Server-Sent Events (SSE)

Server-Sent Events (SSE) is a unidirectional communication protocol that allows servers to push real-time updates to clients over a single HTTP connection.

Usage

To enable SSE in your Serinus application, you need to create a controller that handles SSE connections. This is easily done by augmenting your controller with the SseController mixin and defining SSE routes using the onSse method.

import 'package:serinus/serinus.dart';

class MySseController extends Controller with SseController {
  MySseController() : super('/sse') {
    onSse('/events', handleSse);
  }

  Future<void> handleSse(SseContext context) async* {
    yield 'Hello';
    await Future.delayed(Duration(seconds: 3));
    yield 'World';
  }
}

In this example, the MySseController class extends the Controller class and mixes in the SseController. The onSse method is used to define an SSE route at /sse/events, which is handled by the handleSse method. This method is a generator that yields messages to be sent to the client.

Emit events

But what if we want to send data to an open SSE connection from outside the generator function? For this, we can use the SseEmitter provider.

import 'package:serinus/serinus.dart';

class MySseController extends Controller with SseController {
  MySseController() : super('/sse') {
    on('/send', (RequestContext context) {
      final sseEmitter = context.use<SseEmitter>();
      sseEmitter.send('Hello from /send'); // This will send data to all connected clients
      return 'Message sent';
    });
    onSse('/events', handleSse);
  }

  Future<void> handleSse(SseContext context) async* {
    yield 'Hello';
    await Future.delayed(Duration(seconds: 3));
    yield 'World';
  }
}