ThinkPHP 5.0 文件下载

public function download(){
        $equipmentInfoModel = new EquipmentInfoModel();
        $file_name = $equipmentInfoModel->where('id', input('id'))->column('qrcode_img');
        $file_dir = ROOT_PATH.'public'.implode($file_name);
        if (file_exists($file_dir)){
            $file  = fopen($file_dir, 'r');
            // 输入文件标签
            \header('Content-type: application/octet-stream');
            \header('Accept-Ranges: bytes');
            \header('Accept-Length: '.filesize($file_dir));
            \header('Content-Disposition: attachment; filename='.implode($file_name));
            ob_clean();
            flush();
            echo fread($file, filesize($file_dir));
            fclose($file);
            exit();
        }else{
            $equipmentInfoModel->update(['id' => input('id'), 'qrcode_img' => '']);
            $this->error('文件已被删除，下载失败, 请重新生成二维码');
        }
    }