Missing prefetch headers in Middleware

[lucasmotta]

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/nextjs-missing-prefetch-header-5ll75f?file=%2Fapp%2Flayout.tsx%3A38%2C17

To Reproduce

1. Build the application for production
   
2. Run production server
   
3. Inspect the terminal logs when the server starts
   

You will notice that as soon as you load the / page, the middleware logs the pages the current page and also the pages being prefetched, and that later should not happen.

Current vs. Expected behavior

The current documentation suggests that if you don't want the middleware to run for pages that are being prefetched, you can target the next-router-prefetch and purpose headers:

export const config = {
  matcher: [
    {
      source: '/((?!api|_next/static|_next/image|favicon.ico).*)',
      missing: [
        { type: 'header', key: 'next-router-prefetch' },
        { type: 'header', key: 'purpose', value: 'prefetch' },
      ],
    },
  ],
};

Unfortunately that does not seem to work in the latest version of Next.js - those headers are never present, therefore "missing" - so the middleware is running for pages that are being prefetched, which causes issues if you are handling redirects/rewrites, etc...

In my example app, I've a couple Link components in the root layout with a prefetch prop. Those links are being prefetched, but they are also running in the middleware (see the logs) and no prefetch headers are added to those prefetched pages.

I would expect those headers to be available in the middleware for pages that are being prefetched or at least another way for the middleware to know when a page is being prefetched or not.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Sun Aug  6 20:05:33 UTC 2023
Binaries:
  Node: 20.11.1
  npm: 10.2.4
  Yarn: 1.22.19
  pnpm: 8.15.4
Relevant Packages:
  next: 14.1.4
  eslint-config-next: 14.1.4
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.4.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

App Router, Middleware / Edge (API routes, runtime)

Which stage(s) are affected? (Select all that apply)

next build (local), next start (local), Vercel (Deployed)

Additional context

I also tested with version 13.5.6 and the issue remains.

I also remove the missing property and added logs to those headers, but they always return as null no matter what.

[lucasmotta]

Upon some further investigation, it looks like the headers are present when using the pages/ directory. I forked my example and switched to pages/ directory and now the middleware correctly filters out prefetched pages from the middleware.
https://codesandbox.io/p/devbox/nextjs-missing-prefetch-header-pages-5ckpjs

And this can be confirmed by inspecting the Network request:

So is it safe to assume that this discrepancy between pages/ and app/ router is a bug? Or is that intentional?

[akshit-mdr]

It is a major blocker for my project as well, can we fix this for app/ router

[juliansommer]

need this

[lmac-1]

missing: [
    { type: 'header', key: 'next-router-prefetch' },
    { type: 'header', key: 'purpose', value: 'prefetch' },
  ],

is also not working as expected in middleware.ts in our application using v14.0.3 of Next.js.

This is a big problem for us and we are due to go live soon. We don't want to be running our middleware for every link that is prefetched. We are worried that this could run up the quotas for Edge Middleware functions on Vercel if we receive a lot of traffic.

[kamisone]

I encountered the same issue. After some debugging, I discovered that the headers are missing when using <Link prefetch={true} /> where prefetch is explicitly set to true. However, when it's left as the default (undefined), the headers are present in the prefetch request.

[kimhwanhoon]

any solutions yet? I'm making analytics but I can't add all the prefetched routes as visit

[dimitrisnl]

This is pretty annoying as we cant run our own analytics through middleware, as every prefetch triggers it.

[kimhwanhoon]

This is pretty annoying as we cant run our own analytics through middleware, as every prefetch triggers it.

On middleware
if (req.headers.get("next-router-prefetch")) {
return NextResponse.next(); // Ignore Prefetch request
}

[dimitrisnl]

This is pretty annoying as we cant run our own analytics through middleware, as every prefetch triggers it.

On middleware if (req.headers.get("next-router-prefetch")) { return NextResponse.next(); // Ignore Prefetch request }

thank you for the reply, but this does nothing unfortunately.

[bel7aG]

This is currently an issue on the latest canary 15.0.4-canary.24

[blazorin]

This is an issue, any potential fixes?

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