Pluglet Developers Guide
MIME Types and Manifest Files
MIME Types
MIME (Multipurpose Internet Mail Extensions) redefines the standard US-ASCII format for Internet mail messages. (RFCs 2045-2048 extend RFC 822, the earlier standard). In brief, these extensions allow for:
- textual message bodies in other character sets
- body formats other than just text
- multi-part message bodies
- textual header information in other character sets
MIME also defines new header fields such as MIME-Version, Content-Type, Content-Transfer Encoding, etc.
Of particular interest, the Content-Type Header Field consists of a (media) type and subtype, separated by a slash (/). Type declares the general media type, while subtype declares the specific format. For example,
video/mpeg
specifies that the general type of the media is video, while the specific format is mpeg.
For a detailed discussion of this topic, see http://www.oac.uci.edu/indiv/ehood/MIME/toc.html.
The above discussion relates abstractly to Internet mail messages, which contain
header fields and bodies. The idea of MIME Type (type/subtype)
is specifically used by the EMBED and OBJECT elements
of an HTML page. TYPE, meaning MIME Type, is an attribute
of both elements. It is used to inform the client about the type of data specified
by the SCR or DATA attribute so that it can launch
the right Plugin or helper application.
- SRC is used with the EMBED element
- DATA is used with the OBJECT element
Thus TYPE is specifying the MIME Type of the SRC or <
code>DATA URL. However, in the case that the element specifies no
SCR or DATA attribute (i.e., no external data is to be
loaded), then MIME Type is simply being used to inform the browser about what
type of Plugin or helper application should be launched. This usage differs from
that where MIME Type indicates the Content-Type of a mail message (i.e., the media
type of a data object).
One other use of MIME Type relates to browser applications: The navigator
object is a browser object used to provide information about the brower and
the platform on which it is running. It is not part of the Document Object Model.
navigator has an array of objects called mimeTypes[],
each of which specifies some MIME Type supported by the browser. A particular
mimeType[] element, for example navigator.mimeType[n], has
four attributes, one of which is called type. It is a MIME Type
of the kind that we have been discussing, i.e., a Content-Type description consisting
of a media type and subtype.)
Assuming that an SRC or DATA element is present,
then a URL specifies a file to load, and the suffix, as mentioned
in the next section, refers to the suffix of the file. For example,
animationX.swf has the suffix .swf for a the
Shockwave-Flash movie, whose MIME Type is application/x-shockwave-flash.
Manifest Files
A manifest file for a Pluglet should be in the following form:
MIMEDescription: type0; type1;
...; typeN: suffix0; suffix1;
... suffixM: Pluglet name
Pluglet-Class: pluglet_class_name
Wheretype specifies a MIME Type.
suffix specifies a file suffix, as described above.
name is the Pluglet name and is arbitrary.
pluglet_class_name is the specific class name of the PlugletFactory for the Pluglet.
For example,
MIMEDescription: video/mpeg: mpg; mpeg: Pluglet JavaMediaPlayer
Pluglet-Class: JMPlayer
where JMPlayer corresponds to a JMPlayer.class file that is the factory for the Pluglet.