Server-Sent Events

Server-Sent Events (SSE) let the server push updates to the browser over a long-lived HTTP connection. Unlike WebSockets, traffic is one-way (server → client) and uses ordinary HTTP, which plays well with proxies and load balancers that struggle with upgrade headers.

mangoo I/O maps SSE endpoints in routing and sends events from your own controller or service code. Authenticated streams require a valid auth cookie on the initial connection, same as any other authenticated route. For bidirectional or binary protocols, reach for WebSockets instead, see the note in Routing.

Routing

Bind.serverSentEvent().to("/sse");
Bind.serverSentEvent().to("/sseauth").withAuthentication();

Authenticated endpoints require a valid authentication cookie. See Routing and Authentication.

Sending

import io.mangoo.manager.ServerSentEventManager;
import jakarta.inject.Inject;

public class NotifyService {
    private final ServerSentEventManager sse;

    @Inject
    public NotifyService(ServerSentEventManager sse) {
        this.sse = sse;
    }

    public void sendData() {
        sse.send("/sse", "{\"status\":\"ok\"}");
    }
}

The first argument is the route URL the event goes to, and the payload is a plain string. Delivery runs on a virtual thread, so sendData() returns immediately without blocking on connected clients.

Client setup: MDN Server-sent events.