AN INTRODUCTION TO TORNADO

Gavin M. RoyCTO

myYearbook.com

pyCon 2011Atlanta, GA

TORNADO AT MYYEARBOOK.COM

• Currency Connect

• Marketing Website, Portal, RESTful API

• Redirect Engine

• Nerve

• Staplr 2

• Image Upload Service

WHAT IS TORNADO?

• A scalable, non-blocking web server and micro-framework in Python 2.5 & 2.6.

• Python 3 port underway

• Developed at FriendFeed and open-sourced by Facebook

• Similar to web.py in use

• Fast: ~1,500 requests/sec backend** Your milage will vary

FEATURES

• Small barrier to entry to quickly developing applications

• Third Party Authentication via OpenID, OAuth Mixins

• Light-weight template system

• Auto-magical cross-site forgery protection

• WSGI && Google App Engine Support

• Develop using debug mode and automatically reload code and templates when changed on disk

CLEAN, WELL DOCUMENTED CODE

class Application(object):    """A collection of request handlers that make up a web application.

Instances of this class are callable and can be passed directly to HTTPServer to serve the application:

application = web.Application([ (r"/", MainPageHandler), ]) http_server = httpserver.HTTPServer(application) http_server.listen(8080) ioloop.IOLoop.instance().start()

The constructor for this class takes in a list of URLSpec objects or (regexp, request_class) tuples. When we receive requests, we iterate over the list in order and instantiate an instance of the first request class whose regexp matches the request path.

Each tuple can contain an optional third element, which should be a dictionary if it is present. That dictionary is passed as keyword arguments to the contructor of the handler. This pattern is used for the StaticFileHandler below:

application = web.Application([ (r"/static/(.*)", web.StaticFileHandler, {"path": "/var/www"}), ])

WHAT TORNADO ISN’T

• A full stack framework like Django

• Based on Twisted

• There is an unmaintained port, Tornado on Twisted

• Influenced the Cyclone project

• A replacement for a front-end web server

• Run behind a reverse proxy http server (nginx, Cherokee)

TORNADO VS TWISTED

• Tornado doesn’t have to be asynchronous

• It doesn’t have as many asynchronous drivers

• Can introduce blocking behaviors

• The Tornado code is smaller and very easy to understand

• Less mature than Twisted

• You don’t need to buy into a development methodology

• Write Python not Twisted

KEY MODULES

Take only what you need

TORNADO.WEB

• Most development is focused around this module

• Multiple classes used in a web application

• Includes decorators

• Asynchronous function: @tornado.web.asynchronous

• Authentication Required: @tornado.web.authenticated

TORNADO APPLICATION• tornado.web.Application: Main controller class

• Canonical Tornado Hello World:

import tornado.httpserverimport tornado.ioloopimport tornado.web

class MainHandler(tornado.web.RequestHandler): def get(self): self.write("Hello, world")

if __name__ == "__main__": application = tornado.web.Application([ (r"/", MainHandler), ])

http_server = tornado.httpserver.HTTPServer(application) http_server.listen(8888) tornado.ioloop.IOLoop.instance().start()

REQUEST HANDLERS

• tornado.web.RequestHandler

• Extend RequestHandler for larger web apps

• Session Handling

• Database, Cache Connections

• Localization

• Implement for your Application

REQUEST HANDLERS

• Classes implementing define functions for processing

• get, head, post, delete, put, options

• Hooks on Initialization, Prepare, Close

• Functions for setting HTTP Status, Headers, Cookies, Redirects and more

REQUEST HANDLER EXAMPLE

import redisimport tornado.web

class MyRequestHandler(tornado.web.RequestHandler): def initialize(self):

host = self.application.settings['Redis']['host'] port = self.application.settings['Redis']['port'] self.redis = redis.Redis(host, port)

class Homepage(MyRequestHandler):

@tornado.web.asynchronous def get(self):

content = self.redis.get('homepage') self.write(content) self.finish()

TORNADO.TEMPLATE

• Not required

• Similar to other engines

• Limited python exposure in template

• Fast, extensible

• Built-in support in the RequestHandler class

• Adds cache busting static content delivery

REQUESTHANDLER.RENDER

class Home(RequestHandler):

def get(self):

self.render('home.html', username='Leeroy Jenkins');

<html> <body> Hi {{username}}, welcome to our site. </body></html>

Cod

eTe

mpl

ate

BASE TEMPLATE

<html> <head> <title>My Site :: {% block title %}Unextended Template{% end %}</title> <link rel="stylesheet" type="text/css" href="{{ static_url('css/site.css') }}" /> <script type="text/javascript" src="{{ static_url('javascript/site.js') }}"></script> {% if not current_user %}

<script type="text/javascript" src="http://api.recaptcha.net/js/recaptcha_ajax.js"></script>

{% end %} </head> <body{% if current_user %} class="authenticated"{% end %}> {% include "header.html" %} {% if request.uri not in ['/', ''] and current_user %} {{ modules.MemberBar() }} {% end %} <div id="content"> {% block content %} No Content Specified {% end %} </div> <ul id="footer"> <li><a href="/terms">{{_("Terms and Conditions")}}</a></li> <li class="center">{{_("Version")}}: {{ handler.application.settings['version'] }}</li> <li class="right">{{_("Copyright")}} &copy; {{ datetime.date.today().year }}</li> </ul> </body></html>

CONTENT TEMPLATE

{% extends "base.html" %}{% block title %}{{_("Error Title")}}{% end %}{% block content %}<h1>{{_("Error Title")}}</h1><img src="/static/images/sad_robot.png" class="error_robot" /><p class="error_message">{{_("Error Message")}}</p><h2 class="error">{{status_code}} - {{exception}}</h2>{% end %}

TEMPLATE XSRF EXAMPLE

<form action="/login" method="post"> {{ xsrf_form_html() }} <div>Username: <input type="text" name="username"/></div> <div>Password: <input type="password" name="password"/></div> <div><input type="submit" value="Sign in"/></div></form>

No additional work required.

UI MODULES

• Extend templates with reusable widgets across the site

• One import assigned when Application is created

• Similar to RequestHandler in behavior

UIMODULE EXAMPLE

UIMODULE EXAMPLE

class HTTPSCheck(tornado.web.UIModule):

def render(self):

if 'X-Forwarded-Ssl' not in self.request.headers or \ self.request.headers['X-Forwarded-Ssl'] != 'on':

return self.render_string("modules/ssl.html")

return ''

<div class="information"> <a href="https://{{request.host}}{{request.uri}}"> {{_("Click here to use a secure connection")}} </a></div>

 <div>{{ modules.HTTPSCheck() }}</div>

UIM

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lass

Tem

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TORNADO.LOCALE

• Locale files in one directory

• In a csv format

• Named as locale.csv, e.g. en_US.csv

• tornado.locale.load_translations(path)

• Pass path where files are located

• Invoked as _ method in templates

ADDING LOCALIZATION

import tornado.locale as localeimport tornado.web

class RequestHandler(tornado.web.RequestHandler):

def get_user_locale(self): # Fake user object has a get_locale() function user_locale = self.user.get_locale() # If our locale is supported return it if user_locale in locale.get_supported_locales(None): return user_locale # Defaults to Accept-Language header if supported return None

USING LOCALIZATION

<html> <body> {{_("Welcome to our site.")}} </body></html>

LOCALE FILE EXAMPLE: DE_DE"New","Neu""Donate","Spenden""New Paste","Neuer Paste""Secure, Private Pasting","Sicheres Pasten""Unclaimed Hostname","Sie benutzen einen offenen Hostnamen. Klicken Sie heir für weitere Informationen.""Paste Options","Paste Optionen""Formatting","Formatierung""No Formatting","Keine Formatierung""Line Numbers","Zeilennummern""On","An""Off","Aus""Minutes","Minuten""Hour","Stunde""Day","Tag""Week","Woche""Year","Jahr""Expire Paste","Wann soll der Paste gelöscht werden?""Encryption","Verschlüsselung""Encryption Key","Passwort-Verschlüsselung""Encryption Algorithm","Algorithm-Verschlüsselung""Save Paste","Paste speichern""All Rights Reserved","Alle Rechte vorbehalten"

TEMPLATE EXAMPLE AGAIN

<html> <head> <title>My Site :: {% block title %}Unextended Template{% end %}</title> <link rel="stylesheet" type="text/css" href="{{ static_url('css/site.css') }}" /> <script type="text/javascript" src="{{ static_url('javascript/site.js') }}"></script> {% if not current_user %}

<script type="text/javascript" src="http://api.recaptcha.net/js/recaptcha_ajax.js"></script>

{% end %} </head> <body{% if current_user %} class="authenticated"{% end %}> {% include "header.html" %} {% if request.uri not in ['/', ''] and current_user %} {{ modules.MemberBar() }} {% end %} <div id="content"> {% block content %} No Content Specified {% end %} </div> <ul id="footer"> <li><a href="/terms">{{_("Terms and Conditions")}}</a></li> <li class="center">{{_("Version")}}: {{ handler.application.settings['version'] }}</li> <li class="right">{{_("Copyright")}} &copy; {{ datetime.date.today().year }}</li> </ul> </body></html>

TORNADO.AUTH

• Built in Mixins for OpenID, OAuth, OAuth2

• Google, Twitter, Facebook, Facebook Graph, Friendfeed

• Use RequestHandler to extend your own login functions with the mixins if wanted

• Is asynchronous

• Not supported in WSGI and Google App Engine

USING TORNADO.AUTH

class LoginFriendFeed(RequestHandler, tornado.auth.FriendFeedMixin):

@tornado.web.asynchronous def get(self): if self.get_argument("oauth_token", None): self.get_authenticated_user(self.async_callback(self._on_auth)) return self.authorize_redirect()

def _on_auth(self, ffuser): if not ffuser: raise tornado.web.HTTPError(500, "FriendFeed auth failed") return

username = ffuser['username']

- [/login/form, site.auth_reg.LoginForm]- [/login/friendfeed, site.auth_reg.LoginFriendFeed]

TORNADO.IOLOOP

• Protocol independent

• tornado.httpserver.HTTPServer uses ioloop.IOLoop

• RabbitMQ driver Pika uses ioloop.IOLoop

• Built in timer functionality

• tornado.ioloop.add_timeout

• tornado.ioloop.PeriodicCallback

TORNADO.IOLOOP EXAMPLE

class MyClient(object):

def connect(self, host, port):

# Create our socket self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) self.sock.connect((host, port)) self.sock.setblocking(0) self.io_loop = tornado.ioloop.IOLoop.instance()

# Append our handler to tornado's ioloop for our socket events = tornado.ioloop.IOLoop.READ | \ tornado.ioloop.IOLoop.ERROR self.io_loop.add_handler(self.sock.fileno(), self._handle_events, events)

https://github.com/pika/pika/blob/master/pika/adapters/tornado_connection.py

OTHER MODULES OF NOTE• tornado.database

• MySQL wrapper

• tornado.escape

• Misc escape functions

• tornado.httpclient

• Async HTTP client

• tornado.iostream

• Non-blocking TCP helper class

• tornado.options

• Similar to optparse

• tornado.testing

• Test support classes

• tornado.websocket

• Websocket Support

• Memcache

• MongoDB

• PostgreSQL

• RabbitMQ

• Redis

ASYNC DRIVERS

FIN

• Follow me on Twitter @crad

• Blog: http://gavinroy.com

• Pika: http://github.com/pika

• Async RabbitMQ/AMQP Support for Tornado

• We’re hiring at myYearbook.com

• Drop me an email: gmr@myyearbook.com

IMAGE CREDITS

• Lego by Craig A. Rodwayhttp://www.flickr.com/photos/m0php/530526644/

• Delta Clipper X courtesy of NASA

• United Nations San Francisco Conference by Youldhttp://www.flickr.com/photos/un_photo/3450033473/