Set actual transport overhead in rtp_rtcp

webrtc/pc/channel.cc

Index: webrtc/pc/channel.cc
diff --git a/webrtc/pc/channel.cc b/webrtc/pc/channel.cc
index f22bdc4ca41029155f2fe4fe511bb9c2765ee679..7f0195023c5faa1d0ce0a49e001febdfd10d11bc 100644
--- a/webrtc/pc/channel.cc
+++ b/webrtc/pc/channel.cc
@@ -582,10 +582,20 @@ void BaseChannel::OnSelectedCandidatePairChanged(
   std::string transport_name = channel->transport_name();
   rtc::NetworkRoute network_route;
   if (selected_candidate_pair) {
+    selected_candidate_pair_ =
+        rtc::Optional<CandidatePair>(CandidatePair(*selected_candidate_pair));

[honghaiz3, 2016/10/31 17:42:09]

You don't need to save a copy of CandidatePair here. 
It should be sufficient to just use the pointer as the pointer is only accessed
in this class on the network thread and if the candidate pair is deleted, it
should be notified here. 

If you really want to save a copy to avoid the risk of accessing the pointer in
the future, I think we can save either
1. The local candidate, or
2. the overhead itself. 

By doing that, we don't need the changes in p2p/base dir. 

+
     network_route = rtc::NetworkRoute(
         ready_to_send, selected_candidate_pair->local_candidate().network_id(),
         selected_candidate_pair->remote_candidate().network_id(),
         last_sent_packet_id);
+
+    invoker_.AsyncInvoke<void>(
+        RTC_FROM_HERE, worker_thread_,
+        Bind(&MediaChannel::OnTransportOverheadChange, media_channel_,
+             GetTransportOverheadPerPacket()));
+  } else {
+    selected_candidate_pair_ = rtc::Optional<CandidatePair>();
   }
   invoker_.AsyncInvoke<void>(
       RTC_FROM_HERE, worker_thread_,
@@ -1030,11 +1040,15 @@ bool BaseChannel::SetupDtlsSrtp_n(bool rtcp_channel) {
                                     static_cast<int>(recv_key->size()));
   }
 
-  if (!ret)
+  if (!ret) {
     LOG(LS_WARNING) << "DTLS-SRTP key installation failed";
-  else
+  } else {
     dtls_keyed_ = true;
-
+    invoker_.AsyncInvoke<void>(
+        RTC_FROM_HERE, worker_thread_,
+        Bind(&MediaChannel::OnTransportOverheadChange, media_channel_,
+             GetTransportOverheadPerPacket()));
+  }
   return ret;
 }
 
@@ -1661,6 +1675,34 @@ void BaseChannel::UpdateMediaSendRecvState() {
       Bind(&BaseChannel::UpdateMediaSendRecvState_w, this));
 }
 
+int BaseChannel::GetTransportOverheadPerPacket() {
+  constexpr int kIpv4Overhaed = 20;
+  constexpr int kIpv6Overhaed = 40;
+  constexpr int kUdpOverhaed = 8;
+  constexpr int kTcpOverhaed = 20;

[honghaiz3, 2016/10/31 17:42:09]

If you just use the saved selected_candidate_pair pointer, add a RTC_DCHECK to
make sure it is in the network thread. 

[michaelt, 2016/11/01 08:31:37]

Done.

+
+  int transport_overhead_per_packet = 0;
+
+  if (selected_candidate_pair_) {

[honghaiz3, 2016/10/31 17:42:09]

Can you use an early return? That would be more readable. 
if (!selected_candidate_pair_) {
  return 0;
}
....

[michaelt, 2016/11/01 08:31:37]

Done.

+    transport_overhead_per_packet +=
+        selected_candidate_pair_->local_candidate().protocol() ==
+                TCP_PROTOCOL_NAME
+            ? kTcpOverhaed
+            : kUdpOverhaed;
+    transport_overhead_per_packet +=
+        selected_candidate_pair_->local_candidate().address().family() ==
+                AF_INET
+            ? kIpv4Overhaed
+            : kIpv6Overhaed;
+    if (secure()) {
+      int srtp_overhead = 0;
+      if (srtp_filter_.GetSrtpOverhead(&srtp_overhead))
+        transport_overhead_per_packet += srtp_overhead;
+    }
+  }
+  return transport_overhead_per_packet;
+}
+
 void VoiceChannel::UpdateMediaSendRecvState_w() {
   // Render incoming data if we're the active call, and we have the local
   // content. We receive data on the default channel and multiplexed streams.