nodejs post请求抛出TypeError

我想做一个简单的服务器，使用google oauth(没有express和passportjs，因为我想研究交换的数据)。

当我的程序试图向google发送post请求时，nodejs抛出:

http.js:593 throw new TypeError('first argument must be a string or Buffer');

我已经检查并确保查询和选项中的所有参数都是字符串，但错误仍然存在。我还能错过什么呢?

// Load the http module to create an http server.
var http = require('http');
var url = require('url');
var fs = require('fs');
var querystring = require('querystring');
var content;
fs.readFile('./test.html',function(err,data){
    content = data;
});
// Configure our HTTP server to respond with Hello World to all requests.
var server = http.createServer(function (request, response) {
  response.writeHead(200, {"Content-Type": "text/html"});
  var path = url.parse(request.url).pathname;
  var query = querystring.parse(url.parse(request.url).query);
  var code;
  if (query!=null) {
    code = query.code;
  };
  if ('/auth/google/callback'==path){
    var data = querystring.stringify({
        'code':          ''+code,
        'client_id':     'id',
        'client_secret': 'secret',
        'redirect_uri':  'http://localhost:8999/auth/google/code/callback',
        'grant_type':    'authorization_code'
    });
    var options = {
        hostname: 'accounts.google.com',
        port:'80',
        path: '/o/oauth2/token',
        method: 'POST',
        headers: {
          'Content-Type': 'application/x-www-form-urlencoded',
          'Content-Length': ''+data.length
      }
    };
    debugger;
    var post = http.request(options, function(res){
        response.write(res);
        response.end();
    });
    debugger;
    post.write(data);
    debugger;
    post.end();
  }
  else if (path=='/auth/google/code/callback'){
    console.log(request.headers);
    console.log(request.url);
  }
  else response.end(content);
  console.log(request.headers);
  console.log(request.url);
});
// Listen on port 8000, IP defaults to 127.0.0.1
server.listen(8999);
// Put a friendly message on the terminal
console.log("Server running at http://127.0.0.1:8000/");