Advanced Middleware Patterns

// middleware.ts
import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';

// Middleware chain
const middlewares = [
  authMiddleware,
  rateLimitMiddleware,
  localeMiddleware,
];

export async function middleware(request: NextRequest) {
  let response = NextResponse.next();

  for (const mw of middlewares) {
    const result = await mw(request, response);
    if (result instanceof NextResponse) {
      response = result;
    }
    // Check if redirect or rewrite, break chain
    if (response.headers.get('x-middleware-rewrite')) {
      break;
    }
  }

  return response;
}

async function authMiddleware(request: NextRequest, response: NextResponse) {
  const token = request.cookies.get('token');
  if (!token && request.nextUrl.pathname.startsWith('/dashboard')) {
    return NextResponse.redirect(new URL('/login', request.url));
  }
  return response;
}

export function middleware(request: NextRequest) {
  const bucket = request.cookies.get('ab-bucket')?.value
    || (Math.random() < 0.5 ? 'a' : 'b');

  const response = NextResponse.rewrite(
    new URL(`/${bucket}${request.nextUrl.pathname}`, request.url)
  );

  if (!request.cookies.get('ab-bucket')) {
    response.cookies.set('ab-bucket', bucket, { maxAge: 60 * 60 * 24 * 30 });
  }

  return response;
}

export function middleware(request: NextRequest) {
  const country = request.geo?.country || 'US';
  const city = request.geo?.city || 'Unknown';

  // Clone headers and add geo info
  const requestHeaders = new Headers(request.headers);
  requestHeaders.set('x-user-country', country);
  requestHeaders.set('x-user-city', city);

  // Redirect based on country
  if (country === 'DE' && !request.nextUrl.pathname.startsWith('/de')) {
    return NextResponse.redirect(new URL('/de' + request.nextUrl.pathname, request.url));
  }

  return NextResponse.next({
    request: { headers: requestHeaders },
  });
}