Add static frontend server for production

frontend/server.js

@@ -0,0 +1,75 @@
+import http from 'node:http';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+const distDir = path.join(__dirname, 'dist');
+const port = Number(process.env.PORT || 3000);
+const host = process.env.HOST || '127.0.0.1';
+
+const mimeTypes = {
+  '.html': 'text/html; charset=utf-8',
+  '.js': 'application/javascript; charset=utf-8',
+  '.mjs': 'application/javascript; charset=utf-8',
+  '.css': 'text/css; charset=utf-8',
+  '.svg': 'image/svg+xml',
+  '.json': 'application/json; charset=utf-8',
+  '.png': 'image/png',
+  '.jpg': 'image/jpeg',
+  '.jpeg': 'image/jpeg',
+  '.webp': 'image/webp',
+  '.ico': 'image/x-icon',
+  '.woff': 'font/woff',
+  '.woff2': 'font/woff2',
+  '.pdf': 'application/pdf',
+};
+
+const sendFile = (res, filePath) => {
+  fs.readFile(filePath, (error, content) => {
+    if (error) {
+      res.writeHead(404, { 'Content-Type': 'text/plain; charset=utf-8' });
+      res.end('Not found');
+      return;
+    }
+
+    const ext = path.extname(filePath).toLowerCase();
+    res.writeHead(200, {
+      'Content-Type': mimeTypes[ext] || 'application/octet-stream',
+      'Cache-Control': ext === '.html' ? 'no-cache' : 'public, max-age=31536000, immutable',
+    });
+    res.end(content);
+  });
+};
+
+const server = http.createServer((req, res) => {
+  const urlPath = decodeURIComponent((req.url || '/').split('?')[0]);
+  const safePath = path.normalize(urlPath).replace(/^(\.\.[/\\])+/, '');
+  let filePath = path.join(distDir, safePath === '/' ? 'index.html' : safePath);
+
+  if (!filePath.startsWith(distDir)) {
+    res.writeHead(403, { 'Content-Type': 'text/plain; charset=utf-8' });
+    res.end('Forbidden');
+    return;
+  }
+
+  fs.stat(filePath, (err, stats) => {
+    if (!err && stats.isDirectory()) {
+      filePath = path.join(filePath, 'index.html');
+    }
+
+    fs.access(filePath, fs.constants.F_OK, (accessError) => {
+      if (accessError) {
+        sendFile(res, path.join(distDir, 'index.html'));
+        return;
+      }
+      sendFile(res, filePath);
+    });
+  });
+});
+
+server.listen(port, host, () => {
+  console.log(`LinkedSign frontend running on http://${host}:${port}`);
+});