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<div class="section" id="custom-response-codes">
<h1>Custom Response Codes<a class="headerlink" href="#custom-response-codes" title="Permalink to this headline">ΒΆ</a></h1>
<p>The previous example introduced <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.error.NoResource.html">NoResource</a> , a Twisted Web error resource which
responds with a 404 (not found) code. This example will cover the APIs
that <code class="docutils literal"><span class="pre">NoResource</span></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>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">twisted.web.server</span> <span class="kn">import</span> <span class="n">Site</span>
<span class="kn">from</span> <span class="nn">twisted.web.resource</span> <span class="kn">import</span> <span class="n">Resource</span>
<span class="kn">from</span> <span class="nn">twisted.internet</span> <span class="kn">import</span> <span class="n">reactor</span>
</pre></div>
</div>
<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 <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.server.Request.html">Request</a> object has
shown up in a couple of places, but so far we’ve ignored it. It is a parameter
to the <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.resource.Resource.getChild.html">getChild</a>
API as well as to render methods such as <code class="docutils literal"><span class="pre">render_GET</span></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 <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.http.Request.setResponseCode.html">setResponseCode</a> method to - you guessed
it - set the response’s status code.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">PaymentRequired</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">render_GET</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">request</span><span class="p">):</span>
<span class="n">request</span><span class="o">.</span><span class="n">setResponseCode</span><span class="p">(</span><span class="mi">402</span><span class="p">)</span>
<span class="k">return</span> <span class="s">"<html><body>Please swipe your credit card.</body></html>"</span>
</pre></div>
</div>
<p>Just like the other resources I’ve demonstrated, this one returns a
string from its <code class="docutils literal"><span class="pre">render_GET</span></code> method to define the body of
the response. All that’s different is the call
to <code class="docutils literal"><span class="pre">setResponseCode</span></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 class="docutils literal"><span class="pre">/buy</span></code> :</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">root</span> <span class="o">=</span> <span class="n">Resource</span><span class="p">()</span>
<span class="n">root</span><span class="o">.</span><span class="n">putChild</span><span class="p">(</span><span class="s">"buy"</span><span class="p">,</span> <span class="n">PaymentRequired</span><span class="p">())</span>
<span class="n">factory</span> <span class="o">=</span> <span class="n">Site</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="n">reactor</span><span class="o">.</span><span class="n">listenTCP</span><span class="p">(</span><span class="mi">8880</span><span class="p">,</span> <span class="n">factory</span><span class="p">)</span>
<span class="n">reactor</span><span class="o">.</span><span class="n">run</span><span class="p">()</span>
</pre></div>
</div>
<p>Here’s the complete example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">twisted.web.server</span> <span class="kn">import</span> <span class="n">Site</span>
<span class="kn">from</span> <span class="nn">twisted.web.resource</span> <span class="kn">import</span> <span class="n">Resource</span>
<span class="kn">from</span> <span class="nn">twisted.internet</span> <span class="kn">import</span> <span class="n">reactor</span>
<span class="k">class</span> <span class="nc">PaymentRequired</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">render_GET</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">request</span><span class="p">):</span>
<span class="n">request</span><span class="o">.</span><span class="n">setResponseCode</span><span class="p">(</span><span class="mi">402</span><span class="p">)</span>
<span class="k">return</span> <span class="s">"<html><body>Please swipe your credit card.</body></html>"</span>
<span class="n">root</span> <span class="o">=</span> <span class="n">Resource</span><span class="p">()</span>
<span class="n">root</span><span class="o">.</span><span class="n">putChild</span><span class="p">(</span><span class="s">"buy"</span><span class="p">,</span> <span class="n">PaymentRequired</span><span class="p">())</span>
<span class="n">factory</span> <span class="o">=</span> <span class="n">Site</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="n">reactor</span><span class="o">.</span><span class="n">listenTCP</span><span class="p">(</span><span class="mi">8880</span><span class="p">,</span> <span class="n">factory</span><span class="p">)</span>
<span class="n">reactor</span><span class="o">.</span><span class="n">run</span><span class="p">()</span>
</pre></div>
</div>
<p>Run the server and visit <code class="docutils literal"><span class="pre">http://localhost:8880/buy</span></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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