Repair the CWND reduction caused by spurious RTO's in QUIC's congestion

net/quic/quic_sent_packet_manager_test.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 "net/quic/quic_sent_packet_manager.h"
 
 #include "base/stl_util.h"
 #include "net/quic/quic_flags.h"
 #include "net/quic/test_tools/quic_config_peer.h"
 #include "net/quic/test_tools/quic_sent_packet_manager_peer.h"
@@ skipping 405 matching lines @@
   EXPECT_CALL(*send_algorithm_, OnRetransmissionTimeout(true));
   manager_.OnRetransmissionTimeout();
   EXPECT_TRUE(manager_.HasPendingRetransmissions());
 
   // Ack 1 but not 2, before 2 is able to be sent.
   // Since 1 has been retransmitted, it has already been lost, and so the
   // send algorithm is not informed that it has been ACK'd.
   ReceivedPacketInfo received_info;
   received_info.largest_observed = 1;
   ExpectUpdatedRtt(1);
+  EXPECT_CALL(*send_algorithm_, RevertRetransmissionTimeout());
   manager_.OnIncomingAck(received_info, clock_.ApproximateNow());
 
   // Since 2 was marked for retransmit, when 1 is acked, 2 is kept for RTT.
   QuicPacketSequenceNumber unacked[] = { 2 };
   VerifyUnackedPackets(unacked, arraysize(unacked));
   EXPECT_FALSE(QuicSentPacketManagerPeer::HasPendingPackets(&manager_));
   VerifyRetransmittablePackets(NULL, 0);
 
   // Verify that the retransmission alarm would not fire,
   // since there is no retransmittable data outstanding.
@@ skipping 760 matching lines @@
 }
 
 TEST_F(QuicSentPacketManagerTest, GetTransmissionTimeRTO) {
   QuicSentPacketManagerPeer::GetRttStats(&manager_)->UpdateRtt(
       QuicTime::Delta::FromMilliseconds(100),
       QuicTime::Delta::Zero(),
       QuicTime::Zero());
 
   SendDataPacket(1);
   SendDataPacket(2);
+  SendDataPacket(3);
+  SendDataPacket(4);
 
   QuicTime::Delta expected_rto_delay = QuicTime::Delta::FromMilliseconds(500);
   EXPECT_CALL(*send_algorithm_, RetransmissionDelay())
       .WillRepeatedly(Return(expected_rto_delay));
   QuicTime expected_time = clock_.Now().Add(expected_rto_delay);
   EXPECT_EQ(expected_time, manager_.GetRetransmissionTime());
 
   // Retransmit the packet by invoking the retransmission timeout.
   EXPECT_CALL(*send_algorithm_, OnRetransmissionTimeout(true));
   clock_.AdvanceTime(expected_rto_delay);
   manager_.OnRetransmissionTimeout();
-  RetransmitNextPacket(3);
-  RetransmitNextPacket(4);
-  EXPECT_FALSE(manager_.HasPendingRetransmissions());
+  EXPECT_EQ(0u, QuicSentPacketManagerPeer::GetBytesInFlight(&manager_));
+  RetransmitNextPacket(5);
+  RetransmitNextPacket(6);
+  EXPECT_EQ(2 * kDefaultLength,
+            QuicSentPacketManagerPeer::GetBytesInFlight(&manager_));
+  EXPECT_TRUE(manager_.HasPendingRetransmissions());
 
   // The delay should double the second time.
   expected_time = clock_.Now().Add(expected_rto_delay).Add(expected_rto_delay);
   EXPECT_EQ(expected_time, manager_.GetRetransmissionTime());
 
   // Ack a packet and ensure the RTO goes back to the original value.
   ReceivedPacketInfo received_info;
   received_info.largest_observed = 2;
   received_info.missing_packets.insert(1);
   ExpectUpdatedRtt(2);
+  EXPECT_CALL(*send_algorithm_, RevertRetransmissionTimeout());
   manager_.OnIncomingAck(received_info, clock_.ApproximateNow());
+  EXPECT_FALSE(manager_.HasPendingRetransmissions());
+  EXPECT_EQ(4 * kDefaultLength,
+            QuicSentPacketManagerPeer::GetBytesInFlight(&manager_));
 
-  expected_time = clock_.Now().Add(expected_rto_delay);
+  // Wait 2RTTs from now for the RTO, since it's the max of the RTO time
+  // and the TLP time.  In production, there would always be two TLP's first.
+  expected_time = clock_.Now().Add(QuicTime::Delta::FromMilliseconds(200));
   EXPECT_EQ(expected_time, manager_.GetRetransmissionTime());
 }
 
 TEST_F(QuicSentPacketManagerTest, GetTransmissionDelayMin) {
   SendDataPacket(1);
   EXPECT_CALL(*send_algorithm_, RetransmissionDelay())
       .WillRepeatedly(Return(QuicTime::Delta::FromMilliseconds(1)));
   QuicTime::Delta delay = QuicTime::Delta::FromMilliseconds(200);
 
   // If the delay is smaller than the min, ensure it exponentially backs off
@@ skipping 106 matching lines @@
   QuicConfigPeer::SetReceivedConnectionOptions(&config, options);
   EXPECT_CALL(*send_algorithm_, SetFromConfig(_, _));
   manager_.SetFromConfig(config);
 
   EXPECT_TRUE(manager_.using_pacing());
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace net