Messaging (NATS)

This information was adapted from the NATS README. NATS is a lightweight publish-subscribe and distributed queueing messaging system written in Ruby.

Getting Started

$ gem install nats
# or
$ rake geminstall

$ nats-sub foo &
$ nats-pub foo 'Hello World!'

Basic Usage

require "nats/client"

NATS.start do

  # Simple Subscriber
  NATS.subscribe('foo') { |msg| puts "Msg received : '#{msg}'" }

  # Simple Publisher
  NATS.publish('foo.bar.baz', 'Hello World!')

  # Unsubscribing
  sid = NATS.subscribe('bar') { |msg| puts "Msg received : '#{msg}'" }
  NATS.unsubscribe(sid)

  # Requests
  NATS.request('help') { |response| puts "Got a response: '#{response}'" }

  # Replies
  NATS.subscribe('help') { |msg, reply| NATS.publish(reply, "I'll help!") }

  # Stop using NATS.stop, exits EM loop if NATS.start started the loop
  NATS.stop

end

Wildcard Subscriptions

# "*" matches any token, at any level of the subject.
NATS.subscribe('foo.*.baz') { |msg, reply, sub| puts "Msg received on [#{sub}] : '#{msg}'" }
NATS.subscribe('foo.bar.*') { |msg, reply, sub| puts "Msg received on [#{sub}] : '#{msg}'" }
NATS.subscribe('*.bar.*')   { |msg, reply, sub| puts "Msg received on [#{sub}] : '#{msg}'" }

# ">" matches any length of the tail of a subject and can only be the last token
# E.g. 'foo.>' will match 'foo.bar', 'foo.bar.baz', 'foo.foo.bar.bax.22'
NATS.subscribe('foo.>') { |msg, reply, sub| puts "Msg received on [#{sub}] : '#{msg}'" }

Queues Groups

# All subscriptions with the same queue name will form a queue group
# Each message will be delivered to only one subscriber per queue group, queuing semantics
# You can have as many queue groups as you want
# Normal subscribers will continue to work as expected.
NATS.subscribe(subject, :queue => 'job.workers') { |msg| puts "Received '#{msg}'" }

Advanced Usage

# Publish with closure, callback fires when server has processed the message
NATS.publish('foo', 'You done?') { puts 'msg processed!' }

# Timeouts for subscriptions
sid = NATS.subscribe('foo') { received += 1 }
NATS.timeout(sid, TIMEOUT_IN_SECS) { timeout_recvd = true }

# Timeout unless a certain number of messages have been received
NATS.timeout(sid, TIMEOUT_IN_SECS, :expected => 2) { timeout_recvd = true }

# Auto-unsubscribe after MAX_WANTED messages received
NATS.unsubscribe(sid, MAX_WANTED)

# Multiple connections
NATS.subscribe('test') do |msg|
    puts "received msg"
    NATS.stop
end

# Form second connection to send message on
NATS.connect { NATS.publish('test', 'Hello World!') }