header - Download of .zip file runs a corrupted file php

Question

I'm trying to force a download of a protected zip file (I don't want people to access it without logging in first.

I have the function created for the login and such , but I'm running into a problem where the downloaded file is corrupting.

Here's the code I have:

$file='../downloads/'.$filename;
header("Content-type: application/zip;
");
header("Content-Transfer-Encoding: Binary");
header("Content-length: ".filesize($file).";
");
header("Content-disposition: attachment; filename="".basename($file).""");
readfile("$file");
exit();

Here's the error: Cannot open file: It does not appear to be a valid archive.

The file downloads fine otherwise, so it must be something I'm doing wrong with the headers.

Any ideas?

Answer 1

This issue can have several causes. Maybe your file is not found or it can not be read and thus the file’s content is just the PHP error message. Or the HTTP header is already sent. Or you have some additional output that then corrupts your file’s content.

Try to add some error handling into your script like this:

$file='../downloads/'.$filename;
if (headers_sent()) {
    echo 'HTTP header already sent';
} else {
    if (!is_file($file)) {
        header($_SERVER['SERVER_PROTOCOL'].' 404 Not Found');
        echo 'File not found';
    } else if (!is_readable($file)) {
        header($_SERVER['SERVER_PROTOCOL'].' 403 Forbidden');
        echo 'File not readable';
    } else {
        header($_SERVER['SERVER_PROTOCOL'].' 200 OK');
        header("Content-Type: application/zip");
        header("Content-Transfer-Encoding: Binary");
        header("Content-Length: ".filesize($file));
        header("Content-Disposition: attachment; filename="".basename($file).""");
        readfile($file);
        exit;
    }
}