aws-mqtt/src/NodeClient.js

AWS IoT MQTT broker client

import MqttClient from 'mqtt/lib/client'
import {signUrl} from './urlSigner'
import WSStream from './streams/WSStream'
import https from 'https'
import WS from 'ws'
import processOptions from './processOptions'

const createStreamBuilder = aws => {
  return client => {
    const stream = new WSStream(callback => {
      // Need to refresh AWS credentials, which expire after initial creation.
      // For example CognitoIdentity credentials expire after an hour
      signUrl(aws, (err, url) => {
        if (err) return callback(err)
        // MUST include 'mqtt' in the list of supported protocols.
        // See http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718127
        // 'mqttv3.1' is still supported, but it is an old informal sub-protocol
        // AWS IoT message broker now supports 3.1.1, see https://docs.aws.amazon.com/iot/latest/developerguide/protocols.html
        try {
          const agent = new https.Agent()
          const socket = new WS(url, ['mqtt'], { agent }) // somehow without an agent WS struggles to make connection to AWS wss url
          return callback(null, socket)
        } catch (err) {
          return callback(err, null)
        }
      })
    })
    // MQTT.js Client suppresses connection errors (?!), loosing the original error
    // This makes it very difficult to debug what went wrong.
    // Here we setup a once error handler to propagate stream error to client's error
    const propagateConnectionErrors = err => client.emit('error', err)
    stream.once('error', propagateConnectionErrors)
    return stream
  }
}

class NodeClient extends MqttClient {
  constructor(options) {
    const { aws, mqttOptions } = processOptions(options)
    super(createStreamBuilder(aws), mqttOptions)
  }
}

module.exports = NodeClient