docs: Add content negotiation to apps/wiki

apps/wiki/app/llms.mdx/[[...slug]]/route.ts

@@ -11,7 +11,8 @@ export async function GET(_req: Request, props: {params: Promise<{slug?: string[
 
   return new Response(await getLLMText(page), {
     headers: {
-      'Content-Type': 'text/markdown',
+      'Content-Type': 'text/markdown; charset=utf-8',
+      'Vary': 'Accept',
     },
   });
 }

apps/wiki/middleware.ts

@@ -0,0 +1,59 @@
+import { NextResponse } from 'next/server';
+import type { NextRequest } from 'next/server';
+
+type Negotiated = 'markdown' | 'html' | 'none';
+
+function parseAccept(accept: string): Array<{ type: string; q: number }> {
+  return accept.split(',').map(part => {
+    const segments = part.trim().split(';');
+    const type = segments[0]?.trim().toLowerCase() ?? '';
+    const qParam = segments.slice(1).find(s => s.trim().startsWith('q='));
+    const q = qParam ? parseFloat(qParam.split('=')[1] ?? '1') : 1;
+    return { type, q: isNaN(q) ? 1 : q };
+  });
+}
+
+function getQ(types: Array<{ type: string; q: number }>, target: string): number {
+  const exact = types.find(t => t.type === target);
+  if (exact) return exact.q;
+  const [main] = target.split('/');
+  const sub = types.find(t => t.type === `${main}/*`);
+  if (sub) return sub.q;
+  const wildcard = types.find(t => t.type === '*/*');
+  return wildcard ? wildcard.q : -1;
+}
+
+function negotiate(accept: string): Negotiated {
+  if (!accept) return 'html';
+  const types = parseAccept(accept);
+  const mdQ = getQ(types, 'text/markdown');
+  const htmlQ = getQ(types, 'text/html');
+  if (mdQ <= 0 && htmlQ <= 0) return 'none';
+  if (mdQ > 0 && mdQ >= htmlQ) return 'markdown';
+  return 'html';
+}
+
+export function middleware(request: NextRequest) {
+  const accept = request.headers.get('accept') ?? '';
+  const { pathname } = request.nextUrl;
+  const result = negotiate(accept);
+
+  if (result === 'none') {
+    return new NextResponse(null, { status: 406, headers: { 'Vary': 'Accept' } });
+  }
+
+  if (result === 'markdown') {
+    const rewriteUrl = new URL(`/llms.mdx${pathname}`, request.url);
+    const response = NextResponse.rewrite(rewriteUrl);
+    response.headers.set('Vary', 'Accept');
+    return response;
+  }
+
+  const response = NextResponse.next();
+  response.headers.set('Vary', 'Accept');
+  return response;
+}
+
+export const config = {
+  matcher: ['/((?!llms\\.mdx|api/search|_next|.*\\.(?:png|jpg|jpeg|gif|svg|ico|webp|woff|woff2|ttf|css|js)).*)',],
+};