FileValidator.php

<?php

namespace Drupal\file\Validation;

use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Validation\ConstraintManager;
use Drupal\file\FileInterface;
use Symfony\Component\Validator\ConstraintViolationListInterface;
use Symfony\Component\Validator\Validator\ValidatorInterface;
use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;

/**
 * Provides a class for file validation.
 */
class FileValidator implements FileValidatorInterface {
    
    /**
     * Creates a new FileValidator.
     *
     * @param \Symfony\Component\Validator\Validator\ValidatorInterface $validator
     *   The validator.
     * @param \Drupal\Core\Validation\ConstraintManager $constraintManager
     *   The constraint factory.
     * @param \Symfony\Contracts\EventDispatcher\EventDispatcherInterface $eventDispatcher
     *   The event dispatcher.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $moduleHandler
     *   The module handler.
     */
    public function __construct(ValidatorInterface $validator, ConstraintManager $constraintManager, EventDispatcherInterface $eventDispatcher, ModuleHandlerInterface $moduleHandler) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate(FileInterface $file, array $validators) : ConstraintViolationListInterface {
        $constraints = [];
        foreach ($validators as $validator => $options) {
            // Create the constraint.
            // Options are an associative array of constraint properties and values.
            $constraints[] = $this->constraintManager
                ->create($validator, $options);
        }
        // Get the typed data.
        $fileTypedData = $file->getTypedData();
        $violations = $this->validator
            ->validate($fileTypedData, $constraints);
        $this->eventDispatcher
            ->dispatch(new FileValidationEvent($file, $violations));
        // Always check the insecure upload constraint.
        if (count($violations) === 0) {
            $insecureUploadConstraint = $this->constraintManager
                ->create('FileExtensionSecure', []);
            $violations = $this->validator
                ->validate($fileTypedData, $insecureUploadConstraint);
        }
        return $violations;
    }

}