WebSocket server: Per-socket state
Most WebSocket servers need to know who each socket belongs to: a username, a room, a session. This example attaches state to every connection and uses it when handling messages.
State for one connection. The upgrade request is the natural place to pull it from: query parameters, cookies, or an auth header.
interface Session {
username: string;
joined: Date;
}
const sessions = new Map<WebSocket, Session>();
Deno.serve((req) => {
if (req.headers.get("upgrade") !== "websocket") {
return new Response("This endpoint expects a WebSocket", { status: 426 });
}
const { socket, response } = Deno.upgradeWebSocket(req);Read the username from the connection URL, e.g. /?username=ada.
const username = new URL(req.url).searchParams.get("username") ?? "guest";Each handler closes over this connection's socket, and the Map lets any other part of the server look the session up later.
socket.onopen = () => {
sessions.set(socket, { username, joined: new Date() });
socket.send(`welcome, ${username}`);
};
socket.onmessage = (event) => {
const session = sessions.get(socket)!;
socket.send(`${session.username} said: ${event.data}`);
};
socket.onclose = () => {
sessions.delete(socket);
};
return response;
});Connecting with a username tags every reply: const ws = new WebSocket("ws://localhost:8000/?username=ada"); ws.onmessage = (event) => console.log(event.data); ws.onopen = () => ws.send("hi"); welcome, ada ada said: hi
Note that Deno's WebSocket upgrade does not negotiate per-message compression; large payloads are sent as-is, so compress them yourself if it matters.
Run this example locally using the Deno CLI:
deno run -N https://docs.deno.com/examples/scripts/websocket_context.ts