How do I access the body of a POST request from a page.tsx?

[firelizzard18]

Summary

Given /a/page.tsx:

export default async function () {
  return <form action="/b" method="post">
    <input type="file" name="file" />
    <button type="submit">Submit</button>
  </form>
}

How do I access the request body/form data from /b/page.tsx?

Additional information

I am using the app router.

Example

No response

[icyJoseph]

This was possible in GetServerSideProps, in Pages Router, but I've been missing this in App Router, as far as I know, the exposed request API's are only, cookies and headers. I guess there could be some middleware hack, but nothing "native" so to speak.