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<!-- PUT IN download.php: -->

<?php
/*
* This code delivers a file, specified in the URL parameter, as a forced "Save As" download.
*/

// First, get WordPress loaded
require_once('../../../wp-load.php');  // Modify this if necessary

// Grab the requested URL
$request_file = $_REQUEST['url'];

// Get WordPress's upload directory details - this returns an array of things - see the Codex for details
$upload_path_info = wp_upload_dir();

// Translate the requested URL into a local file path
$request_file_path = str_replace( $upload_path_info['baseurl'], $upload_path_info['basedir'], $request_file );

// Because you could ask for, say, /wp-content/uploads/2013/01/../../../../wp-config.php we need a security check
// to make sure we're actually getting a file form /uploads.  The canonical directory of the request MUST be the
// basedir of the uploads directory.
$realdir = realpath(dirname($request_file_path));
// Make sure this is a === test as a successful result will be 0 !!
if (strpos($realdir, $upload_path_info['basedir']) === false) {
    echo "Haha! Nice try. I don't think so.";
    exit;
}

// Check if the file exists
if (file_exists($request_file_path)) {

    // Send appropriate headers (this from the examples here: http://php.net/manual/en/function.readfile.php);
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename='.basename($request_file_path));
    header('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($request_file_path));
    ob_clean();
    flush();
    readfile($request_file_path);
    exit;
}
?>

<!-- PUT IN TEMPLATE: -->
<?php
	if ($resource_url):
		$download_url = get_template_directory_uri() . '/download.php?url=' . urlencode($resource_url);
?>

<a href="<?php echo $download_url; ?>">Download</a>

<?php
	endif;
?>