Build a WebSocket server with WebSocket Hibernation

This example is similar to the Build a WebSocket server example, but uses the WebSocket Hibernation API. The WebSocket Hibernation API should be preferred for WebSocket server applications built on Durable Objects, since it significantly decreases duration charge, and provides additional features that pair well with WebSocket applications. For more information, refer to Use Durable Objects with WebSockets.

import { DurableObject } from "cloudflare:workers";

// Worker
export default {
	async fetch(request, env, ctx) {
		if (request.url.endsWith("/websocket")) {
			// Expect to receive a WebSocket Upgrade request.
			// If there is one, accept the request and return a WebSocket Response.
			const upgradeHeader = request.headers.get("Upgrade");
			if (!upgradeHeader || upgradeHeader !== "websocket") {
				return new Response("Worker expected Upgrade: websocket", {
					status: 426,
				});
			}

			if (request.method !== "GET") {
				return new Response("Worker expected GET method", {
					status: 400,
				});
			}

			// Since we are hard coding the Durable Object ID by providing the constant name 'foo',
			// all requests to this Worker will be sent to the same Durable Object instance.
			let stub = env.WEBSOCKET_HIBERNATION_SERVER.getByName("foo");

			return stub.fetch(request);
		}

		return new Response(
			`Supported endpoints:
/websocket: Expects a WebSocket upgrade request`,
			{
				status: 200,
				headers: {
					"Content-Type": "text/plain",
				},
			},
		);
	},
};

// Durable Object
export class WebSocketHibernationServer extends DurableObject {
	// Keeps track of all WebSocket connections
	// When the DO hibernates, gets reconstructed in the constructor
	sessions;

	constructor(ctx, env) {
		super(ctx, env);
		this.sessions = new Map();

		// As part of constructing the Durable Object,
		// we wake up any hibernating WebSockets and
		// place them back in the `sessions` map.

		// Get all WebSocket connections from the DO
		this.ctx.getWebSockets().forEach((ws) => {
			let attachment = ws.deserializeAttachment();
			if (attachment) {
				// If we previously attached state to our WebSocket,
				// let's add it to `sessions` map to restore the state of the connection.
				this.sessions.