5.4 Durable Objects：強一致性的有狀態邊緣#

# wrangler.toml 片段
[durable_objects]
bindings = [
    { name = "ROOMS", class_name = "ChatRoom" }
]

[[migrations]]
tag = "v1"
new_classes = ["ChatRoom"]

// src/room.ts
export class ChatRoom implements DurableObject {
    private users = new Set<string>();   // 房間狀態：線上成員

    async fetch(request: Request): Promise<Response> {
        const url = new URL(request.url);

        // 加入房間：單執行緒內操作 Set，天然原子
        if (url.pathname === "/join" && request.method === "POST") {
            const { user } = await request.json<{ user: string }>();
            this.users.add(user);
            return Response.json({ online: this.users.size });
        }

        // 離開房間
        if (url.pathname === "/leave" && request.method === "POST") {
            const { user } = await request.json<{ user: string }>();
            this.users.delete(user);
            return Response.json({ online: this.users.size });
        }

        return new Response("Not found", { status: 404 });
    }
}

// src/index.ts
export default {
    async fetch(req: Request, env: Env): Promise<Response> {
        const url = new URL(req.url);
        const roomName = url.searchParams.get("room") ?? "lobby";

        // 同名房間永遠路由到同一個 DO 實例
        const id = env.ROOMS.idFromName(roomName);
        const stub = env.ROOMS.get(id);
        const withRoom = new Request(`https://room${url.pathname}${url.search}`, req);
        return stub.fetch(withRoom);
    },
};

export class ChatRoomWS implements DurableObject {
    private sockets = new Set<WebSocket>();

    async fetch(request: Request): Promise<Response> {
        if (request.headers.get("Upgrade") !== "websocket")
            return new Response("expected ws", { status: 426 });

        const pair = new WebSocketPair();
        this.sockets.add(pair[1] as WebSocket);
        (pair[1] as WebSocket).accept();

        return new Response(null, { status: 101, webSocket: pair[0] });
    }

    webSocketMessage(ws: WebSocket, message: string) {
        // 收到某人的訊息 → 廣播給房間所有人
        for (const s of this.sockets) s.send(message);
    }

    webSocketClose(ws: WebSocket) {
        this.sockets.delete(ws);
    }
}