Handle websockets from Durable Objects

const app = new Hono()

app.get('/websocket', async ({ req, env }) => {
    const id = req.param('id');
    const notifierId = env.WEBSOCKET_NOTIFIER.idFromName(id);
    const notifier = env.WEBSOCKET_NOTIFIER.get(id);
    return notifier.fetch(req.url, req);
});


export class WebsocketNotifier extends DurableObject<Env> {
    sessions = new Set<WebSocket>();

    async fetch(request: Request) {
        if (request.headers.get('Upgrade') != 'websocket') {
            return new Response('expected websocket', { status: 400 });
        }

        const pair = new WebSocketPair();

        // We're going to take pair[1] as our end, and return pair[0] to the client.
        await this.handleSession(pair[1]);

        // Now we return the other end of the pair to the client.
        return new Response(null, { status: 101, webSocket: pair[0] });
    }

    // handleSession() implements our WebSocket-based chat protocol.
    async handleSession(webSocket: WebSocket) {
        // Accept our end of the WebSocket. This tells the runtime that we'll be terminating the
        // WebSocket in JavaScript, not sending it elsewhere.
        this.state.acceptWebSocket(webSocket);

        this.sessions.add(webSocket);

        let storage = await this.storage.list<Record<any, any>>({ reverse: true, limit: 100 });
        let backlog = [...storage.values()];
        backlog.reverse();
        backlog.forEach((value) => {
            webSocket.send(JSON.stringify(value));
        });
    }
 ...
}