@Override
    public boolean isOpen() {
        for (StreamMessage<? extends T> source : sources) {
            if (source.isOpen()) {
                return true;
            }
        }
        return false;
    }
Relay items in order from subsequent {@link StreamMessage}s as a single {@link StreamMessage} source.
core/src/main/java/com/linecorp/armeria/common/stream/ConcatArrayStreamMessage.java