Preserve the original host on action redirect streams - #96977
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When an action POST lands on a route that does not bundle the action, it is
forwarded to a worker that does, via an internal self-fetch to
`__NEXT_PRIVATE_ORIGIN`. `host` is a forbidden `fetch` header, so it cannot be
carried onto the subrequest: the action saw `headers().get('host')` as
`localhost:PORT` instead of the host the user requested. That breaks
host-based multi-tenancy for exactly those actions that happen to get
forwarded, which depends on the build's static import graph rather than
anything visible in the application.
Restore `host` from `x-forwarded-host`, which does survive the forward,
guarded on the request being marked `x-action-forwarded` and having arrived at
the internal origin. `x-forwarded-host` is already preferred over `host` by
`parseHostHeader` for the CSRF origin check, so this aligns userland
`headers()` with the value the framework already trusts.
Fixes vercel#96344
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Tests PassedCommit: 7b82386 |
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Stats from current PR🔴 1 regression, 2 improvements
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What
forwarded between workers.
createRedirectRenderResult, used to stream app-relative ServerAction redirects.
x-action-redirect-forwarded: 1marker.Hostfromx-forwarded-hostonly for theexact internal GET + RSC request shape.
subsequently redirect.
Why
Hostbecomes something likelocalhost:PORT.headers().get('host')in the redirect target seesthe internal host instead of the public tenant host.
naturally set
x-action-forwarded.Security details
1;Hostmatching the internal forwarding origin;Verification
pnpm build-allpassed.