@deploybaseline/ws

The WebSocket kit for Baseline emulators. Slack Socket Mode runs on it. It is opt-in: the CLI does not bundle it, and loads it only when a WebSocket feature is used.

npx -p @deploybaseline/cli -p @deploybaseline/ws baseline start
# or, in a project
npm install -D @deploybaseline/cli @deploybaseline/ws

For built-in providers, on core's app.upgrade:

import { webSocketRoute, messageText } from "@deploybaseline/ws";

const registry = webSocketRoute(app, "/rooms/:room", {
  authorize: ({ url, params }) => (url.searchParams.get("token") ? { room: params.room } : 401),
  onConnection(connection) {
    connection.send({ type: "hello" });
    connection.socket.on("message", (data) =>
      registry.broadcast({ text: messageText(data) }, (other) => other.meta.room === connection.meta.room),
    );
  },
});

• webSocketRoute checks the handshake, accepts it, tracks the connection, pings it every 30 seconds, and closes it with code 1001 when the service stops.
• ConnectionRegistry: open connections with message counts, filtered broadcast, change listeners, and closeAll().
• startHeartbeat: pings on an interval and drops a client that misses too many pongs.
• ResumeBuffer: the last events of a session, numbered from 1, for resuming after a reconnect.

WebSocket endpoints run in the CLI (including --single-port) and createEmulator. Custom emulators cannot serve them yet. Tests can connect with connectWs from @deploybaseline/testing.

See WebSockets.