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<h2 id="_a_href_index_html_index_a_8594_a_href_modules_html_modules_a"><a href="index.html">Index</a> → <a href="modules.html">Modules</a></h2>
<div class="sectionbody">
</div>
<h2 id="_modules_encoders">Modules: Encoders</h2>
<div class="sectionbody">
<div class="paragraph"><p>Encoders are Cherokee modules that can be used as filters. The most
common usage is to compress information allowing you to save
bandwidth. You should do that whenever you can since hardware is
mostly inexpensive while bandwidth is not. Besides, the performance
penalization suffered due to the compression process is trivial.</p></div>
<div class="paragraph"><p>Of course it doesn’t make sense to apply a processor intensive filter
to content that can’t take advantage of it (i.e., it doesn’t make
sense to try to compress an already compressed file because there is
nothing to gain).</p></div>
<div class="paragraph"><p>The encoders must be enabled or disabled in a per rule basis. The
acceptable settings for an encoder are <em>Leave unset</em>, <em>Allow</em> and
<em>Forbid</em>.</p></div>
<div class="paragraph"><p>This is the list of currently provided encoders:</p></div>
<div class="olist arabic"><ol class="arabic">
<li>
<p>
<a href="modules_encoders_gzip.html">gzip</a>
</p>
</li>
<li>
<p>
<a href="modules_encoders_deflate.html">deflate</a>
</p>
</li>
</ol></div>
<div class="paragraph"><p>As you might have guessed from the list of acceptable settings, it is
interesting to highlight that Cherokee supports negative encoding
rules. This translates into rules that forbid an encoder to be
used. To prevent encoding files that are already compressed, a pretty
simple rule such as the following one could be included to avoid the
problem.</p></div>
<div class="tableblock">
<table rules="all"
width="100%"
frame="border"
cellspacing="0" cellpadding="4">
<col width="33%" />
<col width="33%" />
<col width="33%" />
<thead>
<tr>
<th align="left" valign="top">Match </th>
<th align="left" valign="top"> Final/Non-Final </th>
<th align="left" valign="top"> Encoder setting</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" valign="top"><p class="table">Extensions (jpg,zip,gz,rar,7z)</p></td>
<td align="left" valign="top"><p class="table">Non-Final</p></td>
<td align="left" valign="top"><p class="table">Gzip forbidden</p></td>
</tr>
</tbody>
</table>
</div>
<div class="paragraph"><p>For a more complex example, imagine the following scenario:</p></div>
<div class="tableblock">
<table rules="all"
width="100%"
frame="border"
cellspacing="0" cellpadding="4">
<col width="33%" />
<col width="33%" />
<col width="33%" />
<thead>
<tr>
<th align="left" valign="top">Match </th>
<th align="left" valign="top"> Final/Non-Final </th>
<th align="left" valign="top"> Encoder setting</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" valign="top"><p class="table">*.php</p></td>
<td align="left" valign="top"><p class="table">Non-Final</p></td>
<td align="left" valign="top"><p class="table">Gzip forbidden</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">a*</p></td>
<td align="left" valign="top"><p class="table">Non-Final</p></td>
<td align="left" valign="top"><p class="table">Gzip leave unset</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">Default</p></td>
<td align="left" valign="top"><p class="table">Final</p></td>
<td align="left" valign="top"><p class="table">Gzip allowed</p></td>
</tr>
</tbody>
</table>
</div>
<div class="paragraph"><p>The rule list is evaluated from top to bottom. The <em>Leave unset</em>
option of the encoders means that, whenever a rule is applied, it will
not change the status of the encoding setting.</p></div>
<div class="paragraph"><p>Under these conditions, the following requests would be evaluated as shown:</p></div>
<div class="ulist"><ul>
<li>
<p>
/foo.php - wouldn’t use Gzip
</p>
</li>
<li>
<p>
/aaa.txt - would use Gzip (a* wouldn’t set it, but since it’s non-final the default rule would)
</p>
</li>
<li>
<p>
/zzz.txt - would use it (set by the default rule)
</p>
</li>
<li>
<p>
/abc.php - it matches the first rule, so Gzip is forbidden, and
since it is no-final the evaluation continues. It also matches the
second rule, but since Gzip support got already forbidden nothing is
changed. When it hits the last rule, the same thing happens: Gzip is
already forbidden, so the value is not overwritten.
</p>
</li>
</ul></div>
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