RequestListener.php

<?php
// src/MyBundle/EventListener/RequestListener.php

namespace MyBundle\EventListener;

use Symfony\Component\HttpKernel\Event\GetResponseEvent;

class RequestListener
{
    protected $twig;

    public function __construct(\Twig_Environment $twig)
    {
        $this->twig = $twig;
    }

    public function onKernelRequest(GetResponseEvent $event)
    {
		$request = $event->getRequest();

		$view = $request->headers->get('view');
		if(!$view){$view = 'desktop';}

		$this->twig->addGlobal('view', $view);
	
    }
}

service.yml

services:
    my.request_listener:
        class: MyBundle\EventListener\RequestListener
        arguments: [@twig]
        tags:
            - { name: kernel.event_listener , event: kernel.request , method: onKernelRequest }