Generating public URLs for Sonata Media objects during serialization

MediaHandler.php

namespace AppBundle\Handlers;

use Application\Sonata\MediaBundle\Entity\Media;
use JMS\Serializer\Context;
use JMS\Serializer\GraphNavigator;
use JMS\Serializer\Handler\SubscribingHandlerInterface;
use JMS\Serializer\JsonSerializationVisitor;

class MediaHandler implements SubscribingHandlerInterface {

    private $container;

    public function __construct($container) {
        $this->container = $container;
    }

    public static function getSubscribingMethods()
    {
        return [
            [
                'direction' => GraphNavigator::DIRECTION_SERIALIZATION,
                'format' => 'json',
                'type' => 'Application\Sonata\MediaBundle\Entity\Media',
                'method' => 'serializeMedia'
            ]
        ];
    }

    public function serializeMedia(JsonSerializationVisitor $visitor, Media $media, array $type, Context $context) {
        $mediaHelper = $this->container->get('templating.helper.media');
        return $mediaHelper->getPublicUrl($media, 'default');
    }

}

MediaHelper.php

<?php
namespace AppBundle\Helpers;

use Application\Sonata\MediaBundle\Entity\Media;
use Symfony\Component\Templating\Helper\Helper;

class MediaHelper extends Helper {

    private $container;

    public function __construct($container) {
        $this->container = $container;
    }

    public function getPublicUrl(Media $media, $size) {
        $provider = $this->container->get($media->getProviderName());
        return $provider->generatePublicUrl($media, $size);
    }

    public function getName() {
        return "MediaHelper";
    }
}

services.yml

services:

    templating.helper.media:
        class: AppBundle\Helpers\MediaHelper
        arguments:
            - '@service_container'
        tags:
            - { name: templating.mediahelper, alias: mediahelper }
            
    jms_media_handler:
        class: AppBundle\Handlers\MediaHandler
        arguments:
            - '@service_container'
        tags:
            - { name: jms_serializer.subscribing_handler }

StuffController.php

<?php

namespace AppBundle\Controller;

use AppBundle\Entity\Stuff;
use JMS\Serializer\Handler\HandlerRegistry;
use JMS\Serializer\SerializerBuilder;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Component\HttpFoundation\Response;

class StuffController extends Controller
{

    /**
     * @Route("/api/stuff/list", name="list_stuff")
     */
    public function listStuffAction()
    {
        $stuff = $this->getDoctrine()->getRepository(Stuff::class)
            ->findAll();

        // Use our custom handler.
        $serializer = SerializerBuilder::create()
            ->configureHandlers(function(HandlerRegistry $registry) {
                $registry->registerSubscribingHandler($this->get('jms_media_handler'));
            })
            ->addDefaultHandlers()
            ->build();

        $data = $serializer->serialize($stuff, 'json');
        $response = new Response($data);
        $response->headers->set('Content-Type', 'application/json');

        return $response;
    }

}