gfe-relnote: In QUIC, making sure there are always enough credits for non-loss retransmission. Protected by gfe2_reloadable_flag_quic_grant_enough_credits. PiperOrigin-RevId: 269791493 Change-Id: I9e841bdc1110ae7600415b428e2371573a8a8687

diff --git a/quic/core/quic_connection_test.cc b/quic/core/quic_connection_test.cc
index a67fc52..fd29785 100644
--- a/quic/core/quic_connection_test.cc
+++ b/quic/core/quic_connection_test.cc

@@ -9117,7 +9117,8 @@
 TEST_P(QuicConnectionTest, RtoPacketAsTwo) {
   if (!QuicConnectionPeer::GetSentPacketManager(&connection_)
            ->fix_rto_retransmission() ||
-      connection_.PtoEnabled()) {
+      connection_.PtoEnabled() ||
+      GetQuicReloadableFlag(quic_grant_enough_credits)) {
     return;
   }
   connection_.SetMaxTailLossProbes(1);
@@ -9190,6 +9191,62 @@
   EXPECT_TRUE(connection_.GetRetransmissionAlarm()->IsSet());
 }
 
+TEST_P(QuicConnectionTest, RetransmitPacketAsTwo) {
+  if (!connection_.session_decides_what_to_write() ||
+      !GetQuicReloadableFlag(quic_grant_enough_credits)) {
+    return;
+  }
+  connection_.SetMaxTailLossProbes(1);
+  connection_.SetDefaultEncryptionLevel(ENCRYPTION_FORWARD_SECURE);
+  std::string stream_data(3000, 's');
+  // Send packets 1 - 66 and exhaust cwnd.
+  for (size_t i = 0; i < 22; ++i) {
+    // 3 packets for each stream, the first 2 are guaranteed to be full packets.
+    SendStreamDataToPeer(i + 2, stream_data, 0, FIN, nullptr);
+  }
+  CongestionBlockWrites();
+
+  if (connection_.PtoEnabled()) {
+    // Fires PTO, packets 1 and 2 are retransmitted as 4 packets.
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(67), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(68), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(69), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(70), _, _));
+  } else {
+    // Fires TLP. Verify 2 packets gets sent.
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(67), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(68), _, _));
+  }
+  connection_.GetRetransmissionAlarm()->Fire();
+
+  if (connection_.PtoEnabled()) {
+    // Fires PTO, packets 3 and 4 are retransmitted as 3 packets.
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(71), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(72), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(73), _, _));
+  } else {
+    // Fires RTO. Verify packets 2 and 3 are retransmitted as 3 packets.
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(69), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(70), _, _));
+    EXPECT_CALL(*send_algorithm_,
+                OnPacketSent(_, _, QuicPacketNumber(71), _, _));
+  }
+  connection_.GetRetransmissionAlarm()->Fire();
+  EXPECT_EQ(
+      0u, connection_.sent_packet_manager().pending_timer_transmission_count());
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic

diff --git a/quic/core/quic_sent_packet_manager.cc b/quic/core/quic_sent_packet_manager.cc
index ee7bb34..8731306 100644
--- a/quic/core/quic_sent_packet_manager.cc
+++ b/quic/core/quic_sent_packet_manager.cc

@@ -67,6 +67,31 @@
   (unacked_packets_.perspective() == Perspective::IS_SERVER ? "Server: " \
                                                             : "Client: ")
 
+QuicSentPacketManager::ScopedCreditGrantor::ScopedCreditGrantor(
+    QuicSentPacketManager* manager)
+    : manager_(manager), credits_granted_(false) {
+  if (!GetQuicReloadableFlag(quic_grant_enough_credits)) {
+    return;
+  }
+  QUIC_RELOADABLE_FLAG_COUNT(quic_grant_enough_credits);
+  if (manager_->pending_timer_transmission_count() > 1) {
+    // There are enough credits to retransmit one packet.
+    return;
+  }
+  // Grant 2 credits because a single packet can be transmitted as 2 (if packet
+  // number length changes).
+  manager_->set_pending_timer_transmission_count(2);
+  credits_granted_ = true;
+}
+
+QuicSentPacketManager::ScopedCreditGrantor::~ScopedCreditGrantor() {
+  if (!credits_granted_) {
+    // Do not clear credits if there is no credit granted.
+    return;
+  }
+  manager_->set_pending_timer_transmission_count(0);
+}
+
 QuicSentPacketManager::QuicSentPacketManager(
     Perspective perspective,
     const QuicClock* clock,
@@ -525,6 +550,7 @@
     // applications may want to use higher priority stream data for bandwidth
     // probing, and some applications want to consider RTO is an indication of
     // loss, etc.
+    ScopedCreditGrantor grantor(this);
     unacked_packets_.RetransmitFrames(*transmission_info, transmission_type);
     return;
   }

diff --git a/quic/core/quic_sent_packet_manager.h b/quic/core/quic_sent_packet_manager.h
index cbb00a9..0199648 100644
--- a/quic/core/quic_sent_packet_manager.h
+++ b/quic/core/quic_sent_packet_manager.h

@@ -108,6 +108,19 @@
     PTO_MODE,
   };
 
+  // Grantor makes sure there are enough credits to retransmit a packet. When
+  // grantor is out of scope, remaining credits will be cleared.
+  class QUIC_EXPORT_PRIVATE ScopedCreditGrantor {
+   public:
+    explicit ScopedCreditGrantor(QuicSentPacketManager* manager);
+    ~ScopedCreditGrantor();
+
+   private:
+    QuicSentPacketManager* manager_;
+    // Indicates whether any credit has been granted.
+    bool credits_granted_;
+  };
+
   QuicSentPacketManager(Perspective perspective,
                         const QuicClock* clock,
                         QuicRandom* random,
@@ -373,6 +386,10 @@
     return pending_timer_transmission_count_;
   }
 
+  void set_pending_timer_transmission_count(size_t count) {
+    pending_timer_transmission_count_ = count;
+  }
+
   QuicTime::Delta peer_max_ack_delay() const { return peer_max_ack_delay_; }
 
   void set_peer_max_ack_delay(QuicTime::Delta peer_max_ack_delay) {