Red Hat DIRECTORY SERVER 2.0 - GATEWAY Manual de usuario descargar pdf (Pagina 28)

Chapter 4. Supporting MIME types

Content analysis

The ﬁrst is to look in the ﬁle’s content and deduce the MIME content type from the

content.

You can see this mechanism in action with the ﬁle command. This command can give

a “human readable” description of a ﬁle’s content type or, with the -i option, it can

give a MIME content type.

$ file course.pdf

course.pdf: PDF document, version 1.2

$ file course.ps

course.ps: PostScript document text conforming at level 2.0

$ file -i course.ps

file: Using regular magic file ‘/usr/share/magic.mime’

course.ps: application/postscript

$ file -i course.ps 2> /dev/null

course.ps: application/postscript

$ file -i course.pdf 2> /dev/null

course.pdf: application/pdf

Figure 4-3. Using the ﬁle command

As you will deduce from the warning message printed on standard error, the ﬁle

/usr/share/magic.mime is used to store the information about how to map from

content to MIME type. The default ﬁle /usr/share/magic is used for the more ver-

bose descriptions.

File name analysis

The other approach is to use the ﬁle name. In particular it is traditional that ﬁles

should have particular sufﬁces according to their MIME content types. This is the

most commonly used approach.

This approach is taken by other utilities than just the web server and there is a system

wide ﬁle giving the correspondence between ﬁle names and MIME content types.

This ﬁle is /etc/mime.types which is part of the base system (as part of the mailcap

package).

application/msword doc

application/pdf pdf

application/postscript ai eps ps

application/rtf rtf

application/x-bzip2 bz2

application/x-dvi dvi

application/xml

audio/mpeg mpga mp2 mp3

image/png png

model/vrml wrl vrml

text/html html htm

text/plain asc txt

video/mpeg mpeg mpg mpe

video/quicktime qt mov

Figure 4-4. Extracts from /etc/mime.types

Apache is capable of both modes of operation. We will use the latter as it is more

common. This is for historical reasons and is not a reﬂection on the relative values of

the two mechanisms.

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