external-release-note: Adding a flag for enforcement of the single-packet-CHLO policy.

net/quic/core/quic_packet_creator.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/core/quic_packet_creator.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/macros.h"
@@ skipping 120 matching lines @@
   if (!HasRoomForStreamFrame(id, offset)) {
     return false;
   }
   CreateStreamFrame(id, iov, iov_offset, offset, fin, frame);
   // Explicitly disallow multi-packet CHLOs.
   if (id == kCryptoStreamId &&
       frame->stream_frame->data_length >= sizeof(kCHLO) &&
       strncmp(frame->stream_frame->data_buffer,
               reinterpret_cast<const char*>(&kCHLO), sizeof(kCHLO)) == 0) {
     DCHECK_EQ(static_cast<size_t>(0), iov_offset);
-    if (frame->stream_frame->data_length < iov.iov->iov_len) {
+    if (FLAGS_quic_enforce_single_packet_chlo &&
+        frame->stream_frame->data_length < iov.iov->iov_len) {
       const string error_details = "Client hello won't fit in a single packet.";
       QUIC_BUG << error_details << " Constructed stream frame length: "
                << frame->stream_frame->data_length
                << " CHLO length: " << iov.iov->iov_len;
       delegate_->OnUnrecoverableError(QUIC_CRYPTO_CHLO_TOO_LARGE, error_details,
                                       ConnectionCloseSource::FROM_SELF);
       delete frame->stream_frame;
       return false;
     }
   }
@@ skipping 529 matching lines @@
   if (bit_mask_ == 0) {
     bit_bucket_ = random_->RandUint64();
     bit_mask_ = 1;
   }
   bool result = ((bit_bucket_ & bit_mask_) != 0);
   bit_mask_ <<= 1;
   return result;
 }
 
 }  // namespace net