How to use absolute path in twig functions

From Symfony2 documentation: Absolute URLs for assets were introduced in Symfony 2.5.

If you need absolute URLs for assets, you can set the third argument (or the absolute argument) to true:

Example:

<img src="{{ asset('images/logo.png', absolute=true) }}" alt="Symfony!" />

For Symfony 2.7 and newer

See this answer here.

1st working option

{{ app.request.scheme ~'://' ~ app.request.httpHost ~ asset('bundles/acmedemo/images/search.png') }}

2nd working option - preferred

Just made a quick test with a clean new Symfony copy. There is also another option which combines scheme and httpHost:

{{ app.request.getSchemeAndHttpHost() ~ asset('bundles/acmedemo/images/search.png') }}
{# outputs #}
{# http://localhost/Symfony/web/bundles/acmedemo/css/demo.css  #}

Symfony 2.7 has a new absolute_url which can be used to generate the absolute url. http://symfony.com/blog/new-in-symfony-2-7-the-new-asset-component#template-function-changes

It will work on those both cases or a path string:

<a href="{{ absolute_url(path('route_name', {'param' : value})) }}">A link</a>

and for assets:

<img src="{{ absolute_url(asset('bundle/myname/img/image.gif')) }}" alt="Title"/>

Or for any string path

<img src="{{ absolute_url('my/absolute/path') }}" alt="Title"/>

on those tree cases you will end up with an absolute URL like

http://www.example.com/my/absolute/path