PHP: files to ZIP

gistfile1.php

<?php
if(isset($_GET['id']) && $_GET['id'] != ''){
    $usr_dir = "upload/".$_GET['id']."/";
    $error = "";
    //checking if zip module loaded
    if(extension_loaded('zip')){

        $zip = new ZipArchive(); // подгружаем библиотеку zip
        $zip_name = time().".zip"; // имя файла
        if($zip->open($zip_name, ZIPARCHIVE::CREATE)!==TRUE){
            $error .= "* Sorry ZIP creation failed at this time";
        }
        //adding files to archive. from usr_dir
        $dirHandle = opendir($usr_dir);
        while (false !== ($file = readdir($dirHandle))) {
            if ($file != "." && $file != "..") {
                $zip->addFile($usr_dir.$file);
            }
        }

        $zip->close();
        if(file_exists($zip_name)){
            // give user a window to download file
            header('Content-type: application/zip');
            header('Content-Disposition: attachment; filename="'.$zip_name.'"');
            readfile($zip_name);
            // deleting zip file if it exists
            unlink($zip_name);
        }
    }
    else
    $error .= "* You dont have ZIP extension";
}
else echo "Choose correct user";