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;
}