gistfile1.txt

<?php

namespace Drupal\sd8\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\Constraints\Url;
use Symfony\Component\Validator\Constraints\UrlValidator;

/**
 * Validates the LinkUriValid constraint.
 */
class LinkUriValidConstraintValidator extends UrlValidator {

  /**
   * {@inheritdoc}
   */
  public function validate($value, Constraint $constraint) {
    if (isset($value)) {
      try {
        /** @var \Drupal\Core\Url $urlObject */
        $urlObject = $value->getUrl();
        $url = $urlObject->setAbsolute()->toString();
        // LinkExternalProtocolsConstraintValidator will deal with external
        // URLs with invalid protocols.
        /** @var \Drupal\sd8\Plugin\Validation\Constraint\LinkUriValidConstraint $constraint */
        $parts = parse_url($url);
        if (!$urlObject->isExternal() || in_array($parts['scheme'], $constraint->protocols)) {
          parent::validate($url, $constraint);
        }
        if ($parts['scheme'] === 'mailto' && !filter_var($parts['path'], FILTER_VALIDATE_EMAIL)) {
          $this->context->buildViolation($constraint->message)
            ->setParameter('{{ value }}', $this->formatValue($value))
            ->setCode(Url::INVALID_URL_ERROR)
            ->addViolation();
        }
      }
      catch (\Exception $e) {
        // This is not our job, it can be invalid internal path and more.
      }
    }
  }

}