server.js

/**
 * NetLearner 开发服务器
 *
 * 职责：
 *   1. 提供静态文件服务
 *   2. 强制所有响应禁用浏览器缓存
 *   3. 零外部依赖，仅用 Node.js 内建模块
 *
 * 启动方式（唯一）：
 *   node server.js
 */

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

const PORT = 8080;
const ROOT = __dirname;

const MIME_TYPES = {
  '.html': 'text/html; charset=utf-8',
  '.css':  'text/css; charset=utf-8',
  '.js':   'application/javascript; charset=utf-8',
  '.json': 'application/json; charset=utf-8',
  '.svg':  'image/svg+xml',
  '.png':  'image/png',
  '.ico':  'image/x-icon',
};

function serveFile(res, filePath) {
  const ext = path.extname(filePath).toLowerCase();
  const contentType = MIME_TYPES[ext] || 'application/octet-stream';

  try {
    const content = fs.readFileSync(filePath);
    res.writeHead(200, {
      'Content-Type': contentType,
      'Cache-Control': 'no-store, no-cache, must-revalidate, proxy-revalidate',
      'Pragma': 'no-cache',
      'Expires': '0',
      'Surrogate-Control': 'no-store',
    });
    res.end(content);
  } catch (err) {
    if (err.code === 'ENOENT') {
      res.writeHead(404, { 'Content-Type': 'text/plain; charset=utf-8' });
      res.end('404 Not Found');
    } else {
      res.writeHead(500, { 'Content-Type': 'text/plain; charset=utf-8' });
      res.end('500 Internal Server Error');
    }
  }
}

const server = http.createServer((req, res) => {
  const urlPath = req.url.split('?')[0].split('#')[0];
  let filePath = path.join(ROOT, urlPath === '/' ? 'index.html' : urlPath);

  // Security: prevent directory traversal
  if (!filePath.startsWith(ROOT)) {
    res.writeHead(403);
    res.end('Forbidden');
    return;
  }

  try {
    if (fs.existsSync(filePath) && fs.statSync(filePath).isDirectory()) {
      filePath = path.join(filePath, 'index.html');
    }
  } catch (_) {
    serveFile(res, filePath);
    return;
  }

  serveFile(res, filePath);
});

server.listen(PORT, () => {
  console.log(`NetLearner → http://localhost:${PORT}`);
  console.log('Cache: DISABLED (all browsers)');
});