import { ServerMiddleware } from "../server.js";
export interface HeartbeatMiddlewareOptions {
    /**
     * heartbeat message to send, defaults to newline (\n)
     */
    payload?: Uint8Array;
    /**
     * time to wait to start sending heartbeat messages, default 30 seconds
     */
    interval?: number;
}
export declare function createHeartbeatMiddleware(options?: HeartbeatMiddlewareOptions): ServerMiddleware;