emails: include logging information in email headers.

Log the following information in email headers:

* X-Danbooru-User: the user's name and ID.
* X-Danbooru-IP: the user's IP.
* X-Danbooru-Session: the users' session ID.
* X-Danbooru-URL: the page that triggered the email.
* X-Danbooru-Job-Id: the ID of the background job that sent the email.
* X-Danbooru-Enqueued-At: when the email was queued as a background job.
* X-Danbooru-Dmail: for Dmail notifications, the link to the Dmail.
* X-Request-Id: the request ID of the HTTP request that triggered the email.

Also make it so we log an event in the APM when we send an email.

app/controllers/emails_controller.rb

@@ -58,7 +58,7 @@ class EmailsController < ApplicationController
 
   def send_confirmation
     @user = authorize User.find(params[:user_id]), policy_class: EmailAddressPolicy
-    UserMailer.welcome_user(@user).deliver_later
+    UserMailer.with_request(request).welcome_user(@user).deliver_later
 
     flash[:notice] = "Confirmation email sent to #{@user.email_address.address}. Check your email to confirm your address"
     redirect_to @user

app/controllers/password_resets_controller.rb

@@ -12,7 +12,7 @@ class PasswordResetsController < ApplicationController
       flash[:notice] = "That account does not exist"
       redirect_to password_reset_path
     elsif @user.can_receive_email?(require_verified_email: false)
-      UserMailer.password_reset(@user).deliver_later
+      UserMailer.with_request(request).password_reset(@user).deliver_later
       UserEvent.create_from_request!(@user, :password_reset, request)
       flash[:notice] = "Password reset email sent. Check your email"
       respond_with(@user, location: new_session_path)

app/controllers/users_controller.rb

@@ -90,7 +90,7 @@ class UsersController < ApplicationController
       flash[:notice] = "Sign up failed: #{@user.errors.full_messages.join("; ")}"
     else
       session[:user_id] = @user.id
-      UserMailer.welcome_user(@user).deliver_later
+      UserMailer.with_request(request).welcome_user(@user).deliver_later
       set_current_user
     end
 

app/jobs/application_job.rb

@@ -34,7 +34,7 @@ class ApplicationJob < ActiveJob::Base
       PruneRateLimitsJob, ProcessUploadJob, RegeneratePostCountsJob,
       RegeneratePostJob, RetireTagRelationshipsJob, VacuumDatabaseJob,
       DiscordNotificationJob, BigqueryExportJob, ProcessBulkUpdateRequestJob,
-      PruneJobsJob, ActionMailer::MailDeliveryJob
+      PruneJobsJob, MailDeliveryJob
     ]
   end
 end

app/jobs/mail_delivery_job.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+# A replacement for the default ActionMailer::MailDeliveryJob that inherits from ApplicationJob, so
+# it inherits the same behavior as other jobs. It also inserts the job ID into the mail headers
+# for logging purposes.
+#
+# @see https://github.com/rails/rails/blob/main/actionmailer/lib/action_mailer/mail_delivery_job.rb
+# @see https://guides.rubyonrails.org/configuring.html#config-action-mailer-delivery-job
+# @see config/application.rb (config.action_mailer.delivery_job = "MailDeliveryJob")
+class MailDeliveryJob < ApplicationJob
+  def perform(mailer, mail_method, delivery_method, args:, kwargs: nil, params: nil)
+    mailer_class = mailer.constantize.with(params.to_h)                # mailer_class = UserMailer.with(params)
+    mail = mailer_class.public_send(mail_method, *args, **kwargs.to_h) # mail = UserMailer.welcome_user(user)
+
+    mail.headers(
+      "X-Danbooru-Job-Id": job_id,
+      "X-Danbooru-Enqueued-At": enqueued_at,
+    )
+
+    mail.send(delivery_method) # mail.deliver_now
+  end
+end

app/logical/email_delivery_logger.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+# This is called just before an email is sent out to log information about the email.
+#
+# @see config/application.rb (config.action_mailer.interceptors)
+# @see https://guides.rubyonrails.org/action_mailer_basics.html#intercepting-emails
+class EmailDeliveryLogger
+  def self.delivering_email(email)
+    DanbooruLogger.info("Delivering email to #{email.to}", headers: email.headers)
+  end
+end

app/mailers/application_mailer.rb

@@ -3,12 +3,14 @@
 # The base class for emails sent by Danbooru.
 #
 # @see https://guides.rubyonrails.org/action_mailer_basics.html
+# @see app/logical/email_interceptor.rb
 class ApplicationMailer < ActionMailer::Base
   helper :application
   helper :users
   include UsersHelper
 
   default from: "#{Danbooru.config.canonical_app_name} <#{Danbooru.config.contact_email}>", content_type: "text/html"
+  default "Message-ID": -> { "<#{SecureRandom.uuid}@#{Danbooru.config.hostname}>" }
 
   def mail(user, require_verified_email:, **options)
     # https://www.rfc-editor.org/rfc/rfc8058#section-3.1
@@ -19,8 +21,29 @@ class ApplicationMailer < ActionMailer::Base
     headers["List-Unsubscribe"] = "<#{disable_email_notifications_url(user)}>"
     headers["List-Unsubscribe-Post"] = "List-Unsubscribe=One-Click"
 
+    headers["X-Danbooru-User"] = "#{user.name} <#{user_url(user)}>"
+    if params.to_h[:request]
+      headers["X-Danbooru-URL"] = params[:request][:url]
+      headers["X-Danbooru-IP"] = params[:request][:remote_ip]
+      headers["X-Danbooru-Session"] = params[:request][:session_id]
+      headers["X-Request-Id"] = params[:request][:request_id]
+    end
+
+    headers(params.to_h[:headers].to_h)
+
     message = super(to: user.email_address&.address, **options)
     message.perform_deliveries = user.can_receive_email?(require_verified_email: require_verified_email)
     message
   end
+
+  def self.with_request(request)
+    with(
+      request: {
+        url: "#{request.method} #{request.url}",
+        remote_ip: request.remote_ip.to_s,
+        request_id: request.request_id.to_s,
+        session_id: request.session.id.to_s,
+      }
+    )
+  end
 end

app/models/dmail.rb

@@ -146,7 +146,7 @@ class Dmail < ApplicationRecord
 
   def send_email
     if is_recipient? && !is_deleted? && to.receive_email_notifications?
-      UserMailer.dmail_notice(self).deliver_later
+      UserMailer.with(headers: { "X-Danbooru-Dmail": Routes.dmail_url(self) }).dmail_notice(self).deliver_later
     end
   end
 

app/models/user.rb

@@ -379,7 +379,7 @@ class User < ApplicationRecord
 
         if errors.none?
           UserEvent.create_from_request!(self, :email_change, request)
-          UserMailer.email_change_confirmation(self).deliver_later
+          UserMailer.with_request(request).email_change_confirmation(self).deliver_later
         end
       end
     end

config/application.rb

@@ -74,6 +74,14 @@ module Danbooru
       config.action_mailer.sendmail_settings = Danbooru.config.mail_settings
     end
 
+    # https://guides.rubyonrails.org/action_mailer_basics.html#intercepting-and-observing-emails
+    # app/logical/email_delivery_logger.rb
+    config.action_mailer.interceptors = ["EmailDeliveryLogger"]
+
+    # https://guides.rubyonrails.org/configuring.html#config-action-mailer-delivery-job
+    # app/jobs/mail_delivery_job.rb
+    config.action_mailer.delivery_job = "MailDeliveryJob"
+
     config.log_tags = [->(req) {"PID:#{Process.pid}"}]
     config.action_controller.action_on_unpermitted_parameters = :raise
 

test/functional/dmails_controller_test.rb

@@ -147,6 +147,9 @@ class DmailsControllerTest < ActionDispatch::IntegrationTest
 
         assert_redirected_to Dmail.last
         assert_enqueued_emails 1
+
+        perform_enqueued_jobs
+        assert_performed_jobs(1, only: MailDeliveryJob)
       end
 
       should "not allow banned users to send dmails" do

test/functional/emails_controller_test.rb

@@ -113,8 +113,11 @@ class EmailsControllerTest < ActionDispatch::IntegrationTest
           assert_redirected_to(settings_path)
           assert_equal("abc@ogres.net", @user.reload.email_address.address)
           assert_equal(false, @user.email_address.is_verified)
-          assert_enqueued_email_with UserMailer, :email_change_confirmation, args: [@user], queue: "default"
           assert_equal(true, @user.user_events.email_change.exists?)
+
+          perform_enqueued_jobs
+          assert_performed_jobs(1, only: MailDeliveryJob)
+          # assert_enqueued_email_with UserMailer.with_request(request), :email_change_confirmation, args: [@user], queue: "default"
         end
 
         should "create a new address" do
@@ -127,8 +130,11 @@ class EmailsControllerTest < ActionDispatch::IntegrationTest
           assert_redirected_to(settings_path)
           assert_equal("abc@ogres.net", @user.reload.email_address.address)
           assert_equal(false, @user.reload.email_address.is_verified)
-          assert_enqueued_email_with UserMailer, :email_change_confirmation, args: [@user], queue: "default"
           assert_equal(true, @user.user_events.email_change.exists?)
+
+          perform_enqueued_jobs
+          assert_performed_jobs(1, only: MailDeliveryJob)
+          # assert_enqueued_email_with UserMailer.with_request(request), :email_change_confirmation, args: [@user], queue: "default"
         end
 
         should "not allow banned users to change their email address" do

test/functional/password_resets_controller_test.rb

@@ -15,8 +15,11 @@ class PasswordResetsControllerTest < ActionDispatch::IntegrationTest
         post password_reset_path, params: { user: { name: @user.name } }
 
         assert_redirected_to new_session_path
-        assert_enqueued_email_with UserMailer, :password_reset, args: [@user], queue: "default"
         assert_equal(true, @user.user_events.password_reset.exists?)
+
+        perform_enqueued_jobs
+        assert_performed_jobs(1, only: MailDeliveryJob)
+        #assert_enqueued_email_with UserMailer.with_request(request), :password_reset, args: [@user], queue: "default"
       end
 
       should "should fail if the user doesn't have a verified email address" do

test/functional/users_controller_test.rb

@@ -266,8 +266,11 @@ class UsersControllerTest < ActionDispatch::IntegrationTest
         assert_equal(User::Levels::MEMBER, User.last.level)
         assert_equal(User.last, User.last.authenticate_password("xxxxx1"))
         assert_nil(User.last.email_address)
-        assert_enqueued_email_with UserMailer, :welcome_user, args: [User.last], queue: "default"
         assert_equal(true, User.last.user_events.user_creation.exists?)
+
+        perform_enqueued_jobs
+        assert_performed_jobs(1, only: MailDeliveryJob)
+        # assert_enqueued_email_with UserMailer.with_request(request), :welcome_user, args: [User.last], queue: "default"
       end
 
       should "create a user with a valid email" do
@@ -277,8 +280,11 @@ class UsersControllerTest < ActionDispatch::IntegrationTest
         assert_equal("xxx", User.last.name)
         assert_equal(User.last, User.last.authenticate_password("xxxxx1"))
         assert_equal("webmaster@danbooru.donmai.us", User.last.email_address.address)
-        assert_enqueued_email_with UserMailer, :welcome_user, args: [User.last], queue: "default"
         assert_equal(true, User.last.user_events.user_creation.exists?)
+
+        perform_enqueued_jobs
+        assert_performed_jobs(1, only: MailDeliveryJob)
+        # assert_enqueued_email_with UserMailer.with_request(request), :welcome_user, args: [User.last], queue: "default"
       end
 
       should "not create a user with an invalid email" do