Function compileUserCode

packages/node/src/bundling-handler.js:160–239

* Compile a user module and return a (req, res) handler regardless of * export shape. Mirrors the detection logic in serverless-handler.mts.

(filePath)

 * export shape. Mirrors the detection logic in serverless-handler.mts.
 */
async function compileUserCode(filePath) {
  let server = null;
  let serverFound;

  // Monkey-patch http.Server.prototype.listen to capture server instances
  // created during module import (e.g. Express apps calling app.listen()).
  const originalListen = http.Server.prototype.listen;
  http.Server.prototype.listen = function () {
    server = this;
    http.Server.prototype.listen = originalListen;
    if (serverFound) serverFound();
    return this;
  };

  try {
    let listener = await loadModule(filePath);
    listener = unwrapDefaults(listener);

    // 1. Web handlers (GET, POST, fetch, etc.)
    const isWebHandler =
      HTTP_METHODS.some(m => typeof listener[m] === 'function') ||
      typeof listener.fetch === 'function';

    if (isWebHandler) {
      return createWebHandler(listener);
    }

    // 2. Function handler: (req, res) => { ... }
    if (typeof listener === 'function') {
      return listener;
    }

    // 3. Server handler: http.createServer(...).listen()
    //    Wait briefly for async server creation if not captured yet.
    if (!server) {
      await new Promise(r => {
        serverFound = r;
        setTimeout(r, 1000);
      });
    }

    if (server) {
      // Start the captured server on a random port and proxy requests to it.
      await new Promise(r => server.listen(0, '127.0.0.1', r));
      const { port } = server.address();

      return (req, res) => {
        const proxyReq = http.request(
          {
            hostname: '127.0.0.1',
            port,
            path: req.url,
            method: req.method,
            headers: {
              ...req.headers,
              host: req.headers['x-forwarded-host'] || req.headers.host,
            },
          },