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<title>Twisted Documentation: Custom Response Codes</title>
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<h1 class="title">Custom Response Codes</h1>
<div class="toc"><ol/></div>
<div class="content">
<span/>
<p>The previous example introduced <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.error.NoResource.html" title="twisted.web.error.NoResource">NoResource</a></code>, a Twisted Web error resource which
responds with a 404 (not found) code. This example will cover the APIs
that <code>NoResource</code> uses to do this so that you can generate your own
custom response codes as desired.</p>
<p>First, the now-standard import preamble:</p>
<pre class="python"><p class="py-linenumber">1
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</p><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">web</span>.<span class="py-src-variable">server</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">Site</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">web</span>.<span class="py-src-variable">resource</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">Resource</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">reactor</span>
</pre>
<p>Now we'll define a new resource class that always returns a 402 (payment
required) response. This is really not very different from the resources that
was defined in previous examples. The fact that it has a response code other
than 200 doesn't change anything else about its role. This will require using
the request object, though, which none of the previous examples have done.</p>
<p>The <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.server.Request.html" title="twisted.web.server.Request">Request</a></code> object has
shown up in a couple of places, but so far we've ignored it. It is a parameter
to the <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.resource.Resource.getChild.html" title="twisted.web.resource.Resource.getChild">getChild</a></code>
API as well as to render methods such as <code>render_GET</code>. As you might
have suspected, it represents the request for which a response is to be
generated. Additionally, it also represents the response being generated. In
this example we're going to use its <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.http.Request.setResponseCode.html" title="twisted.web.http.Request.setResponseCode">setResponseCode</a></code> method to - you guessed
it - set the response's status code.</p>
<pre class="python"><p class="py-linenumber">1
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</p><span class="py-src-keyword">class</span> <span class="py-src-identifier">PaymentRequired</span>(<span class="py-src-parameter">Resource</span>):
<span class="py-src-keyword">def</span> <span class="py-src-identifier">render_GET</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">request</span>):
<span class="py-src-variable">request</span>.<span class="py-src-variable">setResponseCode</span>(<span class="py-src-number">402</span>)
<span class="py-src-keyword">return</span> <span class="py-src-string">"<html><body>Please swipe your credit card.</body></html>"</span>
</pre>
<p>Just like the other resources I've demonstrated, this one returns a
string from its <code>render_GET</code> method to define the body of
the response. All that's different is the call
to <code>setResponseCode</code> to override the default response code,
200, with a different one.</p>
<p>Finally, the code to set up the site and reactor. We'll put an instance of
the above defined resource at <code>/buy</code>:</p>
<pre class="python"><p class="py-linenumber">1
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</p><span class="py-src-variable">root</span> = <span class="py-src-variable">Resource</span>()
<span class="py-src-variable">root</span>.<span class="py-src-variable">putChild</span>(<span class="py-src-string">"buy"</span>, <span class="py-src-variable">PaymentRequired</span>())
<span class="py-src-variable">factory</span> = <span class="py-src-variable">Site</span>(<span class="py-src-variable">root</span>)
<span class="py-src-variable">reactor</span>.<span class="py-src-variable">listenTCP</span>(<span class="py-src-number">8880</span>, <span class="py-src-variable">factory</span>)
<span class="py-src-variable">reactor</span>.<span class="py-src-variable">run</span>()
</pre>
<p>Here's the complete example:</p>
<pre class="python"><p class="py-linenumber"> 1
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</p><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">web</span>.<span class="py-src-variable">server</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">Site</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">web</span>.<span class="py-src-variable">resource</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">Resource</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">reactor</span>
<span class="py-src-keyword">class</span> <span class="py-src-identifier">PaymentRequired</span>(<span class="py-src-parameter">Resource</span>):
<span class="py-src-keyword">def</span> <span class="py-src-identifier">render_GET</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">request</span>):
<span class="py-src-variable">request</span>.<span class="py-src-variable">setResponseCode</span>(<span class="py-src-number">402</span>)
<span class="py-src-keyword">return</span> <span class="py-src-string">"<html><body>Please swipe your credit card.</body></html>"</span>
<span class="py-src-variable">root</span> = <span class="py-src-variable">Resource</span>()
<span class="py-src-variable">root</span>.<span class="py-src-variable">putChild</span>(<span class="py-src-string">"buy"</span>, <span class="py-src-variable">PaymentRequired</span>())
<span class="py-src-variable">factory</span> = <span class="py-src-variable">Site</span>(<span class="py-src-variable">root</span>)
<span class="py-src-variable">reactor</span>.<span class="py-src-variable">listenTCP</span>(<span class="py-src-number">8880</span>, <span class="py-src-variable">factory</span>)
<span class="py-src-variable">reactor</span>.<span class="py-src-variable">run</span>()
</pre>
<p>Run the server and visit <code>http://localhost:8880/buy</code> in your
browser. It'll look pretty boring, but if you use Firefox's View Page Info
right-click menu item (or your browser's equivalent), you'll be able to see that
the server indeed sent back a 402 response code.</p>
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