HarmonyOS 通过TCPSocket进行连接时，如何准确的判断是否与服务器已断开连接？

import socket from "@ohos.net.socket"; 
import { BusinessError } from '@ohos.base'; 
let tcp: socket.TCPSocket = socket.constructTCPSocketInstance(); 
tcp.on('error', (err: BusinessError) => { 
  console.log("on error, err:" + JSON.stringify(err)) 
});