Update RateStatistics to handle too-little-data case.

webrtc/base/rate_statistics_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.
  */
 
 #include <algorithm>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/base/rate_statistics.h"
 
 namespace {
 
 using webrtc::RateStatistics;
 
 const int64_t kWindowMs = 500;
 
 class RateStatisticsTest : public ::testing::Test {
  protected:
   RateStatisticsTest() : stats_(kWindowMs, 8000) {}
   RateStatistics stats_;
 };
 
 TEST_F(RateStatisticsTest, TestStrictMode) {
   int64_t now_ms = 0;
-  // Should be initialized to 0.
-  EXPECT_EQ(0u, stats_.Rate(now_ms));
-  stats_.Update(1500, now_ms);
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
+  const uint32_t kPacketSize = 1500u;
+  const uint32_t kExpectedRateBps = kPacketSize * 1000 * 8;
+
+  // Single data point is not enough for valid estimate.
+  stats_.Update(kPacketSize, now_ms++);
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
   // Expecting 1200 kbps since the window is initially kept small and grows as
   // we have more data.
-  EXPECT_EQ(12000000u, stats_.Rate(now_ms));
+  stats_.Update(kPacketSize, now_ms);
+  EXPECT_EQ(kExpectedRateBps, *stats_.Rate(now_ms));
+
   stats_.Reset();
   // Expecting 0 after init.
-  EXPECT_EQ(0u, stats_.Rate(now_ms));
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
+  const int kInterval = 10;
   for (int i = 0; i < 100000; ++i) {
-    if (now_ms % 10 == 0) {
-      stats_.Update(1500, now_ms);
-    }
+    if (i % kInterval == 0)
+      stats_.Update(kPacketSize, now_ms);
+
     // Approximately 1200 kbps expected. Not exact since when packets
     // are removed we will jump 10 ms to the next packet.
-    if (now_ms > 0 && now_ms % kWindowMs == 0) {
-      EXPECT_NEAR(1200000u, stats_.Rate(now_ms), 22000u);
+    if (i > kInterval) {
+      rtc::Optional<uint32_t> rate = stats_.Rate(now_ms);
+      EXPECT_TRUE(static_cast<bool>(rate));
+      uint32_t samples = i / kInterval + 1;
+      uint64_t total_bits = samples * kPacketSize * 8;
+      uint32_t rate_bps = static_cast<uint32_t>((1000 * total_bits) / (i + 1));
+      EXPECT_NEAR(rate_bps, *rate, 22000u);
     }
     now_ms += 1;
   }
   now_ms += kWindowMs;
   // The window is 2 seconds. If nothing has been received for that time
   // the estimate should be 0.
-  EXPECT_EQ(0u, stats_.Rate(now_ms));
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
 }
 
 TEST_F(RateStatisticsTest, IncreasingThenDecreasingBitrate) {
   int64_t now_ms = 0;
   stats_.Reset();
   // Expecting 0 after init.
-  uint32_t bitrate = stats_.Rate(now_ms);
-  EXPECT_EQ(0u, bitrate);
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
+  stats_.Update(1000, ++now_ms);
   const uint32_t kExpectedBitrate = 8000000;
   // 1000 bytes per millisecond until plateau is reached.
   int prev_error = kExpectedBitrate;
+  rtc::Optional<uint32_t> bitrate;
   while (++now_ms < 10000) {
     stats_.Update(1000, now_ms);
     bitrate = stats_.Rate(now_ms);
-    int error = kExpectedBitrate - bitrate;
+    EXPECT_TRUE(static_cast<bool>(bitrate));
+    int error = kExpectedBitrate - *bitrate;
     error = std::abs(error);
     // Expect the estimation error to decrease as the window is extended.
     EXPECT_LE(error, prev_error + 1);
     prev_error = error;
   }
   // Window filled, expect to be close to 8000000.
-  EXPECT_EQ(kExpectedBitrate, bitrate);
+  EXPECT_EQ(kExpectedBitrate, *bitrate);
 
   // 1000 bytes per millisecond until 10-second mark, 8000 kbps expected.
   while (++now_ms < 10000) {
     stats_.Update(1000, now_ms);
     bitrate = stats_.Rate(now_ms);
-    EXPECT_EQ(kExpectedBitrate, bitrate);
+    EXPECT_EQ(kExpectedBitrate, *bitrate);
   }
+
   // Zero bytes per millisecond until 0 is reached.
   while (++now_ms < 20000) {
     stats_.Update(0, now_ms);
-    uint32_t new_bitrate = stats_.Rate(now_ms);
-    if (new_bitrate != bitrate) {
+    rtc::Optional<uint32_t> new_bitrate = stats_.Rate(now_ms);
+    if (static_cast<bool>(new_bitrate) && *new_bitrate != *bitrate) {
       // New bitrate must be lower than previous one.
-      EXPECT_LT(new_bitrate, bitrate);
+      EXPECT_LT(*new_bitrate, *bitrate);
     } else {
       // 0 kbps expected.
-      EXPECT_EQ(0u, bitrate);
+      EXPECT_EQ(0u, *new_bitrate);
       break;
     }
     bitrate = new_bitrate;
   }
+
   // Zero bytes per millisecond until 20-second mark, 0 kbps expected.
   while (++now_ms < 20000) {
     stats_.Update(0, now_ms);
-    EXPECT_EQ(0u, stats_.Rate(now_ms));
+    EXPECT_EQ(0u, *stats_.Rate(now_ms));
   }
 }
 
 TEST_F(RateStatisticsTest, ResetAfterSilence) {
   int64_t now_ms = 0;
   stats_.Reset();
   // Expecting 0 after init.
-  uint32_t bitrate = stats_.Rate(now_ms);
-  EXPECT_EQ(0u, bitrate);
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
   const uint32_t kExpectedBitrate = 8000000;
   // 1000 bytes per millisecond until the window has been filled.
   int prev_error = kExpectedBitrate;
+  rtc::Optional<uint32_t> bitrate;
   while (++now_ms < 10000) {
     stats_.Update(1000, now_ms);
     bitrate = stats_.Rate(now_ms);
-    int error = kExpectedBitrate - bitrate;
-    error = std::abs(error);
-    // Expect the estimation error to decrease as the window is extended.
-    EXPECT_LE(error, prev_error + 1);
-    prev_error = error;
+    if (bitrate) {
+      int error = kExpectedBitrate - *bitrate;
+      error = std::abs(error);
+      // Expect the estimation error to decrease as the window is extended.
+      EXPECT_LE(error, prev_error + 1);
+      prev_error = error;
+    }
   }
   // Window filled, expect to be close to 8000000.
-  EXPECT_EQ(kExpectedBitrate, bitrate);
+  EXPECT_EQ(kExpectedBitrate, *bitrate);
 
   now_ms += kWindowMs + 1;
-  EXPECT_EQ(0u, stats_.Rate(now_ms));
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
   stats_.Update(1000, now_ms);
-  // We expect one sample of 1000 bytes, and that the bitrate is measured over
-  // 1 ms, i.e., 8 * 1000 / 0.001 = 8000000.
-  EXPECT_EQ(kExpectedBitrate, stats_.Rate(now_ms));
+  ++now_ms;
+  stats_.Update(1000, now_ms);
+  // We expect two samples of 1000 bytes, and that the bitrate is measured over
+  // 500 ms, i.e. 2 * 8 * 1000 / 0.500 = 32000.
+  EXPECT_EQ(32000u, *stats_.Rate(now_ms));
+
+  // Reset, add the same samples again.
+  stats_.Reset();
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+  stats_.Update(1000, now_ms);
+  ++now_ms;
+  stats_.Update(1000, now_ms);
+  // We expect two samples of 1000 bytes, and that the bitrate is measured over
+  // 2 ms (window size has been reset) i.e. 2 * 8 * 1000 / 0.002 = 8000000.
+  EXPECT_EQ(kExpectedBitrate, *stats_.Rate(now_ms));
+}
+
+TEST_F(RateStatisticsTest, HandlesChangingWindowSize) {
+  int64_t now_ms = 0;
+  stats_.Reset();
+
+  // Sanity test window size.
+  EXPECT_TRUE(stats_.SetWindowSize(kWindowMs, now_ms));
+  EXPECT_FALSE(stats_.SetWindowSize(kWindowMs + 1, now_ms));
+  EXPECT_FALSE(stats_.SetWindowSize(0, now_ms));
+  EXPECT_TRUE(stats_.SetWindowSize(1, now_ms));
+  EXPECT_TRUE(stats_.SetWindowSize(kWindowMs, now_ms));
+
+  // Fill the buffer at a rate of 1 byte / millisecond (8 kbps).
+  const int kBatchSize = 10;
+  for (int i = 0; i <= kWindowMs; i += kBatchSize)
+    stats_.Update(kBatchSize, now_ms += kBatchSize);
+  EXPECT_EQ(static_cast<uint32_t>(8000), *stats_.Rate(now_ms));
+
+  // Halve the window size, rate should stay the same.
+  EXPECT_TRUE(stats_.SetWindowSize(kWindowMs / 2, now_ms));
+  EXPECT_EQ(static_cast<uint32_t>(8000), *stats_.Rate(now_ms));
+
+  // Double the window size again, rate should stay the same. (As the window
+  // won't actually expand until new bit and bobs fall into it.
+  EXPECT_TRUE(stats_.SetWindowSize(kWindowMs, now_ms));
+  EXPECT_EQ(static_cast<uint32_t>(8000), *stats_.Rate(now_ms));
+
+  // Fill the now empty half with bits it twice the rate.
+  for (int i = 0; i < kWindowMs / 2; i += kBatchSize)
+    stats_.Update(kBatchSize * 2, now_ms += kBatchSize);
+
+  // Rate should have increase be 50%.
+  EXPECT_EQ(static_cast<uint32_t>((8000 * 3) / 2), *stats_.Rate(now_ms));
+}
+
+TEST_F(RateStatisticsTest, RespectsWindowSizeEdges) {
+  int64_t now_ms = 0;
+  stats_.Reset();
+  // Expecting 0 after init.
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
+  // One byte per ms, using one big sample.
+  stats_.Update(kWindowMs, now_ms);
+  now_ms += kWindowMs - 2;
+  // Shouldn't work! (Only one sample, not full window size.)
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
+  // Window size should be full, and the single data point should be accepted.
+  ++now_ms;
+  rtc::Optional<uint32_t> bitrate = stats_.Rate(now_ms);
+  EXPECT_TRUE(static_cast<bool>(bitrate));
+  EXPECT_EQ(1000 * 8u, *bitrate);
+
+  // Add another, now we have twice the bitrate.
+  stats_.Update(kWindowMs, now_ms);
+  bitrate = stats_.Rate(now_ms);
+  EXPECT_TRUE(static_cast<bool>(bitrate));
+  EXPECT_EQ(2 * 1000 * 8u, *bitrate);
+
+  // Now that first sample should drop out...
+  now_ms += 1;
+  bitrate = stats_.Rate(now_ms);
+  EXPECT_TRUE(static_cast<bool>(bitrate));
+  EXPECT_EQ(1000 * 8u, *bitrate);
+}
+
+TEST_F(RateStatisticsTest, HandlesQuietPeriods) {
+  int64_t now_ms = 0;
+  stats_.Reset();
+  // Expecting 0 after init.
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
+
+  stats_.Update(kWindowMs, now_ms);
+  now_ms += kWindowMs - 1;
+  stats_.Update(0, now_ms);
+  rtc::Optional<uint32_t> bitrate = stats_.Rate(now_ms);
+  EXPECT_TRUE(static_cast<bool>(bitrate));
+  EXPECT_EQ(1000 * 8u, *bitrate);
+
+  // Move window along so first data point falls out.
+  ++now_ms;
+  bitrate = stats_.Rate(now_ms);
+  EXPECT_TRUE(static_cast<bool>(bitrate));
+  EXPECT_EQ(0u, *bitrate);
+
+  // Move window so last data point falls out.
+  now_ms += kWindowMs;
+  EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
 }
 }  // namespace