code: function getPostData(req, res, next) {
      req.body = req.body || {};
  
      const urlWithoutSubdirectoryWithoutAmp = res.locals.relativeUrl.match(/(.*?\/)amp\/?$/)[1];
  
      /**
       * @NOTE
       *
       * We have to figure out the target permalink, otherwise it would be possible to serve a post
       * which lives in two collections.
       *
       * @TODO:
       *
       * This is not optimal and caused by the fact how apps currently work. But apps weren't designed
       * for dynamic routing.
       *
       * I think if the responsible, target router would first take care fetching/determining the post, the
       * request could then be forwarded to this app. Then we don't have to:
       *
       * 1. care about fetching the post
       * 2. care about if the post can be served
       * 3. then this app would act like an extension
       *
       * The challenge is to design different types of apps e.g. extensions of routers, standalone pages etc.
       */
      const permalinks = urlService.getPermalinkByUrl(urlWithoutSubdirectoryWithoutAmp, {withUrlOptions: true});
  
      if (!permalinks) {
          return next(new common.errors.NotFoundError({
              message: common.i18n.t('errors.errors.pageNotFound')
          }));
      }
  
      // @NOTE: amp is not supported for static pages
      // @TODO: https://github.com/TryGhost/Ghost/issues/10548
      helpers.entryLookup(urlWithoutSubdirectoryWithoutAmp, {permalinks, query: {controller: 'postsPublic', resource: 'posts'}}, res.locals)
          .then((result) => {
              if (result && result.entry) {
                  req.body.post = result.entry;
              }
  
              next();
          })
          .catch(next);
  }
docs: This here is a controller. In fact, this whole file is nothing more than a controller + renderer & doesn't need to be a router