Bug 1141749: Prevent collisions in local SSRCs. r=mt

--HG--
extra : rebase_source : f28488aa956b8eb33a6b812e1f88ec9623132f93

media/webrtc/signaling/src/jsep/JsepSessionImpl.cpp

@@ -117,12 +117,16 @@ JsepSessionImpl::AddTrack(const RefPtr<JsepTrack>& track)
 
     if (track->GetSsrcs().empty()) {
       uint32_t ssrc;
-      SECStatus rv = PK11_GenerateRandom(
-          reinterpret_cast<unsigned char*>(&ssrc), sizeof(ssrc));
-      if (rv != SECSuccess) {
-        JSEP_SET_ERROR("Failed to generate SSRC, error=" << rv);
-        return NS_ERROR_FAILURE;
-      }
+      do {
+        SECStatus rv = PK11_GenerateRandom(
+            reinterpret_cast<unsigned char*>(&ssrc), sizeof(ssrc));
+        if (rv != SECSuccess) {
+          JSEP_SET_ERROR("Failed to generate SSRC, error=" << rv);
+          return NS_ERROR_FAILURE;
+        }
+      } while (mSsrcs.count(ssrc));
+
+      mSsrcs.insert(ssrc);
       track->AddSsrc(ssrc);
     }
   }

media/webrtc/signaling/src/jsep/JsepSessionImpl.h

@@ -336,6 +336,9 @@ private:
   std::string mDefaultRemoteStreamId;
   std::map<size_t, std::string> mDefaultRemoteTrackIdsByLevel;
   std::string mCNAME;
+  // Used to prevent duplicate local SSRCs. Not used to prevent local/remote or
+  // remote-only duplication, which will be important for EKT but not now.
+  std::set<uint32_t> mSsrcs;
   UniquePtr<Sdp> mGeneratedLocalDescription; // Created but not set.
   UniquePtr<Sdp> mCurrentLocalDescription;
   UniquePtr<Sdp> mCurrentRemoteDescription;