FileExtensionConstraintValidator.php

<?php

declare (strict_types=1);
namespace Drupal\file\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\Exception\UnexpectedTypeException;

/**
 * Validates the file extension constraint.
 */
class FileExtensionConstraintValidator extends BaseFileConstraintValidator {
    
    /**
     * {@inheritdoc}
     */
    public function validate(mixed $value, Constraint $constraint) {
        $file = $this->assertValueIsFile($value);
        if (!$constraint instanceof FileExtensionConstraint) {
            throw new UnexpectedTypeException($constraint, FileExtensionConstraint::class);
        }
        $extensions = $constraint->extensions;
        $regex = '/\\.(' . preg_replace('/ +/', '|', preg_quote($extensions)) . ')$/i';
        // Filename may differ from the basename, for instance in case files
        // migrated from D7 file entities. Because of that new files are saved
        // temporarily with a generated file name, without the original extension,
        // we will use the generated filename property for extension validation only
        // in case of temporary files; and use the file system file name in case of
        // permanent files.
        $subject = $file->isTemporary() ? $file->getFilename() : $file->getFileUri();
        if (!preg_match($regex, $subject)) {
            $this->context
                ->addViolation($constraint->message, [
                '%files-allowed' => $extensions,
            ]);
        }
    }

}