Magento2 – How to Change Response Before Full Page Cache

full-page-cachemagento2

I know my question is strange and I should change the response in the Magento way.

I have an observer subscribed to controller_front_send_response_before event.

events.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="controller_front_send_response_before">
        <observer name="roland_controller_front_send_response_before"
                  instance="Roland\HelloWorld\Model\Observers\ResponseBefore"/>
    </event>
</config>

Model/Observers/ResponseBefore.php

<?php
namespace Roland\HelloWorld\Model\Observers;

use \Magento\Framework\Event\ObserverInterface;

class ResponseBefore implements ObserverInterface {

    public function execute(\Magento\Framework\Event\Observer $observer) {

        $this->playWithResponse($observer->getEvent()
                                   ->getData('response'));

    }

    public function playWithResponse($response) {

        $head = '<script>alert("'.time().'");</script>';
        $response->setBody(preg_replace('/<\/head>/', $head . '</head>', $response->getBody(), 1));
    }

}

It works fine when Full page cache not enabled. Every time I refresh the page, I get an alert with the current server time. When Full page cache is enabled, I would like to make my code cached into Full page cache. Currently my observer called on every page load as the Full page cache comes before the controller_front_send_response_before event.

So I checked how's Magento 2 Full page cache works in magento/module-page-cache/Observer/Process/LayoutRenderElement.php

    public function execute(\Magento\Framework\Event\Observer $observer)
{
    $event = $observer->getEvent();
    /** @var \Magento\Framework\View\Layout $layout */
    $layout = $event->getLayout();
    if ($this->isFullPageCacheEnabled() && $layout->isCacheable()) {
        $name = $event->getElementName();
        /** @var \Magento\Framework\View\Element\AbstractBlock $block */
        $block = $layout->getBlock($name);
        $transport = $event->getTransport();
        if ($block instanceof \Magento\Framework\View\Element\AbstractBlock) {
            $blockTtl = $block->getTtl();
            $output = $transport->getData('output');
            if (isset($blockTtl) && $this->isVarnishEnabled()) {
                $output = $this->_wrapEsi($block, $layout);
            } elseif ($block->isScopePrivate()) {
                $output = sprintf(
                    '<!-- BLOCK %1$s -->%2$s<!-- /BLOCK %1$s -->',
                    $block->getNameInLayout(),
                    $output
                );
            }
            $transport->setData('output', $output);
        }
    }
}

I saw that it caches every block, but I haven't got any further.

Here is the part of my $event->getElementName():
mailcheck_init
emailCapture
copyright
before.body.end
page.wrapper
root

I thought if I change the content in the observer before the page cache that might worth, but I have no luck.

if($event->getElementName() == 'root'){
    $transport = $event->getTransport();
    $transport->setData('output', 'test');
}

Do you have any suggestion how should I achieve the desired result?

Best Answer

So, finally I have a real solution. So I was able to track down Magento2 full page cache and turned out that it does the caching as a plugin: Magento\PageCache\Model\App\FrontController\BuiltinPlugin in the aroundDispatch.

$this->kernel->process($result);

Does the work of storing the serialized $response object.

So the solution was to create a plugin for the after event:

Roland/HelloWorld/etc/di.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Framework\Controller\ResultInterface">
        <plugin name="change-result-before-cache" type="Roland\HelloWorld\Model\Plugins\ChangeResult"/>
    </type>
</config>

Roland/HelloWorld/Model/Plugins/ChangeResult.php

<?php

namespace Roland\HelloWorld\Model\Plugins;

use Magento\Framework\App\Response\Http as ResponseHttp;


class ChangeResult {

    public function afterRenderResult(ResponseHttp $response) {
        $response->setBody(preg_replace('/<\/head>/', '<script>alert("' . time() . '");</script>' . '</head>', $response->getBody(), 1));
    }

}

The result

When page cache enabled, you should always see the same timestamp for every refresh.

Related Solutions

Magento2 Cache – Built-in Cache vs. Varnish Cache for Full Page Cache

from https://www.section.io/blog/magento-performance-magento-varnish-cache/

"One common mistake when using Magento 2 is believing that Magento 2’s built in “Full Page Cache” feature is sufficient for performance. The Full Page Cache mode is labelled by Magento as to be used in development mode, as developers are not able to see what is being cached and what is not being cached with this setting. In production, it is strongly recommended all Magento 2 stores use Varnish Cache for optimal performance."

Magento recommends Varnish as the full page cache for a production site - the built in cache should be used for development.
Install varnish and configure Magento with the hostname or ip address and port of your varnish server
download a vcl configuration file generated by Magento to use with the varnish server.
make sure you add the external cache to the Magento configuration

php bin/magento setup:config:set --http-cache-hosts=varnishhost

Magento 2 – Set Custom Price of Product When Adding to Cart Code Not Working

Please use this even checkout_cart_product_add_after, and also I suggest you that

ObserverInterface has only one method which is execute, so write your code in this method.

And do not use parent Item because while you are adding to cart any item then price depend upon child item so the best way is to use directly that item object that you are getting. So best practice is to use that item itself.

And also return $this object at the end of your code inside execute method.

For eg: namespace Navin\Testcart\Observer;

use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\App\RequestInterface;

class CustomPrice implements ObserverInterface
{
    public function execute(\Magento\Framework\Event\Observer $observer) {

        $item=$observer->getEvent()->getData('quote_item');
        $product=$observer->getEvent()->getData('product');
        // here i am using item's product final price
        $price = $item->getProduct()->getFinalPrice()+10; // 10 is custom price. It will increase in product price.
        // Set the custom price
        $item->setCustomPrice($price);
        $item->setOriginalCustomPrice($price);
        // Enable super mode on the product.
        $item->getProduct()->setIsSuperMode(true);
        return $this;
    }

}

Hope this will help you. :)

Magento2 – How to Change Response Before Full Page Cache

Best Answer

The result

Related docs

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