[OpenSIPStack] Response routing in OpenSBC

[Andrew P. <and...@po...>]

Hi,

I am trying to understand how the responses are routed in OpenSBC.
B2BUserAgent::ProcessEvent checks if there is a SIPMessage event, 
differentiates between different types of requests, then if event is not 
a request, event dispatcher checks if it already has a session for this 
response. Once session has been found, it calls 
B2BUAEndPoint::ProcessStackEvent. The latter does the following magic to 
handle the responses:
if( !msg.IsRequest() )
       {
         OString meth = msg.GetCSeqMethod();
         if( meth == "SUBSCRIBE" ||
             meth == "NOTIFY" ||
             meth == "PUBLISH" )
         {
           ///this is a response
           SIPSession::GCRef ref = proxy->FindGCRefByCallId( 
msg.GetCallId() );
           if( ref != NULL )
           {
             proxy->ProcessStackEvent( ref, event );
             return;
           }
         }
       }

So far so good. The switch loop inside the 
SIPSessionManager::ProcessStackEvent function calls OnIncomingSIPMessage:

       case SIPStackEvent::Message:
         LOG_CONTEXT( LogDetail(), eventObject->GetCallId(),
         "Event"
         << ": " << "---> Inbound - "
         << 
((SIPMessageArrival&)*eventObject).GetMessage().GetStartLine() );

         OnIncomingSIPMessage( (SIPMessageArrival&)*eventObject, session );
         break;

OnIncomingSIPMessage to dispatch a valid response calls 
SIPSession::OnIncomingSIPMessage. It does the following thing:
   if( messageEvent.GetMessage().IsRequest() )
   {
     if( !messageEvent.GetMessage().IsAck() )
     {
       PWaitAndSignal lock( m_CurrentUASRequestMutex );
       m_CurrentUASRequest = messageEvent.GetMessage();
     }
   }

I have kind of reached a deadlock here. What I want to know is how the 
response if actually delivered to the local transaction layer or remote 
proxy. We've seen a scenario where OpenBSC is serving as a frontend to 
PortaSIP and from it we know that responses are a subject to a check of 
Request-URI and To-URI to distinguish between local handling and relay. 
I just do not see where these checks are done. Thanks,

-- 
Sincerely,
Andrew Pogrebennyk