Merge branch 'add-email-receiver-metrics' into 'master'

Add email receiver metrics

See merge request !10814

changelogs/unreleased/add-email-receiver-metrics.yml

+---
+title: Add metrics events for incoming emails
+merge_request:
+author:

lib/gitlab/email/handler/create_note_handler.rb

@@ -7,6 +7,8 @@ module Gitlab
       class CreateNoteHandler < BaseHandler
         include ReplyProcessing
+        delegate :project, to: :sent_notification, allow_nil: true
+
         def can_handle?
           mail_key =~ /\A\w+\z/
         end
@@ -32,10 +34,6 @@ module Gitlab
           sent_notification.recipient
         end
-        def project
-          sent_notification.project
-        end
-
         def sent_notification
           @sent_notification ||= SentNotification.for(mail_key)
         end

lib/gitlab/email/handler/unsubscribe_handler.rb

@@ -4,6 +4,8 @@ module Gitlab
   module Email
     module Handler
       class UnsubscribeHandler < BaseHandler
+        delegate :project, to: :sent_notification, allow_nil: true
+
         def can_handle?
           mail_key =~ /\A\w+#{Regexp.escape(Gitlab::IncomingEmail::UNSUBSCRIBE_SUFFIX)}\z/
         end

lib/gitlab/email/receiver.rb

@@ -32,6 +32,10 @@ module Gitlab
         raise UnknownIncomingEmail unless handler
+        Gitlab::Metrics.add_event(:receive_email,
+                                  project: handler.try(:project),
+                                  handler: handler.class.name)
+
         handler.execute
       end