composer require sopinet/apihelper-bundle "1.0"

// app/AppKernel.php

// ...
class AppKernel extends Kernel
{
    // ...

    public function registerBundles()
    {
        $bundles = array(
            // ...
            new Sopinet\ApiHelperBundle\SopinetApiHelperBundle(),
            new FOS\RestBundle\FOSRestBundle(),
            new JMS\SerializerBundle\JMSSerializerBundle(),
        );

        // ...
    }
}

fos_rest:
    routing_loader:
        default_format: json

use SopinetApiHelperBundle\Services\ApiHelper;
$apiHelper = $this->get('sopinet_apihelperbundle_apihelper');
...
return $apiHelper->responseOk();