code: public void addServerReadyConsumer(Consumer<Server> consumer) {
          synchronized (readyConsumers) {
              if (ready) {
                  consumer.accept(this);
              } else {
                  readyConsumers.add(consumer);
              }
          }
      }
docs: Adds a consumer which will be informed once the server is ready.
  If the server is already ready, it will immediately call the consumer, otherwise it will be called from the
  websocket reading thread.
  
  @param consumer The consumer which should be called.