@ws-asyncapi/emitter

Emit ws-asyncapi events to connected clients from a process that isn't running a server — the @socket.io/redis-emitter equivalent. Perfect for microservices: a background job, billing service, or cron emits an event and clients connected to your gateway receive it.

How it works

Hand the emitter a backplane shared with your running servers (a RedisBackplane pointed at the same Redis). The emitter publishes through it; each server's backplane delivers to its connected clients. Typed against your channel via typeof channel.

Installation

npm install @ws-asyncapi/emitter @ws-asyncapi/backplane-redis ws-asyncapi

Usage

import { RedisBackplane } from "@ws-asyncapi/backplane-redis";
import { createEmitter } from "@ws-asyncapi/emitter";
import type { chat } from "./contract"; // your Channel's type

const emitter = createEmitter<typeof chat>(
  new RedisBackplane({ url: "redis://localhost:6379" }),
);

// emit to a room — every client in room:1 across the cluster receives it
await emitter.publish("room:1", "message", { from: "billing", text: "payment received" });

// emit to a single socket by id
await emitter.toSocket(socketId, "message", { from: "system", text: "hi" });

Event names and payloads are inferred from the channel's serverMessage declarations, so a wrong event name or payload shape is a compile error.

API

• createEmitter<typeof channel>(backplane, { codec? }) → { publish, toSocket, close }
• One-way only: emit to rooms / sockets. Acknowledgements, presence, and inbound messages require a running server (use an adapter for those).
• The codec must match your servers' codec; recovery offsets are honored if the backplane has recovery enabled (so emitted events are replayable too).

License

MIT