In our current implementation, HTTP/2 Stream and HTTP/1.1 Response use a BlockingPushPublisher to publish received ByteBuffers to the Flow.Subscriber. When the demand made through Subscription.request reaches 0, the BlockingPushPublisher will block before calling onNext() if its acceptData(ByteBuffer) method is called.

A better implementation might be to somehow relay the state of the subscriber's demand upstream (to the selector's loop for HTTP/1.1, and to the HTTP/2 server's through WINDOW_UPDATE frames) so that acceptData is never called if the demand reaches 0.