[Serusers] Rewriting URI in the Contact field

[Maxim Sobolev]

On Sun, Jan 12, 2003 at 11:44:21PM +0100, Jan Janak wrote:
> On 12-01 23:25, Maxim Sobolev wrote:
> > Everything works just fine when I'm calling from UA1 to UA2, i.e.
> > from behind the NAT to the "outside world", however there are
> > some problems when I'm doing it in reverse direction. The problem
> > is that OK INVITE that the UA1 sends in reply to UA2's INVITE when
> > the user picks up the phone is not passed to my helper functions
> > and hence UA2 makes a wrong conclusion about where to send ACK and
> > BYE to.
> > 
> > Do you have any ideas on how to overcome this problem?
> 
>   If I get you right, you need to rewrite Contact in 200 OK response to INVITE
>   comming from the NATed user agent.

Correct.

>   You can do this using TM and it's callbacks. TM is transaction module and
>   you can register callbacks with the module. Among others, there is a callback
>   that will be called upon reception of the final response (200 OK in your
>   case). In the callback, you can modify the response and rewrite the contact.

I see, but IMO this would be not a generic solution, as I'll have to adjust
the code for my particular needs. What I am looking for is some way to
allow it to be modified by properly constructing config file. Perhaps something
like t_on_negative() could be added, i.e. t_on_positive(): the specified
routing block will be called when the transaction is completed with positive
result but before sending final reply. What do you think?

-Maxim

>   First, you need to include t_hooks.h and tm_load.h from the tm module.
> 
>   Then, you need to register a callback function. The following code snippet
>   shows how to do it:
> 
> static int mod_init( void )
> {
> 
>         load_tm_f       load_tm;
> 
>         /* import the TM auto-loading function */
>         if ( !(load_tm=(load_tm_f)find_export("load_tm", NO_SCRIPT))) {
>                 LOG(L_ERR, "radius_acc: mod_init: can't import load_tm\n");
>                 return -1;
>         }
>         /* let the auto-loading function load all TM stuff */
>         if (load_tm( &tmb )==-1) return -1;
> 
>         /* register callback */
>         if (tmb.rngister_tmcb( TMCB_REPLY, rad_acc_onreply, 0) <= 0) 
>                 return -1;
>  	}
>         
>         return 0;
> }
> 
>  The mod_init function registers rad_acc_onreply function, the function will
>  be called when the tm module receives a response.
> 
>  The callback follows. Note that radius_acc module (from which the code
>  snippets were taken) registers TMCB_REPLY callback. This type of callback
>  will be called _AFTER_ the response was sent out - that means there is no way
>  how to modify it. Because of that, your module will have to register another
>  type of callback - TMCB_REPLY_IN. Such callback will be called before the
>  reply gets forwarded which means that you can modify it before it will be
>  sent out. 
> 
>  See modules/tm/t_hooks.h file for more details ! There is a description of
>  the callbacks. 
> 
> /*
>  * Function that gets called on reply
>  * params: struct cell* t The callback structure
>  *         struct sip_msg *msg The sip message.
>  *         int code The status code
>  *         void* param Passed parameter
>  * returns: nothing
>  */
> static void rad_acc_onreply( struct cell* t, struct sip_msg *reply, int code, 
>                                                                 void *param ) 
> {
> 
>         struct sip_msg *rq;
> 
>         rq = t->uas.request;
> 
>         if (t->is_invite && missed_flag && isflagset( rq, missed_flag)==1
>                         && ((code>=400 && code<500) || code>=600))
>                                 rad_acc_missed_report( t, reply, code);
> 
> 
>         /* if acc enabled for flagged transaction, check if flag matches */
>         if (acc_flag && isflagset( rq, acc_flag )==-1) return;
>         /* early media is reported only if explicitely demanded, 
>            other provisional responses are always dropped  */
>         if (code < 200 && ! (early_media && code==183)) 
>                 return;
>         /* negative transactions reported only if explicitely demanded */
>         if (!failed_transactions && code >=300) return;
> 
>         /* anything else, i.e., 2xx, always reported */
>         radius_log_reply(t, reply);
> 
> }
> 
>    regards, Jan.