Comet web applications with Python, Django & Orbited

Comet web applications with Python,
Django & Orbited

@ PyCon Italia Qu4ttro Massimo Scamarcia
http://www.pycon.it/ http://www.webright.it/

Django & Orbited

How to push real-time data to
web browsers?

Django & Orbited

AJAX Polling
 Client: sends AJAX request.
 Server:
 Data available: sends response.
 No data: sends empty response.
 Client: sends AJAX request again.

Django & Orbited

Latency, bandwidth, memory usage and scaling issues!

Django & Orbited

What about Comet?

Django & Orbited

Not a technology in itself
Long Polling, IFRAME stream, HTMLFile, XHR Streaming, HTML5 SSE

Django & Orbited

It's an hack!
Still waiting for an unanimous way to do it.

Django & Orbited

Long Polling
 Client: sends AJAX request.
 Server: holds the request.
 Data available: sends response.
 Timeout reached: empty response.
 Client: sends AJAX request again.

Django & Orbited

Http Push (HTTP Streaming*)
 Client: sends HTTP request.
 Server: doesn't terminate the connection.
 Server: sends data when available.
 Connection closed:
 Data is queued.
 Client reconnects.

[*] http://ajaxpatterns.org/HTTP_Streaming

Django & Orbited
 HTTP Push: better for heavily-loaded apps.
 Not cross-browser.
 Long Polling: cross-browser and easy.
 Bandwidth usage.
 Too many connections.
 Async Python servers* are better for both:
 Twisted, Tornado, Dieselweb, Eventlet, Concurrence,
Circuits, Gevent, Cogen.

[*] http://nichol.as/asynchronous-servers-in-python

Django & Orbited

What about Orbited?

Django & Orbited

He's here to solve problems!

Django & Orbited

 Based on Twisted.
 STOMP* (ActiveMQ, RabbitMQ), IRC and XMPP
protocol support.
 Ready-to-use and cross-browser JavaScript client
code.
 You don't have to reinvent the wheel!

[*] http://stomp.codehaus.org/

Django & Orbited

Using Django and Orbited
Example app developed for PyConIt4:
http://pyconquiz.webright.it/

Django & Orbited

Django is used for:
 Application logic.
 Template rendering.
 User auth and registration.
 Handling AJAX requests.
 Sending messages to STOMP server.

...Orbited and jQuery do the rest!

Django & Orbited

Django & Orbited

orbited.cfg settings.py
[global] # Available using context
#reactor=select # processor or templatetag
#reactor=kqueue
reactor = epoll ORBITED_HOST = 'localhost'
proxy.enabled = 1 ORBITED_PORT = 8080
session.ping_interval = 300
STOMP_HOST = 'localhost'
[listen] STOMP_PORT = 61613
http://localhost:8080
stomp://localhost:61613

[access]
* -> localhost:61613

Django & Orbited

Django base template (<head /> tag)
<script>document.domain = document.domain;</script>
<script src="{{ ORBITED_MEDIA_URL }}Orbited.js"></script>
<script type="text/javascript">
Orbited.settings.port = {{ ORBITED_PORT }};
Orbited.settings.hostname = "{{ ORBITED_HOST }}";
Orbited.settings.streaming = true;

TCPSocket = Orbited.TCPSocket;
</script>

<script src="{{ ORBITED_MEDIA_URL }}JSON.js"></script>
<script
src="{{ ORBITED_MEDIA_URL }}protocols/stomp/stomp.js"></script>

Django & Orbited
<script>
$(document).ready(function() {
stomp = new STOMPClient();
stomp.onopen = function() { debug('Connected.');};
stomp.onclose = function(c) { debug(Lost Connection, Code: '+c);};
stomp.onerror = function(error){ debug("Error: " + error);};
stomp.onerrorframe = function(frame){ debug("Error: " + frame.body);};
stomp.onconnectedframe = function() {
{% if game %}
stomp.subscribe('/games/{{ game.id }}/status');
stomp.subscribe('/games/{{ game.id }}/players');
{% else %}// subscribe to other channels...{% endif %}
};
stomp.onmessageframe = function(frame){
// frame.headers.destination for channel, frame.body for JSON data
destpatterns.dispatch(frame);
};
stomp.connect('{{ STOMP_HOST }}', {{ STOMP_PORT }});
});
</script>

Django & Orbited

Django view
@require_POST
@login_required
def game_start(request, game_id):
game = get_object_or_404(Game, id=game_id)
if request.user != game.author:
return HttpResponseForbidden()
try:
# start() method set game start_time and send JSON
# to ”/games/{{ game.id }}/status” using stomp.py
game.start()
except GameError, e:
return JSONResponse({'error': str(e)})
return JSONResponse({})

Django & Orbited

Does it scale?

Django & Orbited

Thank you
and have fun with the quiz game!

Comet web applications with Python, Django & Orbited

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