19 Mar
2020
19 Mar
'20
4:49 a.m.
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.in…
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(a)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=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@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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--
Alex Balashov | Principal | Evariste Systems LLC
Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free)
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