[OpenSIPS-Devel] [opensips] b2bua pending request handling (#679)

[DMOsipov]

I have opensips and opensips-b2bua-module modules of version 1.11.5-2~1.gbp1f5df1 installed on Debian Wheezy.

For test purposes I use very simplified opensips.cfg implementing top hiding scenario to connect to FreeSWITCH-based IVR:
```
route {
    if (is_method("INVITE")) {
        b2b_init_request("top hiding");
    }
}
```
- After successful call establishment UAC sends INFO and re-INVITE packets in very short period of time. 
- Upon receiving INFO, opensips correctly sends it to B-leg (towards FreeSWITCH).
- Then re-INVITE packet arrives from UAC before INFO answer received.
- Opensips answers "491 Request Pending" for packet INFO and inspite of error sends re-INVITE towards FreeSWITCH.
- Opensips receives "200 OK" for INFO from FreeSWITCH and got error "ERROR:b2b_entities:b2b_send_reply: Mismatch between the method in tm[16] and the method to send reply to[1]"
- Opensips receives "200 OK" for re-INVITE and passes it to UAC

Please find call flow below
```
UAC                      Opensips          FreeSWITCH
 |----------INVITE(1)------->|                  |
 |<-------100 Trying(1)------|                  |
 |                           |-----INVITE(1)--->|
 |                           |<--100 Trying(1)--|
 |                           |<----200 OK(1)----|
 |<---------200 OK(1)--------|                  |
 |------------ACK(1)-------->|                  |
 |                           |------ACK(1)----->|

================Call established=================

 |-----------INFO(2)-------->|                  |
 |----------INVITE(3)------->|                  |
 |                           |------INFO(2)---->|
 |<--491 Request Pending(2)--|                  |
 |<-------100 Trying(3)------|                  |
 |                           |-----INVITE(3)--->|
 |                           |<--100 Trying(3)--|
 |                           |<----200 OK(2)----|
 |                           |                  |
                            ERROR:b2b_entities:b2b_send_reply: 
                            Mismatch between the method in tm[16] 
                            and the method to send reply to[1]

 |                           |<----200 OK(3)----|
 |<---------200 OK(3)--------|                  |
 |                           |                  |
Never receive answer
for INFO  
```

I see two issues here 
- "491 Request Pending" should be answered for re-INVITE packet, not for INFO
- re-INVITE should NOT be passed to B-leg

So correct call flow should look like this
```
UAC                      Opensips          FreeSWITCH
 |----------INVITE(1)------->|                  |
 |<-------100 Trying(1)------|                  |
 |                           |-----INVITE(1)--->|
 |                           |<--100 Trying(1)--|
 |                           |<----200 OK(1)----|
 |<---------200 OK(1)--------|                  |
 |------------ACK(1)-------->|                  |
 |                           |------ACK(1)----->|

================Call established=================

 |-----------INFO(2)-------->|                  |
 |----------INVITE(3)------->|                  |
 |                           |------INFO(2)---->|
 |<--491 Request Pending(3)--|                  |
 |                           |<----200 OK(2)----|
 |<---------200 OK(2)--------|                  |
 |                           |                  |
```

I've tried to make patch to fix issue but I'm not sure if it's correct.
Hope you will find this helpful.
```
diff --git a/modules/b2b_entities/dlg.c b/modules/b2b_entities/dlg.c
index e656d8b..6798d3d 100644
--- a/modules/b2b_entities/dlg.c
+++ b/modules/b2b_entities/dlg.c
@@ -863,15 +863,17 @@ logic_notify:
                                                LM_DBG("Received another request when the previous "
                                                        "one was in process\n");
                                                str text = str_init("Request Pending");
-                                               if(tmb.t_reply_with_body(dlg->uas_tran, 491,
+                                               if(tmb.t_reply_with_body(tm_tran, 491,
                                                &text, 0, 0, &to_tag) < 0)
                                                {
                                                        LM_ERR("failed to send reply with tm\n");
                                                }
                                                LM_DBG("Sent reply [491] and unreffed the cell %p\n",
-                                                       dlg->uas_tran);
+                                                       tm_tran);
                                        }
-                                       tmb.unref_cell(dlg->uas_tran);
+                                       tmb.unref_cell(tm_tran);
+                                       lock_release(&table[hash_index].lock);
+                                       return SCB_DROP_MSG;
                                }
                                dlg->uas_tran = tm_tran;
                                LM_DBG("Saved uas_tran=[%p] for dlg[%p]\n", tm_tran, dlg);
```

---
Reply to this email directly or view it on GitHub:
https://github.com/OpenSIPS/opensips/issues/679
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