webframeworks experiment 404 handling incorrect

[MidnightLightning]

When running a NextJS app using "App Routing" in a Firebase emulator, it doesn't handle 404 page generation properly. The default NextJS 404 page generates a "This page could not be found" error styled in the middle of the page. When running in Firebase Emulator suite, the 404 page generates as . This makes it impossible to test custom 404 page appearances for a NextJS application within the Firebase emulator.

[REQUIRED] Environment info

firebase-tools: 13.24.2

Platform: Docker running inside macOS

[REQUIRED] Test case

https://gitlab.com/MidnightLightning/firebase-404-test

[REQUIRED] Steps to reproduce

Run docker compose up, then visit http://localhost:25602/foobarbaz.

[REQUIRED] Expected behavior

To see the NextJS custom 404 page (text "This page could not be found" in the center of screen)

[REQUIRED] Actual behavior

A plain textual response of "Cannot GET /pathname"

[aalej]

Thanks for the detailed report, @MidnightLightning! I was able to reproduce the behavior you mentioned. From what I can gather, the issue only occurs on the emulator. When deploying the app to Firebase Hosting, accessing "https://<SITE_ID>.web.app/foobarbaz" shows the Next.js 404 page.

I'll raise this to our engineering team and mark this as reproducible.

[MidnightLightning]

Agreed @aalej, this is a bug with the Emulator Suite, not with Firebase overall. A production deploy of a NextJS app using the webframeworks experiment handles 404 pages appropriately; I've only seen this issue in how the Emulator Suite mocks that functionality for local development.