[sr-dev] [kamailio/kamailio] topos module may not be able to transparently transmit the update message (#2659)

[zhangyang]

**Description**
We use below config to test the topology hiding function，when kamailio receive “update” message，doesn't send out，it will send to itself with destination port 5060；
Sorry for raising this question again，I really don’t know what parameters need to be configured。And after I modified some codes, it could succeed probabilistically...
Sorry again, excuse me

**Troubleshooting**
```
loadmodule "ndb_redis.so"
loadmodule "topos_redis.so"
loadmodule "topos.so"
modparam("ndb_redis", "server", "name=srv8;addr=127.0.0.1;port=6381;db=2")
modparam("topos", "storage", "redis")
modparam("topos", "db_url", "redis://127.0.0.1:6381/2")
modparam("topos_redis", "serverid", "srv8")

...Omit the configuration in the middle...

route[WITHINDLG] {
        if (has_totag()) {
        # sequential request withing a dialog should
        # take the path determined by record-routing
                xlog("L_INFO","yang yangyang testin to not here");
                if (loose_route()){
                        if(is_method("INFO")){
                                route("INFO_SELF");
                        }

                        route(BYE);
                        route(REINVITE);
                        route(ACK);
                        route(RELAY);
                } else {
                        if ( is_method("ACK")) {
                                if ( t_check_trans() ) {
                                # no loose-route, but stateful ACK;
                                # must be an ACK after a 487
                                # or e.g. 404            $var(obj) = $sht(call_objects=>$ci);
                                        xlog("L_INFO","Call $ci: ACK received in A-Leg, $fU@$si:$sp -----> $rU@$Ri:$Rp relaying downstreamrouteWITHINDLG\n");
                                        t_relay();
                                        exit;
                                } else {
                                        exit;
                                }
                        }
                        xlog("L_INFO","yang in to not here");
                        sl_send_reply("404","Not here");
                }
                exit;
        }
}



```
--------
Call flow

```
UE-----------------PROXY-------------B2bua
invite-------------->|------------------>invite
183<----------------|<------------------183
Prack------------ ->|------------------>Prack
200ok<-------------|<-----------------200ok
update1---------->|
                              |update2<-----------|
                              | 404 not here------->     |                              
````

**Additional Information**

```
version: kamailio master (x86_64/linux) 

```


### Possible Solutions

I set the log level to debug, and the comparison found that the logic of prack and update is different。After checking the code of topos, it is found that kamailio/src/modules/topos/tps_msg.c has a separate processing for prack.according to
commit [37830f5](https://github.com/kamailio/kamailio/commit/37830f53b1f21fba5beef5d8e22913c431dcd708)
So I added update to the prack processing method，Later I found that when the B-side update message comes, it should follow the original logic。
So I distinguish whether to follow the modified logic according to ONREPLY_ROUTE。
But after probabilistic success，The problem is that the value returned by get_route_type（） is sometimes 1 and sometimes 4
Call flow after modification：

```
UE-----------------PROXY-------------B2bua
invite-------------->|------------------>invite
183<----------------|<------------------183
Prack------------ ->|------------------>Prack
200ok<-------------|<-----------------200ok
update1---------->|----------------->|update
200ok<-------------|<-----------------200ok
                         |<-----------------|update2
                        | 404 not here---------> |                              
````


Here is the code I modified：
/src/modules/topos/tps_msg.c 
![image](https://user-images.githubusercontent.com/16113837/109925737-107b0580-7cfd-11eb-9eaf-7a66ba224b55.png)





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