import { type MultipartFile } from '../file.ts';
/**
 * Validates the file extension against a list of allowed extensions
 */
export declare class ExtensionValidator {
    #private;
    /**
     * Whether the file has been validated
     */
    validated: boolean;
    /**
     * Update the expected file extensions
     */
    get extensions(): string[] | undefined;
    set extensions(extnames: string[] | undefined);
    /**
     * Creates a new ExtensionValidator instance
     *
     * @param file - The multipart file to validate
     */
    constructor(file: MultipartFile);
    /**
     * Validates the file extension against the list of allowed extensions.
     * During streaming, validation waits until the extension is detected.
     *
     * @example
     * ```ts
     * const validator = new ExtensionValidator(file)
     * validator.extensions = ['jpg', 'png', 'gif']
     * validator.validate()
     *
     * if (!file.isValid) {
     *   console.log(file.errors) // Extension validation errors
     * }
     * ```
     */
    validate(): void;
}