next.js server router no longer exposed in 10.0.8+

[lineape]

What version of Next.js are you using?

10.0.8, 10.0.9, 10.1.x

What version of Node.js are you using?

14

What browser are you using?

chrome

What operating system are you using?

macOS

How are you deploying your application?

AWS

Describe the Bug

In next.js 10.0.8+, the return value of calling the next custom server function (i.e. const app = next({})) no longer has a router field.

This router was exposed in previous versions and was not marked as internal or deprecated.

(Note the 'old' server with the router is still accessible via the .server field, but that is marked as a private field in the new NextServer class)

Expected Behavior

Accessing the router is possible

To Reproduce

install next 10.0.8, 10.0.9, or 10.1.x

  const next = require('next');
  const app = next({});

  app.router.pageChecker('/hello').then(console.log); // logs true or false in 10.0.7, but throws Uncaught TypeError: Cannot read property 'pageChecker' of undefined in new versions

[lineape]

The change happened in commit 1ebc9bb in packages/next/server/next.ts when the return type of createServer was changed from Server to the newly introduced NextServer class

Would it be possible to make the getServer method in NextServer public so that we can access the underlying Server instance (and the router)?

[timneutkens]

app.router has never been a public method for use in any application. Please make sure you only use methods that are documented in the documentation as backwards compat can't be guaranteed when your application is using Next.js internals.

I've opened a PR to update the automatically generated typing: #23573

[KODerFunk]

@timneutkens No information in docs about checking routes in custom servers.
I use custom server for multilayer caching (api-cache + ssr-cache), and need to predict request type (page | resource) for pre-SSR handling, for make routine around user-agent and cookie/session (we progressive split large legacy Rails+custom_ssr+React monolith/hybrid).
It is very important. Many people fight with this and other features (https://stackoverflow.com/questions/59749983/how-to-check-if-a-page-exist-in-a-custom-server-using-next-js).

Now I have to make ugly crutches in the code and track the changes in the Next.js code 😞

[KODerFunk]

@timneutkens fyi, my crutches checkIsPagePath.ts:

import type { NextServer } from 'next/dist/server/next'
import type Server from 'next/dist/next-server/server/next-server'
import LRUCache from 'mnemonist/lru-cache'

const pageCheckingCacheSize = 1000
// Cache for `checkIsPagePath()` results with limit size (LRU) to avoid memory overflow attack.
// Cache-key is a "pathname", without query parameters.
const pageCheckingCache = new LRUCache<string, boolean>(pageCheckingCacheSize)

/**
 * Ugly crutches for detection of page request,
 * coherent with Next.js undocumented protected mechanics.
 * !!! Be careful when update Next.js !!!
 * @see https://github.com/vercel/next.js/issues/23558#issuecomment-820655560
 * @param app - Accessible next-server.
 * @param path - Request path.
 * @returns Promise with answer to question "Is this SSR page path?"
 */
export default async function checkIsSSRPath(app: NextServer, path: string): Promise<boolean> {
  // https://nodejs.org/api/url.html#url_url_strings_and_url_objects
  const searchPosition = path.indexOf('?')
  const pathname = searchPosition > -1 ? path.slice(0, searchPosition) : path
  let result = pageCheckingCache.get(pathname)

  if (result === undefined) {
    result =
      // Fast cutoff static and SSP (SSP detected separately outside).
      !pathname.startsWith('/_next/')
      // @ts-expect-error Need access to protected router.
      && ((app.server as Server).router.dynamicRoutes.some(({ match }) => match(pathname))
        // @ts-expect-error Need access to protected router.
        || await (app.server as Server).router.pageChecker(pathname))

    pageCheckingCache.set(pathname, result)
  }

  return result
}

[balazsorban44]

This issue has been automatically locked due to no recent activity. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.