distributed-eventemitter

Why?

The library solve the need of a multi process and multi server oriented messaging API in Node.js.
Using the known EventEmitter API, listeners registration and events emitting is super simple.
A new 'emitToOne' method allows one-to-one events notification, intended for request/response flows on clustered services.
The classic 'emit' method broadcast custom events to local and distributed listeners.

For non-distributed usage of this API (browser, single node process or development) developers can use: process-eventemitter

Donate to support the evolution of this project:

Quick Start

1. Mailer server (A.js):

var EventEmitter = require('distributed-eventemitter');
var events = new EventEmitter(); // host: localhost, port: 61613
events.connect().then(() => {
  events.on('email.send', (message, resolve, reject) => {
    console.log('sending email...');
    //... send email
    // ...
 
    resolve('sent');
  });
});

1. Run mailer server as a cluster with PM2:

pm2 start A.js -i 4 --node-args="--harmony"

1. Mailer client (B.js):

var EventEmitter = require('distributed-eventemitter');
var events = new EventEmitter(); // host: localhost, port: 61613
events.connect().then(() => {
  events.emitToOne('email.send', {
    to: '[e-mail]',
    subject: 'Hello Node.js',
    body: 'Introducing easy distributed messaging for Node.js...'
  }, 3000).then((response) => {
    if ('sent' === response) {
      console.log('email was sent!');
    }
  }).catch(console.log.bind());
});

1. Run mailer client:

node --harmony B.js

Example using ES6 generators

"use strict";
 
const EventEmitter = require('distributed-eventemitter');
const co = require('co');
const events = new EventEmitter(); // host: localhost, port: 61613
 
co(function* () {
    try {
        yield events.connect();
        let response = yield events.emitToOne('email.send', {
            to: '[e-mail]',
            subject: 'Hello Node.js',
            body: 'Introducing easy distributed messaging for Node.js...'
        }, 3000);
 
        if ('sent' === response) {
            console.log('email was sent!');
        }
        yield events.disconnect();
    } catch (error) {
        console.log('error: ' + error);
    }
});

Requirements

• Running STOMP compliant server instance. Default client destinations are:

  1. /topic/distributed-eventemitter: Used for events broadcast (emit)

  • /queue/distributed-eventemitter: Used for one-to-one events (emitToOne)

    If the server require clients to be authenticated, you can use:

  {
    'host': 'localhost',
    'connectHeaders': {
      'heart-beat': '5000,5000',
      'host': '',
      'login': 'username',
      'passcode': 'password'
    }
  }

Installation

$ npm install distributed-eventemitter

Features

• Extends eventemitter2. (wildcards are enabled).
• ECMA6 Promise based API.
• Request/Response communication intended for service clusters (emitToOne). Uncaught exceptions automatically invoke 'reject(error.message)'
• Events broadcast to local and distributed listeners (emit)
• Works with any STOMP compliant server (ie. ActiveMQ, RabbitMQ, ...).
• Uses stompit as STOMP client. (automated server reconnection is supported)

Config params

var config = {};
config.destination = 'distributed-eventemitter'; // server topic and queue destinations
config.excludedEvents = []; // events that are not distributed
config.servers = [{
  'host': 'localhost',
  'port': 61613,
  'connectHeaders': {
    'heart-beat': '5000,5000',
    'host': '',
    'login': '',
    'passcode': ''
  }
}];
config.reconnectOpts = {
  maxReconnects: 10;
}
 
var events = new EventEmitter(config);

For more details about 'servers' and 'reconnectOpts' params please check: http://gdaws.github.io/node-stomp/api/connect-failover/

Internal events

events.on('connected', (emitterId) => {
    // triggered when the emitter has been connected to the network (STOMP server)
});
 
events.on('disconnected', (emitterId) => {
    // triggered when the emitter has been disconnected from the network (STOMP server)
});
 
events.on('error', (error) => {
   // triggered when an error occurs in the connection channel. 
}):
 
events.on('connecting', (connector) => {
   // triggered when the STOMP client is trying to connect to a server.
}):
 
events.on('request', (event, request, raw) => {
   // triggered before invoke a listener using emitToOne feature
   
   // request data filtering and modification is allowed
   // example:
   request.data = ('string' === typeof request.data) ? request.data.toUpperCase() : request.data
}):
 
events.on('response', (event, response, raw) => {
   // triggered after invoke a listener using emitToOne feature
   
   // response data filtering and modification is allowed
   // example:
   if (response.ok)
     response.data = ('string' === typeof response.data) ? response.data.toUpperCase() : response.data
   else 
     console.log('error ocurred: ' + response.data.message);
}):
 

API

getId: Get the emitter instance unique id.

events.getId(); // UUID v4 value

connect: Connect the emitter to the server. Emit the 'connected' event.

events.connect().then(()=> {
  console.log('connected');
});

disconnect: Disconnect the emitter from the server. Emit the 'disconnected' event.

events.disconnect().then(()=> {
  console.log('disconnected');
});

emitToOne: Notify a custom event to only one target listener (locally or in the network). The method accept only one argument as event data.

events.on('my.event', (data, resolve, reject) => {
  if ('hello' === data){
    resolve('world');
  } else {
    reject('invalid args');
  }
});
 
// calling without timeout
events.emitToOne('my.event', 'hello').then((response) => {
  console.log('world' === response);
});
 
// calling with timeout (ms)
events.emitToOne('my.event', {data: 'hello'}, 100).catch((error) => {
  console.log('invalid args' === error);
});

Roadmap

1. Express integration.

Known limitations

• The feature 'emitAsync' from the EventEmitter2, only work locally(not distributed).

Tests

$ npm install
$ npm test

History changes

1.1.x

• From version 1.1.0+ we use Stompit as STOMP client because Stompjs does not support server reconnections and is also unmaintained.
• No API changes from 1.0 version except the configuration params, since now we consider a list of STOMP servers to connect/reconnect.

1.1.1

• Supporting request/request events intended for pre invocation content filtering and modification.

1.1.2

• Fixing dependencies declaration (due to automatic modification from 'npm update --save').

1.1.3

• Fixing issue on distributed events broadcast(emit) that caused repeated broadcasts.

1.1.4

• Updating dependencies and adding generators example to docs.

1.1.5

• Updating dependencies and docs.

1.1.6

• Improving unexpected error handling when data can't be transmited because the STOMP connection is closed. Produced exceptions are notified as an 'error' event on the emitter.

1.2.0

• Supporting jWebSocket EventBus. JVM based applications using the jWebSocket EventBus component, can communicate with nodejs services through this module.

1.2.1

• Minor source code refactorization.
• Package updates.