docs: public ZMsg configure(ZMsg msg)
      {
          msg.addFirst(CONFIG);
  
          if (agent.send(msg)) {
              // consume the status in the pipe
              recvStatus();
  
              ZMsg reply = agent.recv();
              assert (reply != null);
  
              // refill the pipe with status
              agent.send(STATUS);
              return reply;
          }
          return null;
      }