export interface FetchEventSourceConfiguration {
    /** custom fetch implementation */
    fetch?: typeof fetch;
    /** custom headers to add to SSE request */
    headers?: Headers;
    /** automatically starts the SSE request */
    autoStart?: boolean;
    /** send cookies to cross-origin URLs */
    withCredentials?: boolean;
    /** initial reconnection delay */
    reconnectionDelay?: number;
}
export default abstract class BaseFetchEventSource extends EventTarget {
    #private;
    url: string;
    withCredentials: boolean;
    readyState: number;
    onopen: () => void | undefined;
    onmessage: (e?: MessageEvent) => void | undefined;
    onerror: (error?: ErrorEvent) => void | undefined;
    protected abstract _fetch: typeof fetch | any;
    protected abstract _decode: (bytes: any) => string;
    protected abstract _getOrigin: () => string;
    protected _transformStream: (stream: any) => any;
    constructor(url: string, config?: FetchEventSourceConfiguration);
    start(): Promise<void>;
    private _connect;
    private _process;
    close(): void;
    _error(error: any): void;
}