private Action1<O> onNextStarted(Link onNextLinkIn) {
            return o -> {
                try (TaskCloseable ignored = PerfMark.traceTask(filter, f -> f.filterName() + ".onNext")) {
                    PerfMark.linkIn(onNextLinkIn);
                    onNextLinkOut.compareAndSet(null, PerfMark.linkOut());
                }
            };
        }
This is typically set by a filter when wanting to reject a request and also reduce load on the server by
 not processing anymore filterChain
zuul-core/src/main/java/com/netflix/zuul/netty/filter/BaseZuulFilterRunner.java