with import <nixpkgs> {};

fetchurl {
  url = "https://example.com/some-file";
  sha256 = "0000000000000000000000000000000000000000000000000000";
  downloadToTemp = true;
  recursiveHash = true;
  curlOpts = "-D headers";
  postFetch = ''
    mkdir $out
    mv "$downloadedFile" $out
    mv headers $out
  '';
}