Apache Module mod_mime_magic
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.
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:
| 1 |
byte number to begin checking from
">" indicates a dependency upon the previous
non-">" line |
| 2 |
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
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.
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.
- Copyright (c) Ian F. Darwin, 1987. Written by Ian F. Darwin.
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.
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
