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Bun’s server-side WebSocket API provides a native pub-sub API. Sockets can be subscribed to a set of named channels using socket.subscribe(<name>); messages can be published to a channel using socket.publish(<name>, <message>). This code snippet implements a simple single-channel chat server.
https://mintcdn.com/bun-1dd33a4e/Hq64iapoQXHbYMEN/icons/typescript.svg?fit=max&auto=format&n=Hq64iapoQXHbYMEN&q=85&s=c6cceedec8f82d2cc803d7c6ec82b240server.ts
const server = Bun.serve<{ username: string }>({
	fetch(req, server) {
		const cookies = req.headers.get("cookie");
		const username = getUsernameFromCookies(cookies);
		const success = server.upgrade(req, { data: { username } });
		if (success) return undefined;

		return new Response("Hello world");
	},
	websocket: {
		open(ws) {
			const msg = `${ws.data.username} has entered the chat`;
			ws.subscribe("the-group-chat");
			server.publish("the-group-chat", msg);
		},
		message(ws, message) {
			// the server re-broadcasts incoming messages to everyone
			server.publish("the-group-chat", `${ws.data.username}: ${message}`);
		},
		close(ws) {
			const msg = `${ws.data.username} has left the chat`;
			server.publish("the-group-chat", msg);
			ws.unsubscribe("the-group-chat");
		},
	},
});

console.log(`Listening on ${server.hostname}:${server.port}`);