Handle the case when SETTINGS_ENABLE_WEBTRANSPORT = 0 correctly.

PiperOrigin-RevId: 367167774
Change-Id: Ib48a0e9afe59987ee00b6056aeb5d3ce2567997b

quic/core/http/quic_spdy_session.cc

diff --git a/quic/core/http/quic_spdy_session.cc b/quic/core/http/quic_spdy_session.cc
index fe75a05..8a4058c 100644
--- a/quic/core/http/quic_spdy_session.cc
+++ b/quic/core/http/quic_spdy_session.cc
@@ -1187,7 +1187,23 @@
         break;
       }
       case SETTINGS_WEBTRANS_DRAFT00:
-        peer_supports_webtransport_ = true;
+        if (!WillNegotiateWebTransport()) {
+          break;
+        }
+        QUIC_DVLOG(1) << ENDPOINT
+                      << "SETTINGS_ENABLE_WEBTRANSPORT received with value "
+                      << value;
+        if (value != 0 && value != 1) {
+          std::string error_details = absl::StrCat(
+              "received SETTINGS_ENABLE_WEBTRANSPORT with invalid value ",
+              value);
+          QUIC_PEER_BUG(invalid SETTINGS_ENABLE_WEBTRANSPORT value)
+              << ENDPOINT << error_details;
+          CloseConnectionWithDetails(QUIC_HTTP_RECEIVE_SPDY_SETTING,
+                                     error_details);
+          return false;
+        }
+        peer_supports_webtransport_ = (value == 1);
         break;
       default:
         QUIC_DVLOG(1) << ENDPOINT << "Unknown setting identifier " << id

quic/core/http/quic_spdy_session_test.cc

diff --git a/quic/core/http/quic_spdy_session_test.cc b/quic/core/http/quic_spdy_session_test.cc
index 7c22389..d8bfa78 100644
--- a/quic/core/http/quic_spdy_session_test.cc
+++ b/quic/core/http/quic_spdy_session_test.cc
@@ -3586,6 +3586,36 @@
   EXPECT_TRUE(session_.SupportsWebTransport());
 }
 
+TEST_P(QuicSpdySessionTestClient, WebTransportSettingSetToZero) {
+  if (!version().UsesHttp3()) {
+    return;
+  }
+  SetQuicReloadableFlag(quic_h3_datagram, true);
+  session_.set_supports_webtransport(true);
+
+  EXPECT_FALSE(session_.SupportsWebTransport());
+
+  StrictMock<MockHttp3DebugVisitor> debug_visitor;
+  // Note that this does not actually fill out correct settings because the
+  // settings are filled in at the construction time.
+  EXPECT_CALL(debug_visitor, OnSettingsFrameSent(_));
+  session_.set_debug_visitor(&debug_visitor);
+  CompleteHandshake();
+
+  SettingsFrame server_settings;
+  server_settings.values[SETTINGS_H3_DATAGRAM] = 1;
+  server_settings.values[SETTINGS_WEBTRANS_DRAFT00] = 0;
+  std::string data =
+      std::string(1, kControlStream) + EncodeSettings(server_settings);
+  QuicStreamId stream_id =
+      GetNthServerInitiatedUnidirectionalStreamId(transport_version(), 3);
+  QuicStreamFrame frame(stream_id, /*fin=*/false, /*offset=*/0, data);
+  EXPECT_CALL(debug_visitor, OnPeerControlStreamCreated(stream_id));
+  EXPECT_CALL(debug_visitor, OnSettingsFrameReceived(server_settings));
+  session_.OnStreamFrame(frame);
+  EXPECT_FALSE(session_.SupportsWebTransport());
+}
+
 TEST_P(QuicSpdySessionTestServer, WebTransportSetting) {
   if (!version().UsesHttp3()) {
     return;