Stop using next_packet_sequence_number_length in QuicPacketCreator. No functional change. Protect…

net/quic/quic_connection.cc

Index: net/quic/quic_connection.cc
diff --git a/net/quic/quic_connection.cc b/net/quic/quic_connection.cc
index a9a38c5525d3ae6200298bfaa8992bbd78bffec4..c5290627776318ae666da1feaef253a66fc17f5a 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -1681,12 +1681,14 @@ bool QuicConnection::WritePacket(SerializedPacket* packet) {
   DVLOG(1) << ENDPOINT << "time we began writing last sent packet: "
            << packet_send_time.ToDebuggingValue();
 
-  // TODO(ianswett): Change the packet number length and other packet creator
-  // options by a more explicit API than setting a struct value directly,
-  // perhaps via the NetworkChangeVisitor.
-  packet_generator_.UpdateSequenceNumberLength(
-      sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
-      sent_packet_manager_->EstimateMaxPacketsInFlight(max_packet_length()));
+  if (!FLAGS_quic_simple_packet_number_length) {
+    // TODO(ianswett): Change the packet number length and other packet creator
+    // options by a more explicit API than setting a struct value directly,
+    // perhaps via the NetworkChangeVisitor.
+    packet_generator_.UpdateSequenceNumberLength(
+        sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
+        sent_packet_manager_->EstimateMaxPacketsInFlight(max_packet_length()));
+  }
 
   bool reset_retransmission_alarm = sent_packet_manager_->OnPacketSent(
       packet, packet->original_path_id, packet->original_packet_number,
@@ -1696,6 +1698,14 @@ bool QuicConnection::WritePacket(SerializedPacket* packet) {
     SetRetransmissionAlarm();
   }
 
+  if (FLAGS_quic_simple_packet_number_length) {
+    // The packet number length must be updated after OnPacketSent, because it
+    // may change the packet number length in packet.
+    packet_generator_.UpdateSequenceNumberLength(
+        sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
+        sent_packet_manager_->EstimateMaxPacketsInFlight(max_packet_length()));
+  }
+
   stats_.bytes_sent += result.bytes_written;
   ++stats_.packets_sent;
   if (packet->transmission_type != NOT_RETRANSMISSION) {