Although I share your distaste for the boundary and prefer Content-Length,
I expect that we would have to do it through some new construct.
RFC 1521 is very clear in its initial paragraph on multipart:
7.2. The Multipart Content-Type
In the case of multiple part entities, in which one or more different
sets of data are combined in a single body, a "multipart" Content-
Type field must appear in the entity's header. The body must then
contain one or more "body parts," each preceded by an encapsulation
boundary, and the last one followed by a closing boundary. Each part
starts with an encapsulation boundary, and then contains a body part
consisting of header area, a blank line, and a body area. Thus a
body part is similar to an RFC 822 message in syntax, but different
I don't think this leaves any room for a new subtype of multipart which
does not have a boundary string.
> From rdebry at us.ibm.com Thu Dec 19 05:50:32 1996
>> We had some discussion of this at the IETF meeting. The multipart/mixed mime
> type apparently allows content-length, but it is not used for anything in the
> server. In fact, we were told that if a content-length field exists, the
> boundary string must still be present and must be used as the boundary.
> Therefore I would like to suggest a new mime type called multipart/IPP (or
> something similar) where we can define the rules for boundaries, I would
> suggest that if no content-length field is present in a sub-part then boundary
> strings are used as defined in the current multipart/mixed mime type. However,
> if a content-length field is present in a sub-part, no boundary string is
> defined and the content-length field is used.
>> Lengths are extremely valuable for processing on the server side and can make a
> significant difference in error recovery and in moving data around. I'd agree
> with Scott's assessment - if the lengths are known, use them!