`AggregatedHttpResponseHandler` doesn't respect `ServiceRequestContext.additionalResponse{Headers,Trailers}`

Unlike HttpResponseSubscriber, AggregatedHttpResponseHandler doesn’t merge ServiceRequestContext.additionalResponseHeaders and additionalResponseTrailers when encoding response headers and trailers:

https://github.com/line/armeria/blob/871d87297e4d051241589cb1ae95641cbc83f880/core/src/main/java/com/linecorp/armeria/server/AbstractHttpResponseHandler.java#L103-L134

The following patch reproduces the problem by modifying AbstractUnaryGrpcServiceTest:

diff --git grpc/src/test/java/com/linecorp/armeria/server/grpc/protocol/AbstractUnaryGrpcServiceTest.java grpc/src/test/java/com/linecorp/armeria/server/grpc/protocol/AbstractUnaryGrpcServiceTest.java
index 0e07caee8..9da85a810 100644
--- grpc/src/test/java/com/linecorp/armeria/server/grpc/protocol/AbstractUnaryGrpcServiceTest.java
+++ grpc/src/test/java/com/linecorp/armeria/server/grpc/protocol/AbstractUnaryGrpcServiceTest.java
@@ -21,6 +21,7 @@ import static org.assertj.core.api.Assertions.assertThatThrownBy;

 import java.io.UncheckedIOException;
 import java.util.concurrent.CompletionStage;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Stream;

 import org.junit.jupiter.api.Test;
@@ -61,8 +62,10 @@ import com.linecorp.armeria.testing.server.ServiceRequestContextCaptor;

 import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
+import io.grpc.Metadata;
 import io.grpc.Status;
 import io.grpc.StatusRuntimeException;
+import io.grpc.stub.MetadataUtils;

 class AbstractUnaryGrpcServiceTest {
     private static final String METHOD_NAME = "/armeria.grpc.testing.TestService/UnaryCall";
@@ -94,6 +97,7 @@ class AbstractUnaryGrpcServiceTest {
             } catch (InvalidProtocolBufferException e) {
                 throw new UncheckedIOException(e);
             }
+            ctx.setAdditionalResponseTrailer("mytest", "value");
             if (request.hasResponseStatus()) {
                 // For statusExceptionUpstream() and statusExceptionDownstream()
                 assertThat(request).isEqualTo(EXCEPTION_REQUEST_MESSAGE);
@@ -125,15 +129,23 @@ class AbstractUnaryGrpcServiceTest {
     @ParameterizedTest
     @ArgumentsSource(UnaryGrpcSerializationFormatArgumentsProvider.class)
     void normalDownstream(SerializationFormat serializationFormat) throws Exception {
+        final AtomicReference<Metadata> headersCapture = new AtomicReference<>();
+        final AtomicReference<Metadata> trailersCapture = new AtomicReference<>();
         final TestServiceBlockingStub stub =
                 GrpcClients.newClient(server.httpUri(serializationFormat),
-                                      TestServiceBlockingStub.class);
+                                      TestServiceBlockingStub.class).withInterceptors(
+                        MetadataUtils.newCaptureMetadataInterceptor(headersCapture, trailersCapture));
         final SimpleResponse response = stub.unaryCall(REQUEST_MESSAGE);
         assertThat(response).isEqualTo(RESPONSE_MESSAGE);
         final ServiceRequestContextCaptor captor = server.requestContextCaptor();
         final HttpHeaders trailers = GrpcWebTrailers.get(captor.take());
         assertThat(trailers).isNotNull();
         assertThat(trailers.getInt(GrpcHeaderNames.GRPC_STATUS)).isZero();
+        if (serializationFormat.toString().equals("gproto")) {
+            assertThat(trailersCapture.get().get(Metadata.Key.of("mytest",
+                                                                 Metadata.ASCII_STRING_MARSHALLER))).isEqualTo(
+                    "value");
+        }
     }

     @Test
@@ -153,9 +165,12 @@ class AbstractUnaryGrpcServiceTest {
     @ParameterizedTest
     @ArgumentsSource(UnaryGrpcSerializationFormatArgumentsProvider.class)
     void statusExceptionDownstream(SerializationFormat serializationFormat) throws Exception {
+        final AtomicReference<Metadata> headersCapture = new AtomicReference<>();
+        final AtomicReference<Metadata> trailersCapture = new AtomicReference<>();
         final TestServiceBlockingStub stub =
                 GrpcClients.newClient(server.httpUri(serializationFormat),
-                                      TestServiceBlockingStub.class);
+                                      TestServiceBlockingStub.class).withInterceptors(
+                        MetadataUtils.newCaptureMetadataInterceptor(headersCapture, trailersCapture));
         assertThatThrownBy(() -> stub.unaryCall(EXCEPTION_REQUEST_MESSAGE))
                 .isInstanceOfSatisfying(StatusRuntimeException.class, cause -> {
                     final Status status = cause.getStatus();
@@ -167,6 +182,10 @@ class AbstractUnaryGrpcServiceTest {
         final HttpHeaders trailers = GrpcWebTrailers.get(captor.take());
         assertThat(trailers).isNotNull();
         assertThat(trailers.getInt(GrpcHeaderNames.GRPC_STATUS)).isEqualTo(StatusCodes.PERMISSION_DENIED);
+        if ("gproto".equals(serializationFormat.toString())) {
+            assertThat(trailersCapture.get().get(
+                    Metadata.Key.of("mytest", Metadata.ASCII_STRING_MARSHALLER))).isEqualTo("value");
+        }
     }

     @Test

[trustin]

At second thought, I came to the conclusion that this is not what we really want because:

• It’s not efficient; and
• It doesn’t work for gRPC-Web.

Let me close this issue and open a new one with a better idea, given the original issue description is not correct anyway.

[trustin]

I see. According to gRPC specification:

Response-Headers & Trailers-Only are each delivered in a single HTTP2 HEADERS frame block. Most responses are expected to have both headers and trailers but Trailers-Only is permitted for calls that produce an immediate error. Status must be sent in Trailers even if the status code is OK.

What if we put grpc-status and grpc-message in HTTP/2 trailers, then?