modules/rtp_rtcp/source/remote_ntp_time_estimator_unittest.cc

/*
 *  Copyright (c) 2014 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/remote_ntp_time_estimator.h"
#include "absl/types/optional.h"
#include "system_wrappers/include/clock.h"
#include "system_wrappers/include/ntp_time.h"
#include "test/gmock.h"
#include "test/gtest.h"

namespace webrtc {

constexpr int64_t kTestRtt = 10;
constexpr int64_t kLocalClockInitialTimeMs = 123;
constexpr int64_t kRemoteClockInitialTimeMs = 345;
constexpr uint32_t kTimestampOffset = 567;
constexpr int64_t kRemoteToLocalClockOffsetMs =
    kLocalClockInitialTimeMs - kRemoteClockInitialTimeMs;

class RemoteNtpTimeEstimatorTest : public ::testing::Test {
 protected:
  RemoteNtpTimeEstimatorTest()
      : local_clock_(kLocalClockInitialTimeMs * 1000),
        remote_clock_(kRemoteClockInitialTimeMs * 1000),
        estimator_(new RemoteNtpTimeEstimator(&local_clock_)) {}
  ~RemoteNtpTimeEstimatorTest() override = default;

  void AdvanceTimeMilliseconds(int64_t ms) {
    local_clock_.AdvanceTimeMilliseconds(ms);
    remote_clock_.AdvanceTimeMilliseconds(ms);
  }

  uint32_t GetRemoteTimestamp() {
    return static_cast<uint32_t>(remote_clock_.TimeInMilliseconds()) * 90 +
           kTimestampOffset;
  }

  NtpTime GetRemoteNtpTime() { return remote_clock_.CurrentNtpTime(); }

  void SendRtcpSr() {
    uint32_t rtcp_timestamp = GetRemoteTimestamp();
    NtpTime ntp = GetRemoteNtpTime();

    AdvanceTimeMilliseconds(kTestRtt / 2);
    ReceiveRtcpSr(kTestRtt, rtcp_timestamp, ntp.seconds(), ntp.fractions());
  }

  void SendRtcpSrInaccurately(int64_t ntp_error_ms,
                              int64_t networking_delay_ms) {
    uint32_t rtcp_timestamp = GetRemoteTimestamp();
    int64_t ntp_error_fractions =
        ntp_error_ms * static_cast<int64_t>(NtpTime::kFractionsPerSecond) /
        1000;
    NtpTime ntp(static_cast<uint64_t>(GetRemoteNtpTime()) +
                ntp_error_fractions);
    AdvanceTimeMilliseconds(kTestRtt / 2 + networking_delay_ms);
    ReceiveRtcpSr(kTestRtt, rtcp_timestamp, ntp.seconds(), ntp.fractions());
  }

  void UpdateRtcpTimestamp(int64_t rtt,
                           uint32_t ntp_secs,
                           uint32_t ntp_frac,
                           uint32_t rtp_timestamp,
                           bool expected_result) {
    EXPECT_EQ(expected_result, estimator_->UpdateRtcpTimestamp(
                                   rtt, ntp_secs, ntp_frac, rtp_timestamp));
  }

  void ReceiveRtcpSr(int64_t rtt,
                     uint32_t rtcp_timestamp,
                     uint32_t ntp_seconds,
                     uint32_t ntp_fractions) {
    UpdateRtcpTimestamp(rtt, ntp_seconds, ntp_fractions, rtcp_timestamp, true);
  }

  SimulatedClock local_clock_;
  SimulatedClock remote_clock_;
  std::unique_ptr<RemoteNtpTimeEstimator> estimator_;
};

TEST_F(RemoteNtpTimeEstimatorTest, Estimate) {
  // Failed without valid NTP.
  UpdateRtcpTimestamp(kTestRtt, 0, 0, 0, false);

  AdvanceTimeMilliseconds(1000);
  // Remote peer sends first RTCP SR.
  SendRtcpSr();

  // Remote sends a RTP packet.
  AdvanceTimeMilliseconds(15);
  uint32_t rtp_timestamp = GetRemoteTimestamp();
  int64_t capture_ntp_time_ms = local_clock_.CurrentNtpInMilliseconds();

  // Local peer needs at least 2 RTCP SR to calculate the capture time.
  const int64_t kNotEnoughRtcpSr = -1;
  EXPECT_EQ(kNotEnoughRtcpSr, estimator_->Estimate(rtp_timestamp));
  EXPECT_EQ(absl::nullopt, estimator_->EstimateRemoteToLocalClockOffsetMs());

  AdvanceTimeMilliseconds(800);
  // Remote sends second RTCP SR.
  SendRtcpSr();

  // Local peer gets enough RTCP SR to calculate the capture time.
  EXPECT_EQ(capture_ntp_time_ms, estimator_->Estimate(rtp_timestamp));
  EXPECT_EQ(kRemoteToLocalClockOffsetMs,
            estimator_->EstimateRemoteToLocalClockOffsetMs());
}

TEST_F(RemoteNtpTimeEstimatorTest, AveragesErrorsOut) {
  // Remote peer sends first 10 RTCP SR without errors.
  for (int i = 0; i < 10; ++i) {
    AdvanceTimeMilliseconds(1000);
    SendRtcpSr();
  }

  AdvanceTimeMilliseconds(150);
  uint32_t rtp_timestamp = GetRemoteTimestamp();
  int64_t capture_ntp_time_ms = local_clock_.CurrentNtpInMilliseconds();
  // Local peer gets enough RTCP SR to calculate the capture time.
  EXPECT_EQ(capture_ntp_time_ms, estimator_->Estimate(rtp_timestamp));
  EXPECT_EQ(kRemoteToLocalClockOffsetMs,
            estimator_->EstimateRemoteToLocalClockOffsetMs());

  // Remote sends corrupted RTCP SRs
  AdvanceTimeMilliseconds(1000);
  SendRtcpSrInaccurately(/*ntp_error_ms=*/2, /*networking_delay_ms=*/-1);
  AdvanceTimeMilliseconds(1000);
  SendRtcpSrInaccurately(/*ntp_error_ms=*/-2, /*networking_delay_ms=*/1);

  // New RTP packet to estimate timestamp.
  AdvanceTimeMilliseconds(150);
  rtp_timestamp = GetRemoteTimestamp();
  capture_ntp_time_ms = local_clock_.CurrentNtpInMilliseconds();

  // Errors should be averaged out.
  EXPECT_EQ(capture_ntp_time_ms, estimator_->Estimate(rtp_timestamp));
  EXPECT_EQ(kRemoteToLocalClockOffsetMs,
            estimator_->EstimateRemoteToLocalClockOffsetMs());
}

}  // namespace webrtc