Fix 'Pre-hydration redirect from server actions does not prepend base…

[greenlynx]

Fixes #85462

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: dd1ac32

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: b5c0bf9

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[vercel]

Suggested change

	appRelativeRedirectUrl?.toString() ?? redirectUrl
	appRelativeRedirectUrl
	? `${appRelativeRedirectUrl.pathname}${appRelativeRedirectUrl.search}${appRelativeRedirectUrl.hash}`
	: redirectUrl

The Location header is being set to the full URL string including a dummy protocol/host (e.g., http://n/path) instead of just the pathname and search/hash. This will cause redirects to fail or behave unexpectedly.

View Details

Analysis

Location header includes invalid dummy host instead of just pathname

What fails: MPA (Multi-Page Application) action redirects set Location header to full URL with dummy host http://n/path instead of just /path

How to reproduce: In packages/next/src/server/app-render/action-handler.ts, when an MPA Server Action redirects with redirect('/'), the Location header is set using appRelativeRedirectUrl?.toString() which includes the dummy host used for URL parsing.

Result: Location header is set to http://n/path?query#hash instead of /path?query#hash. Browsers attempting to follow this redirect would try to connect to host "n" and fail.

Expected: According to RFC 7231, the Location header should contain either:

• An absolute URI with real host: https://example.com/path
• A URI-reference (pathname-only): /path

The code already demonstrates the correct pattern in lines 283 and 344, where it accesses pathname, search, and hash properties directly instead of calling .toString() on the URL object.

Fix: Changed line 1096 from appRelativeRedirectUrl?.toString() ?? redirectUrl to:

appRelativeRedirectUrl
  ? `