add action mailer instrumentation

Rakefile

@@ -78,6 +78,7 @@ namespace :spec do
 
   [
     :action_cable,
+    :action_mailer,
     :action_pack,
     :action_view,
     :active_model_serializers,
@@ -618,9 +619,11 @@ task :ci do
     declare 'bundle exec appraisal rails6-postgres rake spec:railsdisableenv'
     # Rails specs
     declare 'bundle exec appraisal rails5-mysql2 rake spec:action_cable'
+    declare 'bundle exec appraisal rails5-mysql2 rake spec:action_mailer'
     declare 'bundle exec appraisal rails5-mysql2 rake spec:rails'
     declare 'bundle exec appraisal rails5-postgres rake spec:rails'
     # declare 'bundle exec appraisal rails6-mysql2 rake spec:action_cable' # TODO: Hangs CI jobs... fix and re-enable.
+    declare 'bundle exec appraisal rails6-mysql2 rake spec:action_mailer'
     declare 'bundle exec appraisal rails6-mysql2 rake spec:rails'
     declare 'bundle exec appraisal rails6-postgres rake spec:rails'
 
@@ -702,9 +705,11 @@ task :ci do
       declare 'bundle exec appraisal rails6-postgres rake spec:railsdisableenv'
       # Rails specs
       declare 'bundle exec appraisal rails5-mysql2 rake spec:action_cable'
+      declare 'bundle exec appraisal rails5-mysql2 rake spec:action_mailer'
       declare 'bundle exec appraisal rails5-mysql2 rake spec:rails'
       declare 'bundle exec appraisal rails5-postgres rake spec:rails'
       # declare 'bundle exec appraisal rails6-mysql2 rake spec:action_cable' # TODO: Hangs CI jobs... fix and re-enable.
+      declare 'bundle exec appraisal rails6-mysql2 rake spec:action_mailer'
       declare 'bundle exec appraisal rails6-mysql2 rake spec:rails'
       declare 'bundle exec appraisal rails6-postgres rake spec:rails'
 
@@ -787,8 +792,10 @@ task :ci do
       # Rails specs
       declare 'bundle exec appraisal rails5-mysql2 rake spec:rails'
       declare 'bundle exec appraisal rails5-postgres rake spec:rails'
+      declare 'bundle exec appraisal rails5-mysql2 rake spec:action_mailer'
       declare 'bundle exec appraisal rails6-mysql2 rake spec:rails'
       declare 'bundle exec appraisal rails6-postgres rake spec:rails'
+      declare 'bundle exec appraisal rails6-mysql2 rake spec:action_mailer'
 
       # explicitly test resque-2x compatability
       declare 'bundle exec appraisal resque2-redis3 rake spec:resque'

docs/GettingStarted.md

@@ -28,6 +28,7 @@ To contribute, check out the [contribution guidelines][contribution docs] and [d
  - [Integration instrumentation](#integration-instrumentation)
      - [Action Cable](#action-cable)
      - [Action View](#action-view)
+     - [Action Mailer](#action-mailer)
      - [Active Model Serializers](#active-model-serializers)
      - [Action Pack](#action-pack)
      - [Active Record](#active-record)
@@ -334,14 +335,15 @@ For a list of available integrations, and their configuration options, please re
 | Name                     | Key                        | Versions Supported: MRI  | Versions Supported: JRuby | How to configure                    | Gem source                                                                     |
 | ------------------------ | -------------------------- | ------------------------ | --------------------------| ----------------------------------- | ------------------------------------------------------------------------------ |
 | Action Cable             | `action_cable`             | `>= 5.0`                 | `>= 5.0`                  | *[Link](#action-cable)*             | *[Link](https://github.com/rails/rails/tree/master/actioncable)*               |
+| Action Mailer            | `action_mailer`            | `>= 5.0`                 | `>= 5.0`                  | *[Link](#action-mailer)*            | *[Link](https://github.com/rails/rails/tree/master/actionmailer)*              |
 | Action View              | `action_view`              | `>= 3.0`                 | `>= 3.0`                  | *[Link](#action-view)*              | *[Link](https://github.com/rails/rails/tree/master/actionview)*                |
 | Active Model Serializers | `active_model_serializers` | `>= 0.9`                 | `>= 0.9`                  | *[Link](#active-model-serializers)* | *[Link](https://github.com/rails-api/active_model_serializers)*                |
 | Action Pack              | `action_pack`              | `>= 3.0`                 | `>= 3.0`                  | *[Link](#action-pack)*              | *[Link](https://github.com/rails/rails/tree/master/actionpack)*                |
 | Active Record            | `active_record`            | `>= 3.0`                 | `>= 3.0`                  | *[Link](#active-record)*            | *[Link](https://github.com/rails/rails/tree/master/activerecord)*              |
 | Active Support           | `active_support`           | `>= 3.0`                 | `>= 3.0`                  | *[Link](#active-support)*           | *[Link](https://github.com/rails/rails/tree/master/activesupport)*             |
 | AWS                      | `aws`                      | `>= 2.0`                 | `>= 2.0`                  | *[Link](#aws)*                      | *[Link](https://github.com/aws/aws-sdk-ruby)*                                  |
 | Concurrent Ruby          | `concurrent_ruby`          | `>= 0.9`                 | `>= 0.9`                  | *[Link](#concurrent-ruby)*          | *[Link](https://github.com/ruby-concurrency/concurrent-ruby)*                  |
-| Cucumber                 | `cucumber`                 | `>= 3.0`                 | `>= 1.7.16`               | *[Link](#cucumber)*                | *[Link](https://github.com/cucumber/cucumber-ruby)*                            |
+| Cucumber                 | `cucumber`                 | `>= 3.0`                 | `>= 1.7.16`               | *[Link](#cucumber)*                 | *[Link](https://github.com/cucumber/cucumber-ruby)*                            |
 | Dalli                    | `dalli`                    | `>= 2.0`                 | `>= 2.0`                  | *[Link](#dalli)*                    | *[Link](https://github.com/petergoldstein/dalli)*                              |
 | DelayedJob               | `delayed_job`              | `>= 4.1`                 | `>= 4.1`                  | *[Link](#delayedjob)*               | *[Link](https://github.com/collectiveidea/delayed_job)*                        |
 | Elasticsearch            | `elasticsearch`            | `>= 1.0`                 | `>= 1.0`                  | *[Link](#elasticsearch)*            | *[Link](https://github.com/elastic/elasticsearch-ruby)*                        |
@@ -416,6 +418,26 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 | `service_name` | Service name used for rendering instrumentation. | `action_view` |
 | `template_base_path` | Used when the template name is parsed. If you don't store your templates in the `views/` folder, you may need to change this value | `'views/'` |
 
+### Action Mailer
+
+The Action Mailer integration provides tracing for Rails 5 ActionMailer actions.
+
+You can enable it through `Datadog.configure`:
+
+```ruby
+require 'ddtrace'
+ Datadog.configure do |c|
+  c.use :action_mailer, options
+end
+```
+
+Where `options` is an optional `Hash` that accepts the following parameters:
+
+| Key | Description | Default |
+| --- | ----------- | ------- |
+| `analytics_enabled` | Enable analytics for spans produced by this integration. `true` for on, `nil` to defer to global setting, `false` for off. | `false` |
+| `service_name` | Service name used for `action_mailer` instrumentation | `'action_mailer'` |
+
 ### Active Model Serializers
 
 The Active Model Serializers integration traces the `serialize` event for version 0.9+ and the `render` event for version 0.10+.

lib/ddtrace.rb

@@ -38,6 +38,7 @@ module Datadog
 end
 
 require 'ddtrace/contrib/action_cable/integration'
+require 'ddtrace/contrib/action_mailer/integration'
 require 'ddtrace/contrib/action_pack/integration'
 require 'ddtrace/contrib/action_view/integration'
 require 'ddtrace/contrib/active_model_serializers/integration'

lib/ddtrace/contrib/action_mailer/configuration/settings.rb

@@ -0,0 +1,30 @@
+require 'ddtrace/contrib/configuration/settings'
+require 'ddtrace/contrib/action_mailer/ext'
+
+module Datadog
+  module Contrib
+    module ActionMailer
+      module Configuration
+        # Custom settings for the ActionMailer integration
+        class Settings < Contrib::Configuration::Settings
+          option :enabled do |o|
+            o.default { env_to_bool(Ext::ENV_ENABLED, true) }
+            o.lazy
+          end
+
+          option :analytics_enabled do |o|
+            o.default { env_to_bool([Ext::ENV_ANALYTICS_ENABLED, Ext::ENV_ANALYTICS_ENABLED_OLD], false) }
+            o.lazy
+          end
+
+          option :analytics_sample_rate do |o|
+            o.default { env_to_float([Ext::ENV_ANALYTICS_SAMPLE_RATE, Ext::ENV_ANALYTICS_SAMPLE_RATE_OLD], 1.0) }
+            o.lazy
+          end
+
+          option :service_name, default: Ext::SERVICE_NAME
+        end
+      end
+    end
+  end
+end

lib/ddtrace/contrib/action_mailer/event.rb

@@ -0,0 +1,49 @@
+require 'ddtrace/contrib/analytics'
+require 'ddtrace/contrib/active_support/notifications/event'
+require 'ddtrace/contrib/action_mailer/ext'
+
+module Datadog
+  module Contrib
+    module ActionMailer
+      # Defines basic behaviors for an ActionMailer event.
+      module Event
+        def self.included(base)
+          base.send(:include, ActiveSupport::Notifications::Event)
+          base.send(:extend, ClassMethods)
+        end
+
+        # Class methods for ActionMailer events.
+        module ClassMethods
+          def span_options
+            { service: configuration[:service_name] }
+          end
+
+          def tracer
+            -> { configuration[:tracer] }
+          end
+
+          def configuration
+            Datadog.configuration[:action_mailer]
+          end
+
+          def process(span, event, _id, payload)
+            span.service = configuration[:service_name]
+            span.resource = payload[:mailer]
+
+            # Set analytics sample rate
+            if Contrib::Analytics.enabled?(configuration[:analytics_enabled])
+              Contrib::Analytics.set_sample_rate(span, configuration[:analytics_sample_rate])
+            end
+
+            # Measure service stats
+            Contrib::Analytics.set_measured(span)
+
+            report_if_exception(span, payload)
+          rescue StandardError => e
+            Datadog.logger.debug(e.message)
+          end
+        end
+      end
+    end
+  end
+end

lib/ddtrace/contrib/action_mailer/events.rb

@@ -0,0 +1,30 @@
+require 'ddtrace/contrib/action_mailer/events/process'
+require 'ddtrace/contrib/action_mailer/events/deliver'
+
+module Datadog
+  module Contrib
+    module ActionMailer
+      # Defines collection of instrumented ActionMailer events
+      module Events
+        ALL = [
+          Events::Process,
+          Events::Deliver
+        ].freeze
+
+        module_function
+
+        def all
+          self::ALL
+        end
+
+        def subscriptions
+          all.collect(&:subscriptions).collect(&:to_a).flatten
+        end
+
+        def subscribe!
+          all.each(&:subscribe!)
+        end
+      end
+    end
+  end
+end

lib/ddtrace/contrib/action_mailer/events/deliver.rb

@@ -0,0 +1,39 @@
+require 'ddtrace/contrib/action_mailer/ext'
+require 'ddtrace/contrib/action_mailer/event'
+
+module Datadog
+  module Contrib
+    module ActionMailer
+      module Events
+        # Defines instrumentation for process.action_mailer event
+        module Deliver
+          include ActionMailer::Event
+
+          EVENT_NAME = 'deliver.action_mailer'.freeze
+
+          module_function
+
+          def event_name
+            self::EVENT_NAME
+          end
+
+          def span_name
+            Ext::SPAN_DELIVER
+          end
+
+          def span_type
+            # ActionMailer creates emails like a controller
+            Datadog::Ext::AppTypes::Worker
+          end
+
+          def process(span, event, _id, payload)
+            super
+
+            span.set_tag(Ext::TAG_MAILER, payload[:mailer])
+            span.set_tag(Ext::TAG_MSG_ID, payload[:message_id])
+          end
+        end
+      end
+    end
+  end
+end

lib/ddtrace/contrib/action_mailer/events/process.rb

@@ -0,0 +1,39 @@
+require 'ddtrace/contrib/action_mailer/ext'
+require 'ddtrace/contrib/action_mailer/event'
+
+module Datadog
+  module Contrib
+    module ActionMailer
+      module Events
+        # Defines instrumentation for process.action_mailer event
+        module Process
+          include ActionMailer::Event
+
+          EVENT_NAME = 'process.action_mailer'.freeze
+
+          module_function
+
+          def event_name
+            self::EVENT_NAME
+          end
+
+          def span_name
+            Ext::SPAN_PROCESS
+          end
+
+          def span_type
+            # ActionMailer creates emails like a controller
+            Datadog::Ext::AppTypes::Web
+          end
+
+          def process(span, event, _id, payload)
+            super
+
+            span.set_tag(Ext::TAG_ACTION, payload[:action])
+            span.set_tag(Ext::TAG_MAILER, payload[:mailer])
+          end
+        end
+      end
+    end
+  end
+end

lib/ddtrace/contrib/action_mailer/ext.rb

@@ -0,0 +1,23 @@
+module Datadog
+  module Contrib
+    module ActionMailer
+      # ActionMailer integration constants
+      module Ext
+        APP = 'action_mailer'.freeze
+        ENV_ENABLED = 'DD_TRACE_ACTION_MAILER_ENABLED'.freeze
+        ENV_ANALYTICS_ENABLED = 'DD_TRACE_ACTION_MAILER_ANALYTICS_ENABLED'.freeze
+        ENV_ANALYTICS_SAMPLE_RATE = 'DD_TRACE_ACTION_MAILER_ANALYTICS_SAMPLE_RATE'.freeze
+
+        ENV_ANALYTICS_ENABLED_OLD = 'DD_ACTION_MAILER_ANALYTICS_ENABLED'.freeze
+
+        ENV_ANALYTICS_SAMPLE_RATE_OLD = 'DD_ACTION_MAILER_ANALYTICS_SAMPLE_RATE'.freeze
+        SERVICE_NAME = 'action_mailer'.freeze
+        SPAN_PROCESS = 'action_mailer.process'.freeze
+        SPAN_DELIVER = 'action_mailer.deliver'.freeze
+        TAG_ACTION = 'action_mailer.action'.freeze
+        TAG_MAILER = 'action_mailer.mailer'.freeze
+        TAG_MSG_ID = 'action_mailer.message_id'.freeze
+      end
+    end
+  end
+end

lib/ddtrace/contrib/action_mailer/integration.rb

@@ -0,0 +1,38 @@
+require 'ddtrace/contrib/integration'
+require 'ddtrace/contrib/action_mailer/configuration/settings'
+require 'ddtrace/contrib/action_mailer/patcher'
+
+module Datadog
+  module Contrib
+    module ActionMailer
+      # Description of ActionMailer integration
+      class Integration
+        include Contrib::Integration
+
+        MINIMUM_VERSION = Gem::Version.new('5.0.0')
+
+        register_as :action_mailer, auto_patch: false
+
+        def self.version
+          Gem.loaded_specs['actionmailer'] && Gem.loaded_specs['actionmailer'].version
+        end
+
+        def self.loaded?
+          !defined?(::ActionMailer).nil?
+        end
+
+        def self.compatible?
+          super && version >= MINIMUM_VERSION && !defined?(::ActiveSupport::Notifications).nil?
+        end
+
+        def default_configuration
+          Configuration::Settings.new
+        end
+
+        def patcher
+          Patcher
+        end
+      end
+    end
+  end
+end

lib/ddtrace/contrib/action_mailer/patcher.rb

@@ -0,0 +1,26 @@
+require 'ddtrace/contrib/patcher'
+require 'ddtrace/ext/app_types'
+require 'ddtrace/contrib/action_mailer/ext'
+require 'ddtrace/contrib/action_mailer/events'
+
+module Datadog
+  module Contrib
+    module ActionMailer
+      # Patcher enables patching of 'action_mailer' module.
+      module Patcher
+        include Contrib::Patcher
+
+        module_function
+
+        def target_version
+          Integration.version
+        end
+
+        def patch
+          # Subscribe to ActionMailer events
+          Events.subscribe!
+        end
+      end
+    end
+  end
+end