用于提供ZIP的PHP标头。 它下载但是已经腐败......为什么？

Good morning,

I'm working on serving a zip file through the PHP headers, which downloads, but every time I try to extract it shows that the zip is corrupt... I need a 2nd pair of eyes to look over this... what am I missing? Thank you so much!

$file_download = 'example';

if (isset($file_download)) {
$file = 'path/to/file/'.$file_download.'.zip';
if (file_exists($file)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename="'.basename($file).'"');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file));
    readfile($file);
    exit;
} else {
    echo 'File does not exist!';
}   

}