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 that requires opening an external
viewer or using a plug-in.
Internet media types used by HTTP closely resemble MIME
types. MIME (Multipurpose Internet Mail Extension) was designed
as a method for sending attachments in email over the Internet.
Like MIME, media types follow the format type/subtype.
represent a wildcard. For example, the following
client header means that documents of all formats are accepted:
The following client header means that all
types are accepted, regardless of the subtype:
Servers and CGI programs are expected to examine the format 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
sends the document with a
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 ...