SerializedConstraintValidator.php

<?php

namespace Drupal\Core\Validation\Plugin\Validation\Constraint;

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

/**
 * Validates the Serialized constraint.
 */
class SerializedConstraintValidator extends ConstraintValidator {
  
  /**
   * {@inheritdoc}
   */
  public function validate($value, Constraint $constraint) : void {
    if (!isset($value)) {
      return;
    }
    if (!is_string($value)) {
      $this->context
        ->addViolation($constraint->wrongTypeMessage, [
        '{type}' => gettype($value),
      ]);
      return;
    }
    // Unserialize will return false if unserializing "false". It will also
    // return false if unserialization fails. Handle this edge case.
    if ('b:0;' === $value) {
      return;
    }
    $unserialized = @unserialize($value, [
      'allowed_classes' => FALSE,
    ]);
    if ($unserialized === FALSE) {
      $this->context
        ->addViolation($constraint->message);
    }
  }

}