Update to Vercel

{
  "name": "routing-middleware",
  "description": "Vercel Routing Middleware guidance — request interception before cache, rewrites, redirects, personalization. Works with any framework. Supports Edge, Node.js, and Bun runtimes. Use when intercepting requests at the platform level.",
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  "skill_md_contents": "---\nname: routing-middleware\ndescription: Vercel Routing Middleware guidance — request interception before cache, rewrites, redirects, personalization. Works with any framework. Supports Edge, Node.js, and Bun runtimes. Use when intercepting requests at the platform level.\nmetadata:\n  priority: 6\n  docs:\n    - \"https://nextjs.org/docs/app/building-your-application/routing/middleware\"\n    - \"https://vercel.com/docs/routing-middleware\"\n  sitemap: \"https://nextjs.org/sitemap.xml\"\n  pathPatterns: \n    - 'middleware.ts'\n    - 'middleware.js'\n    - 'middleware.mts'\n    - 'middleware.mjs'\n    - 'proxy.ts'\n    - 'proxy.js'\n    - 'proxy.mts'\n    - 'proxy.mjs'\n    - 'src/middleware.ts'\n    - 'src/middleware.js'\n    - 'src/middleware.mts'\n    - 'src/middleware.mjs'\n    - 'src/proxy.ts'\n    - 'src/proxy.js'\n    - 'src/proxy.mts'\n    - 'src/proxy.mjs'\n    - 'vercel.json'\n    - 'apps/*/vercel.json'\n    - 'vercel.ts'\n    - 'vercel.mts'\n  bashPatterns:\n    - '\\bnpx\\s+@vercel/config\\b'\n---\n\n# Vercel Routing Middleware\n\nYou are an expert in Vercel Routing Middleware — the platform-level request interception layer.\n\n## What It Is\n\nRouting Middleware runs **before the cache** on every request matching its config. It is a **Vercel platform** feature (not framework-specific) that works with Next.js, SvelteKit, Astro, Nuxt, or any deployed framework. Built on Fluid Compute.\n\n- **File**: `middleware.ts` or `middleware.js` at the project root\n- **Default export required** (function name can be anything)\n- **Runtimes**: Edge (default), Node.js (`runtime: 'nodejs'`), Bun (Node.js + `bunVersion` in vercel.json)\n\n## CRITICAL: Middleware Disambiguation\n\nThere are THREE \"middleware\" concepts in the Vercel ecosystem:\n\n| Concept | File | Runtime | Scope | When to Use |\n|---------|------|---------|-------|-------------|\n| **Vercel Routing Middleware** | `middleware.ts` (root) | Edge/Node/Bun | Any framework, platform-level | Request interception before cache: rewrites, redirects, geo, A/B |\n| **Next.js 16 Proxy** | `proxy.ts` (root, or `src/proxy.ts` if using `--src-dir`) | Node.js only | Next.js 16+ only | Network-boundary proxy needing full Node APIs. NOT for auth. |\n| **Edge Functions** | Any function file | V8 isolates | General-purpose | Standalone edge compute endpoints, not an interception layer |\n\n**Why the rename in Next.js 16**: `middleware.ts` → `proxy.ts` clarifies it sits at the network boundary (not general-purpose middleware). Partly motivated by CVE-2025-29927 (middleware auth bypass via `x-middleware-subrequest` header). The exported function must also be renamed from `middleware` to `proxy`. Migration codemod: `npx @next/codemod@latest middleware-to-proxy`\n\n**Deprecation**: Next.js 16 still accepts `middleware.ts` but treats it as deprecated and logs a warning. It will be removed in a future version.\n\n## Bun Runtime\n\nTo run Routing Middleware (and all Vercel Functions) on Bun, add `bunVersion` to `vercel.json`:\n\n```json\n{\n  \"bunVersion\": \"1.x\"\n}\n```\n\nSet the middleware runtime to `nodejs` — Bun replaces the Node.js runtime transparently:\n\n```ts\nexport const config = {\n  runtime: 'nodejs', // Bun swaps in when bunVersion is set\n};\n```\n\nBun reduces average latency by ~28% in CPU-bound workloads. Currently in Public Beta — supports Next.js, Express, Hono, and Nitro.\n\n## Basic Example\n\n```ts\n// middleware.ts (project root)\nimport { geolocation, rewrite } from '@vercel/functions';\n\nexport default function middleware(request: Request) {\n  const { country } = geolocation(request);\n  const url = new URL(request.url);\n  url.pathname = country === 'US' ? '/us' + url.pathname : '/intl' + url.pathname;\n  return rewrite(url);\n}\n\nexport const config = {\n  runtime: 'edge', // 'edge' (default) | 'nodejs'\n};\n```\n\n## Helper Methods (`@vercel/functions`)\n\nFor non-Next.js frameworks, import from `@vercel/functions`:\n\n| Helper | Purpose |\n|--------|---------|\n| `next()` | Continue middleware chain (optionally modify headers) |\n| `rewrite(url)` | Transparently serve content from a different URL |\n| `geolocation(request)` | Get `city`, `country`, `latitude`, `longitude`, `region` |\n| `ipAddress(request)` | Get client IP address |\n| `waitUntil(promise)` | Keep function running after response is sent |\n\nFor Next.js, equivalent helpers are on `NextResponse` (`next()`, `rewrite()`, `redirect()`) and `NextRequest` (`request.geo`, `request.ip`).\n\n## Matcher Configuration\n\nMiddleware runs on **every route** by default. Use `config.matcher` to scope it:\n\n```ts\n// Single path\nexport const config = { matcher: '/dashboard/:path*' };\n\n// Multiple paths\nexport const config = { matcher: ['/dashboard/:path*', '/api/:path*'] };\n\n// Regex: exclude static files\nexport const config = {\n  matcher: ['/((?!_next/static|favicon.ico).*)'],\n};\n```\n\n**Tip**: Using `matcher` is preferred — unmatched paths skip middleware invocation entirely (saves compute).\n\n## Common Patterns\n\n### IP-Based Header Injection\n\n```ts\nimport { ipAddress, next } from '@vercel/functions';\n\nexport default function middleware(request: Request) {\n  return next({ headers: { 'x-real-ip': ipAddress(request) || 'unknown' } });\n}\n```\n\n### A/B Testing via Edge Config\n\n```ts\nimport { get } from '@vercel/edge-config';\nimport { rewrite } from '@vercel/functions';\n\nexport default async function middleware(request: Request) {\n  const variant = await get('experiment-homepage'); // <1ms read\n  const url = new URL(request.url);\n  url.pathname = variant === 'B' ? '/home-b' : '/home-a';\n  return rewrite(url);\n}\n```\n\n### Background Processing\n\n```ts\nimport type { RequestContext } from '@vercel/functions';\n\nexport default function middleware(request: Request, context: RequestContext) {\n  context.waitUntil(\n    fetch('https://analytics.example.com/log', { method: 'POST', body: request.url })\n  );\n  return new Response('OK');\n}\n```\n\n## Request Limits\n\n| Limit | Value |\n|-------|-------|\n| Max URL length | 14 KB |\n| Max request body | 4 MB |\n| Max request headers | 64 headers / 16 KB total |\n\n## Three CDN Routing Mechanisms\n\nVercel's CDN supports three routing mechanisms, evaluated in this order:\n\n| Order | Mechanism | Scope | Deploy Required | How to Configure |\n|-------|-----------|-------|-----------------|------------------|\n| 1 | **Bulk Redirects** | Up to 1M static path→path redirects | No (runtime via Dashboard/API/CLI) | Dashboard, CSV upload, REST API |\n| 2 | **Project-Level Routes** | Headers, rewrites, redirects | No (instant publish) | Dashboard, API, CLI, Vercel SDK |\n| 3 | **Deployment Config Routes** | Full routing rules | Yes (deploy) | `vercel.json`, `vercel.ts`, `next.config.ts` |\n\n**Project-level routes** (added March 2026) let you update routing rules — response headers, rewrites to external APIs — without triggering a new deployment. They run after bulk redirects and before deployment config routes. Available on all plans.\n\n### Project-Level Routes — Configuration Methods\n\nProject-level routes take effect instantly (no deploy required). Four ways to manage them:\n\n| Method | How |\n|--------|-----|\n| **Dashboard** | Project → CDN → Routing tab. Live map of global traffic, cache management, and route editor in one view. |\n| **REST API** | `GET/POST/PATCH/DELETE /v1/projects/{projectId}/routes` — 8 dedicated endpoints for CRUD on project routes. |\n| **Vercel CLI** | Managed via `vercel.ts` / `@vercel/config` commands (`compile`, `validate`, `generate`). |\n| **Vercel SDK** | `@vercel/config` helpers: `routes.redirect()`, `routes.rewrite()`, `routes.header()`, plus `has`/`missing` conditions and transforms. |\n\nUse project-level routes for operational changes (CORS headers, API proxy rewrites, A/B redirects) that shouldn't require a full redeploy.\n\n## Programmatic Configuration with `vercel.ts`\n\nInstead of static `vercel.json`, you can use `vercel.ts` (or `.js`, `.mjs`, `.cjs`, `.mts`) with the `@vercel/config` package for type-safe, dynamic routing configuration:\n\n```ts\n// vercel.ts\nimport { defineConfig } from '@vercel/config';\n\nexport default defineConfig({\n  rewrites: [\n    { source: '/api/:path*', destination: 'https://backend.example.com/:path*' },\n  ],\n  headers: [\n    { source: '/(.*)', headers: [{ key: 'X-Frame-Options', value: 'DENY' }] },\n  ],\n});\n```\n\nCLI commands:\n- `npx @vercel/config compile` — compile to JSON (stdout)\n- `npx @vercel/config validate` — validate and show summary\n- `npx @vercel/config generate` — generate `vercel.json` locally for development\n\n**Constraint**: Only one config file per project — `vercel.json` or `vercel.ts`, not both.\n\n## When to Use\n\n- Geo-personalization of static pages (runs before cache)\n- A/B testing rewrites with Edge Config\n- Custom redirects based on request properties\n- Header injection (CSP, CORS, custom headers)\n- Lightweight auth checks (defense-in-depth only — not sole auth layer)\n- Project-level routes for headers/rewrites without redeploying\n\n## When NOT to Use\n\n- Need full Node.js APIs in Next.js → use `proxy.ts`\n- General compute at the edge → use Edge Functions\n- Heavy business logic or database queries → use server-side framework features\n- Auth as sole protection → use Layouts, Server Components, or Route Handlers\n- Thousands of static redirects → use Bulk Redirects (up to 1M per project)\n\n## References\n\n- 📖 docs: https://vercel.com/docs/routing-middleware\n- 📖 API reference: https://vercel.com/docs/routing-middleware/api\n- 📖 getting started: https://vercel.com/docs/routing-middleware/getting-started\n"
}