Flask-socketio: SocketIO.run does not work on anything but the default port

Created on 17 Feb 2017 · 2Comments · Source: miguelgrinberg/Flask-SocketIO

I've been trying to get a basic Flask Socket IO example to work for a while but for some reason the socket appeared to drop out half way through the connection process.

This is my flask server code:

from flask import Flask, render_template
from flask_socketio import SocketIO, emit

import logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

app = Flask(__name__)
socketio = SocketIO(app)

@app.route('/')
def hello_world():
    logger.info('Serving root')
    return render_template('index.html')

@socketio.on('my event')
def respondToRequest(message):
    logger.info('responding to request')
    emit('my response',{'data':'some response'})

if __name__ == '__main__':
    logger.info('Running socket IO')
    socketio.run(app, host='localhost', port=10001)

This is my template:

<!DOCTYPE html>
<html>
  <head>
    <title>Flask Websockets Demo</title>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/1.7.3/socket.io.min.js"></script>
    <script type="text/javascript" src="static/js/application.js"></script>
  </head>
  <body>
    <p>Click me</p>
  </body>
</html>

This is the application js:

$(document).ready(function() {
    connectionString = 'http://' + location.host
    console.log('Connecting web socket: '+connectionString)
    ws = io.connect(connectionString);

    console.log('Registering function clicks')
    $( "p" ).on( "click", function() {
        ws.send('request', {who: $(this).attr('id'), data: $(this).val()});
    });
});

When I run the server up I get this:

C:\Anaconda3\python.exe C:/Projects/Experiments/FlaskSocketIoExperiments/FlaskSocketIoExperiments.py
INFO:engineio:Server initialized for gevent.
INFO:__main__:Running socket IO

When I attempt to connect a client I get repeats of this on the server:

INFO:geventwebsocket.handler:127.0.0.1 - - [2017-02-17 09:33:49] "GET / HTTP/1.1" 200 612 0.005000
INFO:engineio:5aa0b8a12c054b34b5ca30407ba3b33c: Sending packet OPEN data {'sid': '5aa0b8a12c054b34b5ca30407ba3b33c', 'pingTimeout': 60000, 'pingInterval': 25000, 'upgrades': ['websocket']}
INFO:engineio:5aa0b8a12c054b34b5ca30407ba3b33c: Sending packet MESSAGE data 0
INFO:geventwebsocket.handler:127.0.0.1 - - [2017-02-17 09:33:49] "GET /socket.io/?EIO=3&transport=polling&t=LfBQw7Z HTTP/1.1" 200 357 0.000000
INFO:engineio:5aa0b8a12c054b34b5ca30407ba3b33c: Received packet MESSAGE data 0:10001
INFO:geventwebsocket.handler:127.0.0.1 - - [2017-02-17 09:33:49] "POST /socket.io/?EIO=3&transport=polling&t=LfBQw8J&sid=5aa0b8a12c054b34b5ca30407ba3b33c HTTP/1.1" 400 215 0.001000
INFO:engineio:5aa0b8a12c054b34b5ca30407ba3b33c: Received packet CLOSE data None
INFO:geventwebsocket.handler:127.0.0.1 - - [2017-02-17 09:33:49] "POST /socket.io/?EIO=3&transport=polling&t=LfBQwBY&sid=5aa0b8a12c054b34b5ca30407ba3b33c HTTP/1.1" 400 215 0.001000

..and this on browser console (Chrome):

Connecting web socket
application.js:6 Registering function clicks
http://localhost:10001/socket.io/?EIO=3&transport=polling&t=LfBQw8J&sid=5aa0b8a12c054b34b5ca30407ba3b33c Failed to load resource: the server responded with a status of 400 (BAD REQUEST)
localhost/:1 WebSocket connection to 'ws://localhost:10001/socket.io/?EIO=3&transport=websocket&sid=5aa0b8a12c054b34b5ca30407ba3b33c' failed: WebSocket is closed before the connection is established.

If I change the server run method from this:

socketio.run(app, host='localhost', port=10001)

..to this:

socketio.run(app, host='localhost', port=5000)

...it appears to work as expected. With the default port I get a trace like this on the server:

C:\Anaconda3\python.exe C:/Projects/Experiments/FlaskSocketIoExperiments/FlaskSocketIoExperiments.py
INFO:engineio:Server initialized for gevent.
INFO:__main__:Running socket IO
INFO:engineio:d27266d267674b1692d11c97a857a5be: Sending packet OPEN data {'upgrades': ['websocket'], 'pingTimeout': 60000, 'sid': 'd27266d267674b1692d11c97a857a5be', 'pingInterval': 25000}
INFO:engineio:d27266d267674b1692d11c97a857a5be: Sending packet MESSAGE data 0
INFO:geventwebsocket.handler:127.0.0.1 - - [2017-02-17 11:18:46] "GET /socket.io/?EIO=3&transport=polling&t=1487330326586-2 HTTP/1.1" 200 357 0.001000
INFO:engineio:d27266d267674b1692d11c97a857a5be: Received request to upgrade to websocket
INFO:engineio:d27266d267674b1692d11c97a857a5be: Sending packet NOOP data None
INFO:geventwebsocket.handler:127.0.0.1 - - [2017-02-17 11:18:47] "GET /socket.io/?EIO=3&transport=polling&t=1487330326899-3&sid=d27266d267674b1692d11c97a857a5be HTTP/1.1" 200 191 0.303017
INFO:engineio:d27266d267674b1692d11c97a857a5be: Upgrade to websocket successful

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