Live data

Dusk has three ways for the server to keep talking to the page. Take the smallest one that does the job.

Use a timeline model to compare waiting for data with streaming the page shell first.

You need	Use
A stream of results from one call	A server function with `stream: true`
A feed the server pushes	A server-sent events route
Two-way traffic, like chat	A WebSocket route

An SSE route exports SSE. The browser reconnects on its own and sends the last id it saw.

src/routes/live/prices.tsts

import type { RequestEvent, SseStream } from "@shadow-js/dusk/server";

export function SSE(event: RequestEvent, stream: SseStream): void {
  void event;
  stream.send({ event: "price", data: { value: 42 } }).catch(() => undefined);
}

A WebSocket route exports WS. upgrade runs before the socket opens, so it is the place to check who is asking.

src/routes/live/chat.tsts

import type { WebSocketHandlers } from "@shadow-js/dusk/server";

export const WS: WebSocketHandlers = {
  upgrade(event) {
    if (event.cookies.get("session") === undefined) return new Response(null, { status: 401 });
    return undefined;
  },
  message(ws, message) {
    if (typeof message === "string") ws.send(message);
  },
};

These are single-server. When you need named channels, resume after a reconnect, presence or more than one server, use @shadow-js/realtime, which builds on these two routes.

Next: deploy. Limits, heartbeats and shutdown are in Real time.