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330 lines
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330 lines
11 KiB
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Apache module mod_mime_magic</title>
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<img src="../images/sub.gif" alt="[APACHE DOCUMENTATION]" />
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</div>
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<h1 align="CENTER">Module mod_mime_magic</h1>
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<p>This module provides for determining the MIME type of a file
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by looking at a few bytes of its contents.</p>
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<p><a href="module-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="module-dict.html#SourceFile"
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rel="Help"><strong>Source File:</strong></a>
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mod_mime_magic.c<br />
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<a href="module-dict.html#ModuleIdentifier"
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rel="Help"><strong>Module Identifier:</strong></a>
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mime_magic_module</p>
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<h2>Summary</h2>
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<p>This module determines the MIME type of files in the same
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way the Unix file(1) command works: it looks at the first few
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bytes of the file. It is intended as a "second line of defense"
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for cases that <a href="mod_mime.html">mod_mime</a> can't
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resolve. To assure that mod_mime gets first try at determining
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a file's MIME type, be sure to list mod_mime_magic
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<strong>before</strong> mod_mime in the configuration.</p>
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<p>This module is derived from a free version of the
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<code>file(1)</code> command for Unix, which uses "magic
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numbers" and other hints from a file's contents to figure out
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what the contents are. This module is active only if the magic
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file is specified by the <a
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href="#mimemagicfile"><code>MimeMagicFile</code></a>
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directive.</p>
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<h2>Directives</h2>
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<ul>
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<li><a href="#mimemagicfile">MimeMagicFile</a></li>
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</ul>
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<br />
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<br />
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<h2>Format of the Magic File</h2>
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<p>The contents of the file are plain ASCII text in 4-5
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columns. Blank lines are allowed but ignored. Commented lines
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use a hash mark "#". The remaining lines are parsed for the
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following columns:</p>
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<table border="1">
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<tr valign="top">
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<th>Column</th>
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<th>Description</th>
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</tr>
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<tr valign="top">
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<td>1</td>
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<td>byte number to begin checking from<br />
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">" indicates a dependency upon the previous non-">"
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line</td>
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</tr>
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<tr valign="top">
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<td>2</td>
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<td>
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type of data to match
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<table border="1">
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<tr>
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<td>byte</td>
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<td>single character</td>
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</tr>
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<tr>
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<td>short</td>
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<td>machine-order 16-bit integer</td>
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</tr>
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<tr>
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<td>long</td>
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<td>machine-order 32-bit integer</td>
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</tr>
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<tr>
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<td>string</td>
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<td>arbitrary-length string</td>
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</tr>
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<tr>
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<td>date</td>
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<td>long integer date (seconds since Unix
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epoch/1970)</td>
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</tr>
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<tr>
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<td>beshort</td>
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<td>big-endian 16-bit integer</td>
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</tr>
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<tr>
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<td>belong</td>
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<td>big-endian 32-bit integer</td>
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</tr>
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<tr>
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<td>bedate</td>
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<td>big-endian 32-bit integer date</td>
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</tr>
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<tr>
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<td>leshort</td>
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<td>little-endian 16-bit integer</td>
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</tr>
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<tr>
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<td>lelong</td>
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<td>little-endian 32-bit integer</td>
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</tr>
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<tr>
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<td>ledate</td>
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<td>little-endian 32-bit integer date</td>
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</tr>
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</table>
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</td>
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</tr>
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<tr valign="top">
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<td>3</td>
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<td>contents of data to match</td>
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</tr>
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<tr valign="top">
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<td>4</td>
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<td>MIME type if matched</td>
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</tr>
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<tr valign="top">
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<td>5</td>
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<td>MIME encoding if matched (optional)</td>
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</tr>
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</table>
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<p>For example, the following magic file lines would recognize
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some audio formats.</p>
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<pre>
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# Sun/NeXT audio data
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0 string .snd
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>12 belong 1 audio/basic
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>12 belong 2 audio/basic
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>12 belong 3 audio/basic
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>12 belong 4 audio/basic
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>12 belong 5 audio/basic
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>12 belong 6 audio/basic
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>12 belong 7 audio/basic
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>12 belong 23 audio/x-adpcm
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</pre>
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Or these would recognize the difference between "*.doc" files
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containing Microsoft Word or FrameMaker documents. (These are
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incompatible file formats which use the same file suffix.)
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<pre>
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# Frame
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0 string \<MakerFile application/x-frame
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0 string \<MIFFile application/x-frame
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0 string \<MakerDictionary application/x-frame
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0 string \<MakerScreenFon application/x-frame
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0 string \<MML application/x-frame
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0 string \<Book application/x-frame
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0 string \<Maker application/x-frame
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# MS-Word
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0 string \376\067\0\043 application/msword
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0 string \320\317\021\340\241\261 application/msword
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0 string \333\245-\0\0\0 application/msword
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</pre>
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An optional MIME encoding can be included as a fifth column.
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For example, this can recognize gzipped files and set the
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encoding for them.
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<pre>
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# gzip (GNU zip, not to be confused with [Info-ZIP/PKWARE] zip archiver)
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0 string \037\213 application/octet-stream x-gzip
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</pre>
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<h2>Performance Issues</h2>
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This module is not for every system. If your system is barely
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keeping up with its load or if you're performing a web server
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benchmark, you may not want to enable this because the
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processing is not free.
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<p>However, an effort was made to improve the performance of
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the original file(1) code to make it fit in a busy web server.
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It was designed for a server where there are thousands of users
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who publish their own documents. This is probably very common
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on intranets. Many times, it's helpful if the server can make
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more intelligent decisions about a file's contents than the
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file name allows ...even if just to reduce the "why doesn't my
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page work" calls when users improperly name their own files.
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You have to decide if the extra work suits your
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environment.</p>
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<p>When compiling an Apache server, this module should be at or
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near the top of the list of modules in the Configuration file.
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The modules are listed in increasing priority so that will mean
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this one is used only as a last resort, just like it was
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designed to.</p>
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<h2><a id="notes" name="notes">Notes</a></h2>
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The following notes apply to the mod_mime_magic module and are
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included here for compliance with contributors' copyright
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restrictions that require their acknowledgment.
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<pre>
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/*
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* mod_mime_magic: MIME type lookup via file magic numbers
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* Copyright (c) 1996-1997 Cisco Systems, Inc.
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*
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* This software was submitted by Cisco Systems to the Apache Group in July
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* 1997. Future revisions and derivatives of this source code must
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* acknowledge Cisco Systems as the original contributor of this module.
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* All other licensing and usage conditions are those of the Apache Group.
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*
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* Some of this code is derived from the free version of the file command
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* originally posted to comp.sources.unix. Copyright info for that program
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* is included below as required.
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* ---------------------------------------------------------------------------
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* - Copyright (c) Ian F. Darwin, 1987. Written by Ian F. Darwin.
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*
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* This software is not subject to any license of the American Telephone and
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* Telegraph Company or of the Regents of the University of California.
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*
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* Permission is granted to anyone to use this software for any purpose on any
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* computer system, and to alter it and redistribute it freely, subject to
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* the following restrictions:
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*
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* 1. The author is not responsible for the consequences of use of this
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* software, no matter how awful, even if they arise from flaws in it.
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*
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* 2. The origin of this software must not be misrepresented, either by
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* explicit claim or by omission. Since few users ever read sources, credits
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* must appear in the documentation.
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*
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* 3. Altered versions must be plainly marked as such, and must not be
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* misrepresented as being the original software. Since few users ever read
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* sources, credits must appear in the documentation.
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*
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* 4. This notice may not be removed or altered.
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* -------------------------------------------------------------------------
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*
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* For compliance with Mr Darwin's terms: this has been very significantly
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* modified from the free "file" command.
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* - all-in-one file for compilation convenience when moving from one
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* version of Apache to the next.
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* - Memory allocation is done through the Apache API's pool structure.
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* - All functions have had necessary Apache API request or server
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* structures passed to them where necessary to call other Apache API
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* routines. (<em>i.e.</em>, usually for logging, files, or memory allocation in
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* itself or a called function.)
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* - struct magic has been converted from an array to a single-ended linked
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* list because it only grows one record at a time, it's only accessed
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* sequentially, and the Apache API has no equivalent of realloc().
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* - Functions have been changed to get their parameters from the server
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* configuration instead of globals. (It should be reentrant now but has
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* not been tested in a threaded environment.)
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* - Places where it used to print results to stdout now saves them in a
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* list where they're used to set the MIME type in the Apache request
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* record.
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* - Command-line flags have been removed since they will never be used here.
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*
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*/
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</pre>
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<hr />
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<h2><a id="mimemagicfile"
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name="mimemagicfile">MimeMagicFile</a></h2>
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<p><a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> MimeMagicFile
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<em>file-path</em><br />
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<a href="directive-dict.html#Default"
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rel="Help"><strong>Default:</strong></a> none<br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config, virtual
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host<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_mime_magic</p>
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<p>The <code>MimeMagicFile</code> directive can be used to
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enable this module, the default file is distributed at
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<code>conf/magic</code>. Non-rooted paths are relative to the
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ServerRoot. Virtual hosts will use the same file as the main
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server unless a more specific setting is used, in which case
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the more specific setting overrides the main server's file.</p>
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</body>
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</html>
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