PHP实现简单的文件下载通用方法

function download_file($file){
    if(is_file($file)){
        $length = filesize($file);
        $type = mime_content_type($file);
        $showname =  ltrim(strrchr($file,'/'),'/');
        header("Content-Description: File Transfer");
        header('Content-type: ' . $type);
        header('Content-Length:' . $length);
        if (preg_match('/MSIE/', $_SERVER['HTTP_USER_AGENT'])) { //for IE
         header('Content-Disposition: attachment; filename="' . rawurlencode($showname) . '"');
        } else {
         header('Content-Disposition: attachment; filename="' . $showname . '"');
        }
        readfile($file);
        exit;
    } else {
     exit('文件已被删除！');
    }
}