Add ability to define callbacks in ActionMailer using AbstractController::Callbacks.

Prior to this commit, there isn't a good way of adding things like
default inline attachments to an email.  This Stack Overflow thread
shows people using hooks like the 'default' method in ActionMailer::Base
to call a Proc for message configuration:

http://stackoverflow.com/questions/5113121/rails-use-same-attachment-for-all-emails-using-layout

This has the unintended side effect of setting a message header, so it's not a good solution.

This pull request adds support for message modifications by including AbstractController:Callbacks
in ActionMailer::Base. It includes tests and documentation for the functionality
provided by including this module.

1 files changed, 46 insertions, 0 deletions

diff --git a/actionmailer/test/base_test.rb b/actionmailer/test/base_test.rb
index 8d60e028cb..aed3ee1874 100644
--- a/actionmailer/test/base_test.rb
+++ b/actionmailer/test/base_test.rb
@@ -552,6 +552,52 @@ class BaseTest < ActiveSupport::TestCase
     assert_equal("Thanks for signing up this afternoon", mail.subject)
   end
 
+  test "modifying the mail message with a before_filter" do
+    class BeforeFilterMailer < ActionMailer::Base
+      before_filter :add_special_header!
+
+      def welcome ; mail ; end
+
+      private
+      def add_special_header!
+        headers('X-Special-Header' => 'Wow, so special')
+      end
+    end
+
+    assert_equal('Wow, so special', BeforeFilterMailer.welcome['X-Special-Header'].to_s)
+  end
+
+  test "modifying the mail message with an after_filter" do
+    class AfterFilterMailer < ActionMailer::Base
+      after_filter :add_special_header!
+
+      def welcome ; mail ; end
+
+      private
+      def add_special_header!
+        headers('X-Special-Header' => 'Testing')
+      end
+    end
+
+    assert_equal('Testing', AfterFilterMailer.welcome['X-Special-Header'].to_s)
+  end
+
+  test "adding an inline attachment using a before_filter" do
+    class DefaultInlineAttachmentMailer < ActionMailer::Base
+      before_filter :add_inline_attachment!
+
+      def welcome ; mail ; end
+
+      private
+      def add_inline_attachment!
+        attachments.inline["footer.jpg"] = 'hey there'
+      end
+    end
+
+    mail = DefaultInlineAttachmentMailer.welcome
+    assert_equal('image/jpeg; filename=footer.jpg', mail.attachments.inline.first['Content-Type'].to_s)
+  end
+
   test "action methods should be refreshed after defining new method" do
     class FooMailer < ActionMailer::Base
       # this triggers action_methods