middleware.ts

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


export default async function middleware(req: NextRequest) {
  const bot=checkBot(req.headers.user-agent);
  
  if (bot=== true) {
    const url = req.nextUrl;
    url.pathname = `/404`;
    return NextResponse.rewrite(url);
  }
  return NextResponse.next();
}

function checkBot(useragent) {
  //logic to check for a bot user agent
  return true;
}