<?xml version="1.0"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" lang="en"><head><title>Twisted Documentation: The Evolution of Finger: making a finger library</title><link href="../../howto/stylesheet.css" type="text/css" rel="stylesheet" /></head><body bgcolor="white"><h1 class="title">The Evolution of Finger: making a finger library</h1><div class="toc"><ol><li><a href="#auto0">Introduction</a></li><li><a href="#auto1">Organization</a></li><li><a href="#auto2">Easy Configuration</a></li></ol></div><div class="content"><span></span><h2>Introduction<a name="auto0"></a></h2><p> This is the tenth part of the Twisted tutorial <a href="index.html">Twisted from Scratch, or The Evolution of Finger</a>.</p><p>In this part, we separate the application code that launches a finger
service from the library code which defines a finger service, placing the
application in a Twisted Application Configuration (.tac) file. We also move
configuration (such as HTML templates) into separate files.</p><h2>Organization<a name="auto1"></a></h2><p>Now this code, while quite modular and well-designed, isn't
properly organized. Everything above the <code>application=</code> belongs in a
module, and the HTML templates all belong in separate files.
</p><p>We can use the templateFile and templateDirectory attributes to indicate
what HTML template file to use for each Page, and where to look for it.</p><div class="py-listing"><pre>
<span class="py-src-comment"># organized-finger.tac
</span><span class="py-src-comment"># eg: twistd -ny organized-finger.tac
</span>
<span class="py-src-keyword">import</span> <span class="py-src-variable">finger</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">protocol</span>, <span class="py-src-variable">reactor</span>, <span class="py-src-variable">defer</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">spread</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">pb</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-keyword">import</span> <span class="py-src-variable">resource</span>, <span class="py-src-variable">server</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">application</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">internet</span>, <span class="py-src-variable">service</span>, <span class="py-src-variable">strports</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">python</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">log</span>
<span class="py-src-variable">application</span> = <span class="py-src-variable">service</span>.<span class="py-src-variable">Application</span>(<span class="py-src-string">'finger'</span>, <span class="py-src-variable">uid</span>=<span class="py-src-number">1</span>, <span class="py-src-variable">gid</span>=<span class="py-src-number">1</span>)
<span class="py-src-variable">f</span> = <span class="py-src-variable">finger</span>.<span class="py-src-variable">FingerService</span>(<span class="py-src-string">'/etc/users'</span>)
<span class="py-src-variable">serviceCollection</span> = <span class="py-src-variable">service</span>.<span class="py-src-variable">IServiceCollection</span>(<span class="py-src-variable">application</span>)
<span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPServer</span>(<span class="py-src-number">79</span>, <span class="py-src-variable">finger</span>.<span class="py-src-variable">IFingerFactory</span>(<span class="py-src-variable">f</span>)
).<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">serviceCollection</span>)
<span class="py-src-variable">site</span> = <span class="py-src-variable">server</span>.<span class="py-src-variable">Site</span>(<span class="py-src-variable">resource</span>.<span class="py-src-variable">IResource</span>(<span class="py-src-variable">f</span>))
<span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPServer</span>(<span class="py-src-number">8000</span>, <span class="py-src-variable">site</span>
).<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">serviceCollection</span>)
<span class="py-src-variable">internet</span>.<span class="py-src-variable">SSLServer</span>(<span class="py-src-number">443</span>, <span class="py-src-variable">site</span>, <span class="py-src-variable">finger</span>.<span class="py-src-variable">ServerContextFactory</span>()
).<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">serviceCollection</span>)
<span class="py-src-variable">i</span> = <span class="py-src-variable">finger</span>.<span class="py-src-variable">IIRCClientFactory</span>(<span class="py-src-variable">f</span>)
<span class="py-src-variable">i</span>.<span class="py-src-variable">nickname</span> = <span class="py-src-string">'fingerbot'</span>
<span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPClient</span>(<span class="py-src-string">'irc.freenode.org'</span>, <span class="py-src-number">6667</span>, <span class="py-src-variable">i</span>
).<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">serviceCollection</span>)
<span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPServer</span>(<span class="py-src-number">8889</span>, <span class="py-src-variable">pb</span>.<span class="py-src-variable">PBServerFactory</span>(<span class="py-src-variable">finger</span>.<span class="py-src-variable">IPerspectiveFinger</span>(<span class="py-src-variable">f</span>))
).<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">serviceCollection</span>)
</pre><div class="caption">Source listing - <a href="listings/finger/organized-finger.tac"><span class="filename">listings/finger/organized-finger.tac</span></a></div></div><p>
Note that our program is now quite separated. We have:
<ul><li>Code (in the module)</li><li>Configuration (file above)</li><li>Presentation (templates)</li><li>Content (/etc/users)</li><li>Deployment (twistd)</li></ul>
Prototypes don't need this level of separation, so our earlier examples all
bunched together. However, real applications do. Thankfully, if we write our
code correctly, it is easy to achieve a good separation of parts.
</p><h2>Easy Configuration<a name="auto2"></a></h2><p>We can also supply easy configuration for common cases with a makeService method that will also help build .tap files later:</p><div class="py-listing"><pre>
<span class="py-src-comment"># Easy configuration
</span><span class="py-src-comment"># makeService from finger module
</span>
<span class="py-src-keyword">def</span> <span class="py-src-identifier">makeService</span>(<span class="py-src-parameter">config</span>):
<span class="py-src-comment"># finger on port 79
</span> <span class="py-src-variable">s</span> = <span class="py-src-variable">service</span>.<span class="py-src-variable">MultiService</span>()
<span class="py-src-variable">f</span> = <span class="py-src-variable">FingerService</span>(<span class="py-src-variable">config</span>[<span class="py-src-string">'file'</span>])
<span class="py-src-variable">h</span> = <span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPServer</span>(<span class="py-src-number">79</span>, <span class="py-src-variable">IFingerFactory</span>(<span class="py-src-variable">f</span>))
<span class="py-src-variable">h</span>.<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">s</span>)
<span class="py-src-comment"># website on port 8000
</span> <span class="py-src-variable">r</span> = <span class="py-src-variable">resource</span>.<span class="py-src-variable">IResource</span>(<span class="py-src-variable">f</span>)
<span class="py-src-variable">r</span>.<span class="py-src-variable">templateDirectory</span> = <span class="py-src-variable">config</span>[<span class="py-src-string">'templates'</span>]
<span class="py-src-variable">site</span> = <span class="py-src-variable">server</span>.<span class="py-src-variable">Site</span>(<span class="py-src-variable">r</span>)
<span class="py-src-variable">j</span> = <span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPServer</span>(<span class="py-src-number">8000</span>, <span class="py-src-variable">site</span>)
<span class="py-src-variable">j</span>.<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">s</span>)
<span class="py-src-comment"># ssl on port 443
</span> <span class="py-src-keyword">if</span> <span class="py-src-variable">config</span>.<span class="py-src-variable">get</span>(<span class="py-src-string">'ssl'</span>):
<span class="py-src-variable">k</span> = <span class="py-src-variable">internet</span>.<span class="py-src-variable">SSLServer</span>(<span class="py-src-number">443</span>, <span class="py-src-variable">site</span>, <span class="py-src-variable">ServerContextFactory</span>())
<span class="py-src-variable">k</span>.<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">s</span>)
<span class="py-src-comment"># irc fingerbot
</span> <span class="py-src-keyword">if</span> <span class="py-src-variable">config</span>.<span class="py-src-variable">has_key</span>(<span class="py-src-string">'ircnick'</span>):
<span class="py-src-variable">i</span> = <span class="py-src-variable">IIRCClientFactory</span>(<span class="py-src-variable">f</span>)
<span class="py-src-variable">i</span>.<span class="py-src-variable">nickname</span> = <span class="py-src-variable">config</span>[<span class="py-src-string">'ircnick'</span>]
<span class="py-src-variable">ircserver</span> = <span class="py-src-variable">config</span>[<span class="py-src-string">'ircserver'</span>]
<span class="py-src-variable">b</span> = <span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPClient</span>(<span class="py-src-variable">ircserver</span>, <span class="py-src-number">6667</span>, <span class="py-src-variable">i</span>)
<span class="py-src-variable">b</span>.<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">s</span>)
<span class="py-src-comment"># Pespective Broker on port 8889
</span> <span class="py-src-keyword">if</span> <span class="py-src-variable">config</span>.<span class="py-src-variable">has_key</span>(<span class="py-src-string">'pbport'</span>):
<span class="py-src-variable">m</span> = <span class="py-src-variable">internet</span>.<span class="py-src-variable">TCPServer</span>(
<span class="py-src-variable">int</span>(<span class="py-src-variable">config</span>[<span class="py-src-string">'pbport'</span>]),
<span class="py-src-variable">pb</span>.<span class="py-src-variable">PBServerFactory</span>(<span class="py-src-variable">IPerspectiveFinger</span>(<span class="py-src-variable">f</span>)))
<span class="py-src-variable">m</span>.<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">s</span>)
<span class="py-src-keyword">return</span> <span class="py-src-variable">s</span>
</pre><div class="caption">Source listing - <a href="listings/finger/finger_config.py"><span class="filename">listings/finger/finger_config.py</span></a></div></div><p>And we can write simpler files now:</p><div class="py-listing"><pre>
<span class="py-src-comment"># simple-finger.tac
</span><span class="py-src-comment"># eg: twistd -ny simple-finger.tac
</span>
<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">application</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">service</span>
<span class="py-src-keyword">import</span> <span class="py-src-variable">finger</span>
<span class="py-src-variable">options</span> = { <span class="py-src-string">'file'</span>: <span class="py-src-string">'/etc/users'</span>,
<span class="py-src-string">'templates'</span>: <span class="py-src-string">'/usr/share/finger/templates'</span>,
<span class="py-src-string">'ircnick'</span>: <span class="py-src-string">'fingerbot'</span>,
<span class="py-src-string">'ircserver'</span>: <span class="py-src-string">'irc.freenode.net'</span>,
<span class="py-src-string">'pbport'</span>: <span class="py-src-number">8889</span>,
<span class="py-src-string">'ssl'</span>: <span class="py-src-string">'ssl=0'</span> }
<span class="py-src-variable">ser</span> = <span class="py-src-variable">finger</span>.<span class="py-src-variable">makeService</span>(<span class="py-src-variable">options</span>)
<span class="py-src-variable">application</span> = <span class="py-src-variable">service</span>.<span class="py-src-variable">Application</span>(<span class="py-src-string">'finger'</span>, <span class="py-src-variable">uid</span>=<span class="py-src-number">1</span>, <span class="py-src-variable">gid</span>=<span class="py-src-number">1</span>)
<span class="py-src-variable">ser</span>.<span class="py-src-variable">setServiceParent</span>(<span class="py-src-variable">service</span>.<span class="py-src-variable">IServiceCollection</span>(<span class="py-src-variable">application</span>))
</pre><div class="caption">Source listing - <a href="listings/finger/simple-finger.tac"><span class="filename">listings/finger/simple-finger.tac</span></a></div></div><pre class="shell">
% twisted -ny simple-finger.tac
</pre><p>Note: the finger <em>user</em> still has ultimate power: he can use
makeService, or he can use the lower-level interface if he has
specific needs (maybe an IRC server on some other port? maybe we
want the non-SSL webserver to listen only locally? etc. etc.)
This is an important design principle: never force a layer of abstraction:
allow usage of layers of abstractions.</p><p>The pasta theory of design:</p><ul><li>Spaghetti: each piece of code interacts with every other piece of
code [can be implemented with GOTO, functions, objects]</li><li>Lasagna: code has carefully designed layers. Each layer is, in
theory independent. However low-level layers usually cannot be
used easily, and high-level layers depend on low-level layers.</li><li>Ravioli: each part of the code is useful by itself. There is a thin
layer of interfaces between various parts [the sauce]. Each part
can be usefully be used elsewhere.</li><li>...but sometimes, the user just wants to order <q>Ravioli</q>, so one
coarse-grain easily definable layer of abstraction on top of it all
can be useful.</li></ul></div><p><a href="../../howto/index.html">Index</a></p><span class="version">Version: 2.5.0</span></body></html>
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