Invalid SDP answer does not cause SDP negotiation to fail (thanks Andrey Kovalenko for the report)

[bennylp]

For example, we send and offer

v=0
o=- 234 123 IN IP4 192.168.1.1
s=-
c=IN IP4 192.168.1.1
t=0 0
m=audio 8510 RTP/AVP 111 0 101
a=rtpmap:111 SPEEX/16000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=sendrecv

Then answer arrives:

v=0
o=user1 53655765 2353687637 IN IP4 192.168.1.2
s=-
t=0 0
c=IN IP4 192.168.1.2
m=audio 5000 RTP/AVP 112
a=rtpmap:112 dpeex/8000
a=sendrecv

This obviously is an invalid answer, but this answer is accepted by the SDP negotiator, i.e. the negotiation status is returned as PJ_SUCCESS.

Having said that, with PJSUA-LIB, this would still cause the call to be terminated, as the invalid SDP answer would cause other failure to occur further down the processing chain.

[bennylp]

Case II:

We send offer:

v=0
o=- 234 123 IN IP4 192.168.1.1
s=-
c=IN IP4 192.168.1.1
t=0 0
m=audio 16740 RTP/AVP 111 0 101
a=rtpmap:111 SPEEX/16000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=sendrecv

and answer:

v=0
o=- 53655765 2353687637 IN IP4 192.168.1.2
s=-
t=0 0
c=IN IP4 192.168.1.2
m=audio 5000 RTP/AVP 111 0
a=rtpmap:111 speex/8000
a=rtpmap:0 PCMU/8000
a=sendrecv

After negotiation, codec with payload type 111 is removed from offer, but it's still exist in the answer.

[nanang]

(In [3160]) Fixed #1066:

• Added check if the negotiation result of local-offer/remote-answer has no matching format.
• Added routine to remove any unmatching formats in the remote-answer.

[nanang]

Reopened for:

• bug in r3160: the fix "removing any unmatching formats in the remote-answer" only works for static payload types.
• reordering formats priority in the offer based on the answer also only works for static payload types.

[nanang]

(In [3187]) Re #1066, in process_m_answer() of sdp_neg.c:

• Fixed removing any unmatching formats in the remote-answer to also work with dynamic payload type.
• Updated reordering formats priority in the offer based on the answer to also work with dynamic payload type.