Apache Module mod_mime_magic

Available Languages: en

+ + + +

Description:	Determines the MIME type of a file + by looking at a few bytes of its contents
Status:	Extension
Module Identifier:	mime_magic_module
Source File:	mod_mime_magic.c

Summary

+ +

This module determines the MIME type of files in the same + way the Unix file(1) command works: it looks at the first + few bytes of the file. It is intended as a "second line of defense" + for cases that mod_mime can't resolve.

+ +

This module is derived from a free version of the + file(1) command for Unix, which uses "magic + numbers" and other hints from a file's contents to figure out + what the contents are. This module is active only if the magic + file is specified by the MimeMagicFile directive.

Directives

MimeMagicFile

Format of the Magic File

+ +

The contents of the file are plain ASCII text in 4-5 + columns. Blank lines are allowed but ignored. Commented lines + use a hash mark (#). The remaining lines are parsed for + the following columns:

+ + + + + + + + + + + + +

Column Description

1 byte number to begin checking from
+ ">" indicates a dependency upon the previous + non-">" line

type of data to match

+ + + + + + + + + + + + + + + + + + + + + + + + +

`byte`	single character
`short`	machine-order 16-bit integer
`long`	machine-order 32-bit integer
`string`	arbitrary-length string
`date`	long integer date (seconds since Unix epoch/1970)
`beshort`	big-endian 16-bit integer
`belong`	big-endian 32-bit integer
`bedate`	big-endian 32-bit integer date
`leshort`	little-endian 16-bit integer
`lelong`	little-endian 32-bit integer
`ledate`	little-endian 32-bit integer date

3 contents of data to match

4 MIME type if matched

5 MIME encoding if matched (optional)

+ +

For example, the following magic file lines would recognize + some audio formats:

+ +

# Sun/NeXT audio data
+0      string      .snd
+>12    belong      1       audio/basic
+>12    belong      2       audio/basic
+>12    belong      3       audio/basic
+>12    belong      4       audio/basic
+>12    belong      5       audio/basic
+>12    belong      6       audio/basic
+>12    belong      7       audio/basic
+>12    belong     23       audio/x-adpcm

+ +

Or these would recognize the difference between *.doc + files containing Microsoft Word or FrameMaker documents. (These are + incompatible file formats which use the same file suffix.)

+ +

# Frame
+0  string  \<MakerFile        application/x-frame
+0  string  \<MIFFile          application/x-frame
+0  string  \<MakerDictionary  application/x-frame
+0  string  \<MakerScreenFon   application/x-frame
+0  string  \<MML              application/x-frame
+0  string  \<Book             application/x-frame
+0  string  \<Maker            application/x-frame
+
+# MS-Word
+0  string  \376\067\0\043            application/msword
+0  string  \320\317\021\340\241\261  application/msword
+0  string  \333\245-\0\0\0           application/msword

+ +

An optional MIME encoding can be included as a fifth column. + For example, this can recognize gzipped files and set the + encoding for them.

+ +

# gzip (GNU zip, not to be confused with
+#       [Info-ZIP/PKWARE] zip archiver)
+
+0  string  \037\213  application/octet-stream  x-gzip

Performance Issues

This module is not for every system. If your system is barely + keeping up with its load or if you're performing a web server + benchmark, you may not want to enable this because the + processing is not free.

+ +

However, an effort was made to improve the performance of + the original file(1) code to make it fit in a busy web + server. It was designed for a server where there are thousands of users + who publish their own documents. This is probably very common + on intranets. Many times, it's helpful if the server can make + more intelligent decisions about a file's contents than the + file name allows ...even if just to reduce the "why doesn't my + page work" calls when users improperly name their own files. + You have to decide if the extra work suits your + environment.

Notes

The following notes apply to the mod_mime_magic + module and are included here for compliance with contributors' + copyright restrictions that require their acknowledgment.

+ +

mod_mime_magic: MIME type lookup via file magic numbers
+ Copyright (c) 1996-1997 Cisco Systems, Inc.

+ +

This software was submitted by Cisco Systems to the Apache Group + in July 1997. Future revisions and derivatives of this source code + must acknowledge Cisco Systems as the original contributor of this + module. All other licensing and usage conditions are those of the + Apache Group.

+ +

Some of this code is derived from the free version of the file + command originally posted to comp.sources.unix. Copyright info for + that program is included below as required.

+ +

This software is not subject to any license of the American + Telephone and Telegraph Company or of the Regents of the University + of California.

+ +

Permission is granted to anyone to use this software for any + purpose on any computer system, and to alter it and redistribute it + freely, subject to the following restrictions:

+ +

The author is not responsible for the consequences of use of + this software, no matter how awful, even if they arise from flaws + in it.
The origin of this software must not be misrepresented, either + by explicit claim or by omission. Since few users ever read + sources, credits must appear in the documentation.
Altered versions must be plainly marked as such, and must not + be misrepresented as being the original software. Since few users + ever read sources, credits must appear in the documentation.
This notice may not be removed or altered.

+ +

For compliance with Mr Darwin's terms: this has been very + significantly modified from the free "file" command.

+ +

all-in-one file for compilation convenience when moving from + one version of Apache to the next.
Memory allocation is done through the Apache API's pool + structure.
All functions have had necessary Apache API request or server + structures passed to them where necessary to call other Apache API + routines. (i.e., usually for logging, files, or memory + allocation in itself or a called function.)
struct magic has been converted from an array to a single-ended + linked list because it only grows one record at a time, it's only + accessed sequentially, and the Apache API has no equivalent of + realloc().
Functions have been changed to get their parameters from the + server configuration instead of globals. (It should be reentrant + now but has not been tested in a threaded environment.)
Places where it used to print results to stdout now saves them + in a list where they're used to set the MIME type in the Apache + request record.
Command-line flags have been removed since they will never be + used here.

MimeMagicFile Directive

+ + + + + + +

Description:	Enable MIME-type determination based on file contents +using the specified magic file
Syntax:	`MimeMagicFile file-path`
Context:	server config, virtual host
Status:	Extension
Module:	mod_mime_magic

The MimeMagicFile directive can be used to + enable this module, the default file is distributed at + conf/magic. Non-rooted paths are relative to the + ServerRoot. Virtual hosts will use + the same file as the main server unless a more specific setting is + used, in which case the more specific setting overrides the main + server's file.

+ +

Example

+ MimeMagicFile conf/magic +

+ +