I need to do special handling in freeswitch when receiving a REFER message from an Avaya SIP trunk. But I am not sure whether Sofia-SIP allows users to specify a callback hook when REFER is received. I haven't found one.
I want to add a custom freeswitch module just to handle REFER. How can I force Sofia-SIP to cede control to my custom module while handling REFER?
Having FreeSWITCH, i would recommend using the LUA module that provides a Event Callback for the REFER handling. This can allow you control with what you want to do with the REFER message.
mod_lua is well documented as a module in freeswitch. The pain is coding in LUA which is easy or hard based on your preferences.