Access pathname in NextJS generateMetadata

middleware.ts

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

export async function middleware(req: NextRequest) {
  const requestHeaders = new Headers(req.headers)
  requestHeaders.set('x-request-url', req.url);

  const res = NextResponse.next({
    request: {
      headers: requestHeaders
    }
  });

  // other things

  return res;
}

page.tsx

export async function generateMetadata(): Promise<Metadata | null> {
  const pathname = new URL(headers().get('x-request-url')!).pathname;

  // other things
}