HTTP: The Definitive Guide

MIME Type Structure

Each MIME media type consists of a type, a subtype, and a list of optional parameters. The type and subtype are separated by a slash, and the optional parameters begin with a semicolon, if they are present. In HTTP, MIME media types are widely used in Content-Type and Accept headers. Here are a few examples:

Content-Type: video/quicktime
Content-Type: text/html; charset="iso-8859-6"
Content-Type: multipart/mixed; boundary=gc0p4Jq0M2Yt08j34c0p
Accept: image/gif

Discrete Types

MIME types can directly describe the object type, or they can describe collections or packages of other object types. If a MIME type describes an object type directly, it is a discrete type. These include text files, videos, and application-specific file formats.

Composite Types

If a MIME type describes a collection or encapsulation of other content, the MIME type is called a composite type . A composite type describes the format of the enclosing package. When the enclosing package is opened, each enclosed object will have its own type.

Multipart Types

Multipart media types are composite types. A multipart object consists of multiple component types. Here’s an example of multipart/mixed content, where each component has its own MIME type:

Content-Type: multipart/mixed; boundary=unique-boundary-1

--unique-boundary-1
Content-type: text/plain; charset=US-ASCII

Hi there, I'm some boring ASCII text...

--unique-boundary-1
Content-Type: multipart/parallel; boundary=unique-boundary-2 --unique-boundary-2 ...