Fixing some issues with the direction attribute of m-lines in offers.

talk/session/media/mediasession.cc

Index: talk/session/media/mediasession.cc
diff --git a/talk/session/media/mediasession.cc b/talk/session/media/mediasession.cc
index 2cd2d46d9ca5adbf28f61a83b7b501354a99be75..7413026092f1d6f8c8742e407d48376ac5a5ea01 100644
--- a/talk/session/media/mediasession.cc
+++ b/talk/session/media/mediasession.cc
@@ -1036,12 +1036,15 @@ static bool CreateMediaContentAnswer(
       answer->set_direction(MD_RECVONLY);
       break;
     case MD_RECVONLY:
-      answer->set_direction(MD_SENDONLY);
+      answer->set_direction(answer->streams().empty() ? MD_INACTIVE
+                                                      : MD_SENDONLY);
       break;
     case MD_SENDRECV:
-      answer->set_direction(MD_SENDRECV);
+      answer->set_direction(answer->streams().empty() ? MD_RECVONLY
+                                                      : MD_SENDRECV);

[pthatcher, 2015/11/23 18:00:52]

It looks like this breaks data channels.  If we're answering data channels, we
should probably always go to sendrecv/sendonly.  

This was reported for C++ data channels (native/mobile apps), but we should see
if this affects Chrome as well.  If it is, we'll need to merge a fix ASAP. 

https://bugs.chromium.org/p/webrtc/issues/detail?id=5228#c5

       break;
     default:
+      RTC_DCHECK(false && "MediaContentDescription has unexpected direction.");
       break;
   }
 
@@ -1529,8 +1532,18 @@ bool MediaSessionDescriptionFactory::AddAudioContentForOffer(
   bool secure_transport = (transport_desc_factory_->secure() != SEC_DISABLED);
   SetMediaProtocol(secure_transport, audio.get());
 
-  if (!options.recv_audio) {
-    audio->set_direction(MD_SENDONLY);
+  if (!audio->streams().empty()) {
+    if (options.recv_audio) {
+      audio->set_direction(MD_SENDRECV);
+    } else {
+      audio->set_direction(MD_SENDONLY);
+    }
+  } else {
+    if (options.recv_audio) {
+      audio->set_direction(MD_RECVONLY);
+    } else {
+      audio->set_direction(MD_INACTIVE);
+    }
   }
 
   desc->AddContent(CN_AUDIO, NS_JINGLE_RTP, audio.release());
@@ -1574,8 +1587,18 @@ bool MediaSessionDescriptionFactory::AddVideoContentForOffer(
   bool secure_transport = (transport_desc_factory_->secure() != SEC_DISABLED);
   SetMediaProtocol(secure_transport, video.get());
 
-  if (!options.recv_video) {
-    video->set_direction(MD_SENDONLY);
+  if (!video->streams().empty()) {
+    if (options.recv_video) {
+      video->set_direction(MD_SENDRECV);
+    } else {
+      video->set_direction(MD_SENDONLY);
+    }
+  } else {
+    if (options.recv_video) {
+      video->set_direction(MD_RECVONLY);
+    } else {
+      video->set_direction(MD_INACTIVE);
+    }
   }
 
   desc->AddContent(CN_VIDEO, NS_JINGLE_RTP, video.release());