Flask-uWSGI-WebSocket

High-performance WebSockets for your Flask apps powered by uWSGI. Low-level uWSGI WebSocket API access and flexible high-level abstractions for building complex WebSocket applications with Flask. Supports several different concurrency models including Gevent. Inspired by Flask-Sockets.

from flask import Flask
from flask.ext.uwsgi_websocket import GeventWebSocket

app = Flask(__name__)
ws = GeventWebSocket(app)

@ws.route('/echo')
def echo(ws):
    while True:
        msg = ws.receive()
        ws.send(msg)

if __name__ == '__main__':
    app.run(gevent=100)

Installation

Preferred method of installation is via pip:

$ pip install Flask-uWSGI-WebSocket

Deployment

You can use uWSGI's built-in HTTP router to get up and running quickly:

$ uwsgi --master --http :8080 --http-websockets --wsgi echo:app

...which is what app.run does after wrapping your Flask app:

app.run(debug=True, host='localhost', port=8080, master=true, processes=8)

uWSGI supports several concurrency models, in particular it has nice support for Gevent. If you want to use Gevent, import flask.ext.uwsgi_websocket.GeventWebSocket and configure uWSGI to use the gevent loop engine:

$ uwsgi --master --http :8080 --http-websockets --gevent 100 --wsgi echo:app

...or:

app.run(debug=True, gevent=100)

Note that you cannot use multiple threads with gevent loop engine.

For production you'll probably want to run uWSGI behind Haproxy or nginx, instead of using the built-int HTTP router. Explore the uWSGI documentation for more detail about the various concurrency and deployment options.

Development

It's possible to take advantage of Flask's interactive debugger by installing werkzeug's DebuggedApplication middleware:

from werkzeug.debug import DebuggedApplication
app.wsgi_app = DebuggedApplication(app.wsgi_app, True)

...and running uWSGI with only a single worker:

$ uwsgi --master --http :8080 --http-websockets --wsgi-file --workers 1 --threads 8 app.py

If you use app.run(debug=True) or export FLASK_UWSGI_DEBUG, Flask-uWSGI-Websocket will do this automatically for you.

Examples

There are several examples available here.

API

flask_uwsgi_websocket.WebSocket

Applies WebSocketMiddleware to your Flask App, allowing you to decorate routes with the route method, turning them into WebSocket handlers.

Additionally monkey-patches app.run, to run your app directly in uWSGI.

route(url)

run(debug, host, port, **kwargs) **kwargs are passed to uWSGI as command line arguments.

flask_uwsgi_websocket.WebSocketMiddleware

WebSocket Middleware which automatically performs WebSocket handshake and passes WebSocketClient instances to your route.

flask_uwsgi_websocket.WebSocketClient

Exposes the uWSGI WebSocket API.

recv() (alias WebSocket.receive())

recv_nb()

send(msg)

send_binary(msg)

recv_nb()

send_from_sharedarea(id, pos)

send_binary_from_sharedarea(id, pos)

flask_uwsgi_websocket.GeventWebSocket

Fancier WebSocket abstraction that takes advantage of Gevent loop engine. Requires uWSGI to be run with --uwsgi option.

flask_uwsgi_websocket.GeventWebSocketMiddleware

Automatically performs WebSocket handshake and passes a GeventWebSocketClient instance to your route.

flask_uwsgi_websocket.GeventWebSocketClient

WebSocket client abstraction with fully non-blocking methods.

receive() and receive_nowait() differs in that receive_nowait() will raise a gevent.queue.Empty exception immediately if there is no message available.

receive()

receive_nowait()

send(msg)

close()

connected

Application and Request Context

The flask_uwsgi_websocket.GeventWebSocketMiddleware automatically wraps the websocket handler call inside the flask application and request context. This means the flask.current_app and flask.request LocalProxy instances will be bounded and all Flask extensions activated:

from flask import current_app, request

app = Flask(__name__)
ws = GeventWebSocket(app)

@ws.route('/websocket')
def websocket(ws):
    print current_app   #<Flask>
    print request       #<Request 'http://localhost:5000/websocket' [GET]>