Getting the base url of the website and globally passing it to twig in Symfony 2

I'm making the switch from CodeIgniter to Symfony 2. Can someone please give me an example of how to:

• Get the base url (the url without the route specific parts)
• Globally pass this variable to the twig bundle so I can use it in every template.

Why do you need to get this root url ? Can't you generate directly absolute URL's ?

{{ url('_demo_hello', { 'name': 'Thomas' }) }}

This Twig code will generate the full http:// url to the _demo_hello route.

In fact, getting the base url of the website is only getting the full url of the homepage route :

{{ url('homepage') }}

(homepage, or whatever you call it in your routing file).