1 files changed, 691 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/rtp_rtcp/source/flexfec_receiver_unittest.cc b/third_party/libwebrtc/modules/rtp_rtcp/source/flexfec_receiver_unittest.cc
new file mode 100644
index 0000000000..1243858b6b
--- /dev/null
+++ b/third_party/libwebrtc/modules/rtp_rtcp/source/flexfec_receiver_unittest.cc
@@ -0,0 +1,691 @@
+/*
+ *  Copyright (c) 2016 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.
+ */
+
+#include "modules/rtp_rtcp/include/flexfec_receiver.h"
+
+#include <algorithm>
+#include <memory>
+
+#include "modules/rtp_rtcp/mocks/mock_recovered_packet_receiver.h"
+#include "modules/rtp_rtcp/source/fec_test_helper.h"
+#include "modules/rtp_rtcp/source/forward_error_correction.h"
+#include "modules/rtp_rtcp/source/rtp_packet_received.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
+
+namespace webrtc {
+
+namespace {
+
+using ::testing::_;
+using ::testing::Eq;
+using ::testing::Property;
+
+using test::fec::FlexfecPacketGenerator;
+using Packet = ForwardErrorCorrection::Packet;
+using PacketList = ForwardErrorCorrection::PacketList;
+
+constexpr size_t kPayloadLength = 500;
+constexpr uint32_t kFlexfecSsrc = 42984;
+constexpr uint32_t kMediaSsrc = 8353;
+
+RtpPacketReceived ParsePacket(const Packet& packet) {
+  RtpPacketReceived parsed_packet;
+  EXPECT_TRUE(parsed_packet.Parse(packet.data));
+  return parsed_packet;
+}
+
+}  // namespace
+
+class FlexfecReceiverForTest : public FlexfecReceiver {
+ public:
+  FlexfecReceiverForTest(uint32_t ssrc,
+                         uint32_t protected_media_ssrc,
+                         RecoveredPacketReceiver* recovered_packet_receiver)
+      : FlexfecReceiver(Clock::GetRealTimeClock(),
+                        ssrc,
+                        protected_media_ssrc,
+                        recovered_packet_receiver) {}
+  // Expose methods for tests.
+  using FlexfecReceiver::AddReceivedPacket;
+  using FlexfecReceiver::ProcessReceivedPacket;
+};
+
+class FlexfecReceiverTest : public ::testing::Test {
+ protected:
+  FlexfecReceiverTest()
+      : receiver_(kFlexfecSsrc, kMediaSsrc, &recovered_packet_receiver_),
+        erasure_code_(
+            ForwardErrorCorrection::CreateFlexfec(kFlexfecSsrc, kMediaSsrc)),
+        packet_generator_(kMediaSsrc, kFlexfecSsrc) {}
+
+  // Generates `num_media_packets` corresponding to a single frame.
+  void PacketizeFrame(size_t num_media_packets,
+                      size_t frame_offset,
+                      PacketList* media_packets);
+
+  // Generates `num_fec_packets` FEC packets, given `media_packets`.
+  std::list<Packet*> EncodeFec(const PacketList& media_packets,
+                               size_t num_fec_packets);
+
+  FlexfecReceiverForTest receiver_;
+  std::unique_ptr<ForwardErrorCorrection> erasure_code_;
+
+  FlexfecPacketGenerator packet_generator_;
+  ::testing::StrictMock<MockRecoveredPacketReceiver> recovered_packet_receiver_;
+};
+
+void FlexfecReceiverTest::PacketizeFrame(size_t num_media_packets,
+                                         size_t frame_offset,
+                                         PacketList* media_packets) {
+  packet_generator_.NewFrame(num_media_packets);
+  for (size_t i = 0; i < num_media_packets; ++i) {
+    std::unique_ptr<Packet> next_packet(
+        packet_generator_.NextPacket(frame_offset + i, kPayloadLength));
+    media_packets->push_back(std::move(next_packet));
+  }
+}
+
+std::list<Packet*> FlexfecReceiverTest::EncodeFec(
+    const PacketList& media_packets,
+    size_t num_fec_packets) {
+  const uint8_t protection_factor =
+      num_fec_packets * 255 / media_packets.size();
+  constexpr int kNumImportantPackets = 0;
+  constexpr bool kUseUnequalProtection = false;
+  constexpr FecMaskType kFecMaskType = kFecMaskRandom;
+  std::list<Packet*> fec_packets;
+  EXPECT_EQ(0, erasure_code_->EncodeFec(
+                   media_packets, protection_factor, kNumImportantPackets,
+                   kUseUnequalProtection, kFecMaskType, &fec_packets));
+  EXPECT_EQ(num_fec_packets, fec_packets.size());
+  return fec_packets;
+}
+
+TEST_F(FlexfecReceiverTest, ReceivesMediaPacket) {
+  packet_generator_.NewFrame(1);
+  std::unique_ptr<Packet> media_packet(
+      packet_generator_.NextPacket(0, kPayloadLength));
+
+  std::unique_ptr<ForwardErrorCorrection::ReceivedPacket> received_packet =
+      receiver_.AddReceivedPacket(ParsePacket(*media_packet));
+  ASSERT_TRUE(received_packet);
+  receiver_.ProcessReceivedPacket(*received_packet);
+}
+
+TEST_F(FlexfecReceiverTest, ReceivesMediaAndFecPackets) {
+  const size_t kNumMediaPackets = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  const auto& media_packet = media_packets.front();
+  auto fec_packet = packet_generator_.BuildFlexfecPacket(*fec_packets.front());
+
+  std::unique_ptr<ForwardErrorCorrection::ReceivedPacket> received_packet =
+      receiver_.AddReceivedPacket(ParsePacket(*media_packet));
+  ASSERT_TRUE(received_packet);
+  receiver_.ProcessReceivedPacket(*received_packet);
+  received_packet = receiver_.AddReceivedPacket(ParsePacket(*fec_packet));
+  ASSERT_TRUE(received_packet);
+  receiver_.ProcessReceivedPacket(*received_packet);
+}
+
+TEST_F(FlexfecReceiverTest, FailsOnTruncatedFecPacket) {
+  const size_t kNumMediaPackets = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  const auto& media_packet = media_packets.front();
+  // Simulate truncated FlexFEC payload.
+  fec_packets.front()->data.SetSize(1);
+  auto fec_packet = packet_generator_.BuildFlexfecPacket(*fec_packets.front());
+
+  std::unique_ptr<ForwardErrorCorrection::ReceivedPacket> received_packet =
+      receiver_.AddReceivedPacket(ParsePacket(*media_packet));
+  ASSERT_TRUE(received_packet);
+  receiver_.ProcessReceivedPacket(*received_packet);
+  EXPECT_FALSE(receiver_.AddReceivedPacket(ParsePacket(*fec_packet)));
+}
+
+TEST_F(FlexfecReceiverTest, FailsOnUnknownMediaSsrc) {
+  const size_t kNumMediaPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  auto& media_packet = media_packets.front();
+  // Corrupt the SSRC.
+  media_packet->data.MutableData()[8] = 0;
+  media_packet->data.MutableData()[9] = 1;
+  media_packet->data.MutableData()[10] = 2;
+  media_packet->data.MutableData()[11] = 3;
+
+  EXPECT_FALSE(receiver_.AddReceivedPacket(ParsePacket(*media_packet)));
+}
+
+TEST_F(FlexfecReceiverTest, FailsOnUnknownFecSsrc) {
+  const size_t kNumMediaPackets = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  const auto& media_packet = media_packets.front();
+  auto fec_packet = packet_generator_.BuildFlexfecPacket(*fec_packets.front());
+  // Corrupt the SSRC.
+  fec_packet->data.MutableData()[8] = 4;
+  fec_packet->data.MutableData()[9] = 5;
+  fec_packet->data.MutableData()[10] = 6;
+  fec_packet->data.MutableData()[11] = 7;
+
+  std::unique_ptr<ForwardErrorCorrection::ReceivedPacket> received_packet =
+      receiver_.AddReceivedPacket(ParsePacket(*media_packet));
+  ASSERT_TRUE(received_packet);
+  receiver_.ProcessReceivedPacket(*received_packet);
+  EXPECT_FALSE(receiver_.AddReceivedPacket(ParsePacket(*fec_packet)));
+}
+
+TEST_F(FlexfecReceiverTest, ReceivesMultiplePackets) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive all media packets.
+  for (const auto& media_packet : media_packets) {
+    std::unique_ptr<ForwardErrorCorrection::ReceivedPacket> received_packet =
+        receiver_.AddReceivedPacket(ParsePacket(*media_packet));
+    ASSERT_TRUE(received_packet);
+    receiver_.ProcessReceivedPacket(*received_packet);
+  }
+
+  // Receive FEC packet.
+  auto* fec_packet = fec_packets.front();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(*fec_packet);
+  std::unique_ptr<ForwardErrorCorrection::ReceivedPacket> received_packet =
+      receiver_.AddReceivedPacket(ParsePacket(*packet_with_rtp_header));
+  ASSERT_TRUE(received_packet);
+  receiver_.ProcessReceivedPacket(*received_packet);
+}
+
+TEST_F(FlexfecReceiverTest, RecoversFromSingleMediaLoss) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet but drop second.
+  auto media_it = media_packets.begin();
+  receiver_.OnRtpPacket(ParsePacket(**media_it));
+
+  // Receive FEC packet and ensure recovery of lost media packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(
+                  Property(&RtpPacketReceived::Buffer, Eq((*media_it)->data))));
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+}
+
+TEST_F(FlexfecReceiverTest, RecoversFromDoubleMediaLoss) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 2;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Drop both media packets.
+
+  // Receive first FEC packet and recover first lost media packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  auto media_it = media_packets.begin();
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(
+                  Property(&RtpPacketReceived::Buffer, Eq((*media_it)->data))));
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+
+  // Receive second FEC packet and recover second lost media packet.
+  fec_it++;
+  packet_with_rtp_header = packet_generator_.BuildFlexfecPacket(**fec_it);
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(
+                  Property(&RtpPacketReceived::Buffer, Eq((*media_it)->data))));
+
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+}
+
+TEST_F(FlexfecReceiverTest, DoesNotRecoverFromMediaAndFecLoss) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet.
+  auto media_it = media_packets.begin();
+  receiver_.OnRtpPacket(ParsePacket(**media_it));
+
+  // Drop second media packet and FEC packet. Do not expect call back.
+}
+
+TEST_F(FlexfecReceiverTest, DoesNotCallbackTwice) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet but drop second.
+  auto media_it = media_packets.begin();
+  receiver_.OnRtpPacket(ParsePacket(**media_it));
+
+  // Receive FEC packet and ensure recovery of lost media packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(
+                  Property(&RtpPacketReceived::Buffer, Eq((*media_it)->data))));
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+
+  // Receive the FEC packet again, but do not call back.
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+
+  // Receive the first media packet again, but do not call back.
+  media_it = media_packets.begin();
+  receiver_.OnRtpPacket(ParsePacket(**media_it));
+
+  // Receive the second media packet again (the one recovered above),
+  // but do not call back again.
+  media_it++;
+  receiver_.OnRtpPacket(ParsePacket(**media_it));
+}
+
+// Here we are implicitly assuming packet masks that are suitable for
+// this type of 50% correlated loss. If we are changing our precomputed
+// packet masks, this test might need to be updated.
+TEST_F(FlexfecReceiverTest, RecoversFrom50PercentLoss) {
+  const size_t kNumFecPackets = 5;
+  const size_t kNumFrames = 2 * kNumFecPackets;
+  const size_t kNumMediaPacketsPerFrame = 1;
+
+  PacketList media_packets;
+  for (size_t i = 0; i < kNumFrames; ++i) {
+    PacketizeFrame(kNumMediaPacketsPerFrame, i, &media_packets);
+  }
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Drop every second media packet.
+  auto media_it = media_packets.begin();
+  while (media_it != media_packets.end()) {
+    receiver_.OnRtpPacket(ParsePacket(**media_it));
+    ++media_it;
+    if (media_it == media_packets.end()) {
+      break;
+    }
+    ++media_it;
+  }
+
+  // Receive all FEC packets.
+  media_it = media_packets.begin();
+  for (const auto* fec_packet : fec_packets) {
+    std::unique_ptr<Packet> fec_packet_with_rtp_header =
+        packet_generator_.BuildFlexfecPacket(*fec_packet);
+    ++media_it;
+    if (media_it == media_packets.end()) {
+      break;
+    }
+    EXPECT_CALL(recovered_packet_receiver_,
+                OnRecoveredPacket(Property(&RtpPacketReceived::Buffer,
+                                           Eq((*media_it)->data))));
+    receiver_.OnRtpPacket(ParsePacket(*fec_packet_with_rtp_header));
+    ++media_it;
+  }
+}
+
+TEST_F(FlexfecReceiverTest, DelayedFecPacketDoesHelp) {
+  // These values need to be updated if the underlying erasure code
+  // implementation changes.
+  // Delay FEC packet by maximum number of media packets tracked by receiver.
+  const size_t kNumFrames = 192;
+  const size_t kNumMediaPacketsPerFrame = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPacketsPerFrame, 0, &media_packets);
+  PacketizeFrame(kNumMediaPacketsPerFrame, 1, &media_packets);
+  // Protect two first frames.
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  for (size_t i = 2; i < kNumFrames; ++i) {
+    PacketizeFrame(kNumMediaPacketsPerFrame, i, &media_packets);
+  }
+
+  // Drop first media packet and delay FEC packet.
+  auto media_it = media_packets.begin();
+  ++media_it;
+
+  // Receive all other media packets.
+  while (media_it != media_packets.end()) {
+    receiver_.OnRtpPacket(ParsePacket(**media_it));
+    ++media_it;
+  }
+
+  // Receive FEC packet and recover first media packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  media_it = media_packets.begin();
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(
+                  Property(&RtpPacketReceived::Buffer, Eq((*media_it)->data))));
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+}
+
+TEST_F(FlexfecReceiverTest, TooDelayedFecPacketDoesNotHelp) {
+  // These values need to be updated if the underlying erasure code
+  // implementation changes.
+  // Delay FEC packet by one more than maximum number of media packets
+  // tracked by receiver.
+  const size_t kNumFrames = 193;
+  const size_t kNumMediaPacketsPerFrame = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPacketsPerFrame, 0, &media_packets);
+  PacketizeFrame(kNumMediaPacketsPerFrame, 1, &media_packets);
+  // Protect first two frames.
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  for (size_t i = 2; i < kNumFrames; ++i) {
+    PacketizeFrame(kNumMediaPacketsPerFrame, i, &media_packets);
+  }
+
+  // Drop first media packet and delay FEC packet.
+  auto media_it = media_packets.begin();
+  ++media_it;
+
+  // Receive all other media packets.
+  while (media_it != media_packets.end()) {
+    receiver_.OnRtpPacket(ParsePacket(**media_it));
+    ++media_it;
+  }
+
+  // Receive FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+
+  // Do not expect a call back.
+}
+
+TEST_F(FlexfecReceiverTest, SurvivesOldRecoveredPacketBeingReinserted) {
+  // Simulates the behaviour of the
+  // Call->FlexfecReceiveStream->FlexfecReceiver->Call loop in production code.
+  class LoopbackRecoveredPacketReceiver : public RecoveredPacketReceiver {
+   public:
+    LoopbackRecoveredPacketReceiver() : receiver_(nullptr) {}
+
+    void SetReceiver(FlexfecReceiver* receiver) { receiver_ = receiver; }
+
+    // Implements RecoveredPacketReceiver.
+    void OnRecoveredPacket(const RtpPacketReceived& packet) override {
+      EXPECT_TRUE(packet.recovered());
+      RTC_DCHECK(receiver_);
+      receiver_->OnRtpPacket(packet);
+    }
+
+   private:
+    FlexfecReceiver* receiver_;
+  } loopback_recovered_packet_receiver;
+
+  // Feed recovered packets back into `receiver`.
+  FlexfecReceiver receiver(Clock::GetRealTimeClock(), kFlexfecSsrc, kMediaSsrc,
+                           &loopback_recovered_packet_receiver);
+  loopback_recovered_packet_receiver.SetReceiver(&receiver);
+
+  // Receive first set of packets.
+  PacketList first_media_packets;
+  for (int i = 0; i < 46; ++i) {
+    PacketizeFrame(1, 0, &first_media_packets);
+  }
+  for (const auto& media_packet : first_media_packets) {
+    receiver.OnRtpPacket(ParsePacket(*media_packet));
+  }
+
+  // Protect one media packet. Lose the media packet,
+  // but do not receive FEC packet yet.
+  PacketList protected_media_packet;
+  PacketizeFrame(1, 0, &protected_media_packet);
+  const std::list<Packet*> fec_packets = EncodeFec(protected_media_packet, 1);
+  EXPECT_EQ(1u, fec_packets.size());
+  std::unique_ptr<Packet> fec_packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(*fec_packets.front());
+
+  // Lose some packets, thus introducing a sequence number gap.
+  PacketList lost_packets;
+  for (int i = 0; i < 100; ++i) {
+    PacketizeFrame(1, 0, &lost_packets);
+  }
+
+  // Receive one more packet.
+  PacketList second_media_packets;
+  PacketizeFrame(1, 0, &second_media_packets);
+  for (const auto& media_packet : second_media_packets) {
+    receiver.OnRtpPacket(ParsePacket(*media_packet));
+  }
+
+  // Receive delayed FEC packet.
+  receiver.OnRtpPacket(ParsePacket(*fec_packet_with_rtp_header));
+
+  // Expect no crash.
+}
+
+TEST_F(FlexfecReceiverTest, RecoversWithMediaPacketsOutOfOrder) {
+  const size_t kNumMediaPackets = 6;
+  const size_t kNumFecPackets = 2;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Lose two media packets, and receive the others out of order.
+  auto media_it = media_packets.begin();
+  auto media_packet0 = media_it++;
+  auto media_packet1 = media_it++;
+  auto media_packet2 = media_it++;
+  auto media_packet3 = media_it++;
+  auto media_packet4 = media_it++;
+  auto media_packet5 = media_it++;
+  receiver_.OnRtpPacket(ParsePacket(**media_packet5));
+  receiver_.OnRtpPacket(ParsePacket(**media_packet2));
+  receiver_.OnRtpPacket(ParsePacket(**media_packet3));
+  receiver_.OnRtpPacket(ParsePacket(**media_packet0));
+
+  // Expect to recover lost media packets.
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(Property(&RtpPacketReceived::Buffer,
+                                         Eq((*media_packet1)->data))));
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(Property(&RtpPacketReceived::Buffer,
+                                         Eq((*media_packet4)->data))));
+  // Add FEC packets.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header;
+  while (fec_it != fec_packets.end()) {
+    packet_with_rtp_header = packet_generator_.BuildFlexfecPacket(**fec_it);
+    receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+    ++fec_it;
+  }
+}
+
+// Recovered media packets may be fed back into the FlexfecReceiver by the
+// callback. This test ensures the idempotency of such a situation.
+TEST_F(FlexfecReceiverTest, RecoveryCallbackDoesNotLoopInfinitely) {
+  class LoopbackRecoveredPacketReceiver : public RecoveredPacketReceiver {
+   public:
+    const int kMaxRecursionDepth = 10;
+
+    LoopbackRecoveredPacketReceiver()
+        : receiver_(nullptr),
+          did_receive_call_back_(false),
+          recursion_depth_(0),
+          deep_recursion_(false) {}
+
+    void SetReceiver(FlexfecReceiver* receiver) { receiver_ = receiver; }
+    bool DidReceiveCallback() const { return did_receive_call_back_; }
+    bool DeepRecursion() const { return deep_recursion_; }
+
+    // Implements RecoveredPacketReceiver.
+    void OnRecoveredPacket(const RtpPacketReceived& packet) override {
+      did_receive_call_back_ = true;
+
+      if (recursion_depth_ > kMaxRecursionDepth) {
+        deep_recursion_ = true;
+        return;
+      }
+      ++recursion_depth_;
+      RTC_DCHECK(receiver_);
+      receiver_->OnRtpPacket(packet);
+      --recursion_depth_;
+    }
+
+   private:
+    FlexfecReceiver* receiver_;
+    bool did_receive_call_back_;
+    int recursion_depth_;
+    bool deep_recursion_;
+  } loopback_recovered_packet_receiver;
+
+  // Feed recovered packets back into `receiver`.
+  FlexfecReceiver receiver(Clock::GetRealTimeClock(), kFlexfecSsrc, kMediaSsrc,
+                           &loopback_recovered_packet_receiver);
+  loopback_recovered_packet_receiver.SetReceiver(&receiver);
+
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet but drop second.
+  auto media_it = media_packets.begin();
+  receiver.OnRtpPacket(ParsePacket(**media_it));
+
+  // Receive FEC packet and verify that a packet was recovered.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  receiver.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+  EXPECT_TRUE(loopback_recovered_packet_receiver.DidReceiveCallback());
+  EXPECT_FALSE(loopback_recovered_packet_receiver.DeepRecursion());
+}
+
+TEST_F(FlexfecReceiverTest, CalculatesNumberOfPackets) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet but drop second.
+  auto media_it = media_packets.begin();
+  receiver_.OnRtpPacket(ParsePacket(**media_it));
+
+  // Receive FEC packet and ensure recovery of lost media packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(
+                  Property(&RtpPacketReceived::Buffer, Eq((*media_it)->data))));
+  receiver_.OnRtpPacket(ParsePacket(*packet_with_rtp_header));
+
+  // Check stats calculations.
+  FecPacketCounter packet_counter = receiver_.GetPacketCounter();
+  EXPECT_EQ(2U, packet_counter.num_packets);
+  EXPECT_EQ(1U, packet_counter.num_fec_packets);
+  EXPECT_EQ(1U, packet_counter.num_recovered_packets);
+}
+
+TEST_F(FlexfecReceiverTest, DoesNotDecodeWrappedMediaSequenceUsingOldFec) {
+  const size_t kFirstFrameNumMediaPackets = 2;
+  const size_t kFirstFrameNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kFirstFrameNumMediaPackets, 0, &media_packets);
+
+  // Protect first frame (sequences 0 and 1) with 1 FEC packet.
+  std::list<Packet*> fec_packets =
+      EncodeFec(media_packets, kFirstFrameNumFecPackets);
+
+  // Generate enough media packets to simulate media sequence number wraparound.
+  // Use no FEC for these frames to make sure old FEC is not purged due to age.
+  const size_t kNumFramesSequenceWrapAround =
+      std::numeric_limits<uint16_t>::max();
+  const size_t kNumMediaPacketsPerFrame = 1;
+
+  for (size_t i = 1; i <= kNumFramesSequenceWrapAround; ++i) {
+    PacketizeFrame(kNumMediaPacketsPerFrame, i, &media_packets);
+  }
+
+  // Receive first (`kFirstFrameNumMediaPackets` + 192) media packets.
+  // Simulate an old FEC packet by separating it from its encoded media
+  // packets by at least 192 packets.
+  auto media_it = media_packets.begin();
+  for (size_t i = 0; i < (kFirstFrameNumMediaPackets + 192); i++) {
+    if (i == 1) {
+      // Drop the second packet of the first frame.
+      media_it++;
+    } else {
+      receiver_.OnRtpPacket(ParsePacket(**media_it++));
+    }
+  }
+
+  // Receive FEC packet. Although a protected packet was dropped,
+  // expect no recovery callback since it is delayed from first frame
+  // by more than 192 packets.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> fec_packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  receiver_.OnRtpPacket(ParsePacket(*fec_packet_with_rtp_header));
+
+  // Receive remaining media packets.
+  // NOTE: Because we sent enough to simulate wrap around, sequence 0 is
+  // received again, but is a different packet than the original first
+  // packet of first frame.
+  while (media_it != media_packets.end()) {
+    receiver_.OnRtpPacket(ParsePacket(**media_it++));
+  }
+
+  // Do not expect a recovery callback, the FEC packet is old
+  // and should not decode wrapped around media sequences.
+}
+
+}  // namespace webrtc