[reSIProcate] A suggestion about shifting responsibility of retransmissions of 2xx responses

["yuhuicai" <yuhuicai@xxxxxxxxxxx>]

Since the ServerStale machine state has been introduced into the Server Invite 
Transaction(in transactionstate.cxx), and that type of Transaction will stayed 
for Timer::TS millisecond (equals T2), I think the responsibility of 
retransmitting 2xx could shift to the library, as a result, the TU can  utilize 
the timing mechanism in the library. 

To achive this goal,at first, the 2xx response should retained in 
mMsgToRetransmit:

//      In Transactionstate::processServerInvite():
            else if (code >= 200 && code < 300)
            {
               if (mState == Trying || mState == Proceeding)
               {
                  StackLog (<< "Received 2xx when in Trying or Proceeding State 
of server invite transaction");
                  StackLog (<< *this);
                  sendToWire(msg);
                  
                  // Keep the StaleServer transaction around, so we can keep the
                  // source Tuple that the request was received on. 
                  terminateServerTransaction(mId); 
                  mMachine = ServerStale;
                  mController.mTimers.add(Timer::TimerStaleServer, mId, 
Timer::TS );
         delete msg;

//Should change to:

            else if (code >= 200 && code < 300)
            {
               if (mState == Trying || mState == Proceeding)
               {
                  StackLog (<< "Received 2xx when in Trying or Proceeding State 
of server invite transaction");
                  StackLog (<< *this);
                  if (mMsgToRetransmit) delete mMsgToRetransmit; //added by 
yuhuicai
                  mMsgToRetransmit = sip; //added by yuhuicai
                  sendToWire(msg);
                  
                  // Keep the StaleServer transaction around, so we can keep the
                  // source Tuple that the request was received on. 
                  terminateServerTransaction(mId); 
                  mMachine = ServerStale;
                  mController.mTimers.add(Timer::TimerStaleServer, mId, 
Timer::TS );
//       delete msg; // Modified by yuhuicai


Second, when the reinvite msg come, the saved 2xx could be send:

//In TransactionState::processServerStale():
   else if (sip && isRequest(sip) && sip->header(h_RequestLine).getMethod() == 
INVITE)
   {
      // this can happen when an upstream UAC never received the 200 and
      // retransmits the INVITE when using unreliable transport
      // Drop the INVITE since the 200 will get retransmitted by the downstream 
UAS
      StackLog (<< "Dropping retransmitted INVITE in stale server transaction" 
<< sip->brief());
      delete msg;
   }


//Should change to:

   else if (sip && isRequest(sip) && sip->header(h_RequestLine).getMethod() == 
INVITE)
   {
      // this can happen when an upstream UAC never received the 200 and
      // retransmits the INVITE when using unreliable transport
      // Drop the INVITE since the 200 will get retransmitted by the downstream 
UAS
      StackLog (<< "Dropping retransmitted INVITE in stale server transaction" 
<< sip->brief());
      sendToWire(mMsgToRetransmit); //added by yuhuicai
      delete msg;
   }


Maybe an interface should be added to let user choose rertansmit 2xx by TU or 
by library, and the default behavior is rertansmit  by TU.

I have tested these codes and it works well. But  it do not according to 
RFC3261(17.2.1):
     "If, while in the "Proceeding" state, the TU passes a 2xx response to the 
server transaction, the server transaction MUST pass this response to the 
transport layer for transmission. It is not retransmitted by the server 
transaction; retransmissions of 2xx responses are handled by the TU. The server 
transaction MUST then transition to the "Terminated" state."

So, if you think it's unreasonable, just disregard it. :-)