@khaosdoctor/hermod

Hermod

MQTT message client to, you know, send messages

Summary

• Hermod
  • Summary
  • Usage examples
    • Instalation:
    • Posting a message
    • Listening to a queue
    • Switching queues
    • Acking, Nacking and rejecting messages
  • Config object
  • API
    • postMessage
    • listenToQueue
    • changeQueue
    • ackMessage
    • nackMessage
    • rejectMessage

Usage examples

Instalation:

npm i @khaosdoctor/hermod

Posting a message

const { MessageClient: Hermod } = require('@khaosdoctor/hermod')
const config = {
  queueHostname: 'localhost'
}
const messenger = new Hermod(config)
messenger.postMessage('message', 'queueName') // Returns a promise

Listening to a queue

const { MessageClient: Hermod } = require('@khaosdoctor/hermod')
const config = {
  queueHostname: 'localhost'
}
const messenger = new Hermod(config)

function handler (message) {
  console.log(message.content.toString())
}

// Will call `handler` everytime a message arrives
messenger.listenToQueue('queueName', handler)

Switching queues

const { MessageClient: Hermod } = require('@khaosdoctor/hermod')
const config = {
  queueHostname: 'localhost'
}

function handler (message) {
  console.log(message.content.toString())
}

const messenger = new Hermod(config)
messenger.listenToQueue('queueName', handler)
messenger.changeQueue('anotherQueue').then((queueObject) => /* ... */)

Acking, Nacking and rejecting messages

Acking

const { MessageClient: Hermod } = require('@khaosdoctor/hermod')
const config = {
  queueHostname: 'localhost'
}
const messenger = new Hermod(config)

function handler (message) {
  console.log(message.content.toString())
  messenger.ackMessage(message)
}

messenger.listenToQueue('queueName', handler)

Nacking

const { MessageClient: Hermod } = require('@khaosdoctor/hermod')
const config = {
  queueHostname: 'localhost'
}
const messenger = new Hermod(config)

function handler (message) {
  console.log(message.content.toString())
  messenger.nackMessage(message)
}

messenger.listenToQueue('queueName', handler)

Rejecting

const { MessageClient: Hermod } = require('@khaosdoctor/hermod')
const config = {
  queueHostname: 'localhost'
}
const messenger = new Hermod(config)

function handler (message) {
  console.log(message.content.toString())
  messenger.rejectMessage(message)
}

messenger.listenToQueue('queueName', handler)

Config object

Hermod takes a config object like the following:

{
  queueHostname: string
  queueName?: string
  queueProtocol?: 'amqp' | 'amqps'
  queuePort?: number
  username?: string
  password?: string
  maxConnectionAttemps?: number
  connectionRetryInterval?: number
  durable?: boolean
  noAck?: boolean
  persistent?: boolean
}

• queueHostname (required): The broker hostname, without the protocol
• queueName: Default queue to be used when posting messages, if this is null you'll have to pass the name directly to the function, defaults to undefined
• queueProtocol: amqp or amqps depending on your implementation, defaults to amqp
• queuePort: Broker port, defaults to 5672, which is rabbitMQ's default port
• username: Username in case of authentication. If not, leave it blank
• password: Password in case of authentication. If not, leave it blank
• maxConnectionAttemps: Max connection attemps that will be made in case of error on first connection, defaults to 5
• connectionRetryInternal: The interval between connection attemps (in ms), this number will be multiplied by the number of attempts made in order to create a crescent interval, defaults to 1000
• durable: Defines if a queue should be durable, defaults to true
• noAck: Defines if a consuming channel should auto acknowledge the messages it receives, defaults to false
• persistent: Defines if a message will be persistently saved, defaults to true

Channel, queue and message configurations such as persistent, durable and noAck can be passed on directly to the function, if not the default config will have the claim

API

postMessage

postMessage (message: any, queueName?: string, persistent?: boolean): Promise<boolean>

Description: Posts message to queueName. If queueName is null or undefined, the config.queueName will be used

Parameters:

• message (required): Message content to be posted, it needs to be something which can be transformed into a Buffer (with Buffer.from)
• queueName: Optional queueName to override the queue from the default configuration (if any)
• persistent: Setting it will override the config.persistent value

Returns: Boolean value indicating succes of operation

listenToQueue

listenToQueue (queueName: string, handler: MessageHandler, noAck?: boolean, durable?: boolean): Promise<{ consumerTag: string }>

Description: Start consuming queueName. Everytime a new message arrives, handler will be called

Parameters:

• queueName (required): Queue name to be listened. This method does not read the default config.queueName
• handler (required): Function which will handle the message. Must have a signature like (message) => any
• noAck: This will override config.noAck value for this specific consumer
• durable: This will override config.durable value for this specific consumer

Returns: Promise with the new consumer tag

changeQueue

changeQueue (queueName: string, durable?: boolean): Promise<{ queue: string, messageCount: number, consumerCount: number }>

Description: Will assert a new queue on the channel

Parameters:

• queueName (required): Name of the queue to be asserted
• durable: Will override config.durable value for this specific queue

Returns:

ackMessage

ackMessage (message: ConsumeMessage, allUpToThis: boolean = false): void

Description: Acknowledges a message

Parameters:

• message (required): The received message object
• allUpToThis: Will acknowledge all messages before the one being sent as well

nackMessage

nackMessage (message: ConsumeMessage, allUpToThis: boolean = false, requeue: boolean = true): void

Description: Nacks a message, requeuing it by default

Parameters:

• message (required): The received message object
• allUpToThis: Will not acknowledge all messages before the one being sent as well
• requeue: Will also requeue the message

rejectMessage

rejectMessage (message: ConsumeMessage, requeue: boolean = false): void

Description: Rejects a message, not requeuing it by default

Parameters:

• message (required): The received message object
• requeue: Will also requeue the message