[SR-Users] Manipulating contacts header results in a malformed SIP packet

[Andrew White]

Hi all,

Hope everyone is well, and looking forward to seeing you all whenever Kamailio World ends up being!

I’m currently dealing with an issue which I’m unsure if it’s due to my own implementation, or a bug.

When attempting to manipulate the Contact header via app_ruby, the SIP message I send ends up being malformed. Here’s the code I’m using:

def replace_contact_header(uri)
  #KSR::HDR.remove("Contact") if KSR::HDR.is_present('Contact') > 0
  #KSR::HDR.append("Contact: #{uri}\r\n")  
  KSR::HDR.rmappend("Contact", "Contact: #{uri}\r\n")
end

Note that I have tried both rmappend and the commented out functions too. I call this with a custom built URI, such as <61400123123 at kamailio.test.uconnected.com.au <mailto:61400123123 at kamailio.test.uconnected.com.au>>. This function is called just before a KSR::TM.t_relay(). Here’s the result I get watching from tshark (some info scrubbed for privacy):

Record-Route: <sip:1.2.3.4;lr;ftag=e3p42efd3635HH;vst=AAAAAAAAAAAAAAAAAAAAAAoUXVFHDQAAs83AEGwAAFgwCQA8QY3RlZC5jb20uYXU-;did=927.f0f2>
…
Call-ID: 3de29646-e423-1238-e712-023563fb337c
CSeq: 17736747 INVITE
sip:4.5.6.7:5060;alias=10.100.1.1~5060~1Content-Type: application/sdp
Content-Length: 483
Contact: <sip:61400123123 at kamailio.test.uconnected.com.au>

In this case, 4.5.6.7 is the PBX I made the call from (and the value of the original Contact header), and 1.2.3.4 is what kamailio.test.uconnected.com.au <http://kamailio.test.uconnected.com.au/> resolves to, and is this Kamailio instance.

Here’s a copy of the same thing when I don’t call my replace_contact_header function and t_relay:

Record-Route: <sip:1.2.3.4;lr;ftag=j6jebCSa5Qap6c;vst=AAAAAAAAAAAAAAAAAAAAAAoUXVND38dTgwEGEAEGwAAFgwCQA8Fdn83lZC5jb20uYXU-;did=827.40b>
...
Call-ID: 249571c5-e91a-ae91-6d8e-023563fb337c
CSeq: 17735867 INVITE
Contact: <sip:4.5.6.7:5060;alias=10.100.1.1~5060~1>
Content-Type: application/sdp
Content-Length: 483

Given the relative simplicity of the function, I have to assume this is an error with how the function is manipulating the existing Contact header? It seems that the “Contact: <“ part of the header is being removed as well as the “>\r\n", but the rest being left.

I’m currently using commit 283e468401d809ca9b71368c32badf3a70d48b8b <https://github.com/kamailio/kamailio/commit/283e46> on Amazon Linux 2, which is CentOS/RHEL based.

Thanks!

Andrew
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