用Yii，Mysql下载longblob文件（adobe Illustrator或png）

I am trying to download ai/png from mysql DB but all I get is an empty file. On the table I only have id and two longblob (file_ai, file_png). For example, file adobe illustrator view is:

echo CHtml::link('<span class="glyphicon glyphicon glyphicon-download-alt" aria-hidden="true"></span>', 
array('User/downloadFile', 'id' => $file->id, 'ext' => 'application/illustrator'), 
$htmlOptions = array('class' => 'toolMes', 'download', 'data-toggle' => 'tooltip', 'data-placement' => 'bottom', 'title' => 'Download Ai'));

In the controller:

public function actionDownloadFile($id, $ext) {
        $file = Files::model()->findByPk($id);
        if ($ext === 'application/illustrator') {
            header("Content-length:" . strlen($file->file_ai));
            header("Content-type: " . $ext . "");
            header('Content-Disposition: attachment; filename="' . $file->id . '_' . date("Y-m-d") . '.ai"');
        } else {
            header("Content-length:" . strlen($file->file_png));
            header("Content-type: image/png");
            header('Content-Disposition: attachment; filename="' . $file->id . '_' . date("Y-m-d") . '"');
        }
    }

Hope it is enough to have your precious suggestions

Your not echoing out the actual file contents!

If you are storing images in your database you need to do the echo after you throw the headers...

echo $file->file_ai;