弹出警告框而不是下载对话框php

如何解决弹出警告框而不是下载对话框php

我编写了以下 PHP 代码来向用户发送文件以供下载

<?PHP
header('Access-Control-Allow-Origin: *');
header("Access-Control-Allow-Methods: GET,POST,OPTIONS,PUT,DELETE");
header("Access-Control-Allow-Headers: Content-Type,Access-Control-Allow-Headers,X-Requested-With");

$filename = "monkey.txt";

if(file_exists($filename)){

    //Get file type and set it as Content Type
    $finfo = finfo_open(FILEINFO_MIME_TYPE);
    header('Content-Type: ' . finfo_file($finfo,$filename));
    finfo_close($finfo);

    //Use Content-disposition: attachment to specify the filename
    header('Content-disposition: attachment; filename='.basename($filename));

    //No cache
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');

    //Define file size
    header('Content-Length: ' . filesize($filename));

    ob_clean();
    flush();
    readfile($filename);
    exit;
}
?>

但是当 PHP 代码在 localhost 上执行时，我得到了一个带有文本的弹出框，而不是在 Firefox 中得到一个下载对话框，我该怎么做才能解决这个问题？