Content validation within Apigility is the process of taking incoming data and determining if it is valid. If it is not then an API Problem response is returned containing details on the validation failures.

For each service, Apigility allows you to configure a fieldset that is to be used when data is passed to the service. To accomplish this, Apigility uses the zf-content-validation module to create Zend Framework 2 input filters, then executes the input filter associated with a service when data is submitted.

Note: Content Validation Request Methods

Content Validation currently only works for POST, PATCH, and PUT requests. If you need to validate query string parameters, you will need to write your own logic for those tasks.

Input filters accomplish the jobs of filtering (via the Zend\Filter component) and validating (via the Zend\Validator component). To quote the Zend Framework manual on the purpose of input filters:

The Zend\InputFilter component can be used to filter and validate generic sets of input data. For instance, you could use it to filter $_GET or $_POST values, CLI arguments, etc.

An input filter is composed of one or more input objects (or even other input filters!). Each input object represents a named incoming field which contains information on how to validate it:

  • Is the value required?
  • If required, is it allowed to be empty?
  • If it is allowed to be empty, should validators be executed anyways?
  • What normalization filters should execute for this value?
  • What validators should the normalized value be passed to?
  • Should the input return validation error messages from the aggregate validators, or present a single error message when invalid?

The input filter iterates over each input (or input filter) it composes, passing it the corresponding field value; only if all inputs validate does it pass validation; if any input is invalid, the entire input filter is considered invalid.

Within the Apigility Admin UI, input filters are defined in the "Fields" tab of a service. This UI allows you to describe what the incoming data fieldset should look like, what options are configured for each field, which filters the field will utilize, and which validators it will execute. The description is saved as an input filter specification which can be consumed by Zend\InputFilter\Factory in order to return a concrete Zend\InputFilter\InputFilter instance - which is then used for validating incoming data.