PHP Download Script Creates Unreadable ZIP File on Mac

Question

For reference, I have already read and tried the answers in these and several other threads:

Creating and serving zipped files with php

Opening downloaded zi

Answer 1

Often the issue is caused by extra characters that have been printed or echo'd to the page before you read out the file. Even a space will cause the failure. To fix that issue, call ob_end_clean(); before you read the file which will clear the output buffer and turn off buffering.

But keep in mind you can have nested output buffers, and this will corrupt your download as well (cheers to Vladamir for figuring this out). So to clear the output buffer completely run this before you read your file:

while (ob_get_level()) {
    ob_end_clean();
}    

This will clear out your entire buffer and you won't have any extra characters to mess up your download.

For those interested i've pasted my download script below. My zip files now download perfectly, and so far this works great.

if (file_exists($zip_file_path)) {

        header("Pragma: public");
        header("Expires: 0");
        header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
        header("Cache-Control: public");
        header("Content-Description: File Transfer");
        //We can likely use the 'application/zip' type, but the octet-stream 'catch all' works just fine.  
        header("Content-type: application/octet-stream");
        header("Content-Disposition: attachment; filename='$zip_file_name'");
        header("Content-Transfer-Encoding: binary");
        header("Content-Length: ".filesize($zip_file_path));

        while (ob_get_level()) {
             ob_end_clean();
        }

        @readfile($zip_file_path);

        exit;
}