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<title>mod_xsendfile</title>
<meta content="Nils Maier" name="author" />
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<h1>mod_xsendfile</h1>
<h2>Overview</h2>
<p>mod_xsendfile is a small Apache2 module that
processes X-SENDFILE headers registered by the original output
handler.</p>
<p>If it encounters the presence of such header it will discard
all output and send the file specified by that header instead using Apache internals
including all optimizations like caching-headers and sendfile or mmap if configured.</p>
<p>It is useful for processing script-output of e.g. php, perl or
any cgi.</p>
<h2>Useful?</h2>
<p>Yep, it is useful.</p>
<ul>
<li>Some applications require checking for special privileges.</li>
<li>Other have to lookup values first (e.g.. from a DB) in order to correctly process a download request.</li>
<li>Or store values (download-counters come into mind).</li>
<li>etc.</li>
</ul>
<h3>Benefits</h3>
<ul>
<li>Uses apache internals</li>
<li>Optimal delivery through sendfile and mmap (if available).</li>
<li>Sets correct cache headers such as Etag and
If-Modified-Since as if the file was statically served.</li>
<li>Processes cache headers such as If-None-Match or
If-Modified-Since.</li>
</ul>
<h2>Download</h2>
<ul>
<li><code><a href="mod_xsendfile.c">mod_xsendfile.c</a></code></li>
<li><code>Source tarball: <a href="mod_xsendfile-0.9.tar.gz">mod_xsendfile-0.9.tar.gz</a></code></li>
<li><code>Win32 binary: <a href="mod_xsendfile-0.9.bin.zip">mod_xsendfile-0.9.bin.zip</a></code></li>
</ul>
<h2>Installation</h2>
<ol>
<li>Grab the <a href="mod_xsendfile.c">source</a>.</li>
<li>Compile and install<br />
<code>apxs -cia mod_xsendfile.c</code></li>
<li>Restart apache</li>
<li>That's all.</li>
</ol>
<h2>Configuration</h2>
<p>Two flags, that all folks ;)</p>
<h3>XSendFile</h3>
<table style="text-align: left; width: 100%;" class="code" border="0" cellpadding="2" cellspacing="0">
<tbody>
<tr>
<th>Description</th>
<td>Enables or disables header processing</td>
</tr>
<tr>
<th>Syntax</th>
<td>XSendFile on|off</td>
</tr>
<tr>
<th>Default</th>
<td>XSendFile off</td>
</tr>
<tr>
<th>Context</th>
<td>server config, virtual host, directory, .htaccess</td>
</tr>
</tbody>
</table>
<p>Setting <code>XSendFile on</code> will enable
processing.</p>
<p>The file specified in <code>X-SENDFILE</code>
header will be sent instead
of the handler output.</p>
<p>If the response lacks the <code>X-SENDFILE</code>
header nothing is done.
</p>
<h3>XSendFileAllowAbove</h3>
<table style="text-align: left; width: 100%;" class="code" border="0" cellpadding="2" cellspacing="0">
<tbody>
<tr>
<th>Description</th>
<td>Allows or disallows sending files above Request path</td>
</tr>
<tr>
<th>Syntax</th>
<td>XSendFileAllowAbove on|off</td>
</tr>
<tr>
<th>Default</th>
<td>XSendFileAllowAbove off</td>
</tr>
<tr>
<th>Context</th>
<td>server config, virtual host, directory, .htaccess</td>
</tr>
</tbody>
</table>
<p>Setting <code>XSendFileAllowAbove on</code> will allow sending files not below
the path of the Request (this refers to the request URI not the translated path).</p>
<h3>Example</h3>
<p><code>.htaccess</code></p>
<p class="code"><code><Files out.php><br />
XSendFile on
<br />
</Files></code></p>
<p><code>out.php</code></p>
<p class="code"><code><span style="color: rgb(0, 0, 0);"><span style="color: rgb(0, 0, 187);"><?php<br />
</span><span style="color: rgb(0, 119, 0);">...<br />
if (</span><span style="color: rgb(0, 0, 187);">$user</span><span style="color: rgb(0, 119, 0);">-></span><span style="color: rgb(0, 0, 187);">isLoggedIn</span><span style="color: rgb(0, 119, 0);">())<br />
{<br />
</span><span style="color: rgb(0, 0, 187);">header</span><span style="color: rgb(0, 119, 0);">(</span><span style="color: rgb(221, 0, 0);">"X-Sendfile: $somefile"</span><span style="color: rgb(0, 119, 0);">);<br />
</span><span style="color: rgb(0, 0, 187);">header</span><span style="color: rgb(0, 119, 0);">(</span><span style="color: rgb(221, 0, 0);">"Content-Type: application/octet-stream"</span><span style="color: rgb(0, 119, 0);">);<br />
</span><span style="color: rgb(0, 0, 187);">header</span><span style="color: rgb(0, 119, 0);">(</span><span style="color: rgb(221, 0, 0);">"Content-Disposition: attachment; file=\"$somefile\""</span><span style="color: rgb(0, 119, 0);">);<br />
exit;<br />
}<br />
</span><span style="color: rgb(0, 0, 187);">?><br />
</span><h1>Permission denied</h1><br />
<p>Login first!</p></span></code></p>
<h2>Limitations / Issues / Security considerations</h2>
<ul>
<li>The <code>Content-Encoding</code>
header - if present - will be dropped, as the module
cannot know if it was set by intention of the programmer or the
handler. E.g. php with output compression enabled will set this header,
but the replacement file send via mod_xsendfile is most likely not
compressed.</li>
<li>The header key (X-SENDFILE) is not case-sensitive.</li>
<li><strong>X-Sendfile will also send files that are
otherwise protected (e.g. Deny from all). This includes .htaccess and
such!</strong><br />
At least as long as one has regular file access permissions defined in
the file system.<br />
But, on the other hand, how is this different from the usual scripting?</li>
</ul>
<h2>Credits</h2>
<p>The idea comes from <a href="http://www.lighttpd.net/">lighttpd</a>
- <span style="font-style: italic;">A fast web server
with minimal memory footprint</span>.</p>
<p>The module itself was inspired by many other Apache2 modules
such as mod_rewrite, mod_headers and such and obviously core.c.</p>
<h2>License</h2>
<p><strong>Copyright 2006 by Nils Maier</strong></p>
<p>Licensed under the <em>Apache License, Version 2.0</em>
(the
"License"); you may not use this file except in compliance with the
License.</p>
<p>You may obtain a copy of the License at<br />
</p>
<p style="text-align: left; margin-left: 40px;"><a href="http://www.apache.org/licenses/LICENSE-2.0">http://www.apache.org/licenses/LICENSE-2.0</a></p>
<p>Unless
required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</p>
<p>
See the License for the specific language governing permissions and
limitations under the License.
</p>
<h2 id="changes">Changes</h2>
<h3>Version 0.9</h3>
<ul>
<li>New configuration directive: XSendFileAllowAbove</li>
<li>Initial FastCGI/CGI support</li>
<li>Filter only added when needed</li>
</ul>
<h3>Version 0.8</h3>
<ul>
<li>This is the initial public release.</li>
</ul>
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