RFC 2388 (rfc2388) - Page 2 of 9

Returning Values from Forms: multipart/form-data

RFC 2388                  multipart/form-data                August 1998


3. Definition of multipart/form-data

   The media-type multipart/form-data follows the rules of all multipart
   MIME data streams as outlined in [RFC 2046].  In forms, there are a
   series of fields to be supplied by the user who fills out the form.
   Each field has a name. Within a given form, the names are unique.

   "multipart/form-data" contains a series of parts. Each part is
   expected to contain a content-disposition header [RFC 2183] where the
   disposition type is "form-data", and where the disposition contains
   an (additional) parameter of "name", where the value of that
   parameter is the original field name in the form. For example, a part
   might contain a header:

        Content-Disposition: form-data; name="user"

   with the value corresponding to the entry of the "user" field.

   Field names originally in non-ASCII character sets may be encoded
   within the value of the "name" parameter using the standard method
   described in RFC 2047.

   As with all multipart MIME types, each part has an optional
   "Content-Type", which defaults to text/plain.  If the contents of a
   file are returned via filling out a form, then the file input is
   identified as the appropriate media type, if known, or
   "application/octet-stream".  If multiple files are to be returned as
   the result of a single form entry, they should be represented as a
   "multipart/mixed" part embedded within the "multipart/form-data".

   Each part may be encoded and the "content-transfer-encoding" header
   supplied if the value of that part does not conform to the default
   encoding.

4. Use of multipart/form-data

4.1 Boundary

   As with other multipart types, a boundary is selected that does not
   occur in any of the data. Each field of the form is sent, in the
   order defined by the sending appliction and form, as a part of the
   multipart stream.  Each part identifies the INPUT name within the
   original form. Each part should be labelled with an appropriate
   content-type if the media type is known (e.g., inferred from the file
   extension or operating system typing information) or as
   "application/octet-stream".





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