code: void messageReceived(MessagePacket packet) {
          if (!getCluster().isMaster())
              return;
          LOG.debug("Received packet {}", packet);
  
          final long now = System.nanoTime();
          packet.setTimestamp(now);
  
          final short node = packet.getNode();
          final NodePeer peer = peers.get(node);
          if (peer == null)
              throw new RuntimeException("Message received from unhandled node " + node);
  
          try {
              peer.receivePacket(packet); // we're now running in the executor we installed in the netty pipeline.
          } catch (InterruptedException ex) {
              LOG.error("InterruptedException", ex);
              throw new RuntimeException(ex);
          }
      }
docs: visible for testing