doc/web/howto/web-in-60/wsgi.html

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   3 <title>Twisted Documentation: WSGI</title>
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   8     <h1 class="title">WSGI</h1>
   9     <div class="toc"><ol/></div>
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  11 <span/>
  12
  13 <p>The goal of this example is to show you how to
  14 use <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.wsgi.WSGIResource.html" title="twisted.web.wsgi.WSGIResource">WSGIResource</a></code>,
  15 another existing <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.resource.Resource.html" title="twisted.web.resource.Resource">Resource</a></code> subclass, to
  16 serve <a href="http://www.python.org/dev/peps/pep-0333/" shape="rect">WSGI applications</a>
  17 in a Twisted Web server.</p>
  18
  19 <p>Note that <code>WSGIResource</code> is a multithreaded WSGI container. Like
  20 any other WSGI container, you can't do anything asynchronous in your WSGI
  21 applications, even though this is a Twisted WSGI container.</p>
  22
  23 <p>The first new thing in this example is the import
  24 of <code>WSGIResource</code>:</p>
  25
  26 <pre class="python"><p class="py-linenumber">1
  27 </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">wsgi</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">WSGIResource</span>
  28 </pre>
  29
  30 <p>Nothing too surprising there. We still need one of the other usual suspects,
  31 too:</p>
  32
  33 <pre class="python"><p class="py-linenumber">1
  34 </p><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>
  35 </pre>
  36
  37 <p>You'll see why in a minute. Next, we need a WSGI application. Here's a really
  38 simple one just to get things going:</p>
  39
  40 <pre class="python"><p class="py-linenumber">1
  41 2
  42 3
  43 </p><span class="py-src-keyword">def</span> <span class="py-src-identifier">application</span>(<span class="py-src-parameter">environ</span>, <span class="py-src-parameter">start_response</span>):
  44     <span class="py-src-variable">start_response</span>(<span class="py-src-string">'200 OK'</span>, [(<span class="py-src-string">'Content-type'</span>, <span class="py-src-string">'text/plain'</span>)])
  45     <span class="py-src-keyword">return</span> [<span class="py-src-string">'Hello, world!'</span>]
  46 </pre>
  47
  48 <p>If this doesn't make sense to you, take a look at one of
  49 these <a href="http://wsgi.org/wsgi/Learn_WSGI" shape="rect">fine tutorials</a>. Otherwise,
  50 or once you're done with that, the next step is to create
  51 a <code>WSGIResource</code> instance, as this is going to be
  52 another <a href="rpy-scripts.html" shape="rect">rpy script</a> example:</p>
  53
  54 <pre class="python"><p class="py-linenumber">1
  55 </p><span class="py-src-variable">resource</span> = <span class="py-src-variable">WSGIResource</span>(<span class="py-src-variable">reactor</span>, <span class="py-src-variable">reactor</span>.<span class="py-src-variable">getThreadPool</span>(), <span class="py-src-variable">application</span>)
  56 </pre>
  57
  58 <p>Let's dwell on this line for a minute. The first parameter passed
  59 to <code>WSGIResource</code> is the reactor. Despite the fact that the
  60 reactor is global and any code that wants it can always just import it
  61 (as, in fact, this rpy script simply does itself), passing it around
  62 as a parameter leaves the door open for certain future possibilities -
  63 for example, having more than one reactor. There are also testing
  64 implications. Consider how much easier it is to unit test a function
  65 that accepts a reactor - perhaps a mock reactor specially constructed
  66 to make your tests easy to write - rather than importing the real
  67 global reactor. That's why <code>WSGIResource</code> requires you to
  68 pass the reactor to it.</p>
  69
  70 <p>The second parameter passed to <code>WSGIResource</code> is
  71 a <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.python.threadpool.ThreadPool.html" title="twisted.python.threadpool.ThreadPool">ThreadPool</a></code>. <code>WSGIResource</code>
  72 uses this to actually call the application object passed in to it. To keep this
  73 example short, we're passing in the reactor's internal threadpool here, letting
  74 us skip its creation and shutdown-time destruction. For finer control over how
  75 many WSGI requests are served in parallel, you may want to create your own
  76 thread pool to use with your <code>WSGIResource</code>, but for simple testing,
  77 using the reactor's is fine.</p>
  78
  79 <p>The final argument is the application object. This is pretty typical of how
  80 WSGI containers work.</p>
  81
  82 <p>The example, sans interruption:</p>
  83
  84 <pre class="python"><p class="py-linenumber">1
  85 2
  86 3
  87 4
  88 5
  89 6
  90 7
  91 8
  92 </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">wsgi</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">WSGIResource</span>
  93 <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>
  94
  95 <span class="py-src-keyword">def</span> <span class="py-src-identifier">application</span>(<span class="py-src-parameter">environ</span>, <span class="py-src-parameter">start_response</span>):
  96     <span class="py-src-variable">start_response</span>(<span class="py-src-string">'200 OK'</span>, [(<span class="py-src-string">'Content-type'</span>, <span class="py-src-string">'text/plain'</span>)])
  97     <span class="py-src-keyword">return</span> [<span class="py-src-string">'Hello, world!'</span>]
  98
  99 <span class="py-src-variable">resource</span> = <span class="py-src-variable">WSGIResource</span>(<span class="py-src-variable">reactor</span>, <span class="py-src-variable">reactor</span>.<span class="py-src-variable">getThreadPool</span>(), <span class="py-src-variable">application</span>)
 100 </pre>
 101
 102 <p>Up to the point where the <code>WSGIResource</code> instance defined here
 103 exists in the resource hierarchy, the normal resource traversal rules
 104 apply: <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>
 105 will be called to handle each segment. Once the <code>WSGIResource</code> is
 106 encountered, though, that process stops and all further URL handling is the
 107 responsibility of the WSGI application. This application does nothing with the
 108 URL, though, so you won't be able to tell that.</p>
 109
 110 <p>Oh, and as was the case with the first static file example, there's also a
 111 command line option you can use to avoid a lot of this. If you just put the
 112 above application function, without all of the <code>WSGIResource</code> stuff,
 113 into a file, say, <code>foo.py</code>, then you can launch a roughly equivalent
 114 server like this:</p>
 115
 116 <pre class="shell" xml:space="preserve">
 117 $ twistd -n web --wsgi foo.application
 118 </pre>
 119
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