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<HTML><HEAD> <TITLE>MIME Data Types</TITLE></HEAD><BODY bgcolor="#ffffff"><H1><A NAME="yDeIvFBSQJ9X3cS">MIME Data Types</H1><P>All predefinedtypes and subtypes, as defined in<A HREF="http://ds.internic.net/rfc/rfc1521.txt">Internet RFC1521 (Multipurpose Internet Mail Extension)</A>, will be handled by<CITE>Ishmail</CITE>. The image, audio, video, and application types will not bedisplayed directly by<CITE>Ishmail</CITE>. Rather,<CITE>Ishmail</CITE> will rely on theavailability of other applications to do this. If defined in a mailcapabilities file (mailcap),<CITE>Ishmail</CITE> will launch the specifiedapplication when it comes across one of these types.<P>Also, two methods of data encoding will be directly supported by<CITE>Ishmail</CITE>; quoted-printable, and base64 (as defined in RFC 1521).Briefly, quoted-printable is for character sets that are a supersetof US-ASCII, and encodes any 8-bit characters into a string of7-bit characters. Base64 is used for parts that are largely (orcompletely) 8 bit. This is superior to<I>uuencode</I>, because itguarantees that the encoded data will only be 1/3 larger than theoriginal. Another advantage is that Base64 does not rely on theASCII character set, therefore will decode correctly on a systemusing, for example, EBCDIC character encoding. However, if auser insists on using<I>uuencode</I>, it is possible to define thisthrough the<I>mailcap</I> file.<P><HR><B>NOTE:</B><BR>The<I>mailcap</I> file is a configuration file for"mail capabilities," similar in style to themore familiar BSD UNIX<I>termcap</I> and<I>printcap</I> files.<HR></P><P>Following is an excerpt from the RFC, defining data types:<P><I>Text</I> - Textual information. The primary subtype, "plain",indicates plain unformatted text. No special software is requiredto get the full meaning of the text, aside from support for theindicated character set. Subtypes are to be used for enriched textin forms where application software may enhance theappearance of the text, but such software must not be requiredin order to get the general idea of the content. Possible subtypesthus include any readable word processor format. A very simpleand portable subtype, rich text, is the other predefined subtype.The supported character sets will be US-ASCII and theISO-8859-* set.<P><I>Multipart</I> - Data consisting of multiple parts of independent datatypes. Four initial subtypes are defined; the primary "mixed" subtype, "alternative" for representing the same data in multipleformats, "parallel" for parts intended to be viewedsimultaneously, and "digest" for multipart entities in which eachpart is of type "message".<P><I>Message</I> - An encapsulated message. A body of Content-Type"message" is itself a fully formatted RFC 822 conformingmessage which may contain its own different Content-Typeheader field. The primary subtype is "rfc822". The "partial" subtype is defined for partial messages, to permit the fragmentedtransmission of bodies that are thought to be too large to bepassed through mail transport facilities. Another subtype,"External-body", is defined for specifying large bodies byreference to an external data source (e.g. the MUA might useanon-ftp to get the data for you).<P><I>Image</I> - This format requires a display device (such as agraphical display, a printer, or a FAX machine) to view theinformation. Initial subtypes are defined for two widely-usedimage formats,<CITE>jpeg</CITE> and<CITE>gif</CITE>. The viewer,<CITE>xloadimage</CITE>, may be usedfor<CITE>gif</CITE>. The viewer,<CITE>xv</CITE>, can display<CITE>jpeg</CITE>, but this is not availablefor resale. It may only be distributed as contributed software.<P><I>Audio</I> - With initial subtype "basic". Audio requires an audiooutput device (such as a speaker or a telephone) to "display" thecontents. The "basic" subtype is 8-bit ISDN u-law (PCM), andassumes a 8k Hz sample rate on one channel. This will be thestandard audio device provided by HAL (same as Sun).<P><I>Video</I> - This format requires the capability to display movingimages typically including specialized hardware and software.The initial subtype is "mpeg". A public domain viewer called"<CITE>mpeg_play</CITE>" is available for SunOS.<P><I>Application</I> - Some other kind of data, typically eitherun-interpreted binary data or information to be processed by amail-based application. The primary subtype, "octet-stream", isto be used in the case of uninterpreted binary data, in which casethe simplest recommended action is to offer to write theinformation into a file for the user. Two additional subtypes,"ODA" and "PostScript", are defined for transporting ODA andPostScript documents in bodies. At this time, and ODA viewer isnot defined.<I>Ghostscript</I> is expected to be used as the PostScriptviewer. Other expected uses for "application" includespreadsheets, data for mail-based scheduling systems, andlanguages for "active" (computational) e-mail.<HR>Preceding Section: <A HREF="QDeIvFBSQJ9X3cS.html">Composing MIME Messages</A><BR>Following Section: <A HREF="Xj52wFBX4N9X3cS.html">Ishmail Resources</A><BR>Parent Section: <A HREF="zsPsIGBSYWwA0YK.html">Ishmail User's Guide</A><BR>Contents of <A HREF="zsPsIGBSYWwA0YK.html">Ishmail User's Guide</A><BR><HR></BODY></HTML>⌨️ 快捷键说明
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