[Bug]: No contact header in 180 Ringing responses

[pbalash0v]

Context

I observe the absence of contact header in 180 Ringing responses issued by Linphone. Here is the 180 Ringing response message sampled from linphone app installed on Debian 11 using apt

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP 192.168.1.99:5060;branch=z9hG4bK-524287-1---34707f286261cc45;rport
From: "caller" <sip:caller@localhost>;tag=9829fc7f
To: <sip:[email protected]:50768;transport=udp>;tag=vmzOzr~
Call-ID: ZBo7FCnz3mS8vm_8qi6n1w..
CSeq: 1 INVITE
User-Agent: Linphone Desktop/ (Debian GNU/Linux 11 (bullseye), Qt 5.15.2) LinphoneCore/4.4.21
Supported: replaces, outbound, gruu

There are some discussions on this topic in sip-implementors list: https://lists.cs.columbia.edu/pipermail/sip-implementors/2002-October/003817.html https://lists.cs.columbia.edu/pipermail/sip-implementors/2008-August/019928.html https://lists.cs.columbia.edu/pipermail/sip-implementors/2009-August/023322.html

Although it seems that the topic is a source of confusion, but the majority tends to agree contact header is a MUST requirement in this case (despite the contents of Table 2 of RFC3261).

General information

• Device: amd64 desktop
• OS: Linux Debian11
• Version of the App: LinphoneCore/4.4.2, Debian GNU/Linux 11 (bullseye) repository
• Version of the SDK: LinphoneCore/4.4.21
• Also happens on manually compiled Linphone Desktop/4.5.0-alpha-64-g1ebcc2f5 (debian) Debian GNU/Linux 11 (bullseye), Qt 5.15.2 LinphoneCore/5.2.0-alpha-89-g1b32f644e

Expected behaviour

I expect the contact header to be present in Linphone's 180 Ringing responses

To Reproduce

Make a call towards an Linphone app

Additional context

Here is the 180 Ringing response message sampled from some previous Linphone app installed from native Ubuntu 18 repository:

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP 192.168.1.99:5060;branch=z9hG4bK-524287-1---cd90f47efe296968;rport=5060
From: "callee" <sip:[email protected]>;tag=c83bbd32
To: <sip:[email protected]:50560>;line=dc8a311d7857d48;tag=968821674
Call-ID: 9pDA1zeaUiMSeA3VbUNYeA..
CSeq: 1 INVITE
Contact: <sip:[email protected]:50560>
User-Agent: Linphone/3.6.1 (eXosip2/4.1.0)
Content-Length: 0

As can be seen the contact header is present in the earlier version of Linphone, but gone missing later.

SDK logs URL

No response