Fix P2PSocketHostUdp to handle dropped packets properly.

content/browser/renderer_host/p2p/socket_host_udp.cc

Index: content/browser/renderer_host/p2p/socket_host_udp.cc
diff --git a/content/browser/renderer_host/p2p/socket_host_udp.cc b/content/browser/renderer_host/p2p/socket_host_udp.cc
index 7d511c88fec2c53fda620b794dae94d42b91b7da..012c2ed51936263d63ec09bc3832df7f606e7bac 100644
--- a/content/browser/renderer_host/p2p/socket_host_udp.cc
+++ b/content/browser/renderer_host/p2p/socket_host_udp.cc
@@ -270,23 +270,6 @@ void P2PSocketHostUdp::Send(const net::IPEndPoint& to,
     return;
   }
 
-  if (!base::ContainsKey(connected_peers_, to)) {
-    P2PSocketHost::StunMessageType type = P2PSocketHost::StunMessageType();
-    bool stun = GetStunPacketType(&*data.begin(), data.size(), &type);
-    if (!stun || type == STUN_DATA_INDICATION) {
-      LOG(ERROR) << "Page tried to send a data packet to " << to.ToString()
-                 << " before STUN binding is finished.";
-      OnError();
-      return;
-    }
-
-    if (throttler_->DropNextPacket(data.size())) {
-      VLOG(0) << "STUN message is dropped due to high volume.";
-      // Do not reset socket.
-      return;
-    }
-  }
-
   IncrementTotalSentPackets();
 
   if (send_pending_) {
@@ -294,13 +277,42 @@ void P2PSocketHostUdp::Send(const net::IPEndPoint& to,
     IncrementDelayedBytes(data.size());
     IncrementDelayedPackets();
   } else {
-    // TODO(mallinath: Remove unnecessary memcpy in this case.
     PendingPacket packet(to, data, options, packet_id);
     DoSend(packet);
   }
 }
 
 void P2PSocketHostUdp::DoSend(const PendingPacket& packet) {
+  base::TimeTicks send_time = base::TimeTicks::Now();
+
+  // The peer is considered not connected until the first incoming STUN
+  // request/response. In that state the renderer is allowed to send only STUN
+  // messages to that peer and they are throttled using the |throttler_|. This
+  // has to be done here instead of Send() to ensure P2PMsg_OnSendComplete
+  // messages are sent in correct order.
+  if (!base::ContainsKey(connected_peers_, packet.to)) {
+    P2PSocketHost::StunMessageType type = P2PSocketHost::StunMessageType();
+    bool stun = GetStunPacketType(packet.data->data(), packet.size, &type);
+    if (!stun || type == STUN_DATA_INDICATION) {
+      LOG(ERROR) << "Page tried to send a data packet to "
+                 << packet.to.ToString() << " before STUN binding is finished.";
+      OnError();
+      return;
+    }
+
+    if (throttler_->DropNextPacket(packet.size)) {
+      VLOG(0) << "Throttling outgoing STUN message.";
+      // The renderer expects P2PMsg_OnSendComplete for all packets it generates
+      // and in the same order it generates them, so we need to respond even
+      // when the packet is dropped.
+      message_sender_->Send(new P2PMsg_OnSendComplete(
+          id_, P2PSendPacketMetrics(packet.id, packet.packet_options.packet_id,
+                                    send_time)));
+      // Do not reset the socket.
+      return;
+    }
+  }
+
   TRACE_EVENT_ASYNC_STEP_INTO1("p2p", "Send", packet.id, "UdpAsyncSendTo",
                                "size", packet.size);
   // Don't try to set DSCP in following conditions,
@@ -322,7 +334,6 @@ void P2PSocketHostUdp::DoSend(const PendingPacket& packet) {
     }
   }
 
-  base::TimeTicks send_time = base::TimeTicks::Now();
   cricket::ApplyPacketOptions(reinterpret_cast<uint8_t*>(packet.data->data()),
                               packet.size,
                               packet.packet_options.packet_time_params,
@@ -366,8 +377,8 @@ void P2PSocketHostUdp::OnSend(uint64_t packet_id,
   // Send next packets if we have them waiting in the buffer.
   while (state_ == STATE_OPEN && !send_queue_.empty() && !send_pending_) {
     PendingPacket packet = send_queue_.front();
-    DoSend(packet);
     send_queue_.pop_front();
+    DoSend(packet);
     DecrementDelayedBytes(packet.size);
   }
 }