In quic, add a connection option to enable more aggressive pto timeout before any rtt sample is available. not protected.

PiperOrigin-RevId: 317280920
Change-Id: Ia607d240d11d3365eef0518c76fb9d5e86c1d55e

quic/core/crypto/crypto_protocol.h

diff --git a/quic/core/crypto/crypto_protocol.h b/quic/core/crypto/crypto_protocol.h
index fc7d363..c178aa2 100644
--- a/quic/core/crypto/crypto_protocol.h
+++ b/quic/core/crypto/crypto_protocol.h
@@ -233,6 +233,8 @@
                                                  // earliest in flight sent time
                                                  // and at least 1.5*srtt from
                                                  // last sent packet.
+const QuicTag kAPTO = TAG('A', 'P', 'T', 'O');   // Use 1.5 * initial RTT before
+                                                 // any RTT sample is available.
 
 const QuicTag kELDT = TAG('E', 'L', 'D', 'T');   // Enable Loss Detection Tuning
 

quic/core/quic_sent_packet_manager.cc

diff --git a/quic/core/quic_sent_packet_manager.cc b/quic/core/quic_sent_packet_manager.cc
index d74a487..eeeddf2 100644
--- a/quic/core/quic_sent_packet_manager.cc
+++ b/quic/core/quic_sent_packet_manager.cc
@@ -107,7 +107,8 @@
       one_rtt_packet_acked_(false),
       one_rtt_packet_sent_(false),
       first_pto_srtt_multiplier_(0),
-      use_standard_deviation_for_pto_(false) {
+      use_standard_deviation_for_pto_(false),
+      pto_multiplier_without_rtt_samples_(3) {
   SetSendAlgorithm(congestion_control_type);
   if (pto_enabled_) {
     QUIC_RELOADABLE_FLAG_COUNT_N(quic_default_on_pto, 1, 2);
@@ -197,6 +198,9 @@
     } else if (config.HasClientSentConnectionOption(kPLE2, perspective)) {
       first_pto_srtt_multiplier_ = 1.5;
     }
+    if (config.HasClientSentConnectionOption(kAPTO, perspective)) {
+      pto_multiplier_without_rtt_samples_ = 1.5;
+    }
     if (config.HasClientSentConnectionOption(kPSDA, perspective)) {
       use_standard_deviation_for_pto_ = true;
       rtt_stats_.EnableStandardDeviationCalculation();
@@ -1230,8 +1234,9 @@
   if (rtt_stats_.smoothed_rtt().IsZero()) {
     // Respect kMinHandshakeTimeoutMs to avoid a potential amplification attack.
     QUIC_BUG_IF(rtt_stats_.initial_rtt().IsZero());
-    return std::max(3 * rtt_stats_.initial_rtt(),
-                    QuicTime::Delta::FromMilliseconds(kMinHandshakeTimeoutMs)) *
+    return std::max(
+               pto_multiplier_without_rtt_samples_ * rtt_stats_.initial_rtt(),
+               QuicTime::Delta::FromMilliseconds(kMinHandshakeTimeoutMs)) *
            (1 << consecutive_pto_count_);
   }
   const QuicTime::Delta rtt_var = use_standard_deviation_for_pto_

quic/core/quic_sent_packet_manager.h

diff --git a/quic/core/quic_sent_packet_manager.h b/quic/core/quic_sent_packet_manager.h
index af32eba..ca43d3d 100644
--- a/quic/core/quic_sent_packet_manager.h
+++ b/quic/core/quic_sent_packet_manager.h
@@ -658,6 +658,10 @@
   // If true, use standard deviation (instead of mean deviation) when
   // calculating PTO timeout.
   bool use_standard_deviation_for_pto_;
+
+  // The multiplier for caculating PTO timeout before any RTT sample is
+  // available.
+  float pto_multiplier_without_rtt_samples_;
 };
 
 }  // namespace quic

quic/core/quic_sent_packet_manager_test.cc

diff --git a/quic/core/quic_sent_packet_manager_test.cc b/quic/core/quic_sent_packet_manager_test.cc
index 90c7e15..33b2470 100644
--- a/quic/core/quic_sent_packet_manager_test.cc
+++ b/quic/core/quic_sent_packet_manager_test.cc
@@ -4096,6 +4096,30 @@
             manager_.GetRetransmissionTime());
 }
 
+TEST_F(QuicSentPacketManagerTest,
+       AggressivePtoBeforeAnyRttSamplesAreAvailable) {
+  manager_.EnableMultiplePacketNumberSpacesSupport();
+  EXPECT_CALL(*send_algorithm_, PacingRate(_))
+      .WillRepeatedly(Return(QuicBandwidth::Zero()));
+  EXPECT_CALL(*send_algorithm_, GetCongestionWindow())
+      .WillRepeatedly(Return(10 * kDefaultTCPMSS));
+  RttStats* rtt_stats = const_cast<RttStats*>(manager_.GetRttStats());
+
+  QuicConfig config;
+  QuicTagVector options;
+  options.push_back(kAPTO);
+  QuicConfigPeer::SetReceivedConnectionOptions(&config, options);
+  EXPECT_CALL(*send_algorithm_, SetFromConfig(_, _));
+  EXPECT_CALL(*network_change_visitor_, OnCongestionChange());
+  manager_.SetFromConfig(config);
+
+  // Send INITIAL 1.
+  SendDataPacket(1, ENCRYPTION_INITIAL);
+  // Verify retransmission timeout is expected.
+  EXPECT_EQ(clock_.Now() + 1.5 * rtt_stats->initial_rtt(),
+            manager_.GetRetransmissionTime());
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic