Properly handle different transports having different SSL roles.

talk/app/webrtc/webrtcsession.cc

 /*
  * libjingle
  * Copyright 2012 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 743 matching lines @@
 }
 
 void WebRtcSession::SetSdesPolicy(cricket::SecurePolicy secure_policy) {
   webrtc_session_desc_factory_->SetSdesPolicy(secure_policy);
 }
 
 cricket::SecurePolicy WebRtcSession::SdesPolicy() const {
   return webrtc_session_desc_factory_->SdesPolicy();
 }
 
-bool WebRtcSession::GetSslRole(rtc::SSLRole* role) {
+bool WebRtcSession::GetSslRole(const std::string& transport_name,
+                               rtc::SSLRole* role) {
   if (!local_desc_ || !remote_desc_) {
     LOG(LS_INFO) << "Local and Remote descriptions must be applied to get "
                  << "SSL Role of the session.";
     return false;
   }
 
-  return transport_controller_->GetSslRole(role);
+  return transport_controller_->GetSslRole(transport_name, role);
 }
 
 void WebRtcSession::CreateOffer(
     CreateSessionDescriptionObserver* observer,
     const PeerConnectionInterface::RTCOfferAnswerOptions& options,
     const cricket::MediaSessionOptions& session_options) {
   webrtc_session_desc_factory_->CreateOffer(observer, options, session_options);
 }
 
 void WebRtcSession::CreateAnswer(
@@ skipping 181 matching lines @@
     EnableChannels();
     SetState(source == cricket::CS_LOCAL ? STATE_SENTPRANSWER
                                          : STATE_RECEIVEDPRANSWER);
     if (!PushdownMediaDescription(cricket::CA_PRANSWER, source, err_desc)) {
       SetError(ERROR_CONTENT, *err_desc);
     }
     if (error() != ERROR_NONE) {
       return BadPranswerSdp(source, GetSessionErrorMsg(), err_desc);
     }
   } else if (action == kAnswer) {
-    if (!PushdownTransportDescription(source, cricket::CA_ANSWER, &td_err)) {
-      return BadAnswerSdp(source, MakeTdErrorString(td_err), err_desc);
-    }
     const cricket::ContentGroup* local_bundle =
         local_desc_->description()->GetGroupByName(cricket::GROUP_TYPE_BUNDLE);
     const cricket::ContentGroup* remote_bundle =
         remote_desc_->description()->GetGroupByName(cricket::GROUP_TYPE_BUNDLE);
     if (local_bundle && remote_bundle) {
-      // The answerer decides the transport to bundle on
+      // The answerer decides the transport to bundle on.
       const cricket::ContentGroup* answer_bundle =
           (source == cricket::CS_LOCAL ? local_bundle : remote_bundle);
       if (!EnableBundle(*answer_bundle)) {
         LOG(LS_WARNING) << "Failed to enable BUNDLE.";
         return BadAnswerSdp(source, kEnableBundleFailed, err_desc);
       }
     }
+    if (!PushdownTransportDescription(source, cricket::CA_ANSWER, &td_err)) {
+      return BadAnswerSdp(source, MakeTdErrorString(td_err), err_desc);
+    }

[pthatcher1, 2016/01/07 21:12:03]

What effect does moving this down have?  Can you leave a comment explaining why
it needs to be down here?

[Taylor Brandstetter, 2016/01/07 22:25:55]

If somehow the DTLS roles were "active" for audio and "passive" for video, then
you start BUNDLEing on video, the answer will have "active" for both. But if you
try to push down the transport description before enabling BUNDLE (and
destroying the video transport), it will complain about a DTLS role conflict.

Bottom line is: we shouldn't be pushing down a transport description for a
transport that's about to be destroyed, especially since that description is now
referring to a DIFFERENT transport.

     EnableChannels();
     SetState(STATE_INPROGRESS);
     if (!PushdownMediaDescription(cricket::CA_ANSWER, source, err_desc)) {
       SetError(ERROR_CONTENT, *err_desc);
     }
     if (error() != ERROR_NONE) {
       return BadAnswerSdp(source, GetSessionErrorMsg(), err_desc);
     }
   }
   return true;
@@ skipping 1197 matching lines @@
   }
 }
 
 void WebRtcSession::OnSentPacket_w(cricket::TransportChannel* channel,
                                    const rtc::SentPacket& sent_packet) {
   RTC_DCHECK(worker_thread()->IsCurrent());
   media_controller_->call_w()->OnSentPacket(sent_packet);
 }
 
 }  // namespace webrtc