DTLS-SRTP set up is bypassed when the channel has been writable.

talk/session/media/channel.cc

 /*
  * libjingle
  * Copyright 2004 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 247 matching lines @@
 
   if (transport_name == transport_name_) {
     // Nothing to do if transport name isn't changing
     return true;
   }
 
   // When using DTLS-SRTP, we must reset the SrtpFilter every time the transport
   // changes and wait until the DTLS handshake is complete to set the newly
   // negotiated parameters.
   if (ShouldSetupDtlsSrtp()) {
+    // Set |writable_| to false such that UpdateWritableState_w could set up
+    // DTLS-SRTP again.

[pthatcher1, 2015/12/17 23:38:54]

could => can
again => when the writable_ becomes true again

[guoweis_webrtc, 2015/12/17 23:43:17]

Done.

+    writable_ = false;
     srtp_filter_.ResetParams();
   }
 
+  // TODO(guoweis): Remove this grossness when we remove non-muxed RTCP.
+  if (rtcp_transport_enabled()) {
+    LOG(LS_INFO) << "Create RTCP TransportChannel for " << content_name()
+                 << " on " << transport_name << " transport ";
+    set_rtcp_transport_channel(
+        transport_controller_->CreateTransportChannel_w(
+            transport_name, cricket::ICE_CANDIDATE_COMPONENT_RTCP),
+        false /* update_writablity */);
+    if (!rtcp_transport_channel()) {
+      return false;
+    }
+  }
+
+  // We're not updating the writablity during the transition state.
   set_transport_channel(transport_controller_->CreateTransportChannel_w(
       transport_name, cricket::ICE_CANDIDATE_COMPONENT_RTP));
   if (!transport_channel()) {
     return false;
   }
+
+  // TODO(guoweis): Remove this grossness when we remove non-muxed RTCP.
   if (rtcp_transport_enabled()) {
-    LOG(LS_INFO) << "Create RTCP TransportChannel for " << content_name()
-                 << " on " << transport_name << " transport ";
-    set_rtcp_transport_channel(transport_controller_->CreateTransportChannel_w(
-        transport_name, cricket::ICE_CANDIDATE_COMPONENT_RTCP));
-    if (!rtcp_transport_channel()) {
-      return false;
-    }
+    // Update aggregate writable/ready-to-send state between RTP and RTCP upon
+    // setting new channel

[pthatcher1, 2015/12/17 23:38:54]

This comment isn't accurate any more.  Perhaps something like "We can only
update the RTCP ready to send after set_transport_channel has handled channel
writability."

[guoweis_webrtc, 2015/12/17 23:43:17]

Done.

+    SetReadyToSend(
+        true, rtcp_transport_channel() && rtcp_transport_channel()->writable());
   }
-
   transport_name_ = transport_name;
   return true;
 }
 
 void BaseChannel::set_transport_channel(TransportChannel* new_tc) {
   ASSERT(worker_thread_ == rtc::Thread::Current());
 
   TransportChannel* old_tc = transport_channel_;
   if (!old_tc && !new_tc) {
     // Nothing to do
@@ skipping 15 matching lines @@
       new_tc->SetOption(pair.first, pair.second);
     }
   }
 
   // Update aggregate writable/ready-to-send state between RTP and RTCP upon
   // setting new channel
   UpdateWritableState_w();
   SetReadyToSend(false, new_tc && new_tc->writable());
 }
 
-void BaseChannel::set_rtcp_transport_channel(TransportChannel* new_tc) {
+void BaseChannel::set_rtcp_transport_channel(TransportChannel* new_tc,
+                                             bool update_writablity) {
   ASSERT(worker_thread_ == rtc::Thread::Current());
 
   TransportChannel* old_tc = rtcp_transport_channel_;
   if (!old_tc && !new_tc) {
     // Nothing to do
     return;
   }
   ASSERT(old_tc != new_tc);
 
   if (old_tc) {
     DisconnectFromTransportChannel(old_tc);
     transport_controller_->DestroyTransportChannel_w(
         transport_name_, cricket::ICE_CANDIDATE_COMPONENT_RTCP);
   }
 
   rtcp_transport_channel_ = new_tc;
 
   if (new_tc) {
     RTC_CHECK(!(ShouldSetupDtlsSrtp() && srtp_filter_.IsActive()))
         << "Setting RTCP for DTLS/SRTP after SrtpFilter is active "
         << "should never happen.";
     ConnectToTransportChannel(new_tc);
     for (const auto& pair : rtcp_socket_options_) {
       new_tc->SetOption(pair.first, pair.second);
     }
   }
 
-  // Update aggregate writable/ready-to-send state between RTP and RTCP upon
-  // setting new channel
-  UpdateWritableState_w();
-  SetReadyToSend(true, new_tc && new_tc->writable());
+  if (update_writablity) {
+    // Update aggregate writable/ready-to-send state between RTP and RTCP upon
+    // setting new channel
+    UpdateWritableState_w();
+    SetReadyToSend(true, new_tc && new_tc->writable());
+  }
 }
 
 void BaseChannel::ConnectToTransportChannel(TransportChannel* tc) {
   ASSERT(worker_thread_ == rtc::Thread::Current());
 
   tc->SignalWritableState.connect(this, &BaseChannel::OnWritableState);
   tc->SignalReadPacket.connect(this, &BaseChannel::OnChannelRead);
   tc->SignalReadyToSend.connect(this, &BaseChannel::OnReadyToSend);
   tc->SignalDtlsState.connect(this, &BaseChannel::OnDtlsState);
 }
@@ skipping 700 matching lines @@
 }
 
 void BaseChannel::ActivateRtcpMux() {
   worker_thread_->Invoke<void>(Bind(
       &BaseChannel::ActivateRtcpMux_w, this));
 }
 
 void BaseChannel::ActivateRtcpMux_w() {
   if (!rtcp_mux_filter_.IsActive()) {
     rtcp_mux_filter_.SetActive();
-    set_rtcp_transport_channel(nullptr);
+    set_rtcp_transport_channel(nullptr, true);
     rtcp_transport_enabled_ = false;
   }
 }
 
 bool BaseChannel::SetRtcpMux_w(bool enable, ContentAction action,
                                ContentSource src,
                                std::string* error_desc) {
   bool ret = false;
   switch (action) {
     case CA_OFFER:
       ret = rtcp_mux_filter_.SetOffer(enable, src);
       break;
     case CA_PRANSWER:
       ret = rtcp_mux_filter_.SetProvisionalAnswer(enable, src);
       break;
     case CA_ANSWER:
       ret = rtcp_mux_filter_.SetAnswer(enable, src);
       if (ret && rtcp_mux_filter_.IsActive()) {
         // We activated RTCP mux, close down the RTCP transport.
         LOG(LS_INFO) << "Enabling rtcp-mux for " << content_name()
                      << " by destroying RTCP transport channel for "
                      << transport_name();
-        set_rtcp_transport_channel(nullptr);
+        set_rtcp_transport_channel(nullptr, true);
         rtcp_transport_enabled_ = false;
       }
       break;
     case CA_UPDATE:
       // No RTCP mux info.
       ret = true;
       break;
     default:
       break;
   }
@@ skipping 1226 matching lines @@
   return (data_channel_type_ == DCT_RTP) && BaseChannel::ShouldSetupDtlsSrtp();
 }
 
 void DataChannel::OnStreamClosedRemotely(uint32_t sid) {
   rtc::TypedMessageData<uint32_t>* message =
       new rtc::TypedMessageData<uint32_t>(sid);
   signaling_thread()->Post(this, MSG_STREAMCLOSEDREMOTELY, message);
 }
 
 }  // namespace cricket