@Override
    public final void subscribe(Subscriber<? super U> subscriber, EventExecutor executor,
                                SubscriptionOption... options) {
        requireNonNull(subscriber, "subscriber");
        requireNonNull(executor, "executor");
        requireNonNull(options, "options");
        final boolean withPooledObjects = containsWithPooledObjects(options);
        final boolean notifyCancellation = containsNotifyCancellation(options);
        subscribe(subscriber, executor, withPooledObjects, notifyCancellation);
    }
A callback executed when this {@link StreamMessage} is canceled by the {@link Subscriber}.
core/src/main/java/com/linecorp/armeria/common/stream/FilteredStreamMessage.java