我状态成功 connection":"close", 这是什么原因

Question

var http = require('http');var querystring = require('querystring');var postData = querystring.stringify({    'content': '我的测试  啦啦啦啦',    'mid': 8837})var options = {    hostname: 'www.imooc.com',    prot: 80,    path: '/course/docomment',    method: 'POST',    headers: {        'Accept': ' application / json, text / javascript, */*; q=0.01',        'Accept-Encoding': 'gzip, deflate',        'Accept-Language': 'zh-CN,zh;q=0.9',        'Content-Length': postData.length,        'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',        'Cookie': 'PHPSESSID=jm50e92te6ou8oactqrmu19h66; imooc_uuid=f150235b-37b6-44de-b942-f058be4d748f; imooc_isnew_ct=1509677550; loginstate=1; apsid=MyZDQyYzU4YjBjZWJhYTgyZDk5ZmNmMjhmY2Y0NjcAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAANDE3NTQ3MQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA5MzExNjgzNDhAcXEuY29tAAAAAAAAAAAAAAAAAAAAAGViZTA0NWJjOTkyNmQxNDliY2M4MTFhOWZmZDE0NTc5zOX7Wczl%2B1k%3DZj; last_login_username=931168348%40qq.com; IMCDNS=0; Hm_lvt_f0cfcccd7b1393990c78efdeebff3968=1510104277,1510104318,1510126222,1510192159; Hm_lpvt_f0cfcccd7b1393990c78efdeebff3968=1510193700; imooc_isnew=2; cvde=59fbd9ee4e6ca-380',        'Host': 'www.imooc.com',        'Origin': 'http://www.imooc.com',        'Proxy-Connection': 'keep-alive',        'Referer': 'http://www.imooc.com/video/8837',        'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.75 Safari/537.36',        'X-Requested-With': 'XMLHttpRequest'    }}var req = http.request(options, function (res) {    console.log('status: ' + res.statusCode);    console.log('headers: ' + JSON.stringify(res.headers));    res.on('data', function (chunk) {        console.log(Buffer.isBuffer(chunk));        console.log(typeof chunk)    })    res.on('end', function () {        console.log('评论完毕')    })})req.on('error', function (e) {    console.log('Error ' + e.message)})req.write(postData);req.end()status: 200headers: {"server":"nginx","date":"Thu, 09 Nov 2017 02:57:37 GMT","content-type":"text/html; charset=utf-8","transfer-encoding":"chunked","connection":"close","vary":"Accept-Encoding","expires":"Thu, 19 Nov 1981 08:52:00 GMT","cache-control":"no-store, no-cache, must-revalidate, post-check=0, pre-check=0","pragma":"no-cache","content-encoding":"gzip"}trueobject评论完毕