$ npm install rabbit.js

This library provides a simple, socket-oriented API* for messaging in Node.JS, using RabbitMQ as a backend.

var context = require('rabbit.js').createContext();
context.on('ready', function() {
  var pub = context.socket('PUB'), sub = context.socket('SUB');
  sub.pipe(process.stdout);
  sub.connect('events', function() {
    pub.connect('events', function() {
      pub.write(JSON.stringify({welcome: 'rabbit.js'}), 'utf8');
    });
  });
});

*Yes, rather like ZeroMQ. See below.

Still on major version 0, though in use in a number of places, I believe.

Version 0.3.0 and on are built on amqplib. Previous versions, of which v0.2.2 was the last, used node-amqp.

This library is suitable for co-ordinating peers (e.g., Node.JS programs), acting as a gateway to other kinds of network (e.g., relaying to browsers via SockJS), and otherwise as a really easy way to use RabbitMQ.

The entry point is createContext, which gives you a factory for sockets. You supply it the URL to your RabbitMQ server:

var context = require('rabbit.js').createContext('amqp://localhost');

The context will emit 'ready' when it's connected.

A context will emit 'error' with an Error object if there's a problem with the underlying connection to the server. This invalidates the context and all its sockets.

A context may be disconnected from the server with #close(). It will emit 'close' once the underlying connection has been terminated, by you or by an error.

To start sending or receiving messages you need to acquire a socket:

var pub = context.socket('PUB');
var sub = context.socket('SUB');

and connect it to something:

pub.connect('alerts');
sub.connect('alerts');

Sockets are Streams in object mode, with buffers as the objects. In particular, you can #read() buffers from those that are readable, and you can #write() to those that are writable. If you're using strings, you can setEncoding() to get strings instead of buffers as data, and supply the encoding when writing.

sub.setEncoding('utf8');
sub.on('data', function(note) { console.log("Alarum! " + note); });

pub.write("Emergency. There's an emergency going on", 'utf8');

You can also use #pipe to forward messages to or from another stream, making relaying simple:

sub.pipe(process.stdout);

A socket may be connected more than once, by calling socket.connect(x) with different xs. What this entails depends on the socket type (see below). Messages to and from different connect()ions are not distinguished. For example

var sub2 = context.socket('SUB');
sub2.connect('system');
sub2.connect('notifications');

Here, the socket sub2 will receive all messages published to 'system' and all those published to 'notifications' as well, but it is not possible to distinguish among the sources. If you want to do that, use distinct sockets.

Some socket types have options that may be set with #setsockopt. Presently there's just one option, on PUB, PUSH, REQ and REP sockets, which is message expiration, given as a number of milliseconds:

pub.setsockopt('expiration', 60 * 1000)

In the example, messages written to pub will be discarded by the server if they've not been delivered after 60,000 milliseconds. Message expiration only works with versions of RabbitMQ newer than 3.0.0.

You need to be careful when using expiry with a REQ or REP socket, since losing a request or reply will break ordering. Only sending one request at a time, and giving requests a time limit, may help.

A socket may be closed using #close(); this will clean up resources, and emit 'close' once it's done so.

A writable socket may be closed with a final write by calling #end([chunk [, encoding]]).

The socket types, passed as an argument to Context#socket, determines whether the socket is readable and writable, and what happens to buffers written to it. Socket types (but not necessarily sockets themselves) should be used in the pairs described below.

To make the descriptions a bit easier, we'll say if connect(x) is called on a socket for some , the socket is connected to x and x is a connection of the socket.

PUBlish / SUBscribe: every SUB socket connected to gets each message sent by a PUB socket connected to ; a PUB socket sends every message to each of its connections. SUB sockets are readable only, and PUB sockets are writable only.

PUSH / PULL: a PUSH socket will send each message to a single connection, using round-robin. A PULL socket will receive a share of the messages sent to each to which it is connected, determined by round-robin at . PUSH sockets are writable only, and PULL sockets are readable only.

REQuest / REPly: a REQ socket sends each message to one of its connections, and receives replies in turn; a REP socket receives a share of the messages sent to each to which it is connected, and must send a reply for each, in the order they come in. REQ and REP sockets are both readable and writable.

A few modules have a socket-server-like abstraction; canonically, the net module, but also for example SockJS and Socket.IO. These can be adapted using something similar to the following.

var context = new require('rabbit.js').createContext('amqp://localhost');
var inServer = net.createServer(function(connection) {
  var s = context.socket('PUB');
  s.connect('incoming', function() {
    connection.pipe(s);
  });
});
inServer.listen(5000);

This is a simplistic example: a bare TCP socket won't in general emit data in chunks that are meaningful to applications, even if they are sent that way at the far end.

Each subdirectory of example has code demonstrating using rabbit.js with other modules. Install the prerequisites for rabbit.js first:

rabbit.js$ npm install

Now each example can be run with, e.g.,

rabbit.js$ cd example/sockjs
sockjs$ npm install && npm start

All of the examples assume there is a RabbitMQ server running locally. The SockJS and Socket.IO examples both start a website which you can visit at http://localhost:8080.

rabbit.js was inspired by the RabbitMQ/ZeroMQ adapter I developed with Martin Sústrik. The rationale for using RabbitMQ in a ZeroMQ-based network is largely transferable to rabbit.js:

• RabbitMQ introduces a degree of monitoring and transparency, especially if one uses the web management app;
• RabbitMQ can bridge to other protocols (notably AMQP and STOMP);
• RabbitMQ provides reliable, persistent queues if desired

with some additional benefits:

• since rabbit.js sockets implement the Stream interface, one can easily pipe messages around
• using RabbitMQ as a backend obviates some configuration management -- just supply all instances the broker URL and you're good to go.
• there's room in the API for more involved routing and other behaviour since AMQP is, well, more complicated let's say.

Here are some notable differences and similarities to ZeroMQ in rabbit.js's API and semantics.

To start, there's no distinction in rabbit.js between clients and servers (connect and bind in ZeroMQ, following the BSD socket API), since RabbitMQ is effectively acting as a relaying server for everyone to connect to. Relatedly, the argument supplied to connect() is abstract, in the sense that it's just a name rather than a transport-layer address.

Request and Reply sockets have very similar semantics to those in ZeroMQ. Repliers must respond to requests in the order that they come in, and respond exactly once to each request.

There are no DEALER or ROUTER sockets (a.k.a., XREQ and XREQ) in rabbit.js. In ZeroMQ these are implemented by prefixing messages with a reverse path, which then requires encoding and thereby complication when relaying to other streams or protocols. Instead, rabbit.js notes the reverse path as messages are relayed to a REP socket, and reapplies it when the response appears (giving rise to the ordering requirement on replies).

rabbit.js makes some simplifying assumptions that must be kept in mind when integrating with other protocols that RabbitMQ supports.

PUB and SUB sockets declare non-durable fanout exchanges named for the argument given to connect. To send to SUB sockets or receive from PUB sockets, publish or bind (or subscribe in the case of STOMP) to the exchange with the same name.

PUSH, PULL, REQ and REP sockets use durable, non-exclusive queues named for the argument given to connect. If you are replying via AMQP or STOMP, be sure to follow the convention of sending the response to the queue given in the 'replyTo' property of the request message, and copying the 'correlationId' property from the request in the reply. If you are requesting via AMQP or STOMP, at least supply a replyTo, and consider supplying a correlationId.