Fix issue with send-side bandwidth estimation over TURN TCP connections.

webrtc/p2p/base/asyncstuntcpsocket.cc

Index: webrtc/p2p/base/asyncstuntcpsocket.cc
diff --git a/webrtc/p2p/base/asyncstuntcpsocket.cc b/webrtc/p2p/base/asyncstuntcpsocket.cc
index 296a9d413a12c3b48ffe53a2c98c9dcbcf13e82b..3369bc8b48dc3e9f37f4284ec6e6895bb05f4371 100644
--- a/webrtc/p2p/base/asyncstuntcpsocket.cc
+++ b/webrtc/p2p/base/asyncstuntcpsocket.cc
@@ -79,6 +79,9 @@ int AsyncStunTCPSocket::Send(const void *pv, size_t cb,
     return res;
   }
 
+  rtc::SentPacket sent_packet(options.packet_id, rtc::TimeMillis());

[juberti1, 2017/05/27 23:17:21]

This signal should probably only be fired when the packet has been fully
serialized. 

That said, this change will still be an improvement.

[holmer, 2017/06/02 07:08:00]

Yes, I agree. If I correctly understand how the TCP socket classes interact, I'd
say the signal should be fired in the implementation of socket_:
https://cs.chromium.org/chromium/src/third_party/webrtc/base/asynctcpsocket.c...

which should be where we send the packet to the real socket.


When we run in Chrome, I assume that socket may be the IpcPacketSocket? In that
case we really want the signal fired from the browser process, which maybe this
signal now overrides?

If I've understood correctly, I think we may want to connect to this signal
instead:
https://cs.chromium.org/chromium/src/content/renderer/p2p/ipc_socket_factory....

[Taylor Brandstetter, 2017/06/02 17:42:43]

I guess I don't see how filling a buffer in userspace differs fundamentally from
filling a buffer in kernel space. I thought the main purpose of SignalSentPacket
was to eliminate jitter due to IPC between the browser/renderer processes.

But anyway: this is copying the existing behavior of AsyncTcpSocket, so if this
is an issue it's one that already existed.
In chromium, we connect to that signal; in native apps we connect to this one.
This class is only created by BasicPacketSocketFactory, but chromium uses
IpcPacketSocketFactory as you mentioned.

+  SignalSentPacket(this, sent_packet);
+
   // We claim to have sent the whole thing, even if we only sent partial
   return static_cast<int>(cb);
 }