A micro library providing Ruby objects with Publish-Subscribe capabilities

• Decouple core business logic from external concerns in Hexagonal style architectures
• Use as an alternative to ActiveRecord callbacks and Observers in Rails apps
• Connect objects based on context without permanence
• React to events synchronously or asynchronously

Note: Wisper was originally extracted from a Rails codebase but is not dependant on Rails.

This is the README for the unreleased version 2.0 of Wisper.

Jump to the Version 1.x README.

Add this line to your application's Gemfile:

gem 'wisper', '2.0.0.rc1'

Any class with the Wisper::Publisher module included can broadcast events to subscribed listeners. Listeners subscribe, at runtime, to the publisher.

class CancelOrder include Wisper::Publisher def call(order_id) order = Order.find_by_id(order_id) # business logic... if order.cancelled? broadcast(:cancel_order_successful, order.id) else broadcast(:cancel_order_failed, order.id) end end end

When a publisher broadcasts an event it can include any number of arguments.

The broadcast method is also aliased as publish.

You can also include Wisper.publisher instead of Wisper::Publisher.

Any object can be subscribed as a listener.

cancel_order = CancelOrder.new cancel_order.subscribe(OrderNotifier.new) cancel_order.call(order_id)

The listener would need to implement a method for every event it wishes to receive.

class OrderNotifier def cancel_order_successful(order_id) order = Order.find_by_id(order_id) # notify someone ...  end end

Blocks can be subscribed to single events and can be chained.

cancel_order = CancelOrder.new cancel_order.on(:cancel_order_successful) { |order_id| ... } .on(:cancel_order_failed) { |order_id| ... } cancel_order.call(order_id)

You can also subscribe to multiple events using on by passing additional events as arguments.

cancel_order = CancelOrder.new cancel_order.on(:cancel_order_successful) { |order_id| ... } .on(:cancel_order_failed, :cancel_order_invalid) { |order_id| ... } cancel_order.call(order_id)

Do not return from inside a subscribed block, due to the way Ruby treats blocks this will prevent any subsequent listeners having their events delivered.

cancel_order.subscribe(OrderNotifier.new, async: true)

Wisper has various adapters for asynchronous event handling, please refer to wisper-celluloid, wisper-sidekiq, wisper-activejob, or wisper-que.

Depending on the adapter used the listener may need to be a class instead of an object. In this situation, every method corresponding to events should be declared as a class method, too. For example:

class OrderNotifier # declare a class method if you are subscribing the listener class instead of its instance like: # cancel_order.subscribe(OrderNotifier) # def self.cancel_order_successful(order_id) order = Order.find_by_id(order_id) # notify someone ...  end end

class CancelOrderController < ApplicationController def create cancel_order = CancelOrder.new cancel_order.subscribe(OrderMailer, async: true) cancel_order.subscribe(ActivityRecorder, async: true) cancel_order.subscribe(StatisticsRecorder, async: true) cancel_order.on(:cancel_order_successful) { |order_id| redirect_to order_path(order_id) } cancel_order.on(:cancel_order_failed) { |order_id| render action: :new } cancel_order.call(order_id) end end

If you wish to publish directly from ActiveRecord models you can broadcast events from callbacks:

class Order < ActiveRecord::Base include Wisper::Publisher after_commit :publish_creation_successful, on: :create after_validation :publish_creation_failed, on: :create private def publish_creation_successful broadcast(:order_creation_successful, self) end def publish_creation_failed broadcast(:order_creation_failed, self) if errors.any? end end

There are more examples in the Wiki.

Global listeners receive all broadcast events which they can respond to.

This is useful for cross cutting concerns such as recording statistics, indexing, caching and logging.

Wisper.subscribe(MyListener.new)

In a Rails app you might want to add your global listeners in an initalizer.

Global listeners are threadsafe.

You might want to globally subscribe a listener to publishers with a certain class.

Wisper.subscribe(MyListener.new, scope: :MyPublisher) Wisper.subscribe(MyListener.new, scope: MyPublisher) Wisper.subscribe(MyListener.new, scope: "MyPublisher") Wisper.subscribe(MyListener.new, scope: [:MyPublisher, :MyOtherPublisher])

This will subscribe the listener to all instances of the specified class(es) and their subclasses.

Alternatively you can also do exactly the same with a publisher class itself:

MyPublisher.subscribe(MyListener.new)

You can also globally subscribe listeners for the duration of a block.

Wisper.subscribe(MyListener.new, OtherListener.new) do # do stuff end

Any events broadcast within the block by any publisher will be sent to the listeners.

This is useful for capturing events published by objects to which you do not have access in a given context.

Temporary Global Listeners are threadsafe.

By default a listener will get notified of all events it can respond to. You can limit which events a listener is notified of by passing a string, symbol, array or regular expression to on:

post_creator.subscribe(PusherListener.new, on: :create_post_successful)

If you would prefer listeners to receive events with a prefix, for example on, you can do so by passing a string or symbol to prefix:.

post_creator.subscribe(PusherListener.new, prefix: :on)

If post_creator were to broadcast the event post_created the subscribed listeners would receive on_post_created. You can also pass true which will use the default prefix, "on".

By default the method called on the listener is the same as the event broadcast. However it can be mapped to a different method using with:.

report_creator.subscribe(MailResponder.new, with: :successful)

This is pretty useless unless used in conjunction with on:, since all events will get mapped to :successful. Instead you might do something like this:

report_creator.subscribe(MailResponder.new, on: :create_report_successful, with: :successful)

If you pass an array of events to on: each event will be mapped to the same method when with: is specified. If you need to listen for select events and map each one to a different method subscribe the listener once for each mapping:

report_creator.subscribe(MailResponder.new, on: :create_report_successful, with: :successful) report_creator.subscribe(MailResponder.new, on: :create_report_failed, with: :failed)

You could also alias the method within your listener, as such alias successful create_report_successful.

Testing matchers and stubs are in seperate gems.

• wisper-rspec
• wisper-minitest

If you use global listeners in non-feature tests you might want to clear them in a hook to prevent global subscriptions persisting between tests.

after { Wisper.clear }

The Wiki has more examples, articles and talks.

Got a specific question, try the Wisper tag on StackOverflow.

Tested with MRI 2.x, JRuby and Rubinius.

See the build status for details.

bundle exec rspec 

To run the specs on code changes try entr:

ls **/*.rb | entr bundle exec rspec 

Please read the Contributing Guidelines.

• gem releases are signed (public key)
• commits are GPG signed (public key)

(The MIT License)

Copyright (c) 2013 Kris Leech

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.