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Axon

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

Installation

$ npm install axon

Features

  • message oriented
  • automated reconnection
  • light-weight wire protocol
  • supports arbitrary binary message (msgpack, json, BLOBS, etc)
  • supports JSON messages out of the box

Patterns

  • push / pull
  • pub / sub
  • emitter
  • req / rep
  • router
  • dealer

Push / Pull

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:

push bind

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

pull bind

Pub / Sub

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 recieves 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());
});

EmitterSocket

EmitterSocket's send and receive messages behaving like regular node EventEmitters. This is achieved by using pub / sub sockets behind the scenes and automatically formatting messsages with the "json" codec. Currently we simply define the EmitterSocket as a PubSocket if you .bind(), and SubSocket if you .connect(), providing the natural API you're used to:

server.js:

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

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

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

client.js:

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

sock.connect(3000);
console.log('sub client connected');

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

Req / Rep

ReqSockets send and recieve messages, queueing messages on remote disconnects. There is no "lock step" involved, allowing messages sent later to recieve replies prior to previously sent messages. RepSockets reply to recieved messages, there is no concept of send(). Each recieved message will have a reply callback, which will send the response back to the remote peer:

client.js

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

sock.connect(3000);

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

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

server.js

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

sock.bind(3000);

sock.on('message', function(msg, reply){
  console.log('got: %s', msg.toString());
  reply('pong');
});

Router

RouterSockets send a message to an "identified" peer using the socket's "identity" (see socket options). Sent messages are not queued. The message sent leverages multipart messages by framing the "identity" first, the delimiter second, and then the actual message body.

Note: This will probably change due to the awkwardness of handling your own delimeters.

client.js

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

sock.bind(3000);

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

setInterval(function(){
  sock.send('foo', '\u0000', 'hello foo');
  sock.send('bar', '\u0000', 'hello bar');
}, 150);

server.js

var axon = require('../..')
  , foo = axon.socket('rep')
  , bar = axon.socket('rep');

foo.set('identity', 'foo');
foo.connect(3000);

foo.on('message', function(msg, reply){
  reply('foo: pong');
});

bar.set('identity', 'bar');
bar.connect(3000);

bar.on('message', function(msg, reply){
  reply('bar says: pong');
});

Dealer

DealerSockets receive messages and round-robin sent messages. There is no correlation between the two. They can be thought of as a PushSocket and PullSocket combined. Here the dealer the serves as an "echo-service", sending whatever is recieves:

dealer.js

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

sock.set('identity', 'echo-service');
sock.connect(3000);

sock.on('message', function(msg){
  sock.send(msg);
});

client.js

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

sock.bind(3000);

sock.on('message', function(from, msg){
  console.log('%s said: %s', from.toString(), msg.toString());
});

setInterval(function(){
  sock.send('echo-service', 'hey tobi');
}, 500);

Socket Options

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 additionaly have options for batching:

  • batch max - Max amount of messags to buffer in memory.
  • batch ttl - Amount of time to buffer messages before sending.

Binding / Connecting

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')

Protocol

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.

Codecs

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 paaxon encoded data to .send().

Performance

I haven't profiled or tuned anything yet but so far for on my macbook pro.

64 byte messages:


      min: 22,085 ops/s
     mean: 585,944 ops/s
   median: 606,176 ops/s
    total: 326,7126 ops in 6.5s
  through: 35.76318359375 mb/s

1k messages:


      min: 1,851 ops/s
     mean: 34,0156 ops/s
   median: 449,660 ops/s
    total: 329,831 ops in 4.241s
  through: 332.18359375 mb/s

What's it good for?

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.

Running tests

$ npm install
$ make test

Authors

Links

Todo

  • more tests
  • code cov
  • acks
  • weighted fair queuing
  • use mocha for tests
  • cap batch size
  • zero-copy for batches...
  • make batching configurable... disable for lower latency
  • subscriptions
  • ...

License

(The MIT License)

Copyright (c) 2012 TJ Holowaychuk <tj@vision-media.ca>

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.