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.
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}`);