doc/web/howto/web-in-60/session-endings.html

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   3 <title>Twisted Documentation: Session Endings</title>
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   8     <h1 class="title">Session Endings</h1>
   9     <div class="toc"><ol/></div>
  10     <div class="content">
  11 <span/>
  12
  13 <p>The previous two examples introduced Twisted Web's session APIs. This
  14 included accessing the session object, storing state on it, and retrieving it
  15 later, as well as the idea that the <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.server.Session.html" title="twisted.web.server.Session">Session</a></code> object has a lifetime which is tied to
  16 the notional session it represents. This example demonstrates how to exert some
  17 control over that lifetime and react when it expires.</p>
  18
  19 <p>The lifetime of a session is controlled by the <code>sessionTimeout</code>
  20 attribute of the <code>Session</code> class. This attribute gives the number of
  21 seconds a session may go without being accessed before it expires. The default
  22 is 15 minutes. In this example we'll change that to a different value.</p>
  23
  24 <p>One way to override the value is with a subclass:</p>
  25
  26 <pre class="python"><p class="py-linenumber">1
  27 2
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  30 </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">Session</span>
  31
  32 <span class="py-src-keyword">class</span> <span class="py-src-identifier">ShortSession</span>(<span class="py-src-parameter">Session</span>):
  33     <span class="py-src-variable">sessionTimeout</span> = <span class="py-src-number">60</span>
  34 </pre>
  35
  36 <p>To have Twisted Web actually make use of this session class, rather
  37 than the default, it is also necessary to override
  38 the <code>sessionFactory</code> attribute of <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.server.Site.html" title="twisted.web.server.Site">Site</a></code>. We could do this with another
  39 subclass, but we could also do it to just one instance
  40 of <code>Site</code>:</p>
  41
  42 <pre class="python"><p class="py-linenumber">1
  43 2
  44 3
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  46 </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>
  47
  48 <span class="py-src-variable">factory</span> = <span class="py-src-variable">Site</span>(<span class="py-src-variable">rootResource</span>)
  49 <span class="py-src-variable">factory</span>.<span class="py-src-variable">sessionFactory</span> = <span class="py-src-variable">ShortSession</span>
  50 </pre>
  51
  52 <p>Sessions given out for requests served by this <code>Site</code> will
  53 use <code>ShortSession</code> and only last one minute without activity.</p>
  54
  55 <p>You can have arbitrary functions run when sessions expire,
  56 too. This can be useful for cleaning up external resources associated
  57 with the session, tracking usage statistics, and more. This
  58 functionality is provided via <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.web.server.Session.notifyOnExpire.html" title="twisted.web.server.Session.notifyOnExpire">Session.notifyOnExpire</a></code>. It accepts a
  59 single argument: a function to call when the session expires. Here's a
  60 trivial example which prints a message whenever a session expires:</p>
  61
  62 <pre class="python"><p class="py-linenumber"> 1
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  77 </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">resource</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">Resource</span>
  78
  79 <span class="py-src-keyword">class</span> <span class="py-src-identifier">ExpirationLogger</span>(<span class="py-src-parameter">Resource</span>):
  80     <span class="py-src-variable">sessions</span> = <span class="py-src-variable">set</span>()
  81
  82     <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>):
  83         <span class="py-src-variable">session</span> = <span class="py-src-variable">request</span>.<span class="py-src-variable">getSession</span>()
  84         <span class="py-src-keyword">if</span> <span class="py-src-variable">session</span>.<span class="py-src-variable">uid</span> <span class="py-src-keyword">not</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">sessions</span>:
  85             <span class="py-src-variable">self</span>.<span class="py-src-variable">sessions</span>.<span class="py-src-variable">add</span>(<span class="py-src-variable">session</span>.<span class="py-src-variable">uid</span>)
  86             <span class="py-src-variable">session</span>.<span class="py-src-variable">notifyOnExpire</span>(<span class="py-src-keyword">lambda</span>: <span class="py-src-variable">self</span>.<span class="py-src-variable">_expired</span>(<span class="py-src-variable">session</span>.<span class="py-src-variable">uid</span>))
  87         <span class="py-src-keyword">return</span> <span class="py-src-string">&quot;&quot;</span>
  88
  89     <span class="py-src-keyword">def</span> <span class="py-src-identifier">_expired</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">uid</span>):
  90         <span class="py-src-keyword">print</span> <span class="py-src-string">&quot;Session&quot;</span>, <span class="py-src-variable">uid</span>, <span class="py-src-string">&quot;has expired.&quot;</span>
  91         <span class="py-src-variable">self</span>.<span class="py-src-variable">sessions</span>.<span class="py-src-variable">remove</span>(<span class="py-src-variable">uid</span>)
  92 </pre>
  93
  94 <p>Keep in mind that using a method as the callback will keep the instance (in
  95 this case, the <code>ExpirationLogger</code> resource) in memory until the
  96 session expires.</p>
  97
  98 <p>With those pieces in hand, here's an example that prints a message whenever a
  99 session expires, and uses sessions which last for 5 seconds:</p>
 100
 101 <pre class="python"><p class="py-linenumber"> 1
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 128 28
 129 </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-variable">Session</span>
 130 <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>
 131 <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>
 132
 133 <span class="py-src-keyword">class</span> <span class="py-src-identifier">ShortSession</span>(<span class="py-src-parameter">Session</span>):
 134     <span class="py-src-variable">sessionTimeout</span> = <span class="py-src-number">5</span>
 135
 136 <span class="py-src-keyword">class</span> <span class="py-src-identifier">ExpirationLogger</span>(<span class="py-src-parameter">Resource</span>):
 137     <span class="py-src-variable">sessions</span> = <span class="py-src-variable">set</span>()
 138
 139     <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>):
 140         <span class="py-src-variable">session</span> = <span class="py-src-variable">request</span>.<span class="py-src-variable">getSession</span>()
 141         <span class="py-src-keyword">if</span> <span class="py-src-variable">session</span>.<span class="py-src-variable">uid</span> <span class="py-src-keyword">not</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">sessions</span>:
 142             <span class="py-src-variable">self</span>.<span class="py-src-variable">sessions</span>.<span class="py-src-variable">add</span>(<span class="py-src-variable">session</span>.<span class="py-src-variable">uid</span>)
 143             <span class="py-src-variable">session</span>.<span class="py-src-variable">notifyOnExpire</span>(<span class="py-src-keyword">lambda</span>: <span class="py-src-variable">self</span>.<span class="py-src-variable">_expired</span>(<span class="py-src-variable">session</span>.<span class="py-src-variable">uid</span>))
 144         <span class="py-src-keyword">return</span> <span class="py-src-string">&quot;&quot;</span>
 145
 146     <span class="py-src-keyword">def</span> <span class="py-src-identifier">_expired</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">uid</span>):
 147         <span class="py-src-keyword">print</span> <span class="py-src-string">&quot;Session&quot;</span>, <span class="py-src-variable">uid</span>, <span class="py-src-string">&quot;has expired.&quot;</span>
 148         <span class="py-src-variable">self</span>.<span class="py-src-variable">sessions</span>.<span class="py-src-variable">remove</span>(<span class="py-src-variable">uid</span>)
 149
 150 <span class="py-src-variable">rootResource</span> = <span class="py-src-variable">Resource</span>()
 151 <span class="py-src-variable">rootResource</span>.<span class="py-src-variable">putChild</span>(<span class="py-src-string">&quot;logme&quot;</span>, <span class="py-src-variable">ExpirationLogger</span>())
 152 <span class="py-src-variable">factory</span> = <span class="py-src-variable">Site</span>(<span class="py-src-variable">rootResource</span>)
 153 <span class="py-src-variable">factory</span>.<span class="py-src-variable">sessionFactory</span> = <span class="py-src-variable">ShortSession</span>
 154
 155 <span class="py-src-variable">reactor</span>.<span class="py-src-variable">listenTCP</span>(<span class="py-src-number">8080</span>, <span class="py-src-variable">factory</span>)
 156 <span class="py-src-variable">reactor</span>.<span class="py-src-variable">run</span>()
 157 </pre>
 158
 159 <p>Since <code>Site</code> customization is required, this example can't be
 160 rpy-based, so it brings back the manual <code>reactor.listenTCP</code>
 161 and <code>reactor.run</code> calls. Run it and visit <code>/logme</code> to see
 162 it in action. Keep visiting it to keep your session active. Stop visiting it for
 163 five seconds to see your session expiration message.</p>
 164
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