[sr-dev] RFC: adding new callback mechanism into core API

[Maxim Sobolev]

Gang,

We have some new functionality for the nathelper planned that would need
to know final destination URI for the message to work properly.
Currently this means that we have to require script writer to invoke
this function only after all URI transformations have been applied,
which might quite significantly complicate script logic. Moreover it
might be even impossible in some cases to do so, for example when using
t_relay() function, which uses transaction state to determine message
destination.

Therefore, I see the need for a callback mechanism in core, allowing
callback functions to be registered on per-message basis and then to be
executed in some well-defined points of message processing. The
mechanism could be sufficiently generic to allow different uses. One of
the other use that I have in mind is destructor callback, which is to be
called when the message structure is being freed, so that modules would
be able to release any resources allocated (memory, connections,
descriptors, etc).

Any comments and suggestions are welcome.

Regards,
-- 
Maksym Sobolyev
Sippy Software, Inc.
Internet Telephony (VoIP) Experts
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