Use a field trial to decide if QUIC should attempt to prevent packet fragmentation.

net/quic/chromium/quic_stream_factory.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/chromium/quic_stream_factory.h"
 
 #include <openssl/aead.h>
 
 #include <algorithm>
 #include <tuple>
@@ skipping 725 matching lines @@
     int max_server_configs_stored_in_properties,
     bool close_sessions_on_ip_change,
     bool disable_quic_on_timeout_with_open_streams,
     int idle_connection_timeout_seconds,
     int packet_reader_yield_after_duration_milliseconds,
     bool migrate_sessions_on_network_change,
     bool migrate_sessions_early,
     bool allow_server_migration,
     bool force_hol_blocking,
     bool race_cert_verification,
+    bool quic_do_not_fragment,
     const QuicTagVector& connection_options,
     bool enable_token_binding)
     : require_confirmation_(true),
       net_log_(net_log),
       host_resolver_(host_resolver),
       client_socket_factory_(client_socket_factory),
       http_server_properties_(http_server_properties),
       transport_security_state_(transport_security_state),
       cert_transparency_verifier_(cert_transparency_verifier),
       quic_crypto_client_stream_factory_(quic_crypto_client_stream_factory),
@@ skipping 37 matching lines @@
           packet_reader_yield_after_duration_milliseconds)),
       close_sessions_on_ip_change_(close_sessions_on_ip_change),
       migrate_sessions_on_network_change_(
           migrate_sessions_on_network_change &&
           NetworkChangeNotifier::AreNetworkHandlesSupported()),
       migrate_sessions_early_(migrate_sessions_early &&
                               migrate_sessions_on_network_change_),
       allow_server_migration_(allow_server_migration),
       force_hol_blocking_(force_hol_blocking),
       race_cert_verification_(race_cert_verification),
+      quic_do_not_fragment_(quic_do_not_fragment),
       port_seed_(random_generator_->RandUint64()),
       check_persisted_supports_quic_(true),
       has_initialized_data_(false),
       num_push_streams_created_(0),
       status_(OPEN),
       task_runner_(nullptr),
       ssl_config_service_(ssl_config_service),
       weak_factory_(this) {
   if (ssl_config_service_.get())
     ssl_config_service_->AddObserver(this);
@@ skipping 885 matching lines @@
     HistogramCreateSessionFailure(CREATION_ERROR_CONNECTING_SOCKET);
     return rv;
   }
 
   rv = socket->SetReceiveBufferSize(socket_receive_buffer_size_);
   if (rv != OK) {
     HistogramCreateSessionFailure(CREATION_ERROR_SETTING_RECEIVE_BUFFER);
     return rv;
   }
 
-  rv = socket->SetDoNotFragment();
-  // SetDoNotFragment is not implemented on all platforms, so ignore errors.
-  if (rv != OK && rv != ERR_NOT_IMPLEMENTED) {
-    HistogramCreateSessionFailure(CREATION_ERROR_SETTING_DO_NOT_FRAGMENT);
-    return rv;
+  if (quic_do_not_fragment_) {
+    rv = socket->SetDoNotFragment();
+    // SetDoNotFragment is not implemented on all platforms, so ignore errors.
+    if (rv != OK && rv != ERR_NOT_IMPLEMENTED) {
+      HistogramCreateSessionFailure(CREATION_ERROR_SETTING_DO_NOT_FRAGMENT);
+      return rv;
+    }
   }
 
   // Set a buffer large enough to contain the initial CWND's worth of packet
   // to work around the problem with CHLO packets being sent out with the
   // wrong encryption level, when the send buffer is full.
   rv = socket->SetSendBufferSize(kMaxPacketSize * 20);
   if (rv != OK) {
     HistogramCreateSessionFailure(CREATION_ERROR_SETTING_SEND_BUFFER);
     return rv;
   }
@@ skipping 304 matching lines @@
   // Since the session was active, there's no longer an
   // HttpStreamFactoryImpl::Job running which can mark it broken, unless the TCP
   // job also fails. So to avoid not using QUIC when we otherwise could, we mark
   // it as recently broken, which means that 0-RTT will be disabled but we'll
   // still race.
   http_server_properties_->MarkAlternativeServiceRecentlyBroken(
       alternative_service);
 }
 
 }  // namespace net