server.js

'use strict';

const fs = require('node:fs');
const http = require('node:http');
const path = require('node:path');

const PORT = 8000;

const MIME_TYPES = {
  default: 'application/octet-stream',
  html: 'text/html; charset=UTF-8',
  js: 'application/javascript; charset=UTF-8',
  json: 'application/json',
  css: 'text/css',
  png: 'image/png',
  jpg: 'image/jpg',
  gif: 'image/gif',
};

const folder = process.argv[2];
if (!folder) {
  console.log('Usage:   node server <folder>');
  console.log('Example: node server Pragmatic');
  process.exit(1);
}
const STATIC_PATH = path.join(process.cwd(), folder, 'static');

const toBool = [() => true, () => false];

const prepareFile = async (url) => {
  const paths = [STATIC_PATH, url];
  if (url.endsWith('/')) paths.push('index.html');
  const filePath = path.join(...paths);
  const pathTraversal = !filePath.startsWith(STATIC_PATH);
  const exists = await fs.promises.access(filePath).then(...toBool);
  const found = !pathTraversal && exists;
  const streamPath = found ? filePath : STATIC_PATH + '/404.html';
  const ext = path.extname(streamPath).substring(1).toLowerCase();
  const stream = fs.createReadStream(streamPath);
  return { found, ext, stream };
};

http
  .createServer(async (req, res) => {
    const file = await prepareFile(req.url);
    const statusCode = file.found ? 200 : 404;
    const mimeType = MIME_TYPES[file.ext] || MIME_TYPES.default;
    res.writeHead(statusCode, { 'Content-Type': mimeType });
    file.stream.pipe(res);
    console.log(`${req.method} ${req.url} ${statusCode}`);
  })
  .listen(PORT);

console.log(`Server running at http://127.0.0.1:${PORT}/`);