From c5e61c68bd9661159ef9902fa7f03aed8efd377d Mon Sep 17 00:00:00 2001
From: Jack Carter <128555021+SunsetDrifter@users.noreply.github.com>
Date: Mon, 3 Aug 2026 14:40:12 +0200
Subject: [PATCH] Serve props JSON for /api data requests via middleware
 rewrite (#902)

* fix: serve props JSON for /api data requests via middleware rewrite

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.

* fix: move /api data-request rewrite into existing proxy.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.

* fix: map bare api.json data requests to ipa/introduction.json

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.
---
 src/proxy.js | 40 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/src/proxy.js b/src/proxy.js
index e83805e3..eebb7926 100644
--- a/src/proxy.js
+++ b/src/proxy.js
@@ -1,10 +1,46 @@
 import { NextResponse } from 'next/server';
 
+// Client-side navigations fetch page props from /_next/data/<buildId>/api/....json.
+// Vercel's routing applies the /api/:path* -> /ipa/:path* rewrite from
+// next.config.mjs to those requests but loses the data-request context and
+// serves the page HTML instead of the props JSON
+// (https://github.com/vercel/next.js/issues/39669), so the router never
+// receives pageProps. Proxy rewrites keep data-request semantics, so map
+// /api/* to /ipa/* here for data requests only; regular page requests fall
+// through to the config rewrites, and the /ipa -> /api canonical redirect
+// is unchanged.
+function rewriteApiDataRequest(req) {
+    const isDataRequest =
+        req.headers.get('x-nextjs-data') !== null ||
+        req.nextUrl.pathname.startsWith('/_next/data/');
+    if (!isDataRequest) return null;
+
+    const url = req.nextUrl.clone();
+    if (url.pathname.startsWith('/_next/data/')) {
+        // Raw data-request path, in case the runtime matches it un-normalized.
+        // Bare api.json maps to ipa/introduction.json to mirror the /api ->
+        // /ipa/introduction rewrite; there is no /ipa index page.
+        url.pathname = url.pathname
+            .replace(
+                /^(\/_next\/data\/[^/]+)\/api\.json$/,
+                '$1/ipa/introduction.json',
+            )
+            .replace(/^(\/_next\/data\/[^/]+)\/api\//, '$1/ipa/');
+    } else if (url.pathname === '/api') {
+        url.pathname = '/ipa/introduction';
+    } else if (url.pathname.startsWith('/api/')) {
+        url.pathname = url.pathname.replace(/^\/api\//, '/ipa/');
+    }
+
+    if (url.pathname === req.nextUrl.pathname) return null;
+    return NextResponse.rewrite(url);
+}
+
 export function proxy(req) {
     if (req.nextUrl.href.includes('/docs-static/_next/'))
         return NextResponse.rewrite(
             req.nextUrl.href.replace('/docs-static/_next/', '/_next/'),
         );
 
-    return null;
-}
\ No newline at end of file
+    return rewriteApiDataRequest(req);
+}