.. post:: 2014-02-10
   :tags: Python, Flask, gevent
   :author: Rudi Grinberg

Omegle clone in Flask + Gevent + WebSockets
===========================================

Python ranks fairly high when it comes getting things done without too
much ceremony in the programming community. I briefly had some doubts of
this assertion of until I finally found
`Flask-Sockets <http://kennethreitz.org/introducing-flask-sockets>`__.
This small library makes it very natural to serve WebSockets in
Flask/gevent. You can consider this blog post as an advertisement for
this small but extremely useful library.

In this post, I will show how to create an extremely simple omegle POC
using the Gevent/Flask/Flask-Sockets combo. The end result is that the
javascript client is comparable in code size to the server. Here's the
code for the server (the client is ugly and uninteresting but you can
see it in the repo):

.. code-block:: python

    #!/usr/bin/env python2
    import gevent.monkey
    gevent.monkey.patch_all()

    import flask
    from flask import Flask
    from flask_sockets import Sockets
    import gevent
    import gevent.queue
    from gevent import pywsgi
    from geventwebsocket.handler import WebSocketHandler

    app = Flask(__name__, static_url_path='')

    sockets = Sockets(app)
    seekers = gevent.queue.Queue()


    def relay(from_, to):
        """route messges from_ -> to"""
        try:
            while True:
                to.send(from_.receive())
        except:
            # Notify to about disconnection - unless to disconnected
            try: to.send("Peer disconnected.")
            except: pass


    def session(ws1, ws2):
        for ws in [ws1, ws2]:
            ws.send("/Found a person. Say hello")
        gevent.joinall([
            gevent.spawn(relay, ws1, ws2),
            gevent.spawn(relay, ws2, ws1)
        ])


    def matcher(seekers):
        while True:
            gevent.spawn(session, seekers.get(), seekers.get())

    gevent.spawn(matcher, seekers)

    @sockets.route('/ws')
    def websocket(ws):
        seekers.put(ws)
        ws.send("/Welcome. Seeking a partner")
        while True:  # hack to keep the greenlet alive
            gevent.sleep(0.5)


    @app.route('/')
    def index():
        return app.send_static_file('index.html')


    if __name__ == '__main__':
        pywsgi.WSGIServer(('', 8000), app, handler_class=WebSocketHandler) \
              .serve_forever()

The implementation is very naive but I still wonder how well it would
perform. Many further improvements are possible as well:

-  Limit the number of concurrent sessions
-  Create a pool for matchers to make sure that ``seekers`` empties fast
   enough
-  Allow clients to advertise names

You can see the full code
`here <https://github.com/rgrinberg/flask-gevent-omegle>`__.