Pop out file download message in admin grid massaction

Inside the massaction controller, e.g. Mage_Adminhtml_Sales_OrderController By default, those print invoice options do this:

 
return $this->_prepareDownloadResponse(
                    //edit by leo - change file name
                    $filename.Mage::getSingleton('core/date')->date('Y-m-d_H-i-s').'.pdf', $pdf->render(),
                    'application/pdf'
                );

But you can not just output pdf/file, csv is also ok

 
$data = 'your csv data';
$this->_prepareDownloadResponse('file.csv', $data, 'text/csv');

In my situation, I generate shipping label in HTML format. As massaction action does not allow opening the action in the blank page, so i assign those html content into a html file.

 
$html = $block->toHtml();
        $filename = 'form_'. Mage::getSingleton('core/date')->date('Y-m-d_H-i-s').'.html';
        return $this->_prepareDownloadResponse($filename, $html, 'text/html');