feat(examples): adds middleware example (#38240)

## Documentation / Examples

- [X] Make sure the linting passes by running `pnpm lint`
- [X] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)


Co-authored-by: Lee Robinson <9113740+leerob@users.noreply.github.com>

examples/middleware/.eslintrc.json

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+{
+  "extends": "next/core-web-vitals"
+}

examples/middleware/.gitignore

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+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# local env files
+.env*.local
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo

examples/middleware/README.md

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+# Middleware
+
+This example shows how to use [Middleware in Next.js](https://nextjs.org/docs/advanced-features/middleware) to run code before a request is completed.
+
+The index page ([`pages/index.tsx`](pages/index.js)) has a list of links to pages with `redirect`, `rewrite`, or normal behavior.
+
+On the Middleware file ([`middleware.ts`](middleware.ts)) the routes are already being filtered by defining a `matcher` on the exported config. If you want the Middleware to run for every request, you can remove the `matcher`.
+
+## Deploy your own
+
+Deploy the example using [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example):
+
+[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https://github.com/vercel/next.js/tree/canary/examples/middleware&project-name=middleware&repository-name=middleware)
+
+## How to use
+
+Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init), [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/), or [pnpm](https://pnpm.io) to bootstrap the example:
+
+```bash
+npx create-next-app --example middleware middleware-app
+# or
+yarn create next-app --example middleware middleware-app
+# or
+pnpm create next-app --example middleware middleware-app
+```
+
+Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

examples/middleware/middleware.ts

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+import { NextRequest, NextResponse } from 'next/server'
+
+export function middleware(request: NextRequest) {
+  if (request.nextUrl.pathname === '/about') {
+    return NextResponse.redirect(new URL('/redirected', request.url))
+  }
+  if (request.nextUrl.pathname === '/another') {
+    return NextResponse.rewrite(new URL('/rewrite', request.url))
+  }
+  return NextResponse.next()
+}
+
+export const config = {
+  matcher: ['/about/:path*', '/another/:path*'],
+}

examples/middleware/next-env.d.ts

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+/// <reference types="next" />
+/// <reference types="next/image-types/global" />
+
+// NOTE: This file should not be edited
+// see https://nextjs.org/docs/basic-features/typescript for more information.

examples/middleware/next.config.js

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+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  reactStrictMode: true,
+}
+
+module.exports = nextConfig

examples/middleware/package.json

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+{
+  "private": true,
+  "scripts": {
+    "dev": "next dev",
+    "build": "next build",
+    "start": "next start",
+    "lint": "next lint"
+  },
+  "dependencies": {
+    "next": "latest",
+    "react": "18.2.0",
+    "react-dom": "18.2.0"
+  },
+  "devDependencies": {
+    "@types/node": "18.0.0",
+    "@types/react": "18.0.14",
+    "@types/react-dom": "18.0.5",
+    "eslint": "8.18.0",
+    "eslint-config-next": "12.2.0",
+    "typescript": "4.7.4"
+  }
+}

examples/middleware/pages/_app.tsx

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+import type { AppProps } from 'next/app'
+
+function MyApp({ Component, pageProps }: AppProps) {
+  return <Component {...pageProps} />
+}
+
+export default MyApp

examples/middleware/pages/about.tsx

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+import { NextPage } from 'next'
+
+export const AboutPage: NextPage = () => {
+  return <h1>About</h1>
+}
+
+export default AboutPage

examples/middleware/pages/about2.tsx

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+import { NextPage } from 'next'
+
+export const About2Page: NextPage = () => {
+  return <h1>About 2</h1>
+}
+
+export default About2Page

examples/middleware/pages/another.tsx

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+import { NextPage } from 'next'
+
+export const AnotherPage: NextPage = () => {
+  return <h1>Another</h1>
+}
+
+export default AnotherPage

examples/middleware/pages/index.tsx

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+import type { NextPage } from 'next'
+import Link from 'next/link'
+
+const Home: NextPage = () => {
+  return (
+    <div>
+      <h1>Index</h1>
+      <p>
+        <Link href="/about" passHref>
+          <a>Go to about page (will redirect)</a>
+        </Link>
+      </p>
+      <p>
+        <Link href="/another" passHref>
+          <a>Go to another page (will rewrite)</a>
+        </Link>
+      </p>
+      <p>
+        <Link href="/about2" passHref>
+          <a>Go to about 2 page (no redirect or rewrite)</a>
+        </Link>
+      </p>
+    </div>
+  )
+}
+
+export default Home

examples/middleware/pages/redirected.tsx

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+import { NextPage } from 'next'
+
+export const RedirectedPage: NextPage = () => {
+  return <h1>Redirected from /about</h1>
+}
+
+export default RedirectedPage

examples/middleware/pages/rewrite.tsx

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+import { NextPage } from 'next'
+
+export const RewritePage: NextPage = () => {
+  return <h1>Rewrite</h1>
+}
+
+export default RewritePage

examples/middleware/tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "es5",
+    "lib": ["dom", "dom.iterable", "esnext"],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "strict": true,
+    "forceConsistentCasingInFileNames": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "module": "esnext",
+    "moduleResolution": "node",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "jsx": "preserve",
+    "incremental": true
+  },
+  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"],
+  "exclude": ["node_modules"]
+}