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+---
+name: Build a publish-subscribe WebSocket server
+---
+
+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.
+
+```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 = `${ws.data.username} has entered the chat`;
+      ws.subscribe("the-group-chat");
+      ws.publish("the-group-chat", msg);
+    },
+    message(ws, message) {
+      // the server re-broadcasts incoming messages to everyone
+      ws.publish("the-group-chat", `${ws.data.username}: ${message}`);
+    },
+    close(ws) {
+      const msg = `${ws.data.username} has left the chat`;
+      ws.publish("the-group-chat", msg);
+      ws.unsubscribe("the-group-chat");
+    },
+  },
+});
+
+console.log(`Listening on ${server.hostname}:${server.port}`);
+```