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Active Support Structured Event Subscriber ↑

ActiveSupport::StructuredEventSubscriber consumes ActiveSupport::Notifications in order to emit structured events via Rails.event.

An example would be the Action Controller structured event subscriber, responsible for emitting request processing events:

module ActionController
  class StructuredEventSubscriber < ActiveSupport::StructuredEventSubscriber
    attach_to :action_controller

    def start_processing(event)
      emit_event("controller.request_started",
        controller: event.payload[:controller],
        action: event.payload[:action],
        format: event.payload[:format]
      )
    end
  end
end

After configured, whenever a "start_processing.action_controller" notification is published, it will properly dispatch the event (ActiveSupport::Notifications::Event) to the start_processing method. The subscriber can then emit a structured event via the emit_event method.

Methods
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Class Public methods

new()

Source: show | on GitHub 

# File activesupport/lib/active_support/structured_event_subscriber.rb, line 59
def initialize
  super
  @silenced_events = {}
end

Instance Public methods

call(event)

Source: show | on GitHub 

# File activesupport/lib/active_support/structured_event_subscriber.rb, line 98
def call(event)
  super
rescue => e
  handle_event_error(event.name, e)
end

emit_debug_event(name, payload = nil, caller_depth: 1, **kwargs)

Like emit_event, but only emits when the event reporter is in debug mode

Source: show | on GitHub 

# File activesupport/lib/active_support/structured_event_subscriber.rb, line 92
def emit_debug_event(name, payload = nil, caller_depth: 1, **kwargs)
  ActiveSupport.event_reporter.debug(name, payload, caller_depth: caller_depth + 1, filter_payload: false, **kwargs)
rescue => e
  handle_event_error(name, e)
end

emit_event(name, payload = nil, caller_depth: 1, **kwargs)

Emit a structured event via Rails.event.notify.

Arguments ↑

  • name - The event name as a string or symbol

  • payload - The event payload as a hash or object

  • caller_depth - Stack depth for source location (default: 1)

  • kwargs - Additional payload data merged with the payload hash

Source: show | on GitHub 

# File activesupport/lib/active_support/structured_event_subscriber.rb, line 85
def emit_event(name, payload = nil, caller_depth: 1, **kwargs)
  ActiveSupport.event_reporter.notify(name, payload, caller_depth: caller_depth + 1, filter_payload: false, **kwargs)
rescue => e
  handle_event_error(name, e)
end

emitting?(name)

Whether any event reporter subscriber would currently consume an event with the given name. Handlers can use this to skip building payloads for events that would go nowhere.

Source: show | on GitHub 

# File activesupport/lib/active_support/structured_event_subscriber.rb, line 73
def emitting?(name)
  ActiveSupport.event_reporter.emitting?(name)
end

silenced?(event)

Source: show | on GitHub 

# File activesupport/lib/active_support/structured_event_subscriber.rb, line 64
def silenced?(event)
  ActiveSupport.event_reporter.subscribers.none? || (@silenced_events.key?(event) && !ActiveSupport.event_reporter.debug_mode?)
end