Fix bytes accounting for buffered coalesced packets. Protected by FLAGS_quic_reloadable_flag_quic_fix_bytes_accounting_for_buffered_coalesced_packets. PiperOrigin-RevId: 457607469

diff --git a/quiche/quic/core/quic_connection.cc b/quiche/quic/core/quic_connection.cc
index f5bf7be..2c8d341 100644
--- a/quiche/quic/core/quic_connection.cc
+++ b/quiche/quic/core/quic_connection.cc

@@ -5971,31 +5971,38 @@
   }
   QUIC_DVLOG(1) << ENDPOINT << "Sending coalesced packet "
                 << coalesced_packet_.ToString(length);
-
+  if (GetQuicReloadableFlag(
+          quic_fix_bytes_accounting_for_buffered_coalesced_packets)) {
+    QUIC_RELOADABLE_FLAG_COUNT(
+        quic_fix_bytes_accounting_for_buffered_coalesced_packets);
+  }
   if (!buffered_packets_.empty() || HandleWriteBlocked()) {
     QUIC_DVLOG(1) << ENDPOINT
                   << "Buffering coalesced packet of len: " << length;
     buffered_packets_.emplace_back(
         buffer, static_cast<QuicPacketLength>(length),
         coalesced_packet_.self_address(), coalesced_packet_.peer_address());
-    return true;
-  }
-
-  WriteResult result = writer_->WritePacket(
-      buffer, length, coalesced_packet_.self_address().host(),
-      coalesced_packet_.peer_address(), per_packet_options_);
-  if (IsWriteError(result.status)) {
-    OnWriteError(result.error_code);
-    return false;
-  }
-  if (IsWriteBlockedStatus(result.status)) {
-    visitor_->OnWriteBlocked();
-    if (result.status != WRITE_STATUS_BLOCKED_DATA_BUFFERED) {
-      QUIC_DVLOG(1) << ENDPOINT
-                    << "Buffering coalesced packet of len: " << length;
-      buffered_packets_.emplace_back(
-          buffer, static_cast<QuicPacketLength>(length),
-          coalesced_packet_.self_address(), coalesced_packet_.peer_address());
+    if (!GetQuicReloadableFlag(
+            quic_fix_bytes_accounting_for_buffered_coalesced_packets)) {
+      return true;
+    }
+  } else {
+    WriteResult result = writer_->WritePacket(
+        buffer, length, coalesced_packet_.self_address().host(),
+        coalesced_packet_.peer_address(), per_packet_options_);
+    if (IsWriteError(result.status)) {
+      OnWriteError(result.error_code);
+      return false;
+    }
+    if (IsWriteBlockedStatus(result.status)) {
+      visitor_->OnWriteBlocked();
+      if (result.status != WRITE_STATUS_BLOCKED_DATA_BUFFERED) {
+        QUIC_DVLOG(1) << ENDPOINT
+                      << "Buffering coalesced packet of len: " << length;
+        buffered_packets_.emplace_back(
+            buffer, static_cast<QuicPacketLength>(length),
+            coalesced_packet_.self_address(), coalesced_packet_.peer_address());
+      }
     }
   }
   // Account for added padding.

diff --git a/quiche/quic/core/quic_connection_test.cc b/quiche/quic/core/quic_connection_test.cc
index d33a090..0fea5c6 100644
--- a/quiche/quic/core/quic_connection_test.cc
+++ b/quiche/quic/core/quic_connection_test.cc

@@ -15472,6 +15472,27 @@
             QuicTime::Delta::FromSeconds(5));
 }
 
+TEST_P(QuicConnectionTest, FixBytesAccountingForBufferedCoalescedPackets) {
+  if (!connection_.version().CanSendCoalescedPackets()) {
+    return;
+  }
+  connection_.SetEncrypter(ENCRYPTION_INITIAL,
+                           std::make_unique<TaggingEncrypter>(0x01));
+  // Write is blocked.
+  EXPECT_CALL(visitor_, OnWriteBlocked()).Times(AnyNumber());
+  writer_->SetWriteBlocked();
+  connection_.SetDefaultEncryptionLevel(ENCRYPTION_INITIAL);
+  QuicConnectionPeer::SendPing(&connection_);
+  const QuicConnectionStats& stats = connection_.GetStats();
+  if (GetQuicReloadableFlag(
+          quic_fix_bytes_accounting_for_buffered_coalesced_packets)) {
+    // Verify padding is accounted.
+    EXPECT_EQ(stats.bytes_sent, connection_.max_packet_length());
+  } else {
+    EXPECT_LT(stats.bytes_sent, connection_.max_packet_length());
+  }
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic

diff --git a/quiche/quic/core/quic_flags_list.h b/quiche/quic/core/quic_flags_list.h
index 82d2e6e..8c26b10 100644
--- a/quiche/quic/core/quic_flags_list.h
+++ b/quiche/quic/core/quic_flags_list.h

@@ -29,6 +29,8 @@
 QUIC_FLAG(quic_restart_flag_quic_support_release_time_for_gso, false)
 // If true, TlsHandshaker::AdvanceHandshake will check if connection is closed after SSL_do_handshake.
 QUIC_FLAG(quic_reloadable_flag_quic_tls_handshaker_check_connection_closed, true)
+// If true, account added padding when coalesced packets get buffered.
+QUIC_FLAG(quic_reloadable_flag_quic_fix_bytes_accounting_for_buffered_coalesced_packets, true)
 // If true, ack frequency frame can be sent from server to client.
 QUIC_FLAG(quic_reloadable_flag_quic_can_send_ack_frequency, true)
 // If true, allow client to enable BBRv2 on server via connection option \'B2ON\'.