/**
 * Based entirely on:
 * https://github.com/Polymer/tools/blob/dd1c8bbb44f37f67974fbabf878b7a495ffeb6f6/packages/polyserve/src/transform-middleware.ts
 */
import { Request, RequestHandler, Response } from 'express';
export declare function transformResponse(transformer: ResponseTransformer): RequestHandler;
export interface ResponseTransformer {
    /**
     * Returns `true` if this transformer should be invoked.
     * Transformers should only look at headers, do not call res.write().
     */
    shouldTransform(request: Request, response: Response): boolean;
    transform(request: Request, response: Response, body: string): string;
}