/// <reference types="node" />
import { Readable, Stream, Writable } from 'node:stream';
/**
 * Describes a result object as returned by a middleware transform function.
 * When either stream or metadata changed as part of the middleware function, such a result object containing the
 * new instance must be passed to the next handler.
 */
export interface MiddlewareResult<S extends Stream> {
    stream?: S;
    metadata?: object;
}
/**
 * Call this function to complete the middleware transform.
 */
export type MiddlewareNextFn<S extends Stream> = (err?: Error | undefined | null, result?: MiddlewareResult<S>) => void;
/**
 * A transform function as part of a middleware.
 * Calling next is mandatory, otherwise processing cannot continue. If needed, pass an error as the first argument.
 * When either stream or metadata changed as part of the middleware function, a result object containing the new
 * instance must be passed to the callback.
 */
export type MiddlewareTransformFn<S extends Stream> = (stream: S, metadata: object, options: object | undefined | null, next: MiddlewareNextFn<S>) => void;
/**
 * The interface for middlewares.
 */
export interface Middleware {
    transformReadable?: MiddlewareTransformFn<Readable>;
    transformWritable?: MiddlewareTransformFn<Writable>;
}