Firebase Next.js webframeworks rewrites to external destinations do not work

[eugeneford]

[REQUIRED] Environment info

The one from: https://github.com/FirebaseExtended/action-hosting-deploy/tree/v0/ as I'm deploying with Github Actions. I guess it's the latest.

Platform: Linux

[REQUIRED] Test case

1. See the following public repo: https://github.com/gusarov-studio/langfast/tree/boilerplate
2. I've followed all of the steps from the official guideline: https://firebase.google.com/docs/hosting/frameworks/nextjs
3. I've configured a simple rewrite rule to external destination in next.config.ts
4. All requests to any external destination rewrites fail with 504 Gateway Timeout

[REQUIRED] Steps to reproduce

I've depoyed the app temporarily for you:

1. Simply go to: https://langfast--pr1-boilerplate-akkcei85.web.app/studio or https://langfast--pr1-boilerplate-akkcei85.web.app/replay-xF5c/script.js

[REQUIRED] Expected behavior

The target external destinations are successfully proxied through the Cloud Function that Firebase creates automatically.

[REQUIRED] Actual behavior

504 Gateway Timeout error

[eugeneford]

I have also found a related thread here: https://groups.google.com/g/firebase-talk/c/OWhlFepGxjM . But no one provided the response there either.

[eugeneford]

Checking the implementation in firebase-tools:

firebase-tools/src/frameworks/next/utils.ts

Lines 140 to 161 in ecbbc91

	/**
	* Get which Next.js rewrites will be used before checking supported items individually.
	*
	* Next.js rewrites can be arrays or objects:
	* - For arrays, all supported items can be used.
	* - For objects only `beforeFiles` can be used.
	*
	* See: https://nextjs.org/docs/api-reference/next.config.js/rewrites
	*/
	export function getNextjsRewritesToUse(
	nextJsRewrites: RoutesManifest["rewrites"],
	): RoutesManifestRewrite[] {
	if (Array.isArray(nextJsRewrites)) {
	return nextJsRewrites.map(cleanI18n);
	}
	if (nextJsRewrites?.beforeFiles) {
	return nextJsRewrites.beforeFiles.map(cleanI18n);
	}
	return [];
	}

Looks like that fallback and afterFiles rewrite rules are completely ignored.

I've updated my implementation to use array instead:

https://github.com/gusarov-studio/langfast/blob/5ba1edfc6018b25bb60b345665460d0985205906/hosting/next.config.ts#L8-L40

It does not seem to resolve the issue

UPD: this appears to be unrelated