[SR-Users] callback function of tm module

[Timo Reimann]

Hey Bruno,


On 03.06.2011 16:21, Bruno Bresciani wrote:
> In file t_hook.c line 386 "*cbp->callback( trans, cbp->types, params )*"
> calls the function to record register_tmcb when I received a INVITE. I'd
> like to now how register_tmcb function is call by the function callback.

register_tmcb() isn't called by a callback function, it rather works the
other way around. For clarity, here's the call flow:

(1) A user is interested in being called back on a particular tm event,
e.g., TMCB_DESTROY. To be notified of such events, he calls
tmcb_register() and passes the set of events (callback types) he is
interested in (e.g., TMCB_DESTROY and possibly others) together with the
desired callback function and a few other parameters.
(2) In tmcb_register(), a few sanity checks are done first (e.g.,
callback type is valid, callback function is not NULL, transaction
exists, etc.). If they pass, the callback function and the parameters
are stored in a list of callbacks (called cb_list in register_tmcb()).
(3) When a particular tm event occurs, the tm module checks if any
callbacks were registered for that specific event. If so, it executes
each registered callback function in sequence, with each function being
passed the callback type and callback-specific parameter. The call of
the callback is exactly what

  cbp->callback( trans, type, params )

does, at least for call types other than TMCB_REQUEST_IN.

For TMCB_REQUEST_IN, the handling is slightly different because
callbacks for new SIP requests cannot be associated with an already
existing transaction (after all, they are new). With regards to how
TMCB_REQUEST_IN-typed callback functions are called, the only difference
is that the callback function is being passed the set of all callback
types the registering user was interested in, and not just TMCB_REQUEST_IN:

  cbp->callback( trans, cbp->types, params )

(This is line 386.) Actually, I am not quite sure why the extent of
returned callback types differs here. I'm using tm callbacks myself but
never had to take advantage of that.


Anyways, if all you want to do is use tm callbacks from a module of
yours, just call register_tmcb() passing

- a callback function,
- a transaction cell (unless you're registering for TMCB_REQUEST_IN),
- a void pointer to something you want to be passed back on callback
execution, and
- an optional release function for cleanup purposes.

Implement your callback-specific logic in the callback function, and
that's it. Naturally, your callback function must fit the callback
signature defined in t_hooks.h.


I hope this answers your question. If not, let us know what you
specifically have in mind, i.e., whether you would like to use tm
callbacks, change the framework, or whatever.


Cheers,

--Timo



> 2011/6/3 Timo Reimann <timo.reimann at 1und1.de <mailto:timo.reimann at 1und1.de>>
> 
>     Hi Bruno,
> 
> 
>     On 03.06.2011 00:07, Bruno Bresciani wrote:
>     > I'm having doubts in the implementation of the callback function
>     module
>     > tm. As she calls the function to record register_tmcb ()?
>     > Can someome help me?
> 
>     Could you be more specific on which part of the tm module you are having
>     trouble with?
> 
>     If you need an example on how to use tm's callbacks you may take a look
>     at the dialog module, specifically the files dialog.c and
>     dlg_handlers.c.
> 
> 
>     Cheers,
> 
>     --Timo