How to add extra data at the end of downloading content in PHP

Question

I am developing a security for my downloadable contents simply securing my download content like this.

<?php
$file = 'monkey.gif';

if (file_exists($file)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename='.basename($file));
    header('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file));
    ob_clean();
    flush();
    readfile($file);
    exit;
}
?>

Now I simply want to add 100 extra bytes (my custom details about that download file as per each download)

I want some way to add these 100 bytes after readfile($file); so downloaded file will have this extra information in it.

something like 
readfile($file) + myBytes()

I am new to PHP so please help me

This depends on the type of file you're downloading. Simply pasting extra bytes to the end of a file may render it effectively corrupt. — Alex Howansky, Nov 02 '12 at 17:27
Maybe you should consider an encryption method with a secure key instead? http://stackoverflow.com/questions/2448256/php-mcrypt-encrypting-decrypting-file — Jeremy Harris, Nov 02 '12 at 17:30

score 2 · Accepted Answer · answered Nov 02 '12 at 18:25

Store your extra bytes in a file,variable,db or etc , and echo it after read file function

$file = 'monkey.gif';

if (file_exists($file)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename='.basename($file));
    header('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file));
    ob_clean();
    flush();
    readfile($file);
    readfile("extra_filename.ext");
    /* 
    //or use this
    $extra_bytes = "store extra bytes here";
    echo $extra_bytes;
    */
    exit;
}

As simple as that – thanks to you to save my time Now I have developed my solution and my .net downloadable application is using this additional information for license verification — Jack Gajanan, Nov 04 '12 at 05:47
You need to add the length of the extra bytes to the Content-Length header as well. — Nikhil Dabas, Apr 11 '13 at 16:25

score 0 · Answer 2 · answered Nov 02 '12 at 17:35

0

If you're only dealing with images, I'd recommend using steganography instead of just pasting bytes to the end of a file. Googling "php steganography library" turns up a few hits:

answered Nov 02 '12 at 17:35

Alex Howansky

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I already have implemented steganography in Matlab but this is just a sample code from php.net actually my content is executer file which use this added information for license. – Jack Gajanan Nov 03 '12 at 02:50

How to add extra data at the end of downloading content in PHP

2 Answers2