etherpad-lite/src/node/hooks/express/padurlsanitize.js

const padManager = require('../../db/PadManager');
const url = require('url');

exports.expressCreateServer = function (hook_name, args, cb) {
  // redirects browser to the pad's sanitized url if needed. otherwise, renders the html
  args.app.param('pad', async (req, res, next, padId) => {
    // ensure the padname is valid and the url doesn't end with a /
    if (!padManager.isValidPadId(padId) || /\/$/.test(req.url)) {
      res.status(404).send('Such a padname is forbidden');
      return;
    }

    const sanitizedPadId = await padManager.sanitizePadId(padId);

    if (sanitizedPadId === padId) {
      // the pad id was fine, so just render it
      next();
    } else {
      // the pad id was sanitized, so we redirect to the sanitized version
      let real_url = sanitizedPadId;
      real_url = encodeURIComponent(real_url);
      const query = url.parse(req.url).query;
      if (query) real_url += `?${query}`;
      res.header('Location', real_url);
      res.status(302).send(`You should be redirected to <a href="${real_url}">${real_url}</a>`);
    }
  });
  return cb();
};