~cbehrens/nova/lp844160-build-works-with-zones

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<title>Twisted Documentation: Handling POSTs</title>

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<h1 class="title">Handling POSTs</h1>

All of the previous examples have focused on <code>GET</code>

requests. Unlike <code>GET</code> requests, <code>POST</code> requests can have

a request body - extra data after the request headers; for example, data

representing the contents of an HTML form. Twisted Web makes this data available

to applications via the <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.

Here's an example web server which renders a static HTML form and then

generates a dynamic page when that form is posted back to it. Disclaimer: While

it's convenient for this example, it's often not a good idea to make a resource

that <code>POST</code>s to itself; this isn't about Twisted Web, but the nature

of HTTP in general; if you do this in a real application, make sure you

understand the possible negative consequences.

As usual, we start with some imports. In addition to the Twisted imports,

this example uses the <code>cgi</code> module to <a href="http://en.wikipedia.org/wiki/Cross-site_scripting" shape="rect">escape user-entered

content</a> for inclusion in the output.

<pre class="python">1

from twisted.web.server import Site

from twisted.web.resource import Resource

from twisted.internet import reactor

import cgi

</pre>

Next, we'll define a resource which is going to do two things. First, it will

respond to <code>GET</code> requests with a static HTML form:

<pre class="python">1

class FormPage(Resource):

def render_GET(self, request):

return ''

</pre>

This is similar to the resource used in a <a href="dynamic-content.html" shape="rect">previous installment</a>. However, we'll now add

one more method to give it a second behavior; this <code>render_POST</code>

method will allow it to accept <code>POST</code> requests:

<pre class="python">1

def render_POST(self, request):

return 'You submitted: %s' % (cgi.escape(request.args["the-field"][0]),)

</pre>

The main thing to note here is the use of <code>request.args</code>. This is

a dictionary-like object that provides access to the contents of the form. The

keys in this dictionary are the names of inputs in the form. Each value is a

list containing strings (since there can be multiple inputs with the same name),

which is why we had to extract the first element to pass to

<code>cgi.escape</code>. <code>request.args</code> will be populated from form

contents whenever a <code>POST</code> request is made with a content type of

<code>application/x-www-form-urlencoded</code> or

<code>multipart/form-data</code> (it's also populated by query arguments for any

type of request).

Finally, the example just needs the usual site creation and port setup:

<pre class="python">1

root = Resource()

root.putChild("form", FormPage())

factory = Site(root)

reactor.listenTCP(8880, factory)

reactor.run()

</pre>

Run the server and visit <a href="http://localhost:8880/form" shape="rect">http://localhost:8880/form</a>, submit the

form, and watch it generate a page including the value you entered into the

single field.

Here's the complete source for the example:

<pre class="python"> 1

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import cgi

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class FormPage(Resource):

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def render_GET(self, request):

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return ''

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def render_POST(self, request):

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root = Resource()

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root.putChild("form", FormPage())

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factory = Site(root)

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reactor.listenTCP(8880, factory)

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reactor.run()

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</pre>

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Version: 10.0.0

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