@Override
            public void onComplete() {
                if (!res.isDone()) {
                    // If 'ResponseObserver.onCompleted()' is called without calling 'onNext()',
                    // this callback would be invoked but 'messageRead' callback wouldn't.
                    res.complete(HttpResponse.of(unframedHeaders.build()));
                }
            }
Creates a new instance that decorates the specified {@link HttpService}.
grpc/src/main/java/com/linecorp/armeria/server/grpc/AbstractUnframedGrpcService.java