mysql connection error :Error: Connection lost: The server closed the connection.
{ Error: Connection lost: The server closed the connection.
    at Protocol.end (/home/yeju/server/roomatching/node_modules/mysql/lib/protocol/Protocol.js:112:13)
    at Socket.<anonymous> (/home/yeju/server/roomatching/node_modules/mysql/lib/Connection.js:97:28)
    at Socket.<anonymous> (/home/yeju/server/roomatching/node_modules/mysql/lib/Connection.js:502:10)
    at emitNone (events.js:91:20)
    at Socket.emit (events.js:188:7)
    at endReadableNT (_stream_readable.js:975:12)
    at _combinedTickCallback (internal/process/next_tick.js:80:11)
    at process._tickCallback (internal/process/next_tick.js:104:9)
    --------------------
    at Protocol._enqueue (/home/yeju/server/roomatching/node_modules/mysql/lib/protocol/Protocol.js:144:48)
    at Protocol.handshake (/home/yeju/server/roomatching/node_modules/mysql/lib/protocol/Protocol.js:51:23)
    at Connection.connect (/home/yeju/server/roomatching/node_modules/mysql/lib/Connection.js:118:18)
    at Object.test_open (/home/yeju/server/roomatching/db/db_con.js:17:11)
    at Object.<anonymous> (/home/yeju/server/roomatching/database.js:3:11)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3) fatal: true, code: 'PROTOCOL_CONNECTION_LOST' }

function handleDisconnect() {
  connection = mysql.createConnection(db_config); // Recreate the connection, since
                                                  // the old one cannot be reused.

  connection.connect(function(err) {              // The server is either down
    if(err) {                                     // or restarting (takes a while sometimes).
      console.log('error when connecting to db:', err);
      setTimeout(handleDisconnect, 2000); // We introduce a delay before attempting to reconnect,
    }                                     // to avoid a hot loop, and to allow our node script to
  });                                     // process asynchronous requests in the meantime.
                                          // If you're also serving http, display a 503 error.
  connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
      handleDisconnect();                         // lost due to either server restart, or a
    } else {                                      // connnection idle timeout (the wait_timeout
      throw err;                                  // server variable configures this)
    }
  });
}

module.exports = (function () {
  return {
    local: { // localhost
      host: 'localhost',
      port: '4000',
      user: 'root',
      password: 'password',
      database: 'database'
    },
    real: { // real server db info
      host: '',
      port: '',
      user: '',
      password: '!',
      database: ''
    },
    dev: { // dev server db info
      host: '',
      port: '',
      user: '',
      password: '',
      database: ''
    }
  }
})();

var mysql = require('mysql');
var config = require('../db/db_info').local;

module.exports = function () {
  return {
    init: function () {
      return mysql.createConnection({
        host: config.host,
        port: config.port,
        user: config.user,
        password: config.password,
        database: config.database
      })
    },

    test_open: function (con) {
      con.connect(function (err) {
        console.log('hi');
        if (err) {
          console.error('mysql connection error :' + err);
        } else {
          console.info('mysql is connected successfully.');
        }
      })
    }
  }
};

var mysql_dbc = require('./db/db_con')();
var connection = mysql_dbc.init();
mysql_dbc.test_open(connection);

var express = require('express');
var router = express.Router();
var db = require('../database');