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

-- Henning Westerholt – https://skalatan.de/blog/ Kamailio services – https://gilawa.com -----Original Message----- From: sr-users sr-users-bounces@lists.kamailio.org On Behalf Of Alex Balashov Sent: Thursday, March 19, 2020 2:49 AM To: Kamailio (SER) - Users Mailing List sr-users@lists.kamailio.org Subject: Re: [SR-Users] Manipulating contacts header results in a malformed SIP packet Hi Andrew, The Content-Length header, if present, is the header that must appear last in a SIP message, per RFC 3261 § 7.5 So, any method of manipulation of the Contact must manipulate it in place. A common favourite - if you absolutely must manipulate the Contact - is to substitute it. You can also insert the header at an arbitrary position: https://kamailio.org/docs/modules/5.3.x/modules/textopsx.html#textopsx.f.ins... But a better question might perhaps be: why do you want to manipulate the Contact header? While it may perhaps be legitimately necessary occasionally, my finding has been that in 99% of cases, it's the wrong way to solve a problem. -- Alex On Thu, Mar 19, 2020 at 12:42:51PM +1100, Andrew White wrote: > 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@kamailio.test.uconnected.com.au mailto:61400123123@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=AAAAAAAAAAAAAAAAAAAAAAoUXVFHDQ AAs83AEGwAAFgwCQA8QY3RlZC5jb20uYXU-;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@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=AAAAAAAAAAAAAAAAAAAAAAoUXVND38 dTgwEGEAEGwAAFgwCQA8Fdn83lZC5jb20uYXU-;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 > _______________________________________________ > Kamailio (SER) - Users Mailing List > sr-users@lists.kamailio.org > https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users -- Alex Balashov | Principal | Evariste Systems LLC Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/ _______________________________________________ Kamailio (SER) - Users Mailing List sr-users@lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users