mqemitter

What is mqemitter?

The 'mqemitter' npm package is a simple message queue emitter that allows you to publish and subscribe to messages. It is designed to be lightweight and easy to use, making it suitable for applications that require basic message queuing and event handling.

What are mqemitter's main functionalities?

Publishing Messages

This feature allows you to publish messages to a specific topic. The code sample demonstrates how to create an instance of MQEmitter and publish a message with a topic and payload.

const MQEmitter = require('mqemitter');
const emitter = MQEmitter();

emitter.emit({ topic: 'myTopic', payload: 'Hello, World!' }, (err) => {
  if (err) {
    console.error('Error publishing message:', err);
  } else {
    console.log('Message published successfully');
  }
});

Subscribing to Messages

This feature allows you to subscribe to messages on a specific topic. The code sample shows how to set up a subscription to a topic and handle incoming messages.

const MQEmitter = require('mqemitter');
const emitter = MQEmitter();

emitter.on('myTopic', (message, cb) => {
  console.log('Received message:', message.payload);
  cb();
});

Unsubscribing from Messages

This feature allows you to unsubscribe from messages on a specific topic. The code sample demonstrates how to remove a previously set up subscription.

const MQEmitter = require('mqemitter');
const emitter = MQEmitter();

const handler = (message, cb) => {
  console.log('Received message:', message.payload);
  cb();
};

emitter.on('myTopic', handler);

// Later, to unsubscribe
emitter.removeListener('myTopic', handler);

Other packages similar to mqemitter

eventemitter3

EventEmitter3 is a high-performance event emitter for Node.js and the browser. It provides a similar publish/subscribe pattern but is more general-purpose and not specifically designed for message queuing.

redis

Redis is an in-memory data structure store that can be used as a message broker. It supports publish/subscribe messaging and offers more advanced features like persistence, clustering, and data structures.

mqtt

MQTT.js is a client library for the MQTT protocol, which is a lightweight messaging protocol designed for IoT. It provides more advanced features for message queuing and is suitable for applications requiring reliable message delivery.

README

MQEmitter

An Opinionated Message Queue with an emitter-style API, but with callbacks.

If you need a multi process MQEmitter, check out the table below:

• mqemitter-redis: Redis-powered mqemitter
• mqemitter-mongodb: Mongodb based mqemitter
• mqemitter-child-process: Share the same mqemitter between a hierarchy of child processes
• mqemitter-cs: Expose a MQEmitter via a simple client/server protocol
• mqemitter-p2p: A P2P implementation of MQEmitter, based on HyperEmitter and a Merkle DAG
• mqemitter-aerospike: Aerospike mqemitter

Installation

npm install mqemitter

Examples

const mq = require('mqemitter')
const emitter = mq({ concurrency: 5 })
const message

emitter.on('hello world', function (message, cb) {
  // call callback when you are done
  // do not pass any errors, the emitter cannot handle it.
  cb()
})

// topic is mandatory
message = { topic: 'hello world', payload: 'or any other fields' }
emitter.emit(message, function () {
  // emitter will never return an error
})

API

• new MQEmitter ([options])
• emitter.emit (message, callback)
• emitter.on (topic, listener, [callback])
• emitter.removeListener (topic, listener, [callback])
• emitter.close (callback)

new MQEmitter ([options])

• options <object>
  • concurrency <boolean> maximum number of concurrent messages that can be on concurrent delivery. Default: 0
  • wildcardOne <string> a char to use for matching exactly one non-empty level word. Default: +
  • wildcardSome <string> a char to use for matching multiple level wildcards. Default: #`
  • matchEmptyLevels <boolean> If true then wildcardOne also matches an empty word. Default: true
  • separator <string> a separator character to use for separating words. Default: /

Create a new MQEmitter class.

MQEmitter is the class and function exposed by this module. It can be created by MQEmitter() or using new MQEmitter().

For more information on wildcards, see this explanation or Qlobber.

emitter.emit (message, callback)

• message <object>
• callback <Function> (error) => void
  • error <Error> | null

Emit the given message, which must have a topic property, which can contain wildcards as defined on creation.

emitter.on (topic, listener, [callback])

• topic <string>
• listener <Function> (message, done) => void
• callback <Function> () => void

Add the given listener to the passed topic. Topic can contain wildcards, as defined on creation.

The listener must never error and done must not be called with an err object.

callback will be called when the event subscribe is done correctly.

emitter.removeListener (topic, listener, [callback])

The inverse of on.

emitter.close (callback)

• callback <Function> () => void

Close the given emitter. After, all writes will return an error.

Wildcards

MQEmitter supports the use of wildcards: every topic is splitted according to separator.

The wildcard character + matches exactly non-empty one word:

const mq = require('mqemitter')
const emitter = mq()

emitter.on('hello/+/world', function(message, cb) {
  // will ONLY capture { topic: 'hello/my/world', 'something': 'more' }
  console.log(message)
  cb()
}
emitter.on('hello/+', function(message, cb) {
  // will not be called
  console.log(message)
  cb()
})

emitter.emit({ topic: 'hello/my/world', something: 'more' })
emitter.emit({ topic: 'hello//world', something: 'more' })

The wildcard character + matches one word:

const mq = require('mqemitter')
const emitter = mq({ matchEmptyLevels: true })

emitter.on('hello/+/world', function(message, cb) {
  // will capture { topic: 'hello/my/world', 'something': 'more' }
  // and capture { topic: 'hello//world', 'something': 'more' }
  console.log(message)
  cb()
})

emitter.on('hello/+', function(message, cb) {
  // will not be called
  console.log(message)
  cb()
})

emitter.emit({ topic: 'hello/my/world', something: 'more' })
emitter.emit({ topic: 'hello//world', something: 'more' })

The wildcard character # matches zero or more words:

const mq = require('mqemitter')
const emitter = mq()

emitter.on('hello/#', function(message, cb) {
  // this will print { topic: 'hello/my/world', 'something': 'more' }
  console.log(message)
  cb()
})

emitter.on('#', function(message, cb) {
  // this will print { topic: 'hello/my/world', 'something': 'more' }
  console.log(message)
  cb()
})

emitter.on('hello/my/world/#', function(message, cb) {
  // this will print { topic: 'hello/my/world', 'something': 'more' }
  console.log(message)
  cb()
})

emitter.emit({ topic: 'hello/my/world', something: 'more' })

Of course, you can mix # and + in the same subscription.

LICENSE

MIT