nodejs同步调用获取mysql数据时遇到的大坑

var _getUser = function(name) {
  var sql = "SELECT * FROM " + TABLE + " WHERE user_loginname='" + name + "'";
  connection.query(sql, function(err, results) {
    if(!err) {
      var res = hasUser(results);
      return res;
    }else {
      return error();
    }
  });
  function hasUser(results) {
    if(results.length == 0) {
      return {err: 1, msg: "此用户名不存在"};
    }
    else {
      return results[0];
    }
  }
  function error() {
    return {err: 1, msg: "数据库出错"};
  }
}
var getUser = function(name){
  return _getUser(name);
}

//获取post上来的 data数据中 uname的值
var uname = req.body.uname; 
var User = getUser(uname);
if(User.err){
   res.status(404)
 } else {
  var upwd = md5 (req.body.upwd);
  //查询到匹配用户名的信息，但相应的password属性不匹配
  if(upwd != User.user_passwd){  
     req.session.error = "密码错误";
     res.send(404);
     // res.redirect("/login");
   }else{ 
     //信息匹配成功，则将此对象（匹配到的user) 赋给session.user 并返回成功                  
     req.session.user = {name: uname, password: upwd};
     res.status(200).send("success")
     // res.send(200);
     // res.redirect("/home");
   }
 }
// md5方式加密
function md5 (text) {
  return crypto.createHash('md5').update(text).digest('hex');
};

var _getUser = function(name, callback) {
  var sql = "SELECT * FROM " + TABLE + " WHERE user_loginname='" + name + "'";
  connection.query(sql, function(err, results) {
    if(!err) {
      var res = hasUser(results)
      callback(res);
    }else {
      callback(error());
    }
  });
  function hasUser(results) {
    if(results.length == 0) {
      return {err: 1, msg: "此用户名不存在"};
    }
    else {
      return results[0];
    }
  }
  function error() {
    return {err: 1, msg: "数据库出错"};
  }
}
var getUser = function(name, callback){
  return _getUser(name, callback);
}

//获取post上来的 data数据中 uname的值
var uname = req.body.uname; 
getUser(uname, function(data){
  var User = data;
  if(User.err){
    res.status(404)
  } else {
    var upwd = md5 (req.body.upwd);
    //查询到匹配用户名的信息，但相应的password属性不匹配
    if(upwd != User.user_passwd){  
      req.session.error = "密码错误";
      res.send(404);
      // res.redirect("/login");
    }else{ 
      //信息匹配成功，则将此对象（匹配到的user) 赋给session.user 并返回成功                  
      req.session.user = {name: uname, password: upwd};
      res.status(200).send("success")
      // res.send(200);
      // res.redirect("/home");
    }
  }
});
// md5方式加密
function md5 (text) {
  return crypto.createHash('md5').update(text).digest('hex');
};