Hanami 2.0 Ideas

proposals
48

After discussion with @jodosha, we decided that this library should look like another gem.
Also, we think that hanami-events should use different adapters and be without a global state.

Why different adapters?

I think hanami events should be a library for building Event-Driven Architecture. In this case, a library should work with different hanami project instances:

screenshot 2017-07-29 15 27 13
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In this case, we can provide different transport layers for a event storage like:

  • Memory
  • Postgres
  • Kafka
  • Kinesis
  • etc

And that’s why we need to replace wispers gem as an adapter.

From which hanami events should be?

I think that we need to split all logic to 3 different parts:

  1. Broadcaster
  2. Subscriber
  3. Routing

All these parts should be without a global state. And here my ideas about API for all this.

Broadcaster

events = Hanami::Events.new(:adapter)
events.broadcast('user.created', user: user)

Subscriber

kafka_events = Hanami::Events.new(:kafka)
memory_events = Hanami::Events.new(:memory)

memory_events.subscribe('user.signup', Mailer)

# or in class
class Signup
  inclide Hanami::Events::Subscriber
  subscribe_to memory_events, 'user.signup'
  subscribe_to kafka_events, 'user.signup'

  def call(payload)
    # ...
  end
end

Also, I think we should have an ability for subscribing to all events:

kafka_events = Hanami::Events.new(:kafka)

kafka_events.listen do |event|
  event.name    # => 'user.signup'
  event.payload # => { ... }
end

Routing

Routing should route all events and call specific code for each one. It will be helpful for manage all events in one place (look like HTTP routers):

class WebHandler < Hanami::Events::Handler
  on('user.created') { |payload| UserRepository.new.create(payload) }
  on('user.updated') { |payload| payload }
end

class AnaliticHandler < Hanami::Events::Handler
  on('*', AnaliticSender)
  on('user.*') { |payload| payload }
  on('user.signup') { |payload| payload }
end

class NotificationHandler < Hanami::Events::Handler
  on('user.created') { |payload| payload }
  on('post.created') { |payload| payload }
end

class EventRouting < Hanami::Events::Routing
  mount UserHandler, Hanami.app?(:user_events) # load specific handlers for instance
  mount AnaliticHandler
  mount NotificationHandler
end

events = Hanami::Events.new(:adapter)
events.listen { |event| EventRouter.new.resolve(event) }

Plan

We will start work on proof of concept for this idea. It’s mean that we will implement only broadcaster and simple subscriber without routing and other features.

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