magento2 layout logger

events.xml

<!-- app/code/LayoutLogger/PageXml/etc/events.xml -->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="layout_generate_blocks_after">
        <observer name="layoutlogger_layout_generate_blocks_after" instance="LayoutLogger\PageXml\Model\Layout" />
    </event>
</config>

Layout.php

<?php
// app/code/LayoutLogger/PageXml/Model/Layout.php
namespace LayoutLogger\PageXml\Model;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class Layout  implements ObserverInterface {
    protected $_logger;

    public function __construct(\Psr\Log\LoggerInterface $logger ) {
        $this->_logger = $logger;
    }

    public function execute(\Magento\Framework\Event\Observer $observer) {
        $log_file = BP . '/var/log/page_layout.xml';
        if (file_exists($log_file)) {
            unlink($log_file);
        }
        $xml = $observer->getEvent()->getLayout()->getXmlString();
        /*$this->_logger->debug($xml);*/
        $writer = new \Zend\Log\Writer\Stream($log_file);
        $logger = new \Zend\Log\Logger();
        $logger->addWriter($writer);
        $logger->info($xml);
        return $this;
    }
}

module.xml

<!-- app/code/LayoutLogger/PageXml/etc/module.xml --> 
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="LayoutLogger_PageXml" setup_version="1.0.0" schema_version="1.0.0">
        <sequence>
            <module name="Magento_Catalog"/>
            <module name="Magento_Theme"/>
        </sequence>
    </module>
</config>

registration.php

<?php
// app/code/LayoutLogger/PageXml/registration.php
    \Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'LayoutLogger_PageXml',
    __DIR__
);