Cast: Avoid retransmit if we sent the same packet recently (less than RTT)

media/cast/transport/pacing/paced_sender.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/cast/transport/pacing/paced_sender.h"
 
 #include "base/big_endian.h"
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 
 namespace media {
 namespace cast {
 namespace transport {
 
 namespace {
 
 static const int64 kPacingIntervalMs = 10;
 // Each frame will be split into no more than kPacingMaxBurstsPerFrame
 // bursts of packets.
 static const size_t kPacingMaxBurstsPerFrame = 3;
 static const size_t kTargetBurstSize = 10;
 static const size_t kMaxBurstSize = 20;
+static const size_t kMaxDedupeWindowMs = 500;
 
 }  // namespace
 
 // static
 PacketKey PacedPacketSender::MakePacketKey(const base::TimeTicks& ticks,
                                            uint32 ssrc,
                                            uint16 packet_id) {
   return std::make_pair(ticks, std::make_pair(ssrc, packet_id));
 }
 
@@ skipping 33 matching lines @@
   for (size_t i = 0; i < packets.size(); i++) {
     packet_list_[packets[i].first] =
         make_pair(PacketType_Normal, packets[i].second);
   }
   if (state_ == State_Unblocked) {
     SendStoredPackets();
   }
   return true;
 }
 
-bool PacedSender::ResendPackets(const SendPacketVector& packets) {
+bool PacedSender::ResendPackets(const SendPacketVector& packets,
+                                base::TimeDelta dedupe_window) {
   if (packets.empty()) {
     return true;
   }
+  base::TimeTicks now = clock_->NowTicks();
   for (size_t i = 0; i < packets.size(); i++) {
+    std::map<PacketKey, base::TimeTicks>::const_iterator j =
+        sent_time_.find(packets[i].first);
+
+    if (j != sent_time_.end() && now - j->second < dedupe_window) {
+      LogPacketEvent(packets[i].second->data, PACKET_RTX_REJECTED);
+      continue;
+    }
+
     packet_list_[packets[i].first] =
         make_pair(PacketType_Resend, packets[i].second);
   }
   if (state_ == State_Unblocked) {
     SendStoredPackets();
   }
   return true;
 }
 
 bool PacedSender::SendRtcpPacket(uint32 ssrc, PacketRef packet) {
@@ skipping 10 matching lines @@
     }
 
   }
   return true;
 }
 
 void PacedSender::CancelSendingPacket(const PacketKey& packet_key) {
   packet_list_.erase(packet_key);
 }
 
-PacketRef PacedSender::GetNextPacket(PacketType* packet_type) {
+PacketRef PacedSender::GetNextPacket(PacketType* packet_type,
+                                     PacketKey* packet_key) {
   std::map<PacketKey, std::pair<PacketType, PacketRef> >::iterator i;
   i = packet_list_.begin();
   DCHECK(i != packet_list_.end());
   *packet_type = i->second.first;
+  *packet_key = i->first;
   PacketRef ret = i->second.second;
   packet_list_.erase(i);
   return ret;
 }
 
 bool PacedSender::empty() const {
   return packet_list_.empty();
 }
 
 size_t PacedSender::size() const {
@@ skipping 52 matching lines @@
                                 weak_factory_.GetWeakPtr());
   while (!empty()) {
     if (current_burst_size_ >= max_burst_size_) {
       transport_task_runner_->PostDelayedTask(FROM_HERE,
                                               cb,
                                               burst_end_ - now);
       state_ = State_BurstFull;
       return;
     }
     PacketType packet_type;
-    PacketRef packet = GetNextPacket(&packet_type);
+    PacketKey packet_key;
+    PacketRef packet = GetNextPacket(&packet_type, &packet_key);
+    sent_time_[packet_key] = now;
+    sent_time_buffer_[packet_key] = now;
 
     switch (packet_type) {
       case PacketType_Resend:
-        LogPacketEvent(packet->data, true);
+        LogPacketEvent(packet->data, PACKET_RETRANSMITTED);
         break;
       case PacketType_Normal:
-        LogPacketEvent(packet->data, false);
+        LogPacketEvent(packet->data, PACKET_SENT_TO_NETWORK);
         break;
       case PacketType_RTCP:
         break;
     }
     if (!transport_->SendPacket(packet, cb)) {
       state_ = State_TransportBlocked;
       return;
     }
     current_burst_size_++;
   }
+  // Keep ~0.5 seconds of data (1000 packets)
+  if (sent_time_buffer_.size() >=
+      kMaxBurstSize * kMaxDedupeWindowMs / kPacingIntervalMs) {
+    sent_time_.swap(sent_time_buffer_);
+    sent_time_buffer_.clear();
+  }
+  DCHECK_LE(sent_time_buffer_.size(),
+            kMaxBurstSize * kMaxDedupeWindowMs / kPacingIntervalMs);
+  DCHECK_LE(sent_time_.size(),
+            2 * kMaxBurstSize * kMaxDedupeWindowMs / kPacingIntervalMs);
   state_ = State_Unblocked;
 }
 
-void PacedSender::LogPacketEvent(const Packet& packet, bool retransmit) {
+void PacedSender::LogPacketEvent(const Packet& packet, CastLoggingEvent event) {
   // Get SSRC from packet and compare with the audio_ssrc / video_ssrc to see
   // if the packet is audio or video.
   DCHECK_GE(packet.size(), 12u);
   base::BigEndianReader reader(reinterpret_cast<const char*>(&packet[8]), 4);
   uint32 ssrc;
   bool success = reader.ReadU32(&ssrc);
   DCHECK(success);
   bool is_audio;
   if (ssrc == audio_ssrc_) {
     is_audio = true;
   } else if (ssrc == video_ssrc_) {
     is_audio = false;
   } else {
     DVLOG(3) << "Got unknown ssrc " << ssrc << " when logging packet event";
     return;
   }
 
-  CastLoggingEvent event = retransmit ?
-      PACKET_RETRANSMITTED : PACKET_SENT_TO_NETWORK;
   EventMediaType media_type = is_audio ? AUDIO_EVENT : VIDEO_EVENT;
   logging_->InsertSinglePacketEvent(clock_->NowTicks(), event, media_type,
       packet);
 }
 
 }  // namespace transport
 }  // namespace cast
 }  // namespace media