Service Push

External services, scheduled jobs, queue consumers, and Kafka consumers can call app.publish() to send messages into the MQTT broker. The broker then delivers those messages to MQTT clients that already subscribed to the target topic.

Core path:

external service / worker / consumer
  -> app.publish(topic, payload, options)
  -> @mqttkit/aedes adapter
  -> Aedes broker
  -> subscribed MQTT clients

Declare a Subscribable Topic

const app = new MqttApp()
  .use(aedes({ tcp: { port: 1886 } }))
  .use(
    router().topic('users/:uid/notifications', {
      subscribe: true,
      publish: false,
    }),
  )

This route means:

• Clients may subscribe to users/:uid/notifications.
• Clients may not publish to this topic.
• The server may actively publish to this topic through app.publish().

Send from an External Service

billing.onInvoicePaid(async (event) => {
  await app.publish(`users/${event.uid}/notifications`, event.payload, { qos: 1 })
})

Receive from an MQTT Client

import mqtt from 'mqtt'

const client = mqtt.connect('mqtt://localhost:1886')

client.on('connect', () => {
  client.subscribe('users/demo/notifications', { qos: 1 })
})

client.on('message', (topic, payload) => {
  console.log(topic, payload.toString())
})

Full Example

See examples/service-push:

bun run --cwd examples/service-push dev

After running it, you should see:

• service -> mqtt: the simulated external service called app.publish().
• mqtt client received: the subscribed MQTT client received the broker-delivered message.