使用node实现静态文件服务器，仿nginx 静态服务器

原理：使用node http 模块 createServer 方法创建服务， fs 模块读取文件内容，net 模块判断处理端口被占情况。

let http = require("http")
let url = require("url")
let fs = require("fs")
let net = require('net')

// 默认端口，并检测端口是否被占用
let port = 8100
portIsOccupied(port).then(() => {
  createServerFn();
})

function createServerFn() {
  http.createServer(function (req, res) {
    let reqPath = url.parse(req.url).path
    let filepath = __dirname + reqPath
    fs.exists(filepath, function (exists) {
      if (exists) {
        fs.stat(filepath, function (err, stats) {
          if (err) {
            res.end('<h1>server error</h1><p>' + err + '</p>')
          } else {
            if (stats.isFile()) {
              let file = fs.createReadStream(filepath)
              console.log(filepath.replace(/\\/g, '/'))
              file.pipe(res)
            } else {
              fs.readdir(filepath, function (err, files) {
                if (files.includes('index.html')) {
                  filepath = filepath + '/index.html'
                  let file = fs.createReadStream(filepath)
                  console.log(filepath.replace(/\\/g, '/'))
                  file.pipe(res)
                } else {
                  res.end('<h1>404 no such file or directory</h1><p>no such file or directory</p><p>' + filepath + '/index.html</p>')
                }
              })
            }
          }
        })
      } else {
        res.end('<h1>404 no such file or directory</h1><p>no such file or directory</p><p>' + filepath + '</p>')
      }
    })
  }).listen(port)
  console.log('http.createServer is start, port ' + port)
}
// 检测端口是否被占用
function portIsOccupied() {
  const server = net.createServer().listen(port)
  return new Promise((resolve, reject) => {
    server.on('listening', () => {
      server.close()
      resolve()
    })
    server.on('error', (err) => {
      if (err.code === 'EADDRINUSE') {
        port++
        resolve(portIsOccupied())
      } else {
        reject(err)
      }
    })
  })
}