PHP 弹出文件下载 原理 代码

/** * @author      default7 * @description 演示PHP弹出下载的原理 * * @param $file_name */function downFile($file_name){    $file_path = "/tmp/" . $file_name;    $buffer = 102400; //一次返回102400个字节    if (!file_exists($file_path)) {        echo "<script type='text/javascript'> alert('对不起！该文件不存在或已被删除！'); </script>";        return;    }    $fp = fopen($file_path, "r");    $file_size = filesize($file_path);    $file_data = '';    while (!feof($fp)) {        $file_data .= fread($fp, $buffer);    }    fclose($fp);    //Begin writing headers    header("Pragma: public");    header("Expires: 0");    header("Cache-Control: must-revalidate, post-check=0, pre-check=0");    header("Cache-Control: public");    header("Content-Description: File Transfer");    header("Content-type:application/octet-stream;");    header("Accept-Ranges:bytes");    header("Accept-Length:{$file_size}");    header("Content-Disposition:attachment; filename={$file_name}");    header("Content-Transfer-Encoding: binary");    echo $file_data;}