@kbn/sse-utils

This package exports utility functions that can be used to format and parse server-sent events(SSE). SSE is useful when streaming data back to the browser as part of a long-running process, such as LLM-based inference. It can convert an Observable that emits values of type ServerSentEvent into a response stream on the server, emitting lines in an SSE-compatible format, and it can convert an SSE response stream back into deserialized event.

Server

On the server, you can use observableIntoEventSourceStream to convert an Observable that emits ServerSentEvent values into a Node.js response stream:

import { observableIntoEventSourceStream } from '@kbn/sse-utils-server';

function myRequestHandler(
  context: RequestHandlerContext,
  request: KibanaRequest,
  response: KibanaResponseFactory
) {
  return response.ok({
    body: observableIntoEventSourceStream(
      of({
        type: 'my_event_type',
        data: {
          anyData: {},
        },
      }),
      logger
    ),
  });
}

All emitted values have to be of ServerSentEvent type:

type ServerSentEvent = {
  type: string;
  data: Record<string, any>;
};

Any error that occurs in the Observable is written to the stream as an event, and the stream is closed.

Client

On the client, you can use http @elastic/core-http-browser` to convert the stream of events back into an Observable:

import { httpResponseIntoObservable } from '@kbn/sse-utils-client';
function streamEvents(http: Http) {
  from(
    http.post('/internal/my_event_stream', {
      asResponse: true,
      rawResponse: true,
    })
  ).pipe(httpResponseIntoObservable());
}

Any serialized error events from the stream are de-serialized, and thrown as an error in the Observable.