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<!DOCTYPE html>

<title>WebSockets - Full Stack Python</title>

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<span class="logo-title"><a href="/">Full Stack Python</a></span>

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<h1>WebSockets</h1>

<p>A WebSocket is a <a href="http://tools.ietf.org/html/rfc6455">standard protocol</a> for

two-way data transfer between a client and server. The WebSockets protocol

does not run over HTTP, instead it is a separate implementation on top of

<h2>Why use WebSockets?</h2>

<p>A WebSocket connection allows full-duplex communication between a client

and server so that either side can push data to the other through an

established connection. The reason why WebSockets, along with the related

technologies of

<a href="http://en.wikipedia.org/wiki/Server-sent_events">Server-sent Events</a> (SSE)

and

<a href="https://tools.ietf.org/html/draft-ietf-rtcweb-data-channel-12">WebRTC data channels</a>,

are important is that HTTP is not meant for keeping open a connection for

the server to frequently push data to a web browser. Previously, most web

applications would implement long polling via frequent

Asynchronous JavaScript and XML (AJAX) requests as shown in the below diagram. </p>

<p>Server push is more efficient and scalable than long polling because the

web browser does not have to constantly ask for updates through a stream

of AJAX requests.</p>

<p>The WebSockets approach for server pushed updates works well for certain

categories of web applications such as chat room, which is why that's often

the example application for a WebSocket library.</p>

<p>Both a JavaScript library on the web browser and a WebSockets

implementation on the server are necessary to establish and maintain the

connection between the client and server. Examples of JavaScript client

libraries and WSGI implementations can be found below.</p>

<h2>JavaScript client libraries</h2>

<ul>

<li>

<p><a href="http://socket.io/">Socket.io</a>'s client side JavaScript library can be

used to connect to a server side WebSockets implementation.</p>

</li>

<li>

<p><a href="https://github.com/gimite/web-socket-js">web-socket-js</a> is a Flash-based

client-side WebSockets implementation.</p>

</li>

</ul>

<h2>Nginx WebSocket proxying</h2>

<p>Nginx officially supports WebSocket proxying as of

<a href="http://nginx.com/blog/websocket-nginx/">version 1.3</a>. However, you have

to configure the Upgrade and Connection headers to ensure requests are

passed through Nginx to your WSGI server. It can be tricky to set this up

the first time. </p>

<p>Here are the configuration settings I use in my Nginx file as part of my

WebSockets proxy.</p>

<div class="codehilite"><pre><span class="cp"># this is where my WSGI server sits answering only on localhost</span>

<span class="cp"># usually this is Gunicorn monkey patched with gevent</span>

<span class="n">upstream</span> <span class="n">app_server_wsgiapp</span> <span class="p">{</span>

<span class="n">server</span> <span class="n">localhost</span><span class="o">:</span><span class="mi">5000</span> <span class="n">fail_timeout</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span>

<span class="n">server</span> <span class="p">{</span>

<span class="err">#</span> <span class="n">my</span> <span class="n">typical</span> <span class="n">web</span> <span class="n">server</span> <span class="n">configuration</span> <span class="n">goes</span> <span class="n">here</span>

<span class="err">#</span> <span class="n">this</span> <span class="n">section</span> <span class="n">is</span> <span class="n">specific</span> <span class="n">to</span> <span class="n">the</span> <span class="n">WebSockets</span> <span class="n">proxying</span>

<span class="n">location</span> <span class="o">/</span><span class="n">socket</span><span class="p">.</span><span class="n">io</span> <span class="p">{</span>

<span class="n">proxy_pass</span> <span class="n">http</span><span class="o">:</span><span class="c1">//app_server_wsgiapp/socket.io;</span>

<span class="n">proxy_redirect</span> <span class="n">off</span><span class="p">;</span>

<span class="n">proxy_set_header</span> <span class="n">Host</span> <span class="err">$</span><span class="n">host</span><span class="p">;</span>

<span class="n">proxy_set_header</span> <span class="n">X</span><span class="o">-</span><span class="n">Real</span><span class="o">-</span><span class="n">IP</span> <span class="err">$</span><span class="n">remote_addr</span><span class="p">;</span>

<span class="n">proxy_set_header</span> <span class="n">X</span><span class="o">-</span><span class="n">Forwarded</span><span class="o">-</span><span class="n">For</span> <span class="err">$</span><span class="n">proxy_add_x_forwarded_for</span><span class="p">;</span>

<span class="n">proxy_http_version</span> <span class="mf">1.1</span><span class="p">;</span>

<span class="n">proxy_set_header</span> <span class="n">Upgrade</span> <span class="err">$</span><span class="n">http_upgrade</span><span class="p">;</span>

<span class="n">proxy_set_header</span> <span class="n">Connection</span> <span class="s">"upgrade"</span><span class="p">;</span>

<span class="n">proxy_read_timeout</span> <span class="mi">600</span><span class="p">;</span>

</pre></div>

<p>The following resources are also helpful for setting up the configuration

properly.</p>

<ul>

<li>

<p>Nginx has <a href="http://nginx.org/en/docs/http/websocket.html">an official page for WebSocket proxying</a>.</p>

</li>

<li>

<p><a href="http://blog.martinfjordvald.com/2013/02/websockets-in-nginx/">WebSockets in Nginx</a>

walks through the Nginx WebSockets configuration directives.</p>

</li>

<li>

<p><a href="https://chrislea.com/2013/02/23/proxying-websockets-with-nginx/">Proxying WebSockets with Nginx</a>

shows how to proxy with Socket.io.</p>

</li>

</ul>

<h2>Open source Python examples with WebSockets</h2>

<ul>

<li>

<p>The

<a href="https://github.com/makaimc/python-websockets-example">python-websockets-example</a>

contains code to create a simple web application that provides WebSockets

using Flask, Flask-SocketIO and gevent.</p>

</li>

<li>

<p>The Flask-SocketIO project has a

<a href="https://github.com/miguelgrinberg/Flask-SocketIO/tree/master/example">chat web application</a>

that demos sending server generated events as well as input from users

via a text box input on a form.</p>

</li>

</ul>

<h2>General WebSockets resources</h2>

<ul>

<li>

<p>The official W3C

<a href="http://www.w3.org/TR/websockets/">candidate draft for WebSockets API</a>

and the

<a href="http://dev.w3.org/html5/websockets/">working draft for WebSockets</a> are

good reference material but can be tough for those new to the WebSockets

concepts. I recommend reading the working draft after looking through some

of the more beginner-friendly resources list below.</p>

</li>

<li>

<p><a href="http://lucumr.pocoo.org/2012/9/24/websockets-101/">WebSockets 101</a> by

Armin Ronacher provides a detailed assessment of the subpar state of HTTP

proxying in regards to WebSockets. He also discusses the complexities of

the WebSockets protocol including the packet implementation.</p>

</li>

<li>

<p>The "Can I Use?" website has a

<a href="http://caniuse.com/#feat=websockets">handy WebSockets reference chart</a>

for which web browsers and specific versions support WebSockets.</p>

</li>

<li>

<p>Mozilla's

<a href="https://developer.mozilla.org/en-US/docs/WebSockets">Developer Resources for WebSockets</a>

is a good place to find documentation and tools for developing with

WebSockets.</p>

</li>

</ul>

<h2>Python-specific WebSockets resources</h2>

<ul>

<li>

<p><a href="http://mrjoes.github.io/2013/06/21/python-realtime.html">Real-time in Python</a>

provides Python-specific context for how the server push updates were

implemented in the past and how Python's tools have evolved to perform

server side updates.</p>

</li>

<li>

<p>The <a href="https://www.twilio.com/blog/2014/11/choose-your-own-adventure-presentations-with-reveal-js-python-and-websockets.html">Choose Your Own Adventure Presentations</a>

tutorial uses WebSockets via gevent on the server and socketio.js for

pushing vote count updates from the server to the client. </p>

</li>

<li>

<p><a href="http://bottlepy.org/docs/dev/async.html">Async with Bottle</a> shows how to

use greenlets to support WebSockets with the Bottle web framework.</p>

</li>

<li>

<p>If you're deploying to Heroku, there is a

<a href="https://devcenter.heroku.com/articles/python-websockets">specific WebSockets guide</a>

for getting your Python application up and running.</p>

</li>

</ul>

<h3>What's next for your web application after setting up WebSockets?</h3>

How do I execute Python since the web server doesn't do that?

</p>

</div>

</a>

How should I install Python libraries on the server?

</p>

</div>

What should I use to code my Python application?

</p>

</div>

</div> <div id="mc_embed_signup">

<h4>Interested in major updates to this site or an alert when a complete Full Stack Python book with detailed example code is released? Sign up here and you'll an occasional email only when there's big news to report.</h4>

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<h3 class="panel-head"><a href="/table-of-contents.html" style="color: #fff;">Table of Contents</a></h3>

</div>

<a href="/introduction.html" class="list-group-item smaller-item ">Introduction</a>

<a href="/web-frameworks.html" class="list-group-item smaller-item ">Web Frameworks</a>

<a href="/django.html" class="list-group-item smaller-item ">Django</a>

<a href="/flask.html" class="list-group-item smaller-item ">Flask</a>

<a href="/bottle.html" class="list-group-item smaller-item ">Bottle</a>

<a href="/morepath.html" class="list-group-item smaller-item ">Morepath</a>

<a href="/other-web-frameworks.html" class="list-group-item smaller-item ">Other Web Frameworks</a>

<a href="/deployment.html" class="list-group-item smaller-item ">Deployment</a>

<a href="/servers.html" class="list-group-item smaller-item ">Servers</a>

<a href="/platform-as-a-service.html" class="list-group-item smaller-item ">Platform-as-a-service</a>

<a href="/operating-systems.html" class="list-group-item smaller-item ">Operating Systems</a>

<a href="/web-servers.html" class="list-group-item smaller-item ">Web Servers</a>

<a href="/wsgi-servers.html" class="list-group-item smaller-item ">WSGI Servers</a>

<a href="/source-control.html" class="list-group-item smaller-item ">Source Control</a>

<a href="/application-dependencies.html" class="list-group-item smaller-item ">Application Dependencies</a>

<a href="/databases.html" class="list-group-item smaller-item ">Databases</a>

<a href="/no-sql-datastore.html" class="list-group-item smaller-item ">NoSQL Data Stores</a>

<a href="/web-design.html" class="list-group-item smaller-item ">Web Design</a>

<a href="/cascading-style-sheets.html" class="list-group-item smaller-item ">Cascading Style Sheets</a>

<a href="/javascript.html" class="list-group-item smaller-item ">JavaScript</a>

<a href="/continuous-integration.html" class="list-group-item smaller-item ">Continuous Integration</a>

<a href="/code-metrics.html" class="list-group-item smaller-item ">Code Metrics</a>

<a href="/configuration-management.html" class="list-group-item smaller-item ">Configuration Management</a>

<a href="/static-content.html" class="list-group-item smaller-item ">Static Content</a>

<a href="/caching.html" class="list-group-item smaller-item ">Caching</a>

<a href="/task-queues.html" class="list-group-item smaller-item ">Task Queues</a>

<a href="/application-programming-interfaces.html" class="list-group-item smaller-item ">Application Programming Interfaces</a>

<a href="/api-integration.html" class="list-group-item smaller-item ">API Integration</a>

<a href="/api-creation.html" class="list-group-item smaller-item ">API Creation</a>

<a href="/logging.html" class="list-group-item smaller-item ">Logging</a>

<a href="/monitoring.html" class="list-group-item smaller-item ">Monitoring</a>

<a href="/web-analytics.html" class="list-group-item smaller-item ">Web Analytics</a>

<a href="/web-application-security.html" class="list-group-item smaller-item ">Web Application Security</a>

<a href="/best-python-resources.html" class="list-group-item smaller-item ">Best Python Resources</a>

<a href="/development-environments.html" class="list-group-item smaller-item ">Development Environments</a>

<a href="/about-author.html" class="list-group-item smaller-item ">About the Author</a>

<a href="/change-log.html" class="list-group-item smaller-item ">Change Log</a>

<a href="/future-directions.html" class="list-group-item smaller-item ">Future Directions</a>

<a href="/what-full-stack-means.html" class="list-group-item smaller-item ">What "Full Stack" Means</a>

<a href="/why-use-python.html" class="list-group-item smaller-item ">Why Use Python?</a>

<a href="/websockets.html" class="list-group-item smaller-item active">WebSockets</a>

<a href="/docker.html" class="list-group-item smaller-item ">Docker</a>

</div>

<div class="panel-heading"><h3 class="panel-head">WebSockets</h3></div>

<a href="/">Full Stack Python</a> is an open book that explains

each Python web application stack layer and provides the

best web resources for those topics.

<hr/>

There's a work-in-progress

<a href="/full-stack-python-map.pdf">subjects map (.pdf)</a>

that visually lays out each chapter in addition to the table of

contents found below.

<hr/>

Need more detailed tutorials and walkthroughs than you see here?

<a href="/email.html">Sign up for an email alert when that content is created.</a>

<hr/>

<a href="http://twitter.com/mattmakai">Matt Makai</a> built

this site with greatly appreciated assistance from community

<a href="https://github.com/makaimc/fullstackpython.github.com/pulls">pull requests</a>.

</div>

</div></div>

<hr/>

<a href="http://www.mattmakai.com/" class="underline">Matt Makai</a>

2015

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