/site-packages/flask_socketio/__init__.py", line 766, in _handle_event
    ret = handler(*args)
TypeError: ping() missing 1 required positional argument: 'json'

[miguelgrinberg]

Your ping handler in the server takes one argument, but he client is not sending any data with this event.