How can I restrict external URLs in link field to allow only certain domains?

Question

After creating a Link field and use the Link with service icon format, I find out that there is no option to restrict external URLs to external domains that I want

For example, if I only want to allow Twitter links, something like add https://www.twitter.com/*.

Someone already asked here, but it seems that the Advanced Link module is not available for my Drupal version.

With what module and how can I filter my desired URLs in Drupal 9?

Answer 1

There is a now a new module on drupal.org: Link Allowed Hosts – Will be working on this during the week so next week we can finally restrict the allowed hosts for link fields.

Answer 2

You need to write your own custom validation contraint and add this constraint to your field.

Docs: https://www.drupal.org/docs/drupal-apis/entity-api/entity-validation-api/providing-a-custom-validation-constraint

I've used that example to create a "force HTTPS" link field constraint

src/Plugin/Validation/Constraint/Https.php

<?php

namespace Drupal\MYMODULE\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;

/**
 * Checks that the submitted URL is starting with https://
 *
 * @Constraint(
 *   id = "MY_CONSTRAINT_ID",
 *   label = @Translation("Https", context = "Validation"),
 *   type = "string"
 * )
 */
class Https extends Constraint {
  public $notHttps = '%uri is not a secure site (not starting with https://)';
}

src/Plugin/Validation/Constraint/HttpsValidator.php

<?php

namespace Drupal\MYMODULE\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

/**
 * Validates the Https constraint.
 */
class HttpsValidator extends ConstraintValidator {

  /**
   * {@inheritdoc}
   */
  public function validate($items, Constraint $constraint) {
    $item = $items->first();
    if (!isset($item)) {
      return NULL;
    }

    foreach ($items as $item) {
      /* CHANGE THIS, e.g. here you can check for domain names */
      if (strpos($item->uri, 'https://') !== 0) {
        $this->context->addViolation($constraint->notHttps, ['%uri' => $item->uri]);
      }
    }
  }
}

MYMODULE.module

<?php

use Drupal\Core\Entity\EntityTypeInterface;

function MYMODULE_entity_bundle_field_info_alter(&$fields, EntityTypeInterface $entity_type, $bundle) {
  if ($bundle === 'MY_ENTITY_BUNDLE' && $entity_type->id() == 'MY_ENTITY_TYPE') {
    if (isset($fields['MY_FIELD'])) {
      $fields['MY_FIELD']->addConstraint('MY_CONSTRAINT_ID', []);
    }
  }
}

Answer 3

A module exists with that capability, perhaps try https://www.drupal.org/sandbox/wombatbuddy/3183996