AH-MQTTROUTER

Naive implementation of MqttRouter for MQTT.js library. Route handling similar to Express's router.

Table of contents

• installation
• usage
• API
• MqttRouteCallback (fire-and-forget)
• MqttRouteCallback (request-response) + MqttRequestor
• middleware
• re-routing

Instalation

npm install @sladdky/ah-mqttrouter --save

Usage

import { connect } from 'mqtt';
import { MqttRouter } from '@sladdky/ah-mqttrouter'

const onMyMqttTopic1 = (request, response, next) => {
  //...your route logic
}
const onMyMqttTopic2 = (request, response, next) => {
  //...your route logic
}

const mqttClient = connect(<mqtt://url>);
const mqttRouter = new MqttRouter(mqttClient, {
  routes: [
    {topic: 'my-mqtt-topic-1', callback: [onMyMqttTopic1]},
    {topic: 'my-mqtt-topic-2', callback: [onMyMqttTopic2]},
  ]
});

API

• mqttRouter.subscribe(topic: string, callback: MqttRouteCallback | MqttRouteCallback[])
• mqttRouter.unsubscribe(topic: string, callback: MqttRouteCallback | MqttRouteCallback[])
• mqttRouter.publish(topic: string, message: string | Buffer, opts?: IClientPublishOptions, callback?: PacketCallback | undefined): MqttClient;

MqttRouteCallback (Fire-and-Forget)

That's MQTT primary usage. One MqttClient sends a message to certain topic and other MqttClients that are subscribed to that topic, receive the message. No strings attached, no response expected.

1. mqtt message fired from some client:

topic: "my-mqtt-topic"
message: "This is my message."

2. example route implementation:

const onMyMqttTopic = (request, response, next) => {
  const { topic, payload } = request

  saveToDB(`topic: ${topic}, payload: ${payload}`)

  response.send('Message received and I saved it to the database')
}

MqttRouteCallback (Request-Response)

If you need request-response type of communication it's possible. The message is always expected to be stringified JSON.

1. JSON must be in this form:

{
  responseTopic: "random-topic-the-requester-must-subscribe-before-sending",
  message: "This is my message"
}

2. mqtt message sent will look like this

topic: "my-mqtt-topic"
message: '{"responseTopic":"random-topic-the-requester-must-subscribe-before-sending","message":"This is my message"}'

3. example route implementation:

const onMyMqttTopic = (request, response, next) => {
  const { topic, payload } = request

  saveToDB(`topic: ${topic}, payload: ${payload}`)
}

The MQTTclient that is requesting has to subscribe to 'responseTopic' and unsubscribe after the response comes back. You can either handle this situation youself or use asynchronous mqttRequestor.

Example:

...
import { createMqttRequestor } from '@sladdky/ah-mqttrouter/lib/utils'

const mqttRouter = new MqttRouter(mqttClient)
const mqttRequestor = createMqttRequestor(mqttRouter)
mqttRequestor.send('my-mqtt-topic', 'This is my message').then((response) => {
  console.log(response.payload)
})

Middleware (workaround)

Please add your middleware logic as a route callback.

Example:

const onAuthMiddleware = (request, response, next) => {
  if (!isLoggedIn) {
    //...not-allowed to proccess
  }

  next()
}
const onMyMqttTopic = (request, response) => {
  //...your route logic
}

mqttRouter.subscribe('my-mqtt-topic', [onAuthMiddleware, onMyMqttTopic])

Re-routing

Not implemented.

based on ts-npm-package-boilerplate