Axon is a message-oriented socket library for node.js heavily inspired by zeromq.

$ npm install axon

• message oriented
• automated reconnection
• light-weight wire protocol
• supports arbitrary binary message (msgpack, json, BLOBS, etc)
• supports JSON messages out of the box
• fast (~800 mb/s ~500,000 messages/s)

• close when server or connection is closed
• error (err) when an-handled socket error occurs
• ignored error (err) when an axon-handled socket error occurs, but is ignored
• socket error (err) emitted regardless of handling, for logging purposes
• reconnect attempt when a reconnection attempt is made
• connect when connected to the peer, or a peer connection is accepted
• disconnect when an accepted peer disconnects
• bind when the server is bound

• push / pull
• pub / sub
• req / rep
• pub-emitter / sub-emitter

PushSockets distribute messages round-robin:

var axon = require('axon')
  , sock = axon.socket('push');

sock.bind(3000);
console.log('push server started');

setInterval(function(){
  sock.send('hello');
}, 150);

Receiver of PushSocket messages:

var axon = require('axon')
  , sock = axon.socket('pull');

sock.connect(3000);

sock.on('message', function(msg){
  console.log(msg.toString());
});

Both PushSockets and PullSockets may .bind() or .connect(). In the following configuration the push socket is bound and pull "workers" connect to it to receive work:

This configuration shows the inverse, where workers connect to a "sink" to push results:

PubSockets send messages to all subscribers without queueing. This is an important difference when compared to a PushSocket, where the delivery of messages will be queued during disconnects and sent again upon the next connection.

var axon = require('axon')
  , sock = axon.socket('pub');

sock.bind(3000);
console.log('pub server started');

setInterval(function(){
  sock.send('hello');
}, 500);

SubSocket simply receives any messages from a PubSocket:

var axon = require('axon')
  , sock = axon.socket('sub');

sock.connect(3000);

sock.on('message', function(msg){
  console.log(msg.toString());
});

SubSockets may optionally .subscribe() to one or more "topics" (the first multipart value), using string patterns or regular expressions:

var axon = require('axon')
  , sock = axon.socket('sub');

sock.connect(3000);
sock.subscribe('user:login');
sock.subscribe('upload:*:progress');

sock.on('message', function(topic, msg){

});

ReqSocket is similar to a PushSocket in that it round-robins messages to connected RepSockets, however it differs in that this communication is bi-directional, every req.send() must provide a callback which is invoked when the RepSocket replies.

var axon = require('axon')
  , sock = axon.socket('req');

sock.bind(3000);

sock.send(img, function(res){
  
});

RepSockets receive a reply callback that is used to respond to the request, you may have several of these nodes.

var axon = require('axon')
  , sock = axon.socket('rep');

sock.connect(3000);

sock.on('message', function(img, reply){
  // resize the image
  reply(img);
});

Like other sockets you may provide multiple arguments or an array of arguments, followed by the callbacks. For example here we provide a task name of "resize" to facilitate multiple tasks over a single socket:

var axon = require('axon')
  , sock = axon.socket('req');

sock.bind(3000);

sock.send('resize', img, function(res){
  
});

Respond to the "resize" task:

var axon = require('axon')
  , sock = axon.socket('rep');

sock.connect(3000);

sock.on('message', function(task, img, reply){
  switch (task.toString()) {
    case 'resize':
      // resize the image
      reply(img);
      break;
  }
});

PubEmitter and SubEmitter are higher-level Pub / Sub sockets, using the "json" codec to behave much like node's EventEmitter. When a SubEmitter's .on() method is invoked, the event name is .subscribe()d for you. Each wildcard (*) or regexp capture group is passed to the callback along with regular message arguments.

app.js:

var axon = require('axon')
  , sock = axon.socket('pub-emitter');

sock.connect(3000);

setInterval(function(){
  sock.emit('login', { name: 'tobi' });
}, 500);

logger.js:

var axon = require('axon')
  , sock = axon.socket('sub-emitter');

sock.bind(3000);

sock.on('user:login', function(user){
  console.log('%s signed in', user.name);
});

sock.on('user:*', function(action, user){
  console.log('%s %s', user.name, action);
});

sock.on('*', function(event){
  console.log(arguments);
});

Every socket has associated options that can be configured via get/set.

• identity - The "name" of the socket that uniqued identifies it.
• retry timeout - The amount of time until retries will not be attempted again.

PubSockets additionally have options for batching:

• batch max - Max amount of messages to buffer in memory [10].
• batch ttl - Amount of time in milliesconds to buffer messages before sending [100].

In addition to passing a portno, binding to INADDR_ANY by default, you may also specify the hostname via .bind(port, host), another alternative is to specify the url much like zmq via tcp://<hostname>:<portno>, thus the following are equivalent:

sock.bind(3000)
sock.bind(3000, '0.0.0.0')
sock.bind('tcp://0.0.0.0:3000')

sock.connect(3000)
sock.connect(3000, '0.0.0.0')
sock.connect('tcp://0.0.0.0:3000')

The wire protocol is simple and very much zeromq-like, where <length> is a BE 24 bit unsigned integer representing a maximum length of roughly ~16mb. The <meta> data byte is currently only used to store the codec, for example "json" is simply 1, in turn JSON messages received on the client end will then be automatically decoded for you by selecting this same codec.

 octet:     0      1      2      3      <length>
        +------+------+------+------+------------------...
        | meta | <length>           | data ...
        +------+------+------+------+------------------...

Thus 5 bytes is the smallest message axon supports at the moment. Later if necessary we can use the meta to indicate a small message and ditch octet 2 and 3 allowing for 3 byte messages.

To define a codec simply invoke the axon.codec.define() method, for example here is the JSON codec:

var axon = require('axon');

axon.codec.define('json', {
  encode: JSON.stringify,
  decode: JSON.parse
});

Note: codecs must be defined on both the sending and receiving ends, otherwise axon cannot properly decode the messages. You may of course ignore this feature all together and simply pass encoded data to .send().

Preliminary benchmarks on my Macbook Pro:

15 byte messages:

      min: 280 ops/s
     mean: 472,109 ops/s
   median: 477,309 ops/s
    total: 10,758,780 ops in 24.633s
  through: 6.75 mb/s

64 byte messages:

      min: 218 ops/s
     mean: 462,286 ops/s
   median: 461,512 ops/s
    total: 6,455,160 ops in 15.488s
  through: 28.21 mb/s

1k messages:

      min: 280 ops/s
     mean: 382,829 ops/s
   median: 382,764 ops/s
    total: 3,333,581 ops in 15.126s
  through: 373.85 mb/s

8k messages:

      min: 392 ops/s
     mean: 92,778 ops/s
   median: 87,943 ops/s
    total: 1,257,430 ops in 21.735s
  through: 724.82 mb/s

Axon are not meant to combat zeromq nor provide feature parity, but provide a nice solution when you don't need the insane nanosecond latency or language interoperability that zeromq provides as axon do not rely on any third-party compiled libraries.

$ npm install
$ make test

• visionmedia
• gjohnson

• Screencast
• Axon RPC

(The MIT License)

Copyright (c) 2012 TJ Holowaychuk <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.