fix(http2): reject server push when disabled

pkgs/http2/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 3.0.1-wip
 
 - Gracefully handle receiving headers on a stream that the client has canceled. (#1799)
+- Treat incoming server push streams as connection protocol error when pushes are disabled (SETTINGS_ENABLE_PUSH=0).
 
 ## 3.0.0
 

pkgs/http2/lib/src/streams/stream_handler.dart

@@ -745,6 +745,15 @@ class StreamHandler extends Object with TerminatableMixin, ClosableMixin {
       throw ProtocolException('Expected open state (was: ${stream.state}).');
     }
 
+    // RFC 7540 6.5.2/8.2: An endpoint that has both sent and received
+    // acknowledgement of SETTINGS_ENABLE_PUSH=0 MUST treat receipt of a
+    // PUSH_PROMISE frame as a connection error of type PROTOCOL_ERROR.
+    if (!_localSettings.enablePush) {
+      throw ProtocolException(
+        'Received PUSH_PROMISE although SETTINGS_ENABLE_PUSH is 0.',
+      );
+    }
+
     var pushedStream = newRemoteStream(frame.promisedStreamId);
     _changeState(pushedStream, StreamState.ReservedRemote);
 

pkgs/http2/test/client_test.dart

@@ -883,6 +883,100 @@ void main() {
         await Future.wait([serverFun(), clientFun()]);
       });
 
+      clientTest(
+        'client-reports-connection-error-on-push-when-push-disabled',
+        (
+          ClientTransportConnection client,
+          FrameWriter serverWriter,
+          StreamIterator<Frame> serverReader,
+          Future<Frame> Function() nextFrame,
+        ) async {
+          var handshakeCompleter = Completer<void>();
+          var gotPushPromise = Completer<void>();
+
+          Future serverFun() async {
+            // Server accepts the settings with SETTINGS_ENABLE_PUSH = 0.
+            serverWriter.writeSettingsFrame([]);
+            expect(await nextFrame(), isA<SettingsFrame>());
+            serverWriter.writeSettingsAckFrame();
+            expect(await nextFrame(), isA<SettingsFrame>());
+
+            handshakeCompleter.complete();
+
+            var headers = await nextFrame() as HeadersFrame;
+            var streamId = headers.header.streamId;
+
+            // Push stream on the open stream.
+            var pushStreamId = 2;
+            serverWriter.writePushPromiseFrame(streamId, pushStreamId, [
+              Header.ascii('a', 'b'),
+            ]);
+
+            // Since the client sent SETTINGS_ENABLE_PUSH=0, receiving a
+            // PUSH_PROMISE **must** result in a connection error of type
+            // PROTOCOL_ERROR.
+            try {
+              var frame = await nextFrame().timeout(
+                const Duration(milliseconds: 500),
+              );
+              if (frame is GoawayFrame) {
+                expect(frame.errorCode, ErrorCode.PROTOCOL_ERROR);
+                expect(
+                  ascii.decode(frame.debugData),
+                  contains(
+                    'Received PUSH_PROMISE although SETTINGS_ENABLE_PUSH is 0',
+                  ),
+                );
+              } else {
+                fail('Expected GoawayFrame, but got $frame');
+              }
+            } finally {
+              expect(await serverReader.moveNext(), false);
+              await serverWriter.close();
+            }
+          }
+
+          Future clientFun() async {
+            await handshakeCompleter.future;
+
+            var stream = client.makeRequest([Header.ascii('a', 'b')]);
+
+            // Listen for push stream, which should not happen if pushes are
+            // disabled.
+            stream.peerPushes.listen((push) {
+              gotPushPromise.complete();
+            });
+
+            // Wait for the stream to throw an error.
+            var done = Completer<void>();
+            stream.incomingMessages.listen(
+              (_) {},
+              onError: (Object e) {
+                expect(
+                  e,
+                  isA<TransportConnectionException>().having(
+                    (p0) => p0.message,
+                    'Forcefully terminated message',
+                    contains('Connection is being forcefully terminated'),
+                  ),
+                );
+                if (!done.isCompleted) done.complete();
+              },
+              onDone: () {
+                if (!done.isCompleted) done.complete();
+              },
+            );
+
+            await Future.any([gotPushPromise.future, done.future]);
+
+            await client.terminate();
+          }
+
+          await Future.wait([serverFun(), clientFun()]);
+        },
+        settings: const ClientSettings(allowServerPushes: false),
+      );
+
       clientTest('client-reports-flowcontrol-error-on-negative-window', (
         ClientTransportConnection client,
         FrameWriter serverWriter,
@@ -1095,10 +1189,11 @@ void clientTest(
     StreamIterator<Frame> frameReader,
     Future<Frame> Function() readNext,
   )
-  func,
-) {
+  func, {
+  ClientSettings? settings,
+}) {
   return test(name, () {
-    var streams = ClientStreams();
+    var streams = ClientStreams(settings: settings);
     var serverReader = streams.serverConnectionFrameReader;
 
     Future<Frame> readNext() async {
@@ -1116,8 +1211,12 @@ void clientTest(
 }
 
 class ClientStreams {
+  final ClientSettings? settings;
   final StreamController<List<int>> writeA = StreamController();
   final StreamController<List<int>> writeB = StreamController();
+
+  ClientStreams({this.settings});
+
   Stream<List<int>> get readA => writeA.stream;
   Stream<List<int>> get readB => writeB.stream;
 
@@ -1136,5 +1235,5 @@ class ClientStreams {
   }
 
   ClientTransportConnection get clientConnection =>
-      ClientTransportConnection.viaStreams(readB, writeA);
+      ClientTransportConnection.viaStreams(readB, writeA, settings: settings);
 }