Allow unsubscribing from events

Author: zzak

activesupport/lib/active_support/event_reporter.rb

@@ -231,8 +231,8 @@ def clear
   #   #    payload: { id: 123 },
   #   #  }
   class EventReporter
-    attr_reader :subscribers
-    attr_accessor :raise_on_error
+    attr_reader :subscribers # :nodoc:
+    attr_reader :raise_on_error # :nodoc:
 
     ENCODERS = {
       json: Encoders::JSON,
@@ -272,6 +272,12 @@ def initialize(*subscribers, raise_on_error: false, tags: nil)
       @raise_on_error = raise_on_error
     end
 
+    # Sets whether to raise an error if a subscriber raises an error during
+    # event emission, or when unexpected arguments are passed to +notify+.
+    def raise_on_error=(value)
+      @raise_on_error = value
+    end
+
     # Registers a new event subscriber. The subscriber must respond to
     #
     #   emit(event: Hash)
@@ -293,10 +299,21 @@ def subscribe(subscriber, &filter)
       unless subscriber.respond_to?(:emit)
         raise ArgumentError, "Event subscriber #{subscriber.class.name} must respond to #emit"
       end
-
       @subscribers << { subscriber: subscriber, filter: filter }
     end
 
+    # Unregister an event subscriber. Accepts either a subscriber or a class.
+    #
+    #   subscriber = MyEventSubscriber.new
+    #   Rails.event.subscribe(subscriber)
+    #
+    #   Rails.event.unsubscribe(subscriber)
+    #   # or
+    #   Rails.event.unsubscribe(MyEventSubscriber)
+    def unsubscribe(subscriber)
+      @subscribers.delete_if { |s| subscriber === s }
+    end
+
     # Reports an event to all registered subscribers. An event name and payload can be provided:
     #
     #     Rails.event.notify("user.created", { id: 123 })

activesupport/test/event_reporter_test.rb

@@ -72,6 +72,25 @@ def emit(event)
       assert_equal "Event subscriber Object must respond to #emit", error.message
     end
 
+    test "#unsubscribe" do
+      second_subscriber = EventSubscriber.new
+      @reporter.subscribe(second_subscriber)
+      @reporter.notify(:test_event, key: "value")
+
+      assert event_matcher(name: "test_event", payload: { key: "value" }).call(second_subscriber.events.last)
+
+      @reporter.unsubscribe(second_subscriber)
+
+      assert_not_called(second_subscriber, :emit, [
+        event_matcher(name: "another_event")
+      ]) do
+        @reporter.notify(:another_event, key: "value")
+      end
+
+      @reporter.notify(:last_event, key: "value")
+      assert_empty second_subscriber.events.select(&event_matcher(name: "last_event", payload: { key: "value" }))
+    end
+
     test "#notify with name" do
       assert_called_with(@subscriber, :emit, [
         event_matcher(name: "test_event")