probot/lib/server.js

const http = require('http');

module.exports = function (webhook) {
  return http.createServer((req, res) => {
    webhook(req, res, err => {
      if (err) {
        console.error(err);
        res.statusCode = 500;
        res.end('Something has gone terribly wrong.');
      } else if (req.url.split('?').shift() === '/ping') {
        res.end('PONG');
      } else {
        res.statusCode = 404;
        res.end('no such location');
      }
    });
  });
};