import { type FastifyReply } from 'fastify';
export interface EventMessage {
    /**
     * Message payload
     */
    data?: string;
    /**
     * Message identifier, if set, client will send `Last-Event-ID: <id>` header on reconnect
     */
    id?: string;
    /**
     * Message type
     */
    event?: string;
    /**
     * Update client reconnect interval (how long will client wait before trying to reconnect).
     */
    retry?: number;
}
export declare function addSSEHeaders(reply: FastifyReply): void;
export declare function serializeSSE(chunk: EventMessage): string;