@Override
        public final void onSubscribe(Subscription s) {
            if (Operators.validate(subscription, s)) {
                subscription = s;
                writeCompletionBarrier.connect();
                s.request(1);
            }
        }
The actual writeSubscriber from the HTTP server adapter.
spring/boot3-webflux-autoconfigure/src/main/java/com/linecorp/armeria/spring/web/reactive/ChannelSendOperator.java