NATS - Ruby Client
A Ruby client for the NATS messaging system.
Getting Started
gem install nats
nats-sub foo &
nats-pub foo 'Hello World!'
Starting from v0.11.0 release, you can also optionally install NKEYS in order to use the new NATS v2.0 auth features:
gem install nkeys
If you're looking for a non-EventMachine alternative, check out the nats-pure gem.
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 wish
# Normal subscribers will continue to work as expected.
NATS.subscribe(subject, :queue => 'job.workers') { |msg| puts "Received '#{msg}'" }
Clustered Usage
NATS.start(:servers => ['nats://127.0.0.1:4222', 'nats://127.0.0.1:4223']) do |nc|
puts "NATS is connected to #{nc.connected_server}"
nc.on_reconnect do
puts "Reconnected to server at #{nc.connected_server}"
end
nc.on_disconnect do |reason|
puts "Disconnected: #{reason}"
end
nc.on_close do
puts "Connection to NATS closed"
end
end
opts = {
:dont_randomize_servers => true,
:reconnect_time_wait => 0.5,
:max_reconnect_attempts => 10,
:servers => ['nats://127.0.0.1:4222', 'nats://127.0.0.1:4223', 'nats://127.0.0.1:4224']
}
NATS.connect(opts) do |c|
puts "NATS is connected!"
end
Auto discovery
The client also auto discovers new nodes announced by the server as they attach to the cluster. Reconnection logic parameters such as time to back-off on failure and max attempts apply the same to both discovered nodes and those defined explicitly on connect:
opts = {
:dont_randomize_servers => true,
:reconnect_time_wait => 0.5,
:max_reconnect_attempts => 10,
:servers => ['nats://127.0.0.1:4222', 'nats://127.0.0.1:4223'],
:user => 'secret',
:pass => 'deadbeef'
}
NATS.connect(opts) do |c|
# Confirm number of available servers in cluster.
puts "Connected to NATS! Servers in pool: #{c.server_pool.count}"
end
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"
# Gracefully disconnect from NATS after handling
# messages that have already been delivered by server.
NATS.drain
end
# Form second connection to send message on
NATS.connect { NATS.publish('test', 'Hello World!') }
See examples and benchmarks for more information..
TLS
Advanced customizations options for setting up a secure connection can be done by including them on connect:
= {
:servers => [
'nats://secret:[email protected]:4443',
'nats://secret:[email protected]:4444'
],
:max_reconnect_attempts => 10,
:reconnect_time_wait => 2,
:tls => {
:private_key_file => './spec/configs/certs/key.pem',
:cert_chain_file => './spec/configs/certs/server.pem'
# Can enable verify_peer functionality optionally by passing
# the location of a ca_file.
# :verify_peer => true,
# :ca_file => './spec/configs/certs/ca.pem'
}
}
# Set default callbacks
NATS.on_error do |e|
puts "Error: #{e}"
end
NATS.on_disconnect do |reason|
puts "Disconnected: #{reason}"
end
NATS.on_reconnect do |nats|
puts "Reconnected to NATS server at #{nats.connected_server}"
end
NATS.on_close do
puts "Connection to NATS closed"
EM.stop
end
NATS.start() do |nats|
puts "Connected to NATS at #{nats.connected_server}"
nats.subscribe("hello") do |msg|
puts "Received: #{msg}"
end
nats.flush do
nats.publish("hello", "world")
end
end
Fibers
Requests without a callback can be made to work synchronously and return the result when running in a Fiber. For these type of requests, it is possible to set a timeout of how long to wait for a single or multiple responses.
NATS.start {
NATS.subscribe('help') do |msg, reply|
puts "[Received]: <<- #{msg}"
NATS.publish(reply, "I'll help! - #{msg}")
end
NATS.subscribe('slow') do |msg, reply|
puts "[Received]: <<- #{msg}"
EM.add_timer(1) { NATS.publish(reply, "I'll help! - #{msg}") }
end
10.times do |n|
NATS.subscribe('hi') do |msg, reply|
NATS.publish(reply, "Hello World! - id:#{n}")
end
end
Fiber.new do
# Requests work synchronously within the same Fiber
# returning the message when done.
response = NATS.request('help', 'foo')
puts "[Response]: ->> '#{response}'"
# Specifying a custom timeout to give up waiting for
# a response.
response = NATS.request('slow', 'bar', timeout: 2)
if response.nil?
puts "No response after 2 seconds..."
else
puts "[Response]: ->> '#{response}'"
end
# Can gather multiple responses with the same request
# which will then return a collection with the responses
# that were received before the timeout.
responses = NATS.request('hi', 'quux', max: 10, timeout: 1)
responses.each_with_index do |response, i|
puts "[Response# #{i}]: ->> '#{response}'"
end
# If no replies then an empty collection is returned.
responses = NATS.request('nowhere', '', max: 10, timeout: 2)
if responses.any?
puts "Got #{responses.count} responses"
else
puts "No response after 2 seconds..."
end
NATS.stop
end.resume
# Multiple fibers can make requests concurrently
# under the same Eventmachine loop.
Fiber.new do
10.times do |n|
response = NATS.request('help', "help.#{n}")
puts "[Response]: ->> '#{response}'"
end
end.resume
}
New Authentication (Nkeys and User Credentials)
This requires server with version >= 2.0.0
NATS servers have a new security and authentication mechanism to authenticate with user credentials and NKEYS. A single file containing the JWT and NKEYS to authenticate against a NATS v2 server can be set with the user_credentials option:
require 'nats/client'
NATS.start("tls://connect.ngs.global", user_credentials: "/path/to/creds") do |nc|
nc.subscribe("hello") do |msg|
puts "[Received] #{msg}"
end
nc.publish('hello', 'world')
end
This will create two callback handlers to present the user JWT and sign the nonce challenge from the server. The core client library never has direct access to your private key and simply performs the callback for signing the server challenge. The library will load and wipe and clear the objects it uses for each connect or reconnect.
Bare NKEYS are also supported. The nkey seed should be in a read only file, e.g. seed.txt.
> cat seed.txt
# This is my seed nkey!
SUAGMJH5XLGZKQQWAWKRZJIGMOU4HPFUYLXJMXOO5NLFEO2OOQJ5LPRDPM
Then in the client specify the path to the seed using the nkeys_seed option:
require 'nats/client'
NATS.start("tls://connect.ngs.global", nkeys_seed: "path/to/seed.txt") do |nc|
nc.subscribe("hello") do |msg|
puts "[Received] #{msg}"
end
nc.publish('hello', 'world')
end
License
Unless otherwise noted, the NATS source files are distributed under the Apache Version 2.0 license found in the LICENSE file.