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290 lines
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HTML
290 lines
10 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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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 by
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looking at a few bytes of its contents.</p>
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<P><A
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HREF="module-dict.html#Status"
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REL="Help"
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><STRONG>Status:</STRONG></A> Extension
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<BR>
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<A
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HREF="module-dict.html#SourceFile"
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REL="Help"
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><STRONG>Source File:</STRONG></A> mod_mime_magic.c
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<BR>
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<A
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HREF="module-dict.html#ModuleIdentifier"
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REL="Help"
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><STRONG>Module Identifier:</STRONG></A> mime_magic_module
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</P>
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<H2>Summary</H2>
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<p>This module determines the MIME type of files in the same way the
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Unix file(1) command works: it looks at the first few bytes of
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the file. It is intended as a "second line of defense" for cases
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that <a href="mod_mime.html">mod_mime</a> can't resolve. To assure
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that mod_mime gets first try at determining a file's MIME type,
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be sure to list mod_mime_magic <STRONG>before</STRONG> mod_mime
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in the configuration.
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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 numbers"
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and other hints from a file's contents to figure out what the
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contents are. This module is active only if the magic file is
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specified by the <A
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HREF="#mimemagicfile"><CODE>MimeMagicFile</CODE></A> directive.
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<H2>Directives</H2>
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<P>
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<UL>
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<LI><A HREF="#mimemagicfile">MimeMagicFile</A>
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</LI>
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</UL>
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</P>
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<h2>Format of the Magic File</h2>
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<P>
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The contents of the file are plain ASCII text in 4-5 columns.
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Blank lines are allowed but ignored.
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Commented lines use a hash mark "#".
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The remaining lines are parsed for the following columns:
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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
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<BR>
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">" indicates a dependency upon the previous non-">" line</TD>
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</TR><tr valign=top>
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<TD>2</TD>
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<TD>type of data to match
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<table border=1>
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<TR><TD>byte</TD><TD>single character</TD></TR>
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<TR><TD>short</TD><TD>machine-order 16-bit integer</TD></TR>
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<TR><TD>long</TD><TD>machine-order 32-bit integer</TD></TR>
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<TR><TD>string</TD><TD>arbitrary-length string</TD></TR>
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<TR><TD>date</TD><TD>long integer date
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(seconds since Unix epoch/1970)</TD></TR>
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<TR><TD>beshort</TD><TD>big-endian 16-bit integer</TD></TR>
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<TR><TD>belong</TD><TD>big-endian 32-bit integer</TD></TR>
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<TR><TD>bedate</TD><TD>big-endian 32-bit integer date</TD></TR>
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<TR><TD>leshort</TD><TD>little-endian 16-bit integer</TD></TR>
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<TR><TD>lelong</TD><TD>little-endian 32-bit integer</TD></TR>
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<TR><TD>ledate</TD><TD>little-endian 32-bit integer date</TD></TR>
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</TABLE>
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</TD>
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</TR><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><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><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>
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For example, the following magic file lines
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would recognize some audio formats.
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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 containing
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Microsoft Word or FrameMaker documents. (These are incompatible file
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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 encoding
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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 keeping
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up with its load or if you're performing a web server benchmark,
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you may not want to enable this because the processing is not free.
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<P>
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However, an effort was made to improve the performance of the original
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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 who
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publish their own documents.
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This is probably very common on intranets.
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Many times, it's helpful
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if the server can make more intelligent decisions about a file's
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contents than the file name allows
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...even if just to reduce the "why doesn't my page work" calls
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when users improperly name their own files.
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You have to decide if the extra work suits your environment.
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<P>
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When compiling an Apache server, this module should be at or near the
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top of the list of modules in the Configuration file. The modules are
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listed in increasing priority so that will mean this one is used only
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as a last resort, just like it was designed to.
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<H2><A 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 restrictions
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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 NAME="mimemagicfile">
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MimeMagicFile
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</A></H2>
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<P>
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<A
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HREF="directive-dict.html#Syntax"
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REL="Help"
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><STRONG>Syntax:</STRONG></A> MimeMagicFile <EM>magic-file-name</EM>
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<BR>
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<A
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HREF="directive-dict.html#Default"
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REL="Help"
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><STRONG>Default:</STRONG></A> none
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<BR>
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<A
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HREF="directive-dict.html#Context"
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REL="Help"
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><STRONG>Context:</STRONG></A> server config, virtual host
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<BR>
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<A
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HREF="directive-dict.html#Status"
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REL="Help"
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><STRONG>Status:</STRONG></A> Extension
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<BR>
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<A
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HREF="directive-dict.html#Module"
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REL="Help"
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><STRONG>Module:</STRONG></A> mod_mime_magic
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<P>
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The <CODE>MimeMagicFile</CODE> directive can be used to enable this module,
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the default file is distributed at <CODE>conf/magic</CODE>.
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Non-rooted paths are relative to the ServerRoot. Virtual hosts
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will use the same file as the main server unless a more specific setting
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is used, in which case the more specific setting overrides the main server's
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file.
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<P>
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</BODY>
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</HTML>
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