code: public Single<ByteBuf> getSeqnos() {
      return Single.create(new Single.OnSubscribe<ByteBuf>() {
        @Override
        public void call(final SingleSubscriber<? super ByteBuf> subscriber) {
          if (state() != LifecycleState.CONNECTED) {
            subscriber.onError(new NotConnectedException());
            return;
          }
  
          ByteBuf buffer = Unpooled.buffer();
          DcpGetPartitionSeqnosRequest.init(buffer);
          DcpGetPartitionSeqnosRequest.vbucketState(buffer, VbucketState.ACTIVE);
  
          sendRequest(buffer).addListener(new DcpResponseListener() {
            @Override
            public void operationComplete(Future<DcpResponse> future) throws Exception {
              if (future.isSuccess()) {
                ByteBuf buf = future.getNow().buffer();
                try {
                  subscriber.onSuccess(MessageUtil.getContent(buf).copy());
                } finally {
                  buf.release();
                }
              } else {
                subscriber.onError(future.cause());
              }
            }
          });
        }
      });
    }
docs: Returns all seqnos for all vbuckets on that channel.