Fixes two div by zero bugs in QUIC's BBR pacing code that caused server

net/quic/congestion_control/rtt_stats_test.cc

 // Copyright 2014 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/congestion_control/rtt_stats.h"
 
 #include "base/logging.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
 namespace test {
 
 class RttStatsPeer {
  public:
   static QuicTime::Delta GetHalfWindowRtt(const RttStats* rtt_stats) {
     return rtt_stats->half_window_rtt_.rtt;
   }
 
   static QuicTime::Delta GetQuarterWindowRtt(const RttStats* rtt_stats) {
     return rtt_stats->quarter_window_rtt_.rtt;
   }
 };
 
 class RttStatsTest : public ::testing::Test {
  protected:
   RttStats rtt_stats_;
 };
 
+TEST_F(RttStatsTest, DefaultsBeforeUpdate) {
+  EXPECT_LT(0u, rtt_stats_.initial_rtt_us());
+  EXPECT_EQ(QuicTime::Delta::FromMicroseconds(rtt_stats_.initial_rtt_us()),
+            rtt_stats_.MinRtt());
+  EXPECT_EQ(QuicTime::Delta::FromMicroseconds(rtt_stats_.initial_rtt_us()),
+            rtt_stats_.SmoothedRtt());
+}
+
 TEST_F(RttStatsTest, MinRtt) {
-  rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(100),
+  rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(200),
                        QuicTime::Delta::Zero(),
                        QuicTime::Zero());
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(100), rtt_stats_.min_rtt());
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(100),
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(200), rtt_stats_.MinRtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(200),
             rtt_stats_.recent_min_rtt());
   rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(10),
                        QuicTime::Delta::Zero(),
                        QuicTime::Zero().Add(
                            QuicTime::Delta::FromMilliseconds(10)));
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.recent_min_rtt());
   rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(50),
                        QuicTime::Delta::Zero(),
                        QuicTime::Zero().Add(
                            QuicTime::Delta::FromMilliseconds(20)));
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.recent_min_rtt());
   rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(50),
                        QuicTime::Delta::Zero(),
                        QuicTime::Zero().Add(
                            QuicTime::Delta::FromMilliseconds(30)));
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.recent_min_rtt());
   rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(50),
                        QuicTime::Delta::Zero(),
                        QuicTime::Zero().Add(
                            QuicTime::Delta::FromMilliseconds(40)));
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.recent_min_rtt());
 }
 
 TEST_F(RttStatsTest, RecentMinRtt) {
   rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(10),
                        QuicTime::Delta::Zero(),
                        QuicTime::Zero());
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.recent_min_rtt());
 
   rtt_stats_.SampleNewRecentMinRtt(4);
   for (int i = 0; i < 3; ++i) {
     rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(50),
                        QuicTime::Delta::Zero(),
                        QuicTime::Zero());
-    EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+    EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
     EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10),
               rtt_stats_.recent_min_rtt());
   }
   rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(50),
                         QuicTime::Delta::Zero(),
                         QuicTime::Zero());
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(50), rtt_stats_.recent_min_rtt());
 }
 
 TEST_F(RttStatsTest, WindowedRecentMinRtt) {
   // Set the window to 99ms, so 25ms is more than a quarter rtt.
   rtt_stats_.set_recent_min_rtt_window(QuicTime::Delta::FromMilliseconds(99));
 
   QuicTime now = QuicTime::Zero();
   QuicTime::Delta rtt_sample = QuicTime::Delta::FromMilliseconds(10);
   rtt_stats_.UpdateRtt(rtt_sample, QuicTime::Delta::Zero(), now);
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.recent_min_rtt());
 
   // Gradually increase the rtt samples and ensure the recent_min_rtt starts
   // rising.
   for (int i = 0; i < 8; ++i) {
     now = now.Add(QuicTime::Delta::FromMilliseconds(25));
     rtt_sample = rtt_sample.Add(QuicTime::Delta::FromMilliseconds(10));
     rtt_stats_.UpdateRtt(rtt_sample, QuicTime::Delta::Zero(), now);
-    EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+    EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
     EXPECT_EQ(rtt_sample, RttStatsPeer::GetQuarterWindowRtt(&rtt_stats_));
     EXPECT_EQ(rtt_sample.Subtract(QuicTime::Delta::FromMilliseconds(10)),
               RttStatsPeer::GetHalfWindowRtt(&rtt_stats_));
     if (i < 3) {
       EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10),
                 rtt_stats_.recent_min_rtt());
     } else if (i < 5) {
       EXPECT_EQ(QuicTime::Delta::FromMilliseconds(30),
                 rtt_stats_.recent_min_rtt());
     } else if (i < 7) {
       EXPECT_EQ(QuicTime::Delta::FromMilliseconds(50),
                 rtt_stats_.recent_min_rtt());
     } else {
       EXPECT_EQ(QuicTime::Delta::FromMilliseconds(70),
                 rtt_stats_.recent_min_rtt());
     }
   }
 
   // A new quarter rtt low sets that, but nothing else.
   rtt_sample = rtt_sample.Subtract(QuicTime::Delta::FromMilliseconds(5));
   rtt_stats_.UpdateRtt(rtt_sample, QuicTime::Delta::Zero(), now);
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetQuarterWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample.Subtract(QuicTime::Delta::FromMilliseconds(5)),
             RttStatsPeer::GetHalfWindowRtt(&rtt_stats_));
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(70),
             rtt_stats_.recent_min_rtt());
 
   // A new half rtt low sets that and the quarter rtt low.
   rtt_sample = rtt_sample.Subtract(QuicTime::Delta::FromMilliseconds(15));
   rtt_stats_.UpdateRtt(rtt_sample, QuicTime::Delta::Zero(), now);
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetQuarterWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetHalfWindowRtt(&rtt_stats_));
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(70),
             rtt_stats_.recent_min_rtt());
 
   // A new full window loss sets the recent_min_rtt, but not min_rtt.
   rtt_sample = QuicTime::Delta::FromMilliseconds(65);
   rtt_stats_.UpdateRtt(rtt_sample, QuicTime::Delta::Zero(), now);
-  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.min_rtt());
+  EXPECT_EQ(QuicTime::Delta::FromMilliseconds(10), rtt_stats_.MinRtt());
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetQuarterWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetHalfWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample, rtt_stats_.recent_min_rtt());
 
   // A new all time low sets both the min_rtt and the recent_min_rtt.
   rtt_sample = QuicTime::Delta::FromMilliseconds(5);
   rtt_stats_.UpdateRtt(rtt_sample, QuicTime::Delta::Zero(), now);
 
-  EXPECT_EQ(rtt_sample, rtt_stats_.min_rtt());
+  EXPECT_EQ(rtt_sample, rtt_stats_.MinRtt());
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetQuarterWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetHalfWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample, rtt_stats_.recent_min_rtt());
 }
 
 TEST_F(RttStatsTest, ExpireSmoothedMetrics) {
   QuicTime::Delta initial_rtt = QuicTime::Delta::FromMilliseconds(10);
   rtt_stats_.UpdateRtt(initial_rtt, QuicTime::Delta::Zero(), QuicTime::Zero());
-  EXPECT_EQ(initial_rtt, rtt_stats_.min_rtt());
+  EXPECT_EQ(initial_rtt, rtt_stats_.MinRtt());
   EXPECT_EQ(initial_rtt, rtt_stats_.recent_min_rtt());
   EXPECT_EQ(initial_rtt, rtt_stats_.SmoothedRtt());
 
   EXPECT_EQ(initial_rtt.Multiply(0.5), rtt_stats_.mean_deviation());
 
   // Update once with a 20ms RTT.
   QuicTime::Delta doubled_rtt = initial_rtt.Multiply(2);
   rtt_stats_.UpdateRtt(doubled_rtt, QuicTime::Delta::Zero(), QuicTime::Zero());
   EXPECT_EQ(initial_rtt.Multiply(1.125), rtt_stats_.SmoothedRtt());
 
   // Expire the smoothed metrics, increasing smoothed rtt and mean deviation.
   rtt_stats_.ExpireSmoothedMetrics();
   EXPECT_EQ(doubled_rtt, rtt_stats_.SmoothedRtt());
   EXPECT_EQ(initial_rtt.Multiply(0.875), rtt_stats_.mean_deviation());
 
   // Now go back down to 5ms and expire the smoothed metrics, and ensure the
   // mean deviation increases to 15ms.
   QuicTime::Delta half_rtt = initial_rtt.Multiply(0.5);
   rtt_stats_.UpdateRtt(half_rtt, QuicTime::Delta::Zero(), QuicTime::Zero());
   EXPECT_GT(doubled_rtt, rtt_stats_.SmoothedRtt());
   EXPECT_LT(initial_rtt, rtt_stats_.mean_deviation());
 }
 
 }  // namespace test
 }  // namespace net