Validators
=============

.. objectives:: Objectives

   We will see how to create strong validations for the values ​​of our variables, 
   that is, validations that go beyond those inherent in the initial type definition.

.. prerequisites:: Prerequisites

    - We assume that Rougail's library is :ref:`installed <installation>` on your computer.

    - It is possible to retrieve the current state of the various Rougail files manipulated in this tutorial step
      by checking out the corresponding tag of the `rougail-tutorials` git repository.
      Each tag corresponds to a stage of progress in the tutorial.
      Of course, you can also decide to copy/paste or download the tutorial files contents while following the tutorial steps.

    If you want to follow this tutorial with the help of the corresponding :tutorial:`rougail-tutorials git repository <src/branch/v1.1>`,
    this workshop page corresponds to the tag :tutorial:`v1.1_170 <src/tag/v1.1_170/README.md>`
    in the repository.

    ::

       git clone https://forge.cloud.silique.fr/stove/rougail-tutorials.git
       git switch --detach v1.1_170

Validating a variable's value
-----------------------------------

Now, we would like the :term:`operator` to remember not to forget the http protocol, that is to put `http://` at the beginning of our `web_address` variable's value. What if he has forgotten the http protocol? We can add a reminder in case he has forgotten.

We call it a validator.

.. glossary::

   validator
   
       A validator is a jinja code that parses a variable's value and checks
       that this value corresponds to some stated criteria.
       This is a `validator` parameter of our variable, and another `jinja` sub-parameter
       contains validation code for the variable's value.

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_170/firefox/60-dns_over_https.yml
   :language: yaml
   :caption: The :file:`firefox/60-dns_over_https.yml` with the jinja validator