Don't copy the QuicAckFrame into the QuicPacketGenerator. Protected by quic_dont_copy_acks.

net/quic/quic_connection.cc

 // Copyright (c) 2012 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/quic_connection.h"
 
 #include <string.h>
 #include <sys/types.h>
 
 #include <algorithm>
@@ skipping 567 matching lines @@
 
   // Multipath is not enabled, but a packet with multipath flag on is received.
   if (!multipath_enabled_ && header.public_header.multipath_flag) {
     LOG(DFATAL) << "Received a packet with multipath flag on when multipath is "
                    "not enabled.";
     SendConnectionCloseWithDetails(QUIC_BAD_MULTIPATH_FLAG,
                                    "receive a packet with multipath flag on "
                                    "when multipath is not enabled.");
     return false;
   }
+  if (!packet_generator_.IsPendingPacketEmpty()) {
+    QUIC_BUG << "Pending frames must be serialized before incoming packets are "
+             << "processed, because that may change a queued ack frame.";
+    SendConnectionCloseWithDetails(QUIC_INTERNAL_ERROR,
+                                   "Should not process packets while sending.");
+    return false;
+  }
 
   // If this packet has already been seen, or the sender has told us that it
   // will not be retransmitted, then stop processing the packet.
   if (!received_packet_manager_.IsAwaitingPacket(header.packet_number)) {
     DVLOG(1) << ENDPOINT << "Packet " << header.packet_number
              << " no longer being waited for.  Discarding.";
     if (debug_visitor_ != nullptr) {
       debug_visitor_->OnDuplicatePacket(header.packet_number);
     }
     ++stats_.packets_dropped;
@@ skipping 424 matching lines @@
         QUIC_TOO_MANY_OUTSTANDING_RECEIVED_PACKETS,
         StringPrintf("More than %" PRIu64 " outstanding.", kMaxTrackedPackets));
   }
 }
 
 void QuicConnection::PopulateAckFrame(QuicAckFrame* ack) {
   received_packet_manager_.UpdateReceivedPacketInfo(ack,
                                                     clock_->ApproximateNow());
 }
 
+const QuicFrame QuicConnection::GetUpdatedAckFrame() {
+  return received_packet_manager_.GetUpdatedAckFrame(clock_->ApproximateNow());
+}
+
 void QuicConnection::PopulateStopWaitingFrame(
     QuicStopWaitingFrame* stop_waiting) {
   stop_waiting->least_unacked = GetLeastUnacked();
   stop_waiting->entropy_hash = sent_entropy_manager_.GetCumulativeEntropy(
       stop_waiting->least_unacked - 1);
 }
 
 QuicPacketNumber QuicConnection::GetLeastUnacked() const {
   return sent_packet_manager_.GetLeastUnacked();
 }
@@ skipping 1307 matching lines @@
 }
 
 StringPiece QuicConnection::GetCurrentPacket() {
   if (current_packet_data_ == nullptr) {
     return StringPiece();
   }
   return StringPiece(current_packet_data_, last_size_);
 }
 
 }  // namespace net