New middleware slows down routing in production

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System: Platform: win32 Arch: x64 Version: Windows 10 Pro
Binaries: Node: 16.14.2 npm: N/A Yarn: N/A pnpm: N/A Relevant packages: next: 12.2.0 eslint-config-next: 12.2.0 react: 18.2.0 react-dom: 18.2.0

What browser are you using? (if relevant)

Chrome 103.0.5060.66

How are you deploying your application? (if relevant)

next start

Describe the Bug

New middleware slows down on routing in production (dev is okay), example code that slows down:

import { NextResponse } from 'next/server';

const Middleware = (req) => {
  /** To lower case redirect. */
  if (req.nextUrl.pathname === req.nextUrl.pathname.toLowerCase())
    return NextResponse.next();

  return NextResponse.redirect(new URL(req.nextUrl.origin + req.nextUrl.pathname.toLowerCase()));
};

export default Middleware;

Expected Behavior

Work as expected with no slow down, with previous _middleware.js there was no problem

To Reproduce

Create middleware.js file under root folder and use code from example

[benfavre]

Without a fix for this, the framework is basically unusable right now …

[cdev-enter]

The problem also exists in the 13 release. Just the presence of a middleware increases the response time tenfold.

I did a test with a fresh next@canary release and a request to http://localhost:3000/vercel.svg takes 4ms without middleware. The same request with a middleware present, takes 150 - 300ms on my local machine. There seems to be a problem with the middleware loader, as the middleware does not have to do anything to cause that kind of delay.

// middleware.ts

export function middleware() {}

Is enough to drop the response time