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20. Media Types and Subtypes

Media types are used to communicate the format of the content in HTTP transactions. Clients use media types in their Accept headers to indicate what formats they prefer to receive data in. Servers use media types in their Content-Type headers to tell the client what format the accompanying entity is in--i.e., whether the enclosed text is HTML that needs to be formatted, GIF or JPEG to be rendered, or PDF format that requires opening an external viewer or using a plug-in.

See Chapter 19, HTTP Headers, for more information on the Accept and Content-Type headers.

Internet media types used by HTTP closely resemble MIME types. MIME (Multipurpose Internet Mail Extension) was designed as a method for sending attachments in mail over the Internet. Like MIME, media types follow the format type/subtype. Asterisks (*) represent a wildcard--for example, the following client header means that documents of all formats are accepted:

Accept: */*

The following client header means that all text format types are accepted, regardless of the subtype:

Accept: text/*

Servers and CGI programs are expected to examine the accept types reported by the Accept header and return data of an acceptable type when possible. Most servers determine the format of a document from its filename suffix--for example, a file ending with .htm or .html is assumed to be HTML format, so the server will send the document with a Content-Type of text/html. When calling a CGI program, servers cannot know the format of the data being returned, so the CGI program is responsible for reporting the content type itself. For that reason, every CGI program needs to include a Content-Type header such as:

Content-Type: text/html

The following table lists commonly-used media types along with the filename suffixes recognized by most servers. Most servers can be easily configured to recognize additional suffixes as well.

Type/Subtype Usual extension
application/activemessage  
application/andrew-inset  
application/applefile  
application/atomicmail  
application/cals-1840  
application/commonground  
application/cybercash  
application/dca-rft  
application/dec-dx  
application/eshop  
application/iges  
application/mac-binhex40  
application/macwriteii  
application/mathematica  
application/msword  
application/news-message-id  
application/news-transmission  
application/octet-stream bin
application/oda oda
application/pdf pdf
application/postscript ai, eps, ps
application/remote-printing  
application/riscos  
application/vnd.svd  
application/vnd.truedoc  
application/wita  
application/wordperfect5.1  
application/x-bcpio bcpio
application/x-cpio cpio
application/x-csh csh
application/x-dvi dvi
application/x-gtar gtar
application/x-hdf hdf
application/x-latex latex
application/x-mif mif
application/x-netcdf nc, cdf
application/x-sh sh
application/x-shar shar
application/x-sv4cpio sv4cpio
application/x-sv4crc sv4crc
application/x-tar tar
application/x-tcl tcl
application/x-tex tex
application/x-texinfo texinfo, texi
application/x-troff-man man
application/x-troff-me me
application/x-troff-ms ms
application/x-troff t, tr, roff
application/x-ustar ustar
application/x-wais-source src
application/x400-bp  
application/zip zip
audio/32kadpcm audio/basic au, snd
audio/x-aiff aif, aiff, aifc
audio/x-wav wav
image/cgm  
image/g3fax  
image/gif gif
image/ief ief
image/jpeg jpeg, jpg, jpe
image/naplps  
image/tiff tiff, tif
image/vnd.dwg  
image/vnd.dxf  
image/vnd.svf  
image/x-cmu-raster ras
image/x-portable-anymap rpnm
image/x-portable-bitmap pbm
image/x-portable-graymap pgm
image/x-portable-pixmap ppm
image/x-rgb rgb
image/x-xbitmap xbm
image/x-xpixmap xpm
image/x-xwindowdump xwd
message/external-body  
message/http  
message/news  
message/partial  
message/rfc822  
multipart/alternative  
multipart/appledouble  
multipart/digest  
multipart/form-data  
multipart/header-set  
multipart/mixed  
multipart/parallel  
multipart/related  
multipart/report  
multipart/voice-message  
text/enriched  
text/html html, htm
text/plain txt
text/richtext rtx
text/sgml  
text/tab-separated-values tsv
text/x-setext etx
video/mpeg mpeg, mpg, mpe
video/quicktime qt, mov
video/vnd.vivo  
video/x-msvideo qvi
video/x-sgi-movie movie


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