@Override
        public void onSubscribe(Subscription s) {
            assert subscription == null;
            subscription = s;
            writer.whenComplete().handle((unused, cause) -> {
                if (cause != null) {
                    s.cancel();
                }
                return null;
            });

            s.request(1);
        }
A {@link Subscriber} implementation which writes a streaming response with the contents converted from
the objects published from a publisher.
core/src/main/java/com/linecorp/armeria/internal/server/ResponseConversionUtil.java