RFC: Distinguish navigation from fetch requests on the server (X-React-Router-Request-Intent)

[hasanayan]

Summary

Add a public, non-breaking X-React-Router-Request-Intent request header to data requests so loaders, actions, and middleware can distinguish navigation requests (the user is moving to a new route) from fetch requests (the user stays put — revalidations, useFetcher loads/submits, and form submissions to the current route).

Splitting this out from #14505 per the suggestion to scope a separate RFC for request-type detection.

Motivation: auth-redirect target selection

In our app every loader/middleware may hit a redirect-through-the-auth-provider flow. After the round-trip the app must decide where to land the user, and the correct destination depends on the intent of the original request:

• Navigation → the user asked to be at request.url. Redirect there.
• Fetch / revalidation → the user is already at Referer. Redirect there to preserve their visual location.

Today there is no reliable way to tell these apart on the server. request.url and the _routes query param are not enough — useRevalidator(), useFetcher().load(...), and a <Link> navigation can all produce the same-shaped URL.

We currently handle this with a client-side patch that adds the header (link in the Reference Patch section). This RFC proposes adopting it into the framework.

Scenarios

User is on /dashboard unless noted. Each scenario assumes the request hits an expired session and triggers the auth round-trip.

#	Trigger	Request	Intent	Redirect after auth
1	Initial document load of /dashboard	GET /dashboard	navigation (no header needed)	/dashboard
2	<Link to="/settings"> clicked	GET /settings.data?_routes=…	navigation	/settings
3	useRevalidator()	GET /dashboard.data?_routes=…	fetch	Referer (/dashboard)
4	useFetcher().load("/users")	GET /users.data?_routes=…	fetch	Referer (/dashboard) — user does not land on /users
5	<Form method="post"> to current route	POST /dashboard.data?_routes=…	fetch	Referer; preserve/replay form state
6	useFetcher().submit(…)	POST /target.data?_routes=…	fetch	Referer; preserve/replay form state
7	Navigation reuses ancestor loader (/parent/a → /parent/b)	GET /parent/b.data?_routes=root,parent,b	navigation	/parent/b (single target for the batch)

Cases 3 and 4 are the ones that are impossible to disambiguate from case 2 today.

Proposed API

A request header set client-side by the router on data requests:

X-React-Router-Request-Intent: navigation | fetch

• navigation — originated from a navigation (<Link>, navigate(), <Form> to a different route, etc).
• fetch — originated from anything that does not change the user's location: useRevalidator(), useFetcher().load/submit, <Form> submitted to the current route.

Document requests do not need the header — they can always be treated as navigation requests. The header exists only on .data requests, where the ambiguity is. The proposal in #14505 helps us distinguish between document vs .data requests.

Read in loaders/actions/middleware via request.headers.get("X-React-Router-Request-Intent").

Reference patch

cerbos/react-router @ 8702c05. The patch uses the header name X-Request-Type; this RFC proposes X-React-Router-Request-Intent to align with existing framework-owned headers.

Behaviour:

• createClientSideRequest adds fetch when the header is missing.
• startNavigation accepts opts.isRevalidation; when falsy it adds navigation. When truthy it leaves the header alone, so the request falls through to createClientSideRequest and is tagged fetch.
• revalidate always passes isRevalidation: true to startNavigation.

Net result: navigations get navigation, everything else (revalidations, fetcher loads/submits, current-route form submissions) gets fetch. Manual testing confirmed correct values for all of those. Happy to bring this to PR quality with full test coverage if there's interest.