code: protected void internalMessageHandler(DirectBuffer buffer, int offset, int length, Header header) {
          /**
           * All incoming internal messages are either op commands, or aggregation messages that are tied to commands
           */
          byte[] data = new byte[length];
          buffer.getBytes(offset, data);
  
          VoidMessage message = VoidMessage.fromBytes(data);
  
          messages.add(message);
  
          //    log.info("internalMessageHandler message request incoming: {}", message.getClass().getSimpleName());
      }
docs: This message handler is responsible for receiving coordination messages on Shard side
  
  @param buffer
  @param offset
  @param length
  @param header