Only generate one CNAME per PeerConnection.

webrtc/api/peerconnection.cc

Index: webrtc/api/peerconnection.cc
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index 70a386ec14f8905382893b266589b17afefc5456..70e7a2b79eb94b869c837461b5b8e919004ea90f 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -66,6 +66,9 @@ static const char kTransport[] = "transport";
 // NOTE: Must be in the same order as the ServiceType enum.
 static const char* kValidIceServiceTypes[] = {"stun", "stuns", "turn", "turns"};
 
+// The length of CNAMEs.
+static const int kCnameLength = 16;

[pthatcher1, 2016/05/05 18:50:51]

Can you call this kRtcpCnameLength and RTCP CNAME in the comment?

[Zhi Huang, 2016/05/06 01:36:53]

Done.

+
 // NOTE: A loop below assumes that the first value of this enum is 0 and all
 // other values are incremental.
 enum ServiceType {
@@ -377,6 +380,15 @@ void AddSendStreams(
 
 namespace webrtc {
 
+// Generate a CNAME when a PeerConnection is created.
+std::string GenerateCname() {

[pthatcher1, 2016/05/05 18:50:51]

Can you call this GenerateRtcpCname() and use "RTCP CNAME" in the comment?

[Zhi Huang, 2016/05/06 01:36:53]

Done.

+  std::string cname;
+  if (!rtc::CreateRandomString(kCnameLength, &cname)) {
+    LOG(LS_ERROR) << "Failed to generate CNAME.";

[pthatcher1, 2016/05/05 18:50:51]

We should probably RTC_DCHECK(false) here as well. 

[Zhi Huang, 2016/05/06 01:36:53]

Right. This is a point I should not overlook.

+  }
+  return cname;
+}
+
 bool ExtractMediaSessionOptions(
     const PeerConnectionInterface::RTCOfferAnswerOptions& rtc_options,
     bool is_offer,
@@ -508,6 +520,7 @@ PeerConnection::PeerConnection(PeerConnectionFactory* factory)
       ice_state_(kIceNew),
       ice_connection_state_(kIceConnectionNew),
       ice_gathering_state_(kIceGatheringNew),
+      cname_(GenerateCname()),
       local_streams_(StreamCollection::Create()),
       remote_streams_(StreamCollection::Create()) {}
 
@@ -1503,6 +1516,8 @@ bool PeerConnection::GetOptionsForOffer(
   if (session_->data_channel_type() == cricket::DCT_SCTP && HasDataChannels()) {
     session_options->data_channel_type = cricket::DCT_SCTP;
   }
+
+  session_options->cname = cname_;
   return true;
 }
 
@@ -1540,6 +1555,8 @@ bool PeerConnection::GetOptionsForAnswer(
   if (!ParseConstraintsForAnswer(constraints, session_options)) {
     return false;
   }
+  session_options->cname = cname_;
+
   FinishOptionsForAnswer(session_options);
   return true;
 }
@@ -1552,6 +1569,8 @@ bool PeerConnection::GetOptionsForAnswer(
   if (!ExtractMediaSessionOptions(options, false, session_options)) {
     return false;
   }
+  session_options->cname = cname_;
+
   FinishOptionsForAnswer(session_options);
   return true;
 }