Allow FakeNetworkPipe to drop packets in bursts.

webrtc/test/fake_network_pipe_unittest.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 361 matching lines @@
   last_seq_num = -1;
   for (int seq_num : receiver->delivered_sequence_numbers_) {
     if (last_seq_num > seq_num) {
       reordering_has_occured = true;
       break;
     }
     last_seq_num = seq_num;
   }
   EXPECT_TRUE(reordering_has_occured);
 }
+
+TEST_F(FakeNetworkPipeTest, BurstLoss) {
+  const int kLossPercent = 5;
+  const int kAvgBurstLength = 3;
+  const int kNumPackets = 10000;
+  const int kPacketSize = 10;
+
+  FakeNetworkPipe::Config config;
+  config.queue_length_packets = kNumPackets;
+  config.loss_percent = kLossPercent;
+  config.avg_burst_loss_length = kAvgBurstLength;
+  std::unique_ptr<FakeNetworkPipe> pipe(
+      new FakeNetworkPipe(&fake_clock_, config));
+  ReorderTestReceiver* receiver = new ReorderTestReceiver();
+  receiver_.reset(receiver);
+  pipe->SetReceiver(receiver_.get());
+
+  SendPackets(pipe.get(), kNumPackets, kPacketSize);
+  fake_clock_.AdvanceTimeMilliseconds(1000);
+  pipe->Process();
+
+  // Check that the average loss is |kLossPercent| percent.
+  double loss_percent =

[terelius, 2016/05/30 15:40:23]

nit: maybe call it loss_fraction to make it clear why you don't divide this by
100? (I.e. why this is treated differently from kLossPercent.)

[philipel, 2016/05/30 16:05:40]

Done.

+      (kNumPackets - receiver->delivered_sequence_numbers_.size()) /
+      static_cast<double>(kNumPackets);
+
+  EXPECT_NEAR(kLossPercent / 100.0, loss_percent, 0.01);

[terelius, 2016/05/30 15:40:23]

nit: 0.01 is the relative error, right? Seems rather tight. Does this work with
other parameters and other random seeds?

[philipel, 2016/05/30 16:05:40]

It's a bit tight, adjusted it to 0.05. Also tried a few different values and it
only seems to be the the check on line 423 that fails instead.

+
+  // Find the number of bursts that has occurred.
+  size_t received_packets = receiver->delivered_sequence_numbers_.size();
+  int num_bursts = 0;
+  for (size_t i = 0; i < received_packets - 1; ++i) {
+    int diff = receiver->delivered_sequence_numbers_[i + 1] -
+               receiver->delivered_sequence_numbers_[i];
+    if (diff > 1)
+      ++num_bursts;
+  }
+
+  int lost_packets = kNumPackets - receiver->delivered_sequence_numbers_.size();

[terelius, 2016/05/30 15:40:23]

Move this up and reuse in computation of loss_percent.

[philipel, 2016/05/30 16:05:39]

Done.

+  double average_burst_length = static_cast<double>(lost_packets) / num_bursts;
+
+  EXPECT_NEAR(kAvgBurstLength, average_burst_length, 0.2);
+}
 }  // namespace webrtc