var timeTask = null;
/**
 * 每4分钟向服务器发送心跳包
 */
function scheduleTask(){
    console.log("开始发送心跳包")
    client.write(getHeatBeatMsg());
}

client.on('data', function(data) {
    const buf = Buffer.from(data,'utf-8')
    const msgType = buf[3]
    const msgLenBuf = Buffer.from([buf[4],buf[5],buf[6],buf[7]])
    const msgLength = msgLenBuf.readInt32BE(0)
    const msgBuf = Buffer.alloc(msgLength)
    buf. copy(msgBuf,0,8,msgLength + 8);
    switch (msgType){
      case 3:
        console.log("接收到服务端发送的同步开始返回包，客户端开始定时发送心跳包")
        timeTask = setInterval(scheduleTask, 1000*60*4)
        break;
      default:
        break;
    }
  });

  client.on('close', function() {
    console.log('连接关闭');
    if(timeTask != null){
      clearInterval(timeTask)
    }
    client = net.createConnection(port, host, onConnect);
    client.on('error',onError);
  });

/**
 * 生成心跳包
 */
function getHeatBeatMsg() {
  const bufHead = Buffer.from([0,0,1,0]);
  const bufMsg = Buffer.alloc(0)
  const buflength = Buffer.alloc(4,0)
  buflength.writeIntBE(bufMsg.length, 0, 4);
  const totalLength = bufHead.length + buflength.length + bufMsg.length;
  return Buffer.concat([bufHead,buflength,bufMsg],totalLength);
}