/**
 * Represents a message in the [Server-Sent Event protocol](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#fields)
 *
 * ```js
 * // All fields are optional
 * const message = {
 *   comment: 'hello there',
 *   event: 'my-event',
 *   data: JSON.stringify({ lots: 'of', things: true }),
 *   id: 42,
 *   retry: 3600
 * }
 * ```
 */
export interface ServerSentEventMessage {
    /** Ignored by the client, can be used to prevent connections from timing out */
    comment?: string;
    /** A string identifying the type of event described. If specified this event is triggered, otherwise a "message" will be dispatched. */
    event?: string;
    /** The data field for the message. Split by new lines. */
    data?: string;
    /** The event ID to set the `EventSource` object's last event ID value. */
    id?: string | number;
    /** The reconnection time. If the connection to the server is lost, the browser will wait for the specified time before attempting to reconnect. */
    retry?: number;
}
export declare function _assertHasNoNewline(value: string, variable: string, errPrefix: string): void;
/**
 * Converts a server-sent message object into a string for the client.
 *
 * @see {@link https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format}
 */
export declare function _stringify(message: ServerSentEventMessage): string;
/**
 * Transforms server-sent message objects into strings for the client.
 * [more info](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events).
 *
 * You can then write {@link ServerSentEventMessage} to that stream over time.
 *
 * ```js
 * const data = [{ data: "hello there" }]
 *
 * // Get a stream somehow, then pipe it through
 * const stream = ReadableStream.from<ServerSentEventMessage>(data)
 *   .pipeThrough(new ServerSentEventStream());
 *
 * const response = new Response(stream, {
 *   headers: {
 *     "content-type": "text/event-stream",
 *     "cache-control": "no-cache",
 *   },
 * });
 * ```
 */
export declare class ServerSentEventStream extends TransformStream<ServerSentEventMessage, Uint8Array> {
    constructor();
}
/** @unstable */
export declare const sseHeaders: {
    "content-type": string;
    "cache-control": string;
    connection: string;
};
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