middleware.ts

import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'

export async function middleware(req: NextRequest) {
  const res = NextResponse.rewrite(new URL('/', req.url))
  res.headers.set('x-response-header', 'set in middleware')
  res.headers.set('x-is-deno', 'Deno' in globalThis ? 'true' : 'false')
  return res
}

export const config = {
  matcher: [
    '/foo',
    { source: '/bar' },
    {
      source: '/baz',
      has: [
        {
          type: 'header',
          key: 'x-my-header',
          value: 'my-value',
        },
      ],
    },
    {
      source: '/en/asdf',
      locale: false,
    },
  ],
}