Allow unsubscribing from events

actionpack/lib/action_dispatch.rb

@@ -70,6 +70,7 @@ class MissingController < NameError
     autoload :HostAuthorization
     autoload :RequestId
     autoload :Callbacks
+    autoload :ClearEventReporterContext
     autoload :Cookies
     autoload :ActionableExceptions
     autoload :DebugExceptions

actionpack/lib/action_dispatch/middleware/clear_event_reporter_context.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module ActionDispatch
+  # Middleware that sets up a callback on rack.response_finished to clear
+  # the EventReporter context when the response is finished. This ensures that
+  # context is cleared as late as possible in the request lifecycle.
+  class ClearEventReporterContext # :nodoc:
+    def initialize(app)
+      @app = app
+    end
+
+    def call(env)
+      response = @app.call(env)
+
+      env["rack.response_finished"] ||= []
+      env["rack.response_finished"] << -> do
+        ActiveSupport.event_reporter.clear_context
+      end
+
+      response
+    rescue Exception => e
+      ActiveSupport.event_reporter.clear_context
+      raise e
+    end
+  end
+end

actionpack/test/dispatch/clear_event_reporter_context_test.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+
+class ClearEventReporterContextTest < ActiveSupport::TestCase
+  def setup
+    @app = ->(env) { [200, {}, ["Hello"]] }
+    @middleware = ActionDispatch::ClearEventReporterContext.new(@app)
+    @reporter = ActiveSupport.event_reporter
+  end
+
+  test "clears event reporter context in response finished callback" do
+    @reporter.set_context(shop_id: 123)
+
+    env = {}
+    @middleware.call(env)
+
+    assert env["rack.response_finished"]
+    assert_equal 1, env["rack.response_finished"].length
+
+    env["rack.response_finished"].each(&:call)
+
+    assert_equal({}, @reporter.context)
+  end
+
+  test "clears event reporter context when exception is raised" do
+    @reporter.set_context(shop_id: 123)
+
+    exception_app = ->(env) { raise StandardError, "Test exception" }
+    exception_middleware = ActionDispatch::ClearEventReporterContext.new(exception_app)
+
+    env = {}
+    assert_raises(StandardError) do
+      exception_middleware.call(env)
+    end
+
+    assert_equal({}, @reporter.context)
+  end
+end

activejob/lib/active_job/railtie.rb

@@ -98,6 +98,16 @@ class Railtie < Rails::Railtie # :nodoc:
       end
     end
 
+    initializer "active_job.clear_event_reporter_context" do
+      ActiveSupport.on_load(:active_job) do
+        ActiveJob::Callbacks.singleton_class.set_callback(:execute, :around) do |_, inner|
+          inner.call
+        ensure
+          ActiveSupport.event_reporter.clear_context
+        end
+      end
+    end
+
     initializer "active_job.query_log_tags" do |app|
       query_logs_tags_enabled = app.config.respond_to?(:active_record) &&
         app.config.active_record.query_log_tags_enabled &&

activesupport/CHANGELOG.md

@@ -1,3 +1,44 @@
+*   Add Structured Event Reporter, accessible via `Rails.event`.
+
+    The Event Reporter provides a unified interface for producing structured events in Rails
+    applications:
+
+    ```ruby
+    Rails.event.notify("user.signup", user_id: 123, email: "[email protected]")
+    ```
+
+    It supports adding tags to events:
+
+    ```ruby
+    Rails.event.tagged("graphql") do
+    # Event includes tags: { graphql: true }
+      Rails.event.notify("user.signup", user_id: 123, email: "[email protected]")
+    end
+    ```
+
+    As well as context:
+    ```ruby
+    # All events will contain context: {request_id: "abc123", shop_id: 456}
+    Rails.event.set_context(request_id: "abc123", shop_id: 456)
+    ```
+
+    Events are emitted to subscribers. Applications register subscribers to
+    control how events are serialized and emitted. Rails provides several default
+    encoders that can be used to serialize events to common formats:
+
+    ```ruby
+    class MySubscriber
+      def emit(event)
+        encoded_event = ActiveSupport::EventReporter.encoder(:json).encode(event)
+        StructuredLogExporter.export(encoded_event)
+      end
+    end
+
+    Rails.event.subscribe(MySubscriber.new)
+    ```
+
+    *Adrianna Chang*
+
 *   Make `ActiveSupport::Gzip.compress` deterministic based on input.
 
     `ActiveSupport::Gzip.compress` used to include a timestamp in the output,

activesupport/lib/active_support.rb

@@ -48,6 +48,7 @@ module ActiveSupport
   autoload :ExecutionWrapper
   autoload :Executor
   autoload :ErrorReporter
+  autoload :EventReporter
   autoload :FileUpdateChecker
   autoload :EventedFileUpdateChecker
   autoload :ForkTracker
@@ -110,6 +111,9 @@ def self.eager_load!
   @error_reporter = ActiveSupport::ErrorReporter.new
   singleton_class.attr_accessor :error_reporter # :nodoc:
 
+  @event_reporter = ActiveSupport::EventReporter.new
+  singleton_class.attr_accessor :event_reporter # :nodoc:
+
   def self.cache_format_version
     Cache.format_version
   end