Connection hangs in CLOSE_WAIT state

[sirkonst]

Server:

from flask import Flask
from flask_socketio import SocketIO, emit

app = Flask(__name__)
socketio = SocketIO(
    app, manage_session=True, logger=True, engineio_logger=True,
    async_mode='eventlet'
)


@socketio.on('connect')
def connect_handler(*args, **kwargs):
    # !!! If do comment next line problem is not reproduced !!!
    emit('any_signal', {'data': 'Connected'})


if __name__ == '__main__':
    socketio.run(app, port=9999, log_output=True, debug=True)

Client:

import signal

from socketIO_client import SocketIO

signal.alarm(5)  # kill self after 5 seconds

conn = SocketIO('localhost', 9999)
conn.wait()

Logs:

/home/_/develop/ec-wss/.env/bin/python /home/_/develop/ec-wss/simple_server.py
Server initialized for eventlet.
 * Restarting with stat
Server initialized for eventlet.
 * Debugger is active!
 * Debugger PIN: 407-346-791
(26666) wsgi starting up on http://127.0.0.1:9999
(26666) accepted ('127.0.0.1', 49774)
161f43bd70da42589172c840673d7608: Sending packet OPEN data {'sid': '161f43bd70da42589172c840673d7608', 'upgrades': ['websocket'], 'pingTimeout': 60000, 'pingInterval': 25000}
emitting event "any-signal" to 161f43bd70da42589172c840673d7608 [/]
161f43bd70da42589172c840673d7608: Sending packet MESSAGE data 2["any-signal",{"data":"Connected"}]
161f43bd70da42589172c840673d7608: Sending packet MESSAGE data 0
127.0.0.1 - - [20/Nov/2017 17:57:15] "GET /socket.io/?EIO=3&transport=polling&t=1511189835314-0 HTTP/1.1" 200 417 0.000877
(26666) accepted ('127.0.0.1', 49778)
161f43bd70da42589172c840673d7608: Received request to upgrade to websocket

Socket state:

$ lsof -i -n -P | grep 9999
python    26666 konst    3u  IPv4 10498613      0t0  TCP 127.0.0.1:9999 (LISTEN)
python    26666 konst    6u  IPv4 10499520      0t0  TCP 127.0.0.1:9999->127.0.0.1:49778 (CLOSE_WAIT)

Issue:

Socket in CLOSE_WAIT state will never closed (until restart app). Looks like that upgrade to websocket is hung. It's can case DoS because open sockets is limited resource (in a product count of CLOSE_WAIT always grows :-().

[miguelgrinberg]

Thanks. Need to figure out why this happens with the Python client. It does not happen when using the official JS client.

[miguelgrinberg]

Can I ask you to retest with the git master branch of python-engineio? I'm getting the websocket connection upgraded successfully after the fix I just put in. Thanks!

[sirkonst]

Yes! Not reproduced after update python-engineio to master. Thanks!

I hope the release python-engineio with fix does not take long.

[miguelgrinberg]

@sirkonst No, I just pushed the release out to pypi. Enjoy!