~ntt-pf-lab/nova/monkey_patch_notification

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<head>

<title>Twisted Documentation: Configuring and Using the Twisted.Web Server</title>

</head>

<h1 class="title">Configuring and Using the Twisted.Web Server</h1>

<div class="toc"><ol><li><a href="#auto0">Twisted Web Development</a></li><ul><li><a href="#auto1">Main Concepts</a></li><li><a href="#auto2">Site Objects</a></li><li><a href="#auto3">Resource objects</a></li><li><a href="#auto4">Resource Trees</a></li><li><a href="#auto5">.rpy scripts</a></li><li><a href="#auto6">Resource rendering</a></li><li><a href="#auto7">Session</a></li></ul><li><a href="#auto8">Advanced Configuration</a></li><ul><li><a href="#auto9">Adding Children</a></li><li><a href="#auto10">Modifying File Resources</a></li><li><a href="#auto11">Virtual Hosts</a></li><li><a href="#auto12">Advanced Techniques</a></li></ul><li><a href="#auto13">Running a Twisted Web Server</a></li><ul><li><a href="#auto14">Serving Flat HTML</a></li><li><a href="#auto15">Resource Scripts</a></li><li><a href="#auto16">Web UIs</a></li><li><a href="#auto17">Spreadable Web Servers</a></li><li><a href="#auto18">Serving PHP/Perl/CGI</a></li><li><a href="#auto19">Serving WSGI Applications</a></li><li><a href="#auto20">Using VHostMonster</a></li></ul><li><a href="#auto21">Rewriting URLs</a></li><li><a href="#auto22">Knowing When We're Not Wanted</a></li><li><a href="#auto23">As-Is Serving</a></li></ol></div>

<h2>Twisted Web Development<a name="auto0"/></h2><a name="development" shape="rect"/>

Twisted Web serves Python objects that implement the interface

IResource.

<h3>Main Concepts<a name="auto1"/></h3>

<ul>

<li><a href="#sites" shape="rect">Site Objects</a> are responsible for creating

<code>HTTPChannel</code> instances to parse the HTTP request, and begin the object lookup process. They contain the root Resource, the resource which represents the URL <code>/</code> on the site.</li>

<li><a href="#resources" shape="rect">Resource</a> objects represent a single URL segment. The <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.resource.IResource.html" title="twisted.web.resource.IResource">IResource</a></code> interface describes the methods a Resource object must implement in order to participate in the object publishing process.</li>

<li><a href="#trees" shape="rect">Resource trees</a> are arrangements of Resource objects into a Resource tree. Starting at the root Resource object, the tree of Resource objects defines the URLs which will be valid.</li>

<li><a href="#rpys" shape="rect">.rpy scripts</a> are python scripts which the twisted.web static file server will execute, much like a CGI. However, unlike CGI they must create a Resource object which will be rendered when the URL is visited.</li>

<li><a href="#rendering" shape="rect">Resource rendering</a> occurs when Twisted Web locates a leaf Resource object. A Resource can either return an html string or write to the request object.</li>

<li><a href="#sessions" shape="rect">Session</a> objects allow you to store information across multiple requests. Each individual browser using the system has a unique Session instance.</li>

</ul>

The Twisted.Web server is started through the Twisted Daemonizer, as in:

% twistd web

</pre>

<h3>Site Objects<a name="auto2"/></h3>

Site objects serve as the glue between a port to listen for HTTP requests on, and a root Resource object.

When using <code>twistd -n web --path /foo/bar/baz</code>, a Site object is created with a root Resource that serves files out of the given path.

You can also create a <code>Site</code> instance by hand, passing it a

<code>Resource</code> object which will serve as the root of the site:

<pre class="python"> 1

from twisted.web import server, resource

from twisted.internet import reactor

class Simple(resource.Resource):

isLeaf = True

def render_GET(self, request):

return "<html>Hello, world!</html>"

site = server.Site(Simple())

reactor.listenTCP(8080, site)

reactor.run()

</pre>

<h3>Resource objects<a name="auto3"/></h3>

<code>Resource</code> objects represent a single URL segment of a site. During URL parsing, <code>getChild</code> is called on the current <code>Resource</code> to produce the next <code>Resource</code> object.

When the leaf Resource is reached, either because there were no more URL segments or a Resource had isLeaf set to True, the leaf Resource is rendered by calling <code>render(request)</code>. See <q>Resource Rendering</q> below for more about this.

During the Resource location process, the URL segments which have already been processed and those which have not yet been processed are available in <code>request.prepath</code> and <code>request.postpath</code>.

A Resource can know where it is in the URL tree by looking at <code>request.prepath</code>, a list of URL segment strings.

A Resource can know which path segments will be processed after it by looking at <code>request.postpath</code>.

If the URL ends in a slash, for example <code>http://example.com/foo/bar/</code>, the final URL segment will be an empty string. Resources can thus know if they were requested with or without a final slash.

Here is a simple Resource object:

<pre class="python"> 1

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from twisted.web.resource import Resource

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class Hello(Resource):

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isLeaf = True

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def getChild(self, name, request):

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if name == '':

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return self

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return Resource.getChild(self, name, request)

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def render_GET(self, request):

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return "Hello, world! I am located at %r." % (request.prepath,)

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resource = Hello()

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</pre>

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<h3>Resource Trees<a name="auto4"/></h3>

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Resources can be arranged in trees using <code>putChild</code>. <code>putChild</code> puts a Resource instance into another Resource instance, making it available at the given path segment name:

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<pre class="python">1

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root = Hello()

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root.putChild('fred', Hello())

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root.putChild('bob', Hello())

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</pre>

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If this root resource is served as the root of a Site instance, the following URLs will all be valid:

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<ul>

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<li><code>http://example.com/</code></li>

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<li><code>http://example.com/fred</code></li>

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<li><code>http://example.com/bob</code></li>

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<li><code>http://example.com/fred/</code></li>

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<li><code>http://example.com/bob/</code></li>

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</ul>

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<h3>.rpy scripts<a name="auto5"/></h3>

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Files with the extension <code>.rpy</code> are python scripts which, when placed in a directory served by Twisted Web, will be executed when visited through the web.

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An <code>.rpy</code> script must define a variable, <code>resource</code>, which is the Resource object that will render the request.

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<code>.rpy</code> files are very convenient for rapid development and prototyping. Since they are executed on every web request, defining a Resource subclass in an <code>.rpy</code> will make viewing the results of changes to your class visible simply by refreshing the page:

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<pre class="python">1

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class MyResource(Resource):

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def render_GET(self, request):

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return "<html>Hello, world!</html>"

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resource = MyResource()

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</pre>

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However, it is often a better idea to define Resource subclasses in Python modules. In order for changes in modules to be visible, you must either restart the Python process, or reload the module:

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<pre class="python">1

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import myresource

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## Comment out this line when finished debugging

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reload(myresource)

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resource = myresource.MyResource()

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</pre>

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Creating a Twisted Web server which serves a directory is easy:

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% twistd -n web --path /Users/dsp/Sites

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</pre>

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<h3>Resource rendering<a name="auto6"/></h3>

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Resource rendering occurs when Twisted Web locates a leaf Resource object to handle a web request. A Resource's <code>render</code> method may do various things to produce output which will be sent back to the browser:

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<ul>

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<li>Return a string</li>

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<li>Call <code>request.write("stuff")</code> as many times as desired, then call <code>request.finish()</code> and return <code>server.NOT_DONE_YET</code> (This is deceptive, since you are in fact done with the request, but is the correct way to do this)</li>

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<li>Request a <code>Deferred</code>, return <code>server.NOT_DONE_YET</code>, and call <code>request.write("stuff")</code> and <code>request.finish()</code> later, in a callback on the <code>Deferred</code>.</li>

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</ul>

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The <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.resource.Resource.html" title="twisted.web.resource.Resource">Resource</a></code>

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class, which is usually what one's Resource classes subclass, has a

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convenient default implementation of <code class="python">render</code>. It will call a method named <code class="python">self.render_METHOD</code> where <q>METHOD</q> is

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whatever HTTP method was used to request this resource. Examples:

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request_GET, request_POST, request_HEAD, and so on. It is recommended

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that you have your resource classes subclass <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.resource.Resource.html" title="twisted.web.resource.Resource">Resource</a></code> and implement <code class="python">render_METHOD</code> methods as opposed to <code class="python">render</code> itself. Note that for certain resources,

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<code class="python">request_POST = request_GET</code> may be

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desirable in case one wants to process arguments passed to the

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resource regardless of whether they used GET

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(<code>?foo=bar&baz=quux</code>, and so forth) or POST.

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<h3>Session<a name="auto7"/></h3>

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HTTP is a stateless protocol; every request-response is treated as an individual unit, distinguishable from any other request only by the URL requested. With the advent of Cookies in the mid nineties, dynamic web servers gained the ability to distinguish between requests coming from different browser sessions by sending a Cookie to a browser. The browser then sends this cookie whenever it makes a request to a web server, allowing the server to track which requests come from which browser session.

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Twisted Web provides an abstraction of this browser-tracking behavior called the Session object. Calling <code>request.getSession()</code> checks to see if a session cookie has been set; if not, it creates a unique session id, creates a Session object, stores it in the Site, and returns it. If a session object already exists, the same session object is returned. In this way, you can store data specific to the session in the session object.

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<h2>Advanced Configuration<a name="auto8"/></h2>

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Non-trivial configurations of Twisted Web are achieved with Python

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configuration files. This is a Python snippet which builds up a variable

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called application. Usually, a <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.application.internet.TCPServer.html" title="twisted.application.internet.TCPServer">twisted.application.internet.TCPServer</a></code> instance will

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be used to make the application listen on a TCP port (80, in case direct

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web serving is desired), with the listener being a

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<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.server.Site.html" title="twisted.web.server.Site">twisted.web.server.Site</a></code>. The resulting file can then

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be run with <code class="shell">twistd -y</code>. Alternatively a reactor

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object can be used directly to make a runnable script.

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The <code>Site</code> will wrap a <code>Resource</code> object -- the

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root.

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<pre class="python">1

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from twisted.application import internet, service

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from twisted.web import static, server

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root = static.File("/var/www/htdocs")

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application = service.Application('web')

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site = server.Site(root)

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sc = service.IServiceCollection(application)

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i = internet.TCPServer(80, site)

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i.setServiceParent(sc)

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</pre>

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Most advanced configurations will be in the form of tweaking the

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root resource object.

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<h3>Adding Children<a name="auto9"/></h3>

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Usually, the root's children will be based on the filesystem's contents.

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It is possible to override the filesystem by explicit <code>putChild</code>

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methods.

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Here are two examples. The first one adds a <code>/doc</code> child

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to serve the documentation of the installed packages, while the second

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one adds a <code>cgi-bin</code> directory for CGI scripts.

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<pre class="python">1

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from twisted.internet import reactor

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root = static.File("/var/www/htdocs")

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root.putChild("doc", static.File("/usr/share/doc"))

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reactor.listenTCP(80, server.Site(root))

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reactor.run()

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</pre>

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<pre class="python">1

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root = static.File("/var/www/htdocs")

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root.putChild("cgi-bin", twcgi.CGIDirectory("/var/www/cgi-bin"))

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reactor.run()

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</pre>

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<h3>Modifying File Resources<a name="auto10"/></h3>

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<code>File</code> resources, be they root object or children thereof,

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have two important attributes that often need to be modified:

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<code>indexNames</code> and <code>processors</code>. <code>indexNames</code>

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determines which files are treated as <q>index files</q> -- served

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up when a directory is rendered. <code>processors</code> determine how

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certain file extensions are treated.

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Here is an example for both, creating a site where all <code>.rpy</code>

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extensions are Resource Scripts, and which renders directories by

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searching for a <code>index.rpy</code> file.

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<pre class="python"> 1

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root = static.File("/var/www/htdocs")

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root.indexNames=['index.rpy']

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root.processors = {'.rpy': script.ResourceScript}

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application = service.Application('web')

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sc = service.IServiceCollection(application)

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site = server.Site(root)

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i.setServiceParent(sc)

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</pre>

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<code>File</code> objects also have a method called <code>ignoreExt</code>.

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This method can be used to give extension-less URLs to users, so that

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implementation is hidden. Here is an example:

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<pre class="python"> 1

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root = static.File("/var/www/htdocs")

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root.ignoreExt(".rpy")

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application = service.Application('web')

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sc = service.IServiceCollection(application)

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site = server.Site(root)

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i.setServiceParent(sc)

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</pre>

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Now, a URL such as <code>/foo</code> might be served from a Resource

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Script called <code>foo.rpy</code>, if no file by the name of <code>foo</code>

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exists.

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<h3>Virtual Hosts<a name="auto11"/></h3>

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Virtual hosting is done via a special resource, that should be

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used as the root resource -- <code>NameVirtualHost</code>.

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<code>NameVirtualHost</code> has an attribute named <code>default</code>,

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which holds the default website. If a different root for some other

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name is desired, the <code>addHost</code> method should be called.

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<pre class="python"> 1

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root = vhost.NameVirtualHost()

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# Add a default -- htdocs

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root.default=static.File("/var/www/htdocs")

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# Add a simple virtual host -- foo.com

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root.addHost("foo.com", static.File("/var/www/foo"))

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# Add a simple virtual host -- bar.com

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root.addHost("bar.com", static.File("/var/www/bar"))

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# The "baz" people want to use Resource Scripts in their web site

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baz = static.File("/var/www/baz")

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baz.processors = {'.rpy': script.ResourceScript}

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baz.ignoreExt('.rpy')

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root.addHost('baz', baz)

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application = service.Application('web')

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sc = service.IServiceCollection(application)

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site = server.Site(root)

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i.setServiceParent(sc)

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</pre>

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<h3>Advanced Techniques<a name="auto12"/></h3>

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Since the configuration is a Python snippet, it is possible to

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use the full power of Python. Here are some simple examples:

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<pre class="python"> 1

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# No need for configuration of virtual hosts -- just make sure

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# a directory /var/vhosts/<vhost name> exists:

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from twisted.web import vhost, static, server

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from twisted.application import internet, service

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root = vhost.NameVirtualHost()

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root.default = static.File("/var/www/htdocs")

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for dir in os.listdir("/var/vhosts"):

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root.addHost(dir, static.File(os.path.join("/var/vhosts", dir)))

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application = service.Application('web')

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sc = service.IServiceCollection(application)

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site = server.Site(root)

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i.setServiceParent(sc)

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</pre>

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<pre class="python"> 1

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# Determine ports we listen on based on a file with numbers:

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from twisted.web import vhost, static, server

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root = static.File("/var/www/htdocs")

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site = server.Site(root)

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application = service.Application('web')

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serviceCollection = service.IServiceCollection(application)

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for num in map(int, open("/etc/web/ports").read().split()):

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serviceCollection.addCollection(internet.TCPServer(num, site))

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</pre>

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<h2>Running a Twisted Web Server<a name="auto13"/></h2>

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In many cases, you'll end up repeating common usage patterns of

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twisted.web. In those cases you'll probably want to use Twisted's

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pre-configured web server setup.

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The easiest way to run a Twisted Web server is with the Twisted Daemonizer.

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For example, this command will run a web server which serves static files from

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a particular directory:

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% twistd web --path /path/to/web/content

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</pre>

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If you just want to serve content from your own home directory, the

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following will do:

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% twistd web --path ~/public_html/

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</pre>

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You can stop the server at any time by going back to the directory you

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started it in and running the command:

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% kill `cat twistd.pid`

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</pre>

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Some other configuration options are available as well:

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<ul>

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<li> <code>--port</code>: Specify the port for the web

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server to listen on. This defaults to 8080. </li>

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<li> <code>--logfile</code>: Specify the path to the

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log file. </li>

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</ul>

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The full set of options that are available can be seen with:

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% twistd web --help

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</pre>

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<h3>Serving Flat HTML<a name="auto14"/></h3>

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Twisted.Web serves flat HTML files just as it does any other flat file.

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<h3>Resource Scripts<a name="auto15"/></h3>

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A Resource script is a Python file ending with the extension <code>.rpy</code>, which is required to create an instance of a (subclass of a) <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.resource.Resource.html" title="twisted.web.resource.Resource">twisted.web.resource.Resource</a></code>.

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Resource scripts have 3 special variables:

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<ul>

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<li> <code class="py-src-identifier">__file__</code>: The name of the .rpy file, including the full path. This variable is automatically defined and present within the namespace. </li>

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<li> <code class="py-src-identifier">registry</code>: An object of class <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.static.Registry.html" title="twisted.web.static.Registry">static.Registry</a></code>. It can be used to access and set persistent data keyed by a class.</li>

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<li> <code class="py-src-identifier">resource</code>: The variable which must be defined by the script and set to the resource instance that will be used to render the page. </li>

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</ul>

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A very simple Resource Script might look like:

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<pre class="python">1

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class MyGreatResource(resource.Resource):

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def render_GET(self, request):

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return "<html>foo</html>"

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resource = MyGreatResource()

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</pre>

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A slightly more complicated resource script, which accesses some

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persistent data, might look like:

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<pre class="python"> 1

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from SillyWeb import Counter

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counter = registry.getComponent(Counter)

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if not counter:

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registry.setComponent(Counter, Counter())

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counter = registry.getComponent(Counter)

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class MyResource(resource.Resource):

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def render_GET(self, request):

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counter.increment()

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return "you are visitor %d" % counter.getValue()

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resource = MyResource()

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</pre>

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This is assuming you have the <code>SillyWeb.Counter</code> module,

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implemented something like the following:

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<pre class="python"> 1

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class Counter:

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def __init__(self):

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self.value = 0

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def increment(self):

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self.value += 1

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def getValue(self):

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return self.value

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</pre>

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The

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<a href="http://www.divmod.org/projects/nevow" shape="rect">Nevow</a> framework, available as

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part of the <a href="http://www.divmod.org/projects/quotient" shape="rect">Quotient</a> project,

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is an advanced system for giving Web UIs to your application. Nevow uses Twisted Web but is

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not itself part of Twisted.

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<h3>Spreadable Web Servers<a name="auto17"/></h3>

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One of the most interesting applications of Twisted.Web is the distributed webserver; multiple servers can all answer requests on the same port, using the <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.spread.html" title="twisted.spread">twisted.spread</a></code> package for <q>spreadable</q> computing. In two different directories, run the commands:

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% twistd web --user

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% twistd web --personal [other options, if you desire]

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</pre>

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Once you're running both of these instances, go to <code>http://localhost:8080/your_username.twistd/</code> -- you will see the front page from the server you created with the <code>--personal</code> option. What's happening here is that the request you've sent is being relayed from the central (User) server to your own (Personal) server, over a PB connection. This technique can be highly useful for small <q>community</q> sites; using the code that makes this demo work, you can connect one HTTP port to multiple resources running with different permissions on the same machine, on different local machines, or even over the internet to a remote site.

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By default, a personal server listens on a UNIX socket in the owner's home

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directory. The <code class="shell">--port</code> option can be used to make

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it listen on a different address, such as a TCP or SSL server or on a UNIX

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server in a different location. If you use this option to make a personal

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server listen on a different address, the central (User) server won't be

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able to find it, but a custom server which uses the same APIs as the central

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server might. Another use of the <code class="shell">--port</code> option

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is to make the UNIX server robust against system crashes. If the server

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crashes and the UNIX socket is left on the filesystem, the personal server

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will not be able to restart until it is removed. However, if <code class="shell">--port unix:/home/username/.twistd-web-pb:wantPID=1</code> is

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supplied when creating the personal server, then a lockfile will be used to

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keep track of whether the server socket is in use and automatically delete

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it when it is not.

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<h3>Serving PHP/Perl/CGI<a name="auto18"/></h3>

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Everything related to CGI is located in the

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<code>twisted.web.twcgi</code>, and it's here you'll find the classes that you

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need to subclass in order to support the language of your (or somebody elses)

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taste. You'll also need to create your own kind of resource if you are using a

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non-unix operatingsystem (such as Windows), or if the default resources has

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wrong pathnames to the parsers.

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The following snippet is a .rpy that serves perl-files. Look at <code>twisted.web.twcgi</code>

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for more examples regarding twisted.web and CGI.

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<pre class="python">1

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from twisted.web import static, twcgi

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class PerlScript(twcgi.FilteredScript):

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filter = '/usr/bin/perl' # Points to the perl parser

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resource = static.File("/perlsite") # Points to the perl website

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resource.processors = {".pl": PerlScript} # Files that end with .pl will be

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# processed by PerlScript

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resource.indexNames = ['index.pl']

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</pre>

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<h3>Serving WSGI Applications<a name="auto19"/></h3>

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<a href="http://wsgi.org/wsgi/" shape="rect">WSGI</a> is the Web Server Gateway

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Interface. It is a specification for web servers and application servers to

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communicate with Python web applications. All modern Python web frameworks

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support the WSGI interface.

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The easiest way to get started with WSGI application is to use the twistd

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command:

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% twistd -n web --wsgi=helloworld.application

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</pre>

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This assumes that you have a WSGI application called application in

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your helloworld module/package, which might look like this:

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<pre class="python">1

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def application(environ, start_response):

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"""Basic WSGI Application"""

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start_response('200 OK', [('Content-type','text/plain')])

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return ['Hello World!']

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</pre>

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The above setup will be suitable for many applications where all that is

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needed is to server the WSGI application at the site's root. However, for

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greater control, Twisted provides support for using WSGI applications as

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resources <code class="api">twisted.web.wsgi.WSGIResource</code>.

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Here is an example of a WSGI application being served as the root resource

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for a site, in the following tac file:

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<pre class="python"> 1

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from twisted.web.wsgi import WSGIResource

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from twisted.python.threadpool import ThreadPool

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from twisted.application import service, strports

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# Create and start a thread pool,

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wsgiThreadPool = ThreadPool()

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wsgiThreadPool.start()

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# ensuring that it will be stopped when the reactor shuts down

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reactor.addSystemEventTrigger('after', 'shutdown', wsgiThreadPool.stop)

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def application(environ, start_response):

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"""A basic WSGI application"""

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start_response('200 OK', [('Content-type','text/plain')])

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return ['Hello World!']

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# Create the WSGI resource

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wsgiAppAsResource = WSGIResource(reactor, wsgiThreadPool, application)

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# Hooks for twistd

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application = service.Application('Twisted.web.wsgi Hello World Example')

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server = strports.service('tcp:8080', server.Site(wsgiAppAsResource))

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server.setServiceParent(application)

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</pre>

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This can then be run like any other .tac file:

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% twistd -ny myapp.tac

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</pre>

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Because of the synchronous nature of WSGI, each application call (for

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each request) is called within a thread, and the result is written back to the

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web server. For this, a <code class="api">twisted.python.threadpool.ThreadPool</code>

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instance is used.

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<h3>Using VHostMonster<a name="auto20"/></h3>

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It is common to use one server (for example, Apache) on a site with multiple

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names which then uses reverse proxy (in Apache, via <code>mod_proxy</code>) to different

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internal web servers, possibly on different machines. However, naive

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configuration causes miscommunication: the internal server firmly believes it

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is running on <q>internal-name:port</q>, and will generate URLs to that effect,

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which will be completely wrong when received by the client.

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While Apache has the ProxyPassReverse directive, it is really a hack

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and is nowhere near comprehensive enough. Instead, the recommended practice

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in case the internal web server is Twisted.Web is to use VHostMonster.

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From the Twisted side, using VHostMonster is easy: just drop a file named

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(for example) <code>vhost.rpy</code> containing the following:

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<pre class="python">1

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resource = vhost.VHostMonsterResource()

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</pre>

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Of course, an equivalent <code>.trp</code> can also be used. Make sure

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the web server is configured with the correct processors for the

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<code>rpy</code> or <code>trp</code> extensions (the web server

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<code>twistd web --path</code> generates by default is so configured).

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From the Apache side, instead of using the following ProxyPass directive:

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ProxyPass / http://localhost:8538/

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ServerName example.com

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</VirtualHost>

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</pre>

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Use the following directive:

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ProxyPass / http://localhost:8538/vhost.rpy/http/example.com:80/

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ServerName example.com

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</VirtualHost>

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</pre>

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Here is an example for Twisted.Web's reverse proxy:

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<pre class="python"> 1

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from twisted.web import proxy, server, vhost

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vhostName = 'example.com'

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reverseProxy = proxy.ReverseProxyResource('internal', 8538,

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'/vhost.rpy/http/'+vhostName+'/')

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root = vhost.NameVirtualHost()

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root.addHost(vhostName, reverseProxy)

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site = server.Site(root)

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application = service.Application('web-proxy')

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sc = service.IServiceCollection(application)

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i.setServiceParent(sc)

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</pre>

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<h2>Rewriting URLs<a name="auto21"/></h2>

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Sometimes it is convenient to modify the content of the

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<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.server.Request.html" title="twisted.web.server.Request">Request</a></code> object

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before passing it on. Because this is most often used to rewrite

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either the URL, the similarity to Apache's <code>mod_rewrite</code> has

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inspired the <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.rewrite.html" title="twisted.web.rewrite">twisted.web.rewrite</a></code> module. Using

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this module is done via wrapping a resource with a

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<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.rewrite.RewriterResource.html" title="twisted.web.rewrite.RewriterResource">twisted.web.rewrite.RewriterResource</a></code> which

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then has rewrite rules. Rewrite rules are functions which accept a request

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object, and possible modify it. After all rewrite rules run, the child

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resolution chain continues as if the wrapped resource, rather than

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the <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.rewrite.RewriterResource.html" title="twisted.web.rewrite.RewriterResource">RewriterResource</a></code>,

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was the child.

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Here is an example, using the only rule currently supplied by Twisted

894

itself:

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<pre class="python">1

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default_root = rewrite.RewriterResource(default, rewrite.tildeToUsers)

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</pre>

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This causes the URL <code>/~foo/bar.html</code> to be treated like

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<code>/users/foo/bar.html</code>. If done after setting default's

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<code>users</code> child to a

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<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.distrib.UserDirectory.html" title="twisted.web.distrib.UserDirectory">distrib.UserDirectory</a></code>,

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it gives a configuration similar to the classical configuration of

905

web server, common since the first NCSA servers.

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<h2>Knowing When We're Not Wanted<a name="auto22"/></h2>

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Sometimes it is useful to know when the other side has broken the connection.

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Here is an example which does that:

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<pre class="python"> 1

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from twisted.python.util import println

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class ExampleResource(Resource):

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def render_GET(self, request):

938

request.write("hello world")

939

d = request.notifyFinish()

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d.addCallback(lambda _: println("finished normally"))

941

d.addErrback(println, "error")

942

reactor.callLater(10, request.finish)

943

return server.NOT_DONE_YET

944

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resource = ExampleResource()

946

</pre>

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This will allow us to run statistics on the log-file to see how many users

949

are frustrated after merely 10 seconds.

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<h2>As-Is Serving<a name="auto23"/></h2>

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Sometimes, you want to be able to send headers and status directly. While

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you can do this with a

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<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.script.ResourceScript.html" title="twisted.web.script.ResourceScript">ResourceScript</a></code>, an easier

956

way is to use <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.static.AsIsProcessor.html" title="twisted.web.static.AsIsProcessor">AsIsProcessor</a></code>.

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Use it by, for example, addding it as a processor for the <code>.asis</code>

958

extension. Here is a sample file:

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HTTP/1.0 200 OK

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Content-Type: text/html

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Hello world

965

</pre>

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</div>

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<a href="index.html">Index</a>

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Version: 10.0.0

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</body>

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</html>

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