Post-processing response

Sometimes there's a need to post-process repsonse which is to be sent to browser. A good example is short tags like the ones in Wordpress engine. You use it like the following:

This is [username]. We have [visitor_count] visitors on website.

And both are automatically replaced by corresponding content.

How to do it

Yii is very flexible so it's easy to achieve:

Yii::$app->getResponse()->on(Response::EVENT_AFTER_PREPARE, function($event) {
    /** @var User $user */
    $user = Yii::$app->getUser()->getIdentity();
    $replacements = [
        '[username]' => $user->username,
        '[visitor_count]' => 42,

    $event->sender->content = str_replace(array_keys($replacements), array_values($replacements), $event->sender->content);

In the code above we're using Response::EVENT_AFTER_PREPARE which is triggered right before sending content to a browser. In the callback $event->sender is our response object which keeps data to be sent in content property. So we are finding and replacing short tags there.