realtime

Use Bun's native serve API with a fetch handler that upgrades HTTP requests to WebSocket and a websocket object defining open, message, close, and drain handlers. Connection data like the authenticated user is attached via server.upgrade and accessed through ws.data.

Maintain a RoomManager with maps of connections and rooms, where each room tracks members with roles and join timestamps. Broadcast MEMBER_JOINED and MEMBER_LEFT events to room participants and track cursor positions per connection for presence.

Use a Redis pub/sub adapter where each server instance publishes room messages to channels like room:{roomId} and subscribes to receive broadcasts from other instances. Local broadcast still happens in-process while Redis fans out cross-instance messages.

Implement exponential backoff starting at 1 second, doubling per attempt up to a maximum of 10 retries. On reconnect, send a RE_AUTH message with a fresh token and request FULL_STATE to restore room state lost during disconnection.

Issue short-lived WS tokens from an authenticated HTTP endpoint, then pass the token as a query parameter during the upgrade request. Verify the token in middleware before calling server.upgrade and reject with 401 if invalid or expired.