WebSocket Server in Bun
From the Bun cheat sheet · WebSockets · verified Jul 2026
WebSocket Server
Add WebSocket support to Bun.serve with handlers and pub/sub
typescript
Bun.serve({
fetch(req, server) {
if (server.upgrade(req)) return; // Upgrade to WS
return new Response("Not a WS request", { status: 400 });
},
websocket: {
open(ws) { ws.send("Welcome!"); },
message(ws, msg) { ws.send(`Echo: ${msg}`); },
close(ws) { console.log("Disconnected"); },
},
});💡 Bun WebSockets handle 4x more messages per second than Node.js ws package
⚡ Built-in pub/sub with ws.subscribe/publish — no Redis or external broker needed
📌 Pass per-socket data in server.upgrade() — access it later via ws.data
🟢 WebSocket handlers are defined alongside HTTP routes in the same Bun.serve() call
websocketrealtimepubsub
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