[Freeswitch-dev] What's the easiest way to get all the SIP messages in FS?

Hi, I want to get all(or certain) SIP messages in FS(perhaps I want to write a module), What's the easiest or best way to get that? or where I can find it in code? I know we can see SIP messages with TPORT_LOG enabled, It's in mod_sofia or sofia-lib? Why it is only possible to set that on start time but can't change it lively? If I can get them, I think it's possible to write to a file/db, or even send out from event_socket. I know it will hurt performance, but we don't do high volume calls and want to debug easily. Third party tools maybe work but also hurt performance right? Thanks. Seven