使用http.request 发请求时遇到奇怪的问题：创建一个server，一秒后(确保server启动完成)向该server发1000个请求，按理说1000个请求也就才占用我电脑上1000个端口，不应该是什么大问题。但执行到900个请求左右之后，http.request还是报了ECONNREFUSED错误

const http = require('http');

// create server
http.createServer(function(req, res){
    res.end('ok')
}).listen(9900)

// issue 1000 requests after 1 second
setTimeout( async function(){
    for(let i=0;i<1000;i++) { // werid: it works well after changing 1000 to 800
        request();
    }
}, 1000 )

// actually I don't care if the Promise is resolved or rejected,
// so I don't await or chain then.
function request() {
    return new Promise((resolve, reject) => {
        const option = {
            protocol: 'http:',
            host: 'localhost',
            port: 9900,
            path: '/',
            agent: false,
            method: 'GET'
        };
        const req = http.request(option, function(res) {
            res.setEncoding('utf8');
            let body = '';
            res.on('data', (chunk) => {
                body += chunk;
            });
            res.on('end', () => {
                console.log(body)
                resolve(body)
            });
        });
        req.on('error', (e) => {
            console.error(`problem with request: ${e.message}`);
            console.log(e.stack)
            process.exit(1)
        });
        req.end();
    })
}

错误如下。但是我把for循环的次数改为800就没问题，所有请求都能执行成功。1000就不行。。。 凌乱了，多谢指教

problem with request: connect ECONNREFUSED 127.0.0.1:9900
Error: connect ECONNREFUSED 127.0.0.1:9900
    at Object._errnoException (util.js:1024:11)
    at _exceptionWithHostPort (util.js:1046:20)
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1182:14)