Symfony2 Twig custom filter in asset - symfony

Question

I'm nearly new in Symfony2 and I have a little question:
I'm developing an email template, which has txt and html parts (no problem with it)
The only 'problem' I have is with the absolute paths of assets in TWIG.
Inside my email.html.twig file I have something like this:
<img src="{{ asset('images/my-image.png') }}" alt="My image" /> but it writes the route with relative path.
I discovered a little solution to add absolute paths, something like this:
{% set abs = app.request.scheme ~ '://' ~ app.request.host %}
<img src="{{ abs ~ asset('images/my-image.png') }}" alt="My image" />
It works! But I want to improve this solution and also learn to create custom filters (I read the documentation, but I got a bit lost)
I want to create something like this:
<img src="{{ asset('images/my-image.png' | absolute) }}" alt="My image" />
But I don't know how to properly override the assetics extension. Can you help me?
Thanks a lot!!

Answer 1

Well, it is a little hard to copy paste the solution but I can make a short cookbook so you can go step by step and do it yourself:
1) You will have to implement Assetic/Filter/FilterInterface
2) If you look at the FilterInterface class, you will see that you have to to implement two methods: filterLoad and filterDump.
So, you will do something like this:
<?php
namespace You\YourBundle\Assetic\Filter;
use Assetic\Asset\AssetInterface;
use Assetic\Filter\FilterInterface;
class YourAsseticFilter implements FilterInterface
{
public function filterLoad(AssetInterface $asset)
{
// do something
}
public function filterDump(AssetInterface $asset)
{
$content = $asset->getContent();
// do something
$asset->setContent($content);
}
}
And after you to this, you have to something very similar to registering twig extensions in services.yml in YourBundle. Sure, it depens if you use YML, XML... configuration. I use yml so I will type it in yml :)
parameters:
your_bundle.class: You\YourBundle\Assetic\Filter\YourAsseticFilter
services:
your_bundle.assetic.your_assetic_filter:
class: %your_bundle.class%
tags:
- { name: assetic.filter }
- { alias: yourChosenNameForYourNewAsseticFilter }
And then you call it like | yourChosenNameForYourNewAsseticFilter, of course.