Difference between InputFilterAwareInterface and InputFilterProviderInterface in ZF2

Can someone explain me the difference between both interfaces InputFilterAwareInterface and InputFilterProviderInterface? Both seem to serve to the same purpose, to get an InputFilter, but I know they cannot be the same... And when do they get called?

Thanks

Both interfaces exist for different purposes. The InputFilterAwareInterface guarantees that implemented classes will have a setInputFilter() and getInputFilter() methods which accept and return an InputFilter instance when necessary. On the other hand, the InputFilterProviderInterface guarantees only that implemented classes will have a getInputFilterSpecification() method which returns a filter specification (configuration array) which is ready to use as argument in various input factories.

For example; the snippet below came from Zend\Form\Form.php class:

if ($fieldset === $this && $fieldset instanceof InputFilterProviderInterface) {
    foreach ($fieldset->getInputFilterSpecification() as $name => $spec) {
        $input = $inputFactory->createInput($spec);
        $inputFilter->add($input, $name);
    }
}

As you can see, the Form class creates inputs and binds them to related filter using given specification which is returned by getInputFilterSpecification() method of the implementing class ($fieldset int this case).

Using Traits

Zend Framework 2 also provides lot of traits for commonly used interfaces. For example InputFilterAwareTrait for InputFilterInterface. This means, you can easily implement that interface if you have PHP >= 5.4

namespace MyNamespace;

use Zend\InputFilter\InputFilterInterface;

MyClass implements InputFilterInterface {

    // Here is the trait which provides set and getInputFilter methods
    // with a protected $inputFilter attribute to all MyClass instances.

    use \Zend\InputFilter\InputFilterAwareTrait;

    // Your other methods.
    ...
}

Now anywhere in your code, you can do this:

$myClass->setInputFilter($AnInputFilterInstance);
$myClass->getInputFilter(); // Returns an inputfilter instance.

As you can imagine, no trait exists for InputFilterProviderInterface because its responsibility is only returning a valid config spec. It doesn't deal with any instance or class attribute like is forced in InputFilterInterface.