Force file download using PHP

function download_file($file){ 
	$file = $file; //Set File Location
	if (file_exists($file)) { // Check if file exists
		if(!is_dir($file)){ // Check if it is a directory or a file
			// The following files will set the headers to the file download
		    header('Content-Description: File Transfer');
		    header('Content-Type: application/octet-stream');
		    header('Content-Disposition: attachment; filename='.basename($file));
		    header('Content-Transfer-Encoding: binary');
		    header('Expires: 0');
		    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
		    header('Pragma: public');
		    header('Content-Length: ' . filesize($file));
		    ob_clean(); // Clear any set cookies/headers.
		    flush(); // Flush
		    readfile($file); // Actually Start The Download
		    return "Downloading $file"; // Return Downloading FILE_NAME
		    exit; // Stop Processing
		}else{ // If file is a directory
			return "You have selected to download a directory. Download Cancelled"; // Show error
		}
	}else{ // If file doesnt exist
		return "File doesnt exist";
	}
}