Empty values passed to Zend framework 2 validators

How can I pass an empty value through Zend framework 2 ValidatorChain to my custom validator?

It was possible on ZF1 by allowEmpty(false)

On ZF2 with empty element value :

• If allowEmpty = false, NotEmptyValidator is added to the top of ValidatorChain with breakOnFailure = true, @see Zend/InputFilter/Input#injectNotEmptyValidator.

• If allowEmpty = true, Element is considered as Valid, @see Zend/InputFilter/BaseInputFilter#isValid

  if ($input->allowEmpty()) {
      $this->validInputs[$name] = $input;
      continue;
  }
  

Following works for ZF2 version 2.1.1:

The problem (if I got it correctly) is that in following example, for empty values of 'fieldName', no validation is triggered. This can be quite annoying, though in

$input = new \Zend\InputFilter\Input('fieldName');

$input
    ->setAllowEmpty(true)
    ->setRequired(false)
    ->getValidatorChain()
    ->attach(new \Zend\Validator\Callback(function ($value) {
        echo 'called validator!';

        return true; // valid
    }));

$inputFilter = new \Zend\InputFilter\InputFilter();
$inputFilter->add($input);

$inputFilter->setData(array('fieldName' => 'value'));
var_dump($inputFilter->isValid()); // true, echoes 'called validator!'

$inputFilter->setData(array('fieldName' => ''));
var_dump($inputFilter->isValid()); // true, no output

$inputFilter->setData(array());
var_dump($inputFilter->isValid()); // true, no output

This is quite annoying when you have particular cases, like checking an URL assigned to a page in your CMS and avoiding collisions (empty URL is still an URL!).

There's a way of handling this for empty strings, which is to basically attach the NotEmpty validator on your own, and avoiding calls to setRequired and setAllowEmpty. This will basically tell Zend\InputFilter\Input#injectNotEmptyValidator not to utomatically attach a NotEmpty validator on its own:

$input = new \Zend\InputFilter\Input('fieldName');

$input
    ->getValidatorChain()
    ->attach(new \Zend\Validator\NotEmpty(\Zend\Validator\NotEmpty::NULL))
    ->attach(new \Zend\Validator\Callback(function ($value) {
        echo 'called validator!';

        return true; // valid
    }));

$inputFilter = new \Zend\InputFilter\InputFilter();
$inputFilter->add($input);

$inputFilter->setData(array('fieldName' => 'value'));
var_dump($inputFilter->isValid()); // true, echoes 'called validator!'

$inputFilter->setData(array('fieldName' => ''));
var_dump($inputFilter->isValid()); // true, echoes 'called validator!'

$inputFilter->setData(array());
var_dump($inputFilter->isValid()); // false (null was passed to the validator)

If you also want to check against null, you will need to extend Zend\InputFilter\Input as following:

class MyInput extends \Zend\InputFilter\Input
{
    // disabling auto-injection of the `NotEmpty` validator
    protected function injectNotEmptyValidator() {}
}