Edge function / middleware error: "TypeError: Unable to parse URL" when deployed to Vercel

What version of Next.js are you using?

12.0.3

What version of Node.js are you using?

v16.10.0 (local)

What browser are you using?

Chrome

What operating system are you using?

macOS

How are you deploying your application?

Vercel

Describe the Bug

When testing locally, the following _middleware.ts works perfectly:

export async function middleware(req: NextRequest) {
  const { pathname: redirectUrl } = req.nextUrl;
  const {  userTypeId } = req.cookies;

  if (!userTypeId || Number(userTypeId) !== UserTypeEnum.FIRST_TIME) {
    return Response.redirect("/play");
  }
  return NextResponse.next();
}

However, when deployed to Vercel I get the following error in my function logs:

TypeError: Unable to parse URL: /play
at Object.d [as handler]
at t.V
at Object.a

Expected Behavior

I would expect the page to redirect or continue without the error occuring.

To Reproduce

Create _middleware like above and deploy to vercel and try hit a route that the middleware is linked to

[javivelasco]

@adrianmiles The problem here is that the implementation of Response for Next.js is allowing you to provide a relative URL as a redirection target, while in Vercel production this is not allowed. In this context, we must wonder what’s the hostname for the redirection.

Typically one would expect the hostname to be the same where the request is being performed against, and this is information that you as a user have but the Response does not have on its prototype. For this reason, my recommendation would be that you change the pathname in the incoming request or you specify the host retrieving such information from the request.

What doesn’t make sense for sure is that this works locally but does not work in production for Vercel. I think the best way to approach this is to make not possible for the Response.redirect method to be called with a relative URL.

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