Robert,
You looked at the same text I did, and came to the same conclusion I did about what the spec currently says. But you sidestepped the questions I raised about whether that is what is *should* say.
More below.
Paul
Robert Sparks wrote:
^^^^^So, here's the guiding text:
2. Definition: message/sipfrag
A valid message/sipfrag part is one that could be obtained by
starting with some valid SIP message and deleting any of the
The above requirement to start with a *valid* sip message is questionable. One of the key use cases for sipfrag is for the NOTIFY messages that report on the status of a REFERed request.
Now suppose that the REFER caused an INVITE, and the response to the invite was itself invalid, either in the SIP or the SDP. Is it permissible to put that invalid message in the NOTIFY, as a sipfrag, even though it is an invalid sip message? It would be inconvenient if that were illegal.
I guess I can imagine some other type than sipfrag, that has weaker constrains on what it can contain. Maybe something like message/ostensibly-sip or message/ostensibly-sipfrag. But if there was such a thing, would there still be a use for message/sipfrag?
following:
o the entire start line
o one or more entire header fields
o the body
Thus, the body of any given sipfrag must be able to occur as the body of some valid SIP message (that otherwise matches the rest of the
information in this given sipfrag of course).
So, for the particular example you are exploring, you are correct. Advertising application/sdp and then only including a syntactically incorrect SDP body would be incorrect. You'll need to put that fractional SDP in something that makes sense from a MIME perspective: either create an sdpfrag type, or shove it into a wrapper (text/plain?) and make decoding it part of the semantics of whatever context you're using such a thing in.
RjS
On Mon, 2004-06-21 at 11:19, Paul Kyzivat wrote:
I received a question from a coworker regarding valid content for application/sipfrag. The question was:
if the fragment represents part of a message that contained a body, can the fragment contain just a portion of the body?
(I've generalized this - the actual question was whether the fragment could contain a Content-Type:application/sdp, and then contain just a portion of the actual sdp - a portion that was not syntactically correct SDP.)
Based on my reading of rfc 3420, I think the answer is NO. But it does raise the question whether the answer (to the generalized question) *should* be YES. I'm undecided on this, and would like to hear other opinions, but I am inclined to be pretty lenient.
In part there is an uncertainty principle here. How would you be able to tell a valid usage from an invalid one? Sipfrag is often used to relay messages received from others. It is possible that those received messages were ill-formed. In that case, a sipfrag that conveys the ill-formed message could appear identical to one that was obtained by invalid subsetting from a valid message. If you can't tell the difference, why ban the practice?
Another reason is that there may be increasing reason to subset the body when building a sipfrag. For instance, the original message may have had a large multipart body. But for purposes of the sipfrag only one of the parts is significant.
Paul
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