node.js模拟发送post请求

node.js模拟发送post请求一直返回400错误
求解

var http = require('http');
var querystring = require('querystring');
var contents = querystring.stringify({//序列化一个对象
    phone: '18764285761',
    sn: '123456',
    mac:'test'
});
var option = {
    method: 'post',
    host: 'edu.ishenka.com',
    prot: '80',
    path: '/frontend/web/index.php?r=/test/index',
    headers: {// 必选信息
        "Content-Type":"application/x-www-form-urlencoded; charset=UTF-8",
        "Content-Length":contents.length, // 请求长度, 通过上面计算得到
    }
};
var Dispose = function(response){
    var body='';
    response.on('data',function(data){
        body += data;
    });
    response.on('end',function(){
        console.log(body);
    });
};
var req = http.request(option,Dispose);
req.write(contents);//发送内容
req.end();