/**
 * Simulate the [Fastly ImageOpto](https://docs.fastly.com/api/imageopto/) API.
 * Returns a middleware which attempts to run image responses through `sharp`.
 */
import { ErrorLogger, Middleware, RequestFilter } from './imageopto-types';
export interface ImageOptoOptions {
    errorLog?: ErrorLogger;
    filter: RequestFilter;
    /**
     * Hastily detects when the served image has already been optimized by
     * Hastily or the real Fastly API, by looking for headers. By default, it
     * disables its own optimizer for such images. Set this to `false` explicitly
     * to force hastily to re-optimize those images anyway.
     */
    force?: boolean;
    /**
     * Set true to disable error logging; the errorLog function will never be
     * called.
     */
    quiet?: boolean;
}
export declare const HASTILY_HEADER: {
    NAME: string;
    VALUE: string;
};
export declare const HASTILY_STREAMABLE_FILETYPES: Set<string>;
export declare const HASTILY_STREAMABLE_PATH_REGEXP: RegExp;
/**
 * Use the `sharp.format` manifest to determine if the current request's file
 * extension matches a format that sharp can stream in to optimize.
 * @param req {Request}
 */
export declare const hasSupportedExtension: RequestFilter;
/**
 * Returns a new imageopto middleware for use in Express `app.use()`.
 * Won't do anything if the Express app isn't already serving images!
 *
 */
export declare function imageopto(filterOrOpts: RequestFilter | ImageOptoOptions): Middleware;