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

BUG=641791

Review-Url: https://codereview.chromium.org/2283393002
Cr-Commit-Position: refs/heads/master@{#415385}

components/network_session_configurator/network_session_configurator.cc

@@ -226,6 +226,13 @@ bool ShouldQuicRaceCertVerification(
       "true");
 }
 
+bool ShouldQuicDoNotFragment(
+    const VariationParameters& quic_trial_params) {
+   return base::LowerCaseEqualsASCII(
+      GetVariationParam(quic_trial_params, "do_not_fragment"),
+      "true");
+}
+
 bool ShouldQuicDisablePreConnectIfZeroRtt(
     const VariationParameters& quic_trial_params) {
   return base::LowerCaseEqualsASCII(
@@ -348,6 +355,8 @@ void ConfigureQuicParams(base::StringPiece quic_trial_group,
     }
     params->quic_race_cert_verification =
         ShouldQuicRaceCertVerification(quic_trial_params);
+    params->quic_do_not_fragment =
+        ShouldQuicDoNotFragment(quic_trial_params);
     params->quic_disable_preconnect_if_0rtt =
         ShouldQuicDisablePreConnectIfZeroRtt(quic_trial_params);
     params->quic_host_whitelist = GetQuicHostWhitelist(quic_trial_params);

components/network_session_configurator/network_session_configurator_unittest.cc

@@ -83,6 +83,7 @@ TEST_F(NetworkSessionConfiguratorTest, EnableQuicFromFieldTrialGroup) {
   EXPECT_EQ(net::kQuicYieldAfterDurationMilliseconds,
             params_.quic_packet_reader_yield_after_duration_milliseconds);
   EXPECT_FALSE(params_.quic_race_cert_verification);
+  EXPECT_FALSE(params_.quic_do_not_fragment);
   EXPECT_FALSE(params_.quic_disable_preconnect_if_0rtt);
   EXPECT_FALSE(params_.quic_migrate_sessions_on_network_change);
   EXPECT_FALSE(params_.quic_migrate_sessions_early);
@@ -164,6 +165,17 @@ TEST_F(NetworkSessionConfiguratorTest, QuicRaceCertVerification) {
   EXPECT_TRUE(params_.quic_race_cert_verification);
 }
 
+TEST_F(NetworkSessionConfiguratorTest, QuicDoNotFragment) {
+  std::map<std::string, std::string> field_trial_params;
+  field_trial_params["do_not_fragment"] = "true";
+  variations::AssociateVariationParams("QUIC", "Enabled", field_trial_params);
+  base::FieldTrialList::CreateFieldTrial("QUIC", "Enabled");
+
+  ParseFieldTrials();
+
+  EXPECT_TRUE(params_.quic_do_not_fragment);
+}
+
 TEST_F(NetworkSessionConfiguratorTest, QuicDisablePreConnectIfZeroRtt) {
   std::map<std::string, std::string> field_trial_params;
   field_trial_params["disable_preconnect_if_0rtt"] = "true";

net/http/http_network_session.cc

@@ -131,6 +131,7 @@ HttpNetworkSession::Params::Params()
       quic_disable_bidirectional_streams(false),
       quic_force_hol_blocking(false),
       quic_race_cert_verification(false),
+      quic_do_not_fragment(false),
       proxy_delegate(NULL),
       enable_token_binding(false) {
   quic_supported_versions.push_back(QUIC_VERSION_35);
@@ -193,6 +194,7 @@ HttpNetworkSession::HttpNetworkSession(const Params& params)
           params.quic_allow_server_migration,
           params.quic_force_hol_blocking,
           params.quic_race_cert_verification,
+          params.quic_do_not_fragment,
           params.quic_connection_options,
           params.enable_token_binding),
       spdy_session_pool_(params.host_resolver,

net/http/http_network_session.h

@@ -186,6 +186,8 @@ class NET_EXPORT HttpNetworkSession
     bool quic_force_hol_blocking;
     // If true, race cert verification with host resolution.
     bool quic_race_cert_verification;
+    // If true, configure QUIC sockets to not fragment packets.
+    bool quic_do_not_fragment;
 
     ProxyDelegate* proxy_delegate;
     // Enable support for Token Binding.

net/quic/chromium/quic_stream_factory.cc

@@ -743,6 +743,7 @@ QuicStreamFactory::QuicStreamFactory(
     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),
@@ -800,6 +801,7 @@ QuicStreamFactory::QuicStreamFactory(
       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),
@@ -1705,11 +1707,13 @@ int QuicStreamFactory::ConfigureSocket(DatagramClientSocket* socket,
     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

net/quic/chromium/quic_stream_factory.h

@@ -196,6 +196,7 @@ class NET_EXPORT_PRIVATE QuicStreamFactory
       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);
   ~QuicStreamFactory() override;
@@ -623,6 +624,9 @@ class NET_EXPORT_PRIVATE QuicStreamFactory
   // Set if cert verification is to be raced with host resolution.
   bool race_cert_verification_;
 
+  // If set, configure QUIC sockets to not fragment packets.
+  bool quic_do_not_fragment_;
+
   // Each profile will (probably) have a unique port_seed_ value.  This value
   // is used to help seed a pseudo-random number generator (PortSuggester) so
   // that we consistently (within this profile) suggest the same ephemeral

net/quic/chromium/quic_stream_factory_test.cc

@@ -362,7 +362,7 @@ class QuicStreamFactoryTestBase {
         packet_reader_yield_after_duration_milliseconds_,
         migrate_sessions_on_network_change_, migrate_sessions_early_,
         allow_server_migration_, force_hol_blocking_, race_cert_verification_,
-        QuicTagVector(),
+        /*do_not_fragment*/ true, QuicTagVector(),
         /*enable_token_binding*/ false));
     factory_->set_require_confirmation(false);
     EXPECT_FALSE(factory_->has_quic_server_info_factory());