Howdy,
For a few years my company's provided a free offline-tool to convert from an 
internal SIP message capture format of SIP messages received by our system 
parsers, to pcap format.  This tool does the classic trick of creating fake 
Ethernet+IP+UDP headers and formatting the thing as a pcap.  It made sense to 
do this, because it lets us capture the real IP:port info in the fake IP/UDP 
headers, so that wireshark displays them and the user can sort/filter based on 
ip and do conversation analysis, etc.  We don't want to do real raw packet 
captures as they're received off-the-wire, because SIP could run over TLS or 
IPsec and would only show encrypted data.

This all worked fine when everything was SIP over UDP over IPv4.  But SIP over 
TCP exists as well, and even over IPv6.  Over TCP in particular, when 
"capturing" at the application layer you don't have access to sequence numbers 
and such, and recording them as UDP packets is really misleading (and screws 
up).  Furthermore, we'd like to change our systems to be able to create a file 
format and encap type wireshark will (someday) understand natively.

I could write a patch for wireshark to handle a new WTAP_ENCAP_RAW_SIP_SOCKET 
or some such, with a small header that records the ip:port:transport info we do 
have at the app layer, and dissector that handles that before calling SIP's 
dissector.  But it occurs to me we can't be the first ones with this problem - 
things like HTTP and other application layer parsers/apps must want the ability 
to "capture" into a file like pcap at their layer too, so is there some 
existing solution (encap format, file format, dissector, whatever) that I'm 
overlooking?  I've tried to check the source code of every one that looks like 
it might do it, but I can't find one.

-hadriel

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