sip_inv: Additional multipart support (#2919)

[gtjoseph]

FYI... Although not strictly needed, I created both pjsip_tdata_get_sdp_info and pjsip_tdata_get_sdp_info2 to mirror the existing pjsip_rdata_get_sdp_info and pjsip_rdata_get_sdp_info2 functions. I can eliminate pjsip_tdata_get_sdp_info2 if that's better. Also double check code formatting. I lost my "pjproject" Eclipse code formatter and had to recreate it from scratch. :)

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sip_inv.c:inv_check_sdp_in_incoming_msg() deals with multipart
message bodies in rdata correctly. In the case where early media is
involved though, the existing sdp has to be retrieved from the last
tdata sent in this transaction. This, however, always assumes that
the sdp sent is in a non-multipart body. While there's a function
to retrieve the sdp from multipart and non-multpart rdata bodies,
no similar function for tdata exists. So...

• The existing pjsip_rdata_get_sdp_info2 was refactored to
  find the sdp in any body, multipart or non-multipart, and
  from either an rdata or tdata. The new function is
  pjsip_get_sdp_info. This new function detects whether the
  pjsip_msg->body->data is the text representation of the sdp
  from an rdata or an existing pjmedia_sdp_session object
  from a tdata, or whether pjsip_msg->body is a multipart
  body containing either of the two sdp formats.

• The exsting pjsip_rdata_get_sdp_info and pjsip_rdata_get_sdp_info2
  functions are now wrappers that get the body and Content-Type
  header from the rdata and call pjsip_get_sdp_info.

• Two new wrappers named pjsip_tdata_get_sdp_info and
  pjsip_tdata_get_sdp_info2 have been created that get the body
  from the tdata and call pjsip_get_sdp_info.

• For testing purposes, a new field "create_multipart" was added
  to the pjsip_inv_session structure to allow forcing all bodies
  created to be multipart.

• The internal create_sdp_body function now takes an option to
  indicate that a multipart body should be created.

• inv_offer_answer_test.c was updated to use the create_multipart
  field and additional tests were added.

Fixes #2919

[nanangizz]

Not sure about this setting because:

• Potential behavioral change affecting app or upper level API. For example, currently pjsua seems to always assume that Invite module will always create non-multipart body, see how this pjsua_process_msg_data() implementation creates multipart body, it does not check whether the existing body, which is generated by Invite module, is a multipart (as specified here, nested multipart is not recommended). Some apps may assume the same.
• Even if the pjsip_inv_session structure is public (as opposed to transparent), as far as I know, modifying/writing the field directly should be avoided, it should be done via a function (or an option/flag), which does not seem to be provided here.

Also, as currently this setting seems to be used by a test app only, so perhaps better to handle multipart body generation in the test app if possible?

[gtjoseph]

Hmmm. That flag really was there for internal testing only as the comment states. I wanted the existing unit tests in inv_offer_answer_test to be able to exercise the multipart logic in sip_inv. Having the test do the multipart handling would defeat the purpose. I can just remove the extra tests and the field if you prefer.

[nanangizz]

I mean the app should generate the multipart body (instead of handling the whole multipart things) and leave sip_inv to generate non-multipart body as is (so the new field create_multipart can be avoided), something like this: 2920_diff.txt.
.

[gtjoseph]

Ah, gotcha. Let me try that and see if it still exercises the code paths.

[gtjoseph]

OK, I removed the create_multipart option and applied the diff to inv_offer_answer_test. Seems to work fine. Anything else I need to do?

[nanangizz]

Looks okay to me. Thanks!

[sauwming]

completeness

[gtjoseph]

completemess

That was a Freudian slip :)

[sauwming]

PJ_DECL. Also below.

[gtjoseph]

oops. Cut and paste error.