下面是我的前端代码：

<form action="" method="post">
    <input type="file" name="image" class="input">
</form>

和控制器：

$upload_image = $_FILES['image']['name'];
        if ($upload_image) {
            $config['allowed_types'] = 'xml|docx|jpg|png|pdf|xlsx';
            $config['max_size'] = '999999';
            $config['upload_path'] = './assets/img/image/';
            $this->load->library('upload', $config);
            if ($this->upload->do_upload('image')) {
                $new_image = $this->upload->data('file_name');
                $this->db->set('image', $new_image);
            } else {
                echo $this->upload->display_errors();
            }
        }

在$config中，prog知道刚刚输入的文件类型，如img docx等，我如何才能得到刚刚输入的文件类型为$types？