Serve props JSON for /api data requests via middleware rewrite - #902
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The /api/:path* -> /ipa/:path* rewrite in next.config.mjs is applied by Vercel's routing to client-side props fetches (/_next/data/<buildId>/api/....json), but the data-request context is lost and the prerendered page HTML is returned instead of JSON (vercel/next.js#39669). The router then never receives pageProps, so the API sidebar stays collapsed and the tab title shows undefined until a full reload. This half of the bug only occurs on Vercel infrastructure; the dev server and next start resolve rewrites for data requests correctly, and #900 fixed only the /ipa redirect half. Middleware rewrites preserve data-request semantics, so rewrite /api/* to /ipa/* in middleware for data requests only (x-nextjs-data header). Regular page requests fall through to the existing config rewrites, and the /ipa -> /api canonical redirect is unchanged.
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Actionable comments posted: 2
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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@src/middleware.js`:
- Around line 27-37: Update the `/_next/data/` handling in the middleware so the
bare `/_next/data/<build>/api.json` path maps to
`/_next/data/<build>/ipa/introduction.json` before the generic `/api`
replacement runs. Preserve the existing generic mapping for data requests with
additional path segments and the separate bare `/api` behavior.
- Around line 1-43: Move the data-request rewrite logic from middleware and its
matcher configuration into the existing src/proxy.js, removing
src/middleware.js. Preserve the /api and /_next/data API-to-IPA rewrite behavior
and data-request detection, and expose the handler through a named proxy export
compatible with Next.js 16.
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src/middleware.js
Next 16 uses proxy.js and rejects builds where both middleware.js and proxy.js exist; this repo already had src/proxy.js for the /docs-static/_next asset rewrite. Fold the /api -> /ipa data-request rewrite into it and drop middleware.js. Verified the proxy intercepts: data responses now carry x-middleware-rewrite: /ipa/... and JSON bodies.
The raw data-path fallback rewrote /_next/data/<build>/api.json to /_next/data/<build>/ipa.json, but there is no /ipa index page; mirror the /api -> /ipa/introduction rewrite instead.
2 participants
Problem
#900 fixed one of two causes of the API sidebar not expanding (and the tab title showing
undefined) on client-side navigation. The behavior persisted in production because of a second, Vercel-only cause.Cause
On client-side navigation the router fetches page props from
/_next/data/<buildId>/api/....json. Vercel's routing applies the/api/:path*→/ipa/:path*rewrite fromnext.config.mjsto these requests but loses the data-request context, returning the prerendered page HTML instead of the props JSON (vercel/next.js#39669, closed unresolved). The router never receivespageProps, so the sidebar method list stays collapsed and the title isundefineduntil a full reload. The dev server andnext startresolve rewrites for data requests correctly, which is why this half only reproduces on Vercel infrastructure.Fix
Add
src/middleware.jsthat rewrites/api/*to/ipa/*for data requests only (identified by thex-nextjs-dataheader, matcher scoped to/apipaths). Middleware rewrites preserve data-request semantics, so these requests now return the props JSON. Regular page requests fall through to the existing config rewrites, and the/ipa→/apicanonical redirect is unchanged.Verification
/_next/data/<buildId>/api/resources/networks.jsonand/_next/data/<buildId>/api.jsonreturn props JSON;/ipa-prefixed data URLs unchanged/ipa/*visits still redirect to/api/*Since the remaining cause is Vercel-routing-specific, please confirm on the preview deployment before merging.
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