For better integration between 5.2 (symfony based) kernel and legacy (4.x) kernel, injection is used to inject settings, session and current siteaccess from 5.2 into legacy using an event: kernel.event_subscriber

This page describe how you can do that.  

Adding a kernel.event_subscriber

A legacy kernel event subscriber is added by tagging your event subscriber service.

Bellow is an example of yml configuration involved:

    my_app.legacy_mapper.something:
        class: %my_app.legacy_mapper.something.class%
        arguments: [@service_container]
        tags:
            - { name: kernel.event_subscriber }

 

The class refered to as %my_app.legacy_mapper.something.class% can look like this:

namespace MyApp\LegacyMapper;
use eZ\Publish\Core\MVC\Legacy\LegacyEvents;
use eZ\Publish\Core\MVC\Legacy\Event\PreBuildKernelWebHandlerEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;
/**
 * Maps something into Legacy kernel
 */
class Something implements EventSubscriberInterface
{
    /**
     * @var \Symfony\Component\DependencyInjection\ContainerInterface
     */
    private $container;
 
   /**
    * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
    */
    public function __construct( ContainerInterface $container )
    {
        $this->container = $container;
    }
    public static function getSubscribedEvents()
    {
        return array(
            LegacyEvents::PRE_BUILD_LEGACY_KERNEL_WEB => array( 'onBuildKernelWebHandler', 128 )
        );
    }
    /**
     * Maps matched siteaccess to the legacy parameters
     *
     * @param \eZ\Publish\Core\MVC\Legacy\Event\PreBuildKernelWebHandlerEvent $event
     *
     * @return void
     */
    public function onBuildKernelWebHandler( PreBuildKernelWebHandlerEvent $event )
    {
        // Do something, see eZ\Bundle\EzPublishLegacyBundle\LegacyMapper\* for examples
        // Example for injecting some settings:
 
        $settings = array(
            'site.ini/Block/Setting' => $this->container->getParameter( 'some.setting' ),
            'site.ini/Block/Setting2' => $this->configResolver->getParameter( 'some.setting2' )
        );
 
        $event->getParameters()->set(
            "injected-settings",
            $settings + (array)$event->getParameters()->get( "injected-settings" )
        );
    }
}