fix: redirect and 404 responses in RSC requests

[aheissenberger]

fixes the following rsc POST request specific use cases:

• only process rsc response with a 200 status in ClientProvider
• handle missing routes in rsc requests
• handle redirect in middleware to local routes
• handle redirect in middleware to external urls (fixes CORS Errors)
• handle redirect in middleware to internal API routes (fixes CORS Errors)

fixes: #280 , #289

The tests have for the file-router have been extended to cover all new use cases.

The following cases are handled but could be better:

• a redirect in middleware to an existing local route is handled per redirect on the client. In a perfect word the response from the server would contain the content.
• when a rsc POST/GET request in ClientProvider returns with a status <200 || >=300 the thrown error is only shown on the console
• the changes broke the optional error layout for page not found
• after a redirect a browser back will need to be clicked twice to return to the original page
• I am not sure if this changes break outlets, but there have not been any failed tests

[Copilot]

Pull request overview

This PR fixes RSC (React Server Component) redirect and 404 handling for POST requests and various redirect scenarios. The main goal is to properly handle redirects in middleware (to local routes, external URLs, and API routes) and missing routes in RSC requests, addressing CORS errors and improving error handling.

Key changes:

• Added new client handlers (RedirectHandler and ReloadHandler) to handle RSC redirects and 404s on the client side
• Modified redirect logic to differentiate between RSC component requests and regular requests, preventing premature HTTP redirect responses for RSC requests
• Enhanced 404 handling by triggering page reloads for RSC requests so custom error components can be rendered with proper HTTP status codes
• Removed error boundary support from file-router due to RSC serialization limitations

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
test/test/apps/file-router.spec.mjs	Restructured tests into describe/it blocks and added comprehensive test coverage for new redirect and 404 scenarios
packages/react-server/server/render-rsc.jsx	Core RSC rendering changes: saves request body early to prevent re-reading, handles middleware redirect errors, and adds action redirect logic with rewrite support
packages/react-server/server/redirects.mjs	Updated RedirectError digest format and added isRedirectError helper; conditionally creates redirect responses based on request type
packages/react-server/lib/plugins/file-router/entrypoint.jsx	Removed error boundary support, updated 404 handling to use ReloadHandler for RSC requests, and simplified component loading
packages/react-server/lib/http/middleware.mjs	Improved abort handling for client disconnects with better error suppression and cleanup logic
packages/react-server/lib/dev/ssr-handler.mjs	Added redirect detection for middleware errors and passes them to render for proper RSC serialization
packages/react-server/client/ReloadHandler.jsx	New client component that triggers a full page reload to get proper 404 error rendering
packages/react-server/client/RedirectHandler.jsx	New client component that performs client-side redirects for URLs from RSC redirect errors
packages/react-server/client/ErrorBoundary.jsx	Removed redirect handling logic that used digest-based URL extraction (now handled by RedirectHandler)
packages/react-server/client/ClientProvider.jsx	Added manual redirect handling and error throwing for non-2xx RSC responses
examples/file-router/pages/index.tsx	Added test links for various redirect and 404 scenarios
examples/file-router/pages/GET.api-redirect.server.ts	New API endpoint that redirects to external URL for testing

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[Copilot]

The fallback error.digest?.slice(9) assumes the digest format is always "Location=..." but the RedirectError constructor at line 16 in redirects.mjs sets digest = \Location=${url}`without including the status code. The logic should rely onerror.urlwhich is always available on RedirectError instances. Consider simplifying to justconst redirectUrl = error.url;`

Suggested change

	const redirectUrl = error.url || error.digest?.slice(9); // Extract URL from digest "Location=..."
	const redirectUrl = error.url; // Always use error.url for RedirectError

[Copilot]

The fallback() component is still being loaded in Promise.all() but the result (_FallbackComponent) is never used. Consider removing it from the array to avoid unnecessary loading: ] = await Promise.all([lazy(), loading()]);

[aheissenberger]

@lazarv I will need your expertise to get this finished 😊

[lazarv]

Sorry @aheissenberger for the late review.

As I was reviewing this PR, I ended up leaning towards an RSC native approach which I implemented in #292.
If the change implemented in my PR is working as expected, I would like to go with that approach instead of using browser page navigation and custom redirect handling components.

I'll still need to investigate why production build test is failing on Windows, otherwise it should be good to go.

Redirect implementation with RSC could be still better by leveraging server-side re-render for the page instead of handling the redirect error then fetching the RSC payload for the new location.