Introduce rtc::PacketTransportInterface and let cricket::TransportChannel inherit.

webrtc/p2p/base/dtlstransportchannel.cc

Index: webrtc/p2p/base/dtlstransportchannel.cc
diff --git a/webrtc/p2p/base/dtlstransportchannel.cc b/webrtc/p2p/base/dtlstransportchannel.cc
index d95bdcd916b1814ae4eda1eaeebd4f333e59f2ac..ebfe56dfb9b51c01be4b78ea7b6a1f0e9113cc7f 100644
--- a/webrtc/p2p/base/dtlstransportchannel.cc
+++ b/webrtc/p2p/base/dtlstransportchannel.cc
@@ -14,6 +14,7 @@
 #include "webrtc/p2p/base/dtlstransportchannel.h"
 
 #include "webrtc/p2p/base/common.h"
+#include "webrtc/p2p/base/packettransport.h"
 #include "webrtc/base/buffer.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/base/dscp.h"
@@ -437,9 +438,10 @@ bool DtlsTransportChannelWrapper::IsDtlsConnected() {
 //       start the DTLS handshake
 //     - Once the DTLS handshake completes, the state is that of the
 //       impl again
-void DtlsTransportChannelWrapper::OnWritableState(TransportChannel* channel) {
+void DtlsTransportChannelWrapper::OnWritableState(rtc::PacketTransport* pt) {
+  TransportChannel* channel = static_cast<TransportChannel*>(pt);

[pthatcher1, 2016/10/13 20:26:37]

The only thing this method needs from pt is ->writable(), which is part of the
interface.  So why do we need the type cast?   I guess there's the RTC_DCHECK,
but that's just a pointer compare, and we could move the cast to just that line
if the compiler requires it.

But it might be better to change the member variable "TransportChannel*
channel_" into "PacketTransportInterface* transport_".  Then the check would be
transport_ == transport, which wouldn't need the type cast.

I only see one place where we need anything from channel_ that we wouldn't get
from transport_, and that's the RTC_DCHECK in OnReceivingState, which is the
same as this RTC_DCHECK except in reverse.

[johan, 2016/10/14 16:09:33]

Done.
In the methods above are several lines of forwarding TransportChannel's signals
to subscribers of DtlsTransportChannel. That code won't compile, if we replace
the member variable channel_ by transport_. What are the plans are for this
signal-fowarding code, anyway?

   ASSERT(rtc::Thread::Current() == worker_thread_);
-  ASSERT(channel == channel_);
+  RTC_DCHECK(channel == channel_);
   LOG_J(LS_VERBOSE, this)
       << "DTLSTransportChannelWrapper: channel writable state changed to "
       << channel_->writable();
@@ -471,7 +473,7 @@ void DtlsTransportChannelWrapper::OnWritableState(TransportChannel* channel) {
 
 void DtlsTransportChannelWrapper::OnReceivingState(TransportChannel* channel) {
   ASSERT(rtc::Thread::Current() == worker_thread_);
-  ASSERT(channel == channel_);
+  RTC_DCHECK(channel == channel_);
   LOG_J(LS_VERBOSE, this)
       << "DTLSTransportChannelWrapper: channel receiving state changed to "
       << channel_->receiving();
@@ -482,10 +484,14 @@ void DtlsTransportChannelWrapper::OnReceivingState(TransportChannel* channel) {
 }
 
 void DtlsTransportChannelWrapper::OnReadPacket(
-    TransportChannel* channel, const char* data, size_t size,
-    const rtc::PacketTime& packet_time, int flags) {
+    rtc::PacketTransport* pt,
+    const char* data,
+    size_t size,
+    const rtc::PacketTime& packet_time,
+    int flags) {
+  TransportChannel* channel = static_cast<TransportChannel*>(pt);
   ASSERT(rtc::Thread::Current() == worker_thread_);
-  ASSERT(channel == channel_);
+  RTC_DCHECK(channel == channel_);
   ASSERT(flags == 0);
 
   if (!dtls_active_) {
@@ -558,14 +564,14 @@ void DtlsTransportChannelWrapper::OnReadPacket(
 }
 
 void DtlsTransportChannelWrapper::OnSentPacket(
-    TransportChannel* channel,
+    rtc::PacketTransport* pt,
     const rtc::SentPacket& sent_packet) {
   ASSERT(rtc::Thread::Current() == worker_thread_);
 
   SignalSentPacket(this, sent_packet);
 }
 
-void DtlsTransportChannelWrapper::OnReadyToSend(TransportChannel* channel) {
+void DtlsTransportChannelWrapper::OnReadyToSend(rtc::PacketTransport* pt) {
   if (writable()) {
     SignalReadyToSend(this);
   }