Useful PHP force-download script

It seems there are a million force-download scripts out there for PHP.  Most people will agree that mod_xsendfile is the way to go, but if your web host won't support it (for example, it may conflict with NFS), check out http://www.richnetapps.com/php-download-script-with-resume-option/

P.S. If you use the second script and need to download Mac dmg files, I recommend you first wrap the dmg file into a zip file and have users download the zip file instead of the dmg file directly since the force download script may add a small amount of of binary data to large files and alter the md5 fingerprint.  

Update: this turned out to be an issue with Drupal interjecting error messages into the binary download stream.  Make sure to turn OFF error messaging if using Drupal (see https://drupal.org/node/1036982)

Update #2: the in-memory chunking method described above is still prone to failed downloads, especially on large multi-gigabyte files, when using a slow Internet connection or when there is heavy network congestion.  The best approach is a variation of http://serverfault.com/a/150542 (I recommend using the at command to delete the symbolic link a couple minutes after creating it rather than a cron job that deletes it a day later).  

Pseudo-code:
// ... your authorization logic goes here... // if authorized, download file: $filename = '/path/to/private/files/example_big_file.iso'; $filesize = filesize($filename); $threshold = 1 * (1024 * 1024); // files smaller than 1MB will be served from memory (useful for text files and images) - adjust size as needed if ($filesize > $threshold) { // generate unique id for this download instance $uid = uniqid(); // create symbolic link in public location that points to private file $sdirectory = '/your/web/root/temp/' . $uid; mkdir($sdirectory, 0755); $sfile = $sdirectory . '/' . basename($filename); symlink($filename, $spath); // create temporary file for later removing the symbolic link file_put_contents("/tmp/" . $uid, "rm " . $sfile . "\nrmdir " . $sdirectory . "\nrm /tmp/" . $uid); // redirect user to symbolic link to trigger the download header('Location: http://' . $_SERVER['HTTP_HOST'] . $sfile); // delete symbolic link and temporary file (asynchronous) exec("at -f /tmp/" . $uid . " now + 2 minutes"); exit; } else { // force download of small files (like text files) // required for IE, otherwise Content-Disposition may be ignored if(ini_get('zlib.output_compression')) ini_set('zlib.output_compression', 'Off'); header('Content-Type: application/force-download'); header('Content-Disposition: attachment; filename="'.basename($filename).'"'); header('Content-Transfer-Encoding: binary'); header('Cache-control: no-cache, pre-check=0, post-check=0'); header('Pragma: public'); header('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); if ($handle = fopen($filename, 'rb')) { print(fread($handle, filesize($filename))); fclose($handle); exit; } else { die('Error - cannot open file.'); } }