@Override
    public void emptyCall(EmptyProtos.Empty empty,
                          StreamObserver<Empty> responseObserver) {
        ServiceRequestContext.current().mutateAdditionalResponseTrailers(
                mutator -> mutator.add(
                        STRING_VALUE_KEY.name(),
                        Base64.getEncoder().encodeToString(
                                StringValue.newBuilder().setValue("hello").build().toByteArray()) +
                        ',' +
                        Base64.getEncoder().encodeToString(
                                StringValue.newBuilder().setValue("world").build().toByteArray())));

        responseObserver.onNext(Empty.getDefaultInstance());
        responseObserver.onCompleted();
    }
Constructs a controller using the given executor for scheduling response stream chunks.
grpc/src/test/java/com/linecorp/armeria/internal/common/grpc/TestServiceImpl.java