abstract all of the ActionMailer delivery methods into their own classes. thereby the following are equivalent

ActionMailer::Base.delivery_method = :smtp
  ActionMailer::Base.delivery_method = ActionMailer::DeliveryMethod::Smtp

we could equally set our own custom object
as long as it provides the instance method :perform_delivery(mail)

eg.

  class MySmsDeliveryMethod
    def perform_delivery(mail)
      Sms.send(mail['to'], mail['body'])
    end
  end

  MySmsMailer.delivery_method = MySmsDeliveryMethod.new

Signed-off-by: José Valim <jose.valim@gmail.com>

actionmailer/Rakefile

@@ -44,6 +44,7 @@ Rake::RDocTask.new { |rdoc|
   rdoc.rdoc_files.include('README', 'CHANGELOG')
   rdoc.rdoc_files.include('lib/action_mailer.rb')
   rdoc.rdoc_files.include('lib/action_mailer/*.rb')
+  rdoc.rdoc_files.include('lib/action_mailer/delivery_method/*.rb')
 }
 
 spec = eval(File.read('actionmailer.gemspec'))

actionmailer/lib/action_mailer.rb

@@ -33,6 +33,7 @@ module ActionMailer
 
   autoload :AdvAttrAccessor, 'action_mailer/adv_attr_accessor'
   autoload :Base, 'action_mailer/base'
+  autoload :DeliveryMethod, 'action_mailer/delivery_method'
   autoload :Helpers, 'action_mailer/helpers'
   autoload :Part, 'action_mailer/part'
   autoload :PartContainer, 'action_mailer/part_container'

actionmailer/lib/action_mailer/base.rb

@@ -1,5 +1,3 @@
-require 'tmpdir'
-
 require "active_support/core_ext/class"
 # Use the old layouts until actionmailer gets refactored
 require "action_controller/legacy/layout"
@@ -232,7 +230,7 @@ module ActionMailer #:nodoc:
   # * <tt>raise_delivery_errors</tt> - Whether or not errors should be raised if the email fails to be delivered.
   #
   # * <tt>delivery_method</tt> - Defines a delivery method. Possible values are <tt>:smtp</tt> (default), <tt>:sendmail</tt>, <tt>:test</tt>,
-  #   and <tt>:file</tt>.
+  #   and <tt>:file</tt>. Or you may provide a custom delivery method object eg. MyOwnDeliveryMethodClass.new
   #
   # * <tt>perform_deliveries</tt> - Determines whether <tt>deliver_*</tt> methods are actually carried out. By default they are,
   #   but this can be turned off to help functional testing.
@@ -270,35 +268,21 @@ module ActionMailer #:nodoc:
 
     cattr_accessor :logger
 
-    @@smtp_settings = {
-      :address              => "localhost",
-      :port                 => 25,
-      :domain               => 'localhost.localdomain',
-      :user_name            => nil,
-      :password             => nil,
-      :authentication       => nil,
-      :enable_starttls_auto => true,
-    }
-    cattr_accessor :smtp_settings
+    class << self
+      delegate :settings, :settings=, :to => ActionMailer::DeliveryMethod::File, :prefix => :file
+      delegate :settings, :settings=, :to => ActionMailer::DeliveryMethod::Sendmail, :prefix => :sendmail
+      delegate :settings, :settings=, :to => ActionMailer::DeliveryMethod::Smtp, :prefix => :smtp
 
-    @@sendmail_settings = {
-      :location       => '/usr/sbin/sendmail',
-      :arguments      => '-i -t'
-    }
-    cattr_accessor :sendmail_settings
-
-    @@file_settings = {
-      :location       => defined?(Rails) ? "#{Rails.root}/tmp/mails" : "#{Dir.tmpdir}/mails"
-    }
-
-    cattr_accessor :file_settings
+      def delivery_method=(method_name)
+        @delivery_method = ActionMailer::DeliveryMethod.lookup_method(method_name)
+      end
+    end
+    self.delivery_method = :smtp
+    superclass_delegating_reader :delivery_method
 
     @@raise_delivery_errors = true
     cattr_accessor :raise_delivery_errors
 
-    superclass_delegating_accessor :delivery_method
-    self.delivery_method = :smtp
-
     @@perform_deliveries = true
     cattr_accessor :perform_deliveries
 
@@ -552,7 +536,7 @@ module ActionMailer #:nodoc:
 
       ActiveSupport::Notifications.instrument(:deliver_mail, :mail => @mail) do
         begin
-          __send__("perform_delivery_#{delivery_method}", mail) if perform_deliveries
+          self.delivery_method.perform_delivery(mail) if perform_deliveries
         rescue Exception => e # Net::SMTP errors or sendmail pipe errors
           raise e if raise_delivery_errors
         end
@@ -720,39 +704,6 @@ module ActionMailer #:nodoc:
         @mail = m
       end
 
-      def perform_delivery_smtp(mail)
-        destinations = mail.destinations
-        mail.ready_to_send
-        sender = (mail['return-path'] && mail['return-path'].spec) || mail['from']
-
-        smtp = Net::SMTP.new(smtp_settings[:address], smtp_settings[:port])
-        smtp.enable_starttls_auto if smtp_settings[:enable_starttls_auto] && smtp.respond_to?(:enable_starttls_auto)
-        smtp.start(smtp_settings[:domain], smtp_settings[:user_name], smtp_settings[:password],
-                   smtp_settings[:authentication]) do |smtp|
-          smtp.sendmail(mail.encoded, sender, destinations)
-        end
-      end
-
-      def perform_delivery_sendmail(mail)
-        sendmail_args = sendmail_settings[:arguments]
-        sendmail_args += " -f \"#{mail['return-path']}\"" if mail['return-path']
-        IO.popen("#{sendmail_settings[:location]} #{sendmail_args}","w+") do |sm|
-          sm.print(mail.encoded.gsub(/\r/, ''))
-          sm.flush
-        end
-      end
-
-      def perform_delivery_test(mail)
-        deliveries << mail
-      end
-
-      def perform_delivery_file(mail)
-        FileUtils.mkdir_p file_settings[:location]
-
-        (mail.to + mail.cc + mail.bcc).uniq.each do |to|
-          File.open(File.join(file_settings[:location], to), 'a') { |f| f.write(mail) }
-        end
-      end
   end
 
   Base.class_eval do

actionmailer/lib/action_mailer/delivery_method.rb

@@ -0,0 +1,58 @@
+require "active_support/core_ext/class"
+module ActionMailer
+  module DeliveryMethod
+
+    autoload :File, 'action_mailer/delivery_method/file'
+    autoload :Sendmail, 'action_mailer/delivery_method/sendmail'
+    autoload :Smtp, 'action_mailer/delivery_method/smtp'
+    autoload :Test, 'action_mailer/delivery_method/test'
+
+    # Creates a new DeliveryMethod object according to the given options.
+    #
+    # If no arguments are passed to this method, then a new
+    # ActionMailer::DeliveryMethod::Stmp object will be returned.
+    #
+    # If you pass a Symbol as the first argument, then a corresponding
+    # delivery method class under the ActionMailer::DeliveryMethod namespace
+    # will be created.
+    # For example:
+    #
+    #   ActionMailer::DeliveryMethod.lookup_method(:sendmail)
+    #   # => returns a new ActionMailer::DeliveryMethod::Sendmail object
+    #
+    # If the first argument is not a Symbol, then it will simply be returned:
+    #
+    #   ActionMailer::DeliveryMethod.lookup_method(MyOwnDeliveryMethod.new)
+    #   # => returns MyOwnDeliveryMethod.new
+    def self.lookup_method(delivery_method)
+      case delivery_method
+      when Symbol
+        method_name = delivery_method.to_s.camelize
+        method_class = ActionMailer::DeliveryMethod.const_get(method_name)
+        method_class.new()
+      when nil
+        Smtp.new
+      else
+        delivery_method
+      end
+    end
+
+    # An abstract delivery method class. There are multiple delivery method
+    # classes, documented under
+    # See the classes under the ActionMailer::DeliveryMethod, e.g.
+    # ActionMailer::DeliveryMethod::Smtp.
+    # Smtp is the default delivery method for production
+    # while Test is used in testing.
+    #
+    # each delivery method exposes just one method
+    #
+    #   delivery_method = ActionMailer::DeliveryMethod::Smtp.new
+    #
+    #   delivery_method.perform_delivery(mail) # send the mail via smtp
+    class Method
+      superclass_delegating_accessor :settings
+      self.settings = {}
+    end
+    
+  end
+end

actionmailer/lib/action_mailer/delivery_method/file.rb

@@ -0,0 +1,21 @@
+require 'tmpdir'
+module ActionMailer
+  module DeliveryMethod
+
+    # A delivery method implementation which writes all mails to a file.
+    class File < Method
+
+      self.settings = {
+        :location       => defined?(Rails) ? "#{Rails.root}/tmp/mails" : "#{Dir.tmpdir}/mails"
+      }
+
+      def perform_delivery(mail)
+        FileUtils.mkdir_p settings[:location]
+
+        (mail.to + mail.cc + mail.bcc).uniq.each do |to|
+          ::File.open(::File.join(settings[:location], to), 'a') { |f| f.write(mail) }
+        end
+      end
+    end
+  end
+end

actionmailer/lib/action_mailer/delivery_method/sendmail.rb

@@ -0,0 +1,22 @@
+module ActionMailer
+  module DeliveryMethod
+
+    # A delivery method implementation which sends via sendmail.
+    class Sendmail < Method
+
+      self.settings = {
+        :location       => '/usr/sbin/sendmail',
+        :arguments      => '-i -t'
+      }
+
+      def perform_delivery(mail)
+        sendmail_args = settings[:arguments]
+        sendmail_args += " -f \"#{mail['return-path']}\"" if mail['return-path']
+        IO.popen("#{settings[:location]} #{sendmail_args}","w+") do |sm|
+          sm.print(mail.encoded.gsub(/\r/, ''))
+          sm.flush
+        end
+      end
+    end
+  end
+end

actionmailer/lib/action_mailer/delivery_method/smtp.rb

@@ -0,0 +1,31 @@
+module ActionMailer
+  module DeliveryMethod
+    
+    # A delivery method implementation which sends via smtp.
+    class Smtp < Method
+
+      self.settings = {
+        :address              => "localhost",
+        :port                 => 25,
+        :domain               => 'localhost.localdomain',
+        :user_name            => nil,
+        :password             => nil,
+        :authentication       => nil,
+        :enable_starttls_auto => true,
+      }
+
+      def perform_delivery(mail)
+        destinations = mail.destinations
+        mail.ready_to_send
+        sender = (mail['return-path'] && mail['return-path'].spec) || mail['from']
+
+        smtp = Net::SMTP.new(settings[:address], settings[:port])
+        smtp.enable_starttls_auto if settings[:enable_starttls_auto] && smtp.respond_to?(:enable_starttls_auto)
+        smtp.start(settings[:domain], settings[:user_name], settings[:password],
+                   settings[:authentication]) do |smtp|
+          smtp.sendmail(mail.encoded, sender, destinations)
+        end
+      end
+    end
+  end
+end

actionmailer/lib/action_mailer/delivery_method/test.rb

@@ -0,0 +1,12 @@
+module ActionMailer
+  module DeliveryMethod
+
+    # A delivery method implementation designed for testing, which just appends each record to the :deliveries array
+    class Test < Method
+
+      def perform_delivery(mail)
+        ActionMailer::Base.deliveries << mail
+      end
+    end
+  end
+end

actionmailer/test/delivery_method_test.rb

@@ -11,6 +11,21 @@ class FileDeliveryMethodMailer < ActionMailer::Base
   self.delivery_method = :file
 end
 
+class CustomDeliveryMethod
+  attr_accessor :custom_deliveries
+  def initialize()
+    @customer_deliveries = []
+  end
+
+  def self.perform_delivery(mail)
+    self.custom_deliveries << mail
+  end
+end
+
+class CustomerDeliveryMailer < ActionMailer::Base
+  self.delivery_method = CustomDeliveryMethod.new
+end
+
 class ActionMailerBase_delivery_method_Test < Test::Unit::TestCase
   def setup
     set_delivery_method :smtp
@@ -21,7 +36,7 @@ class ActionMailerBase_delivery_method_Test < Test::Unit::TestCase
   end
 
   def test_should_be_the_default_smtp
-    assert_equal :smtp, ActionMailer::Base.delivery_method
+    assert_instance_of ActionMailer::DeliveryMethod::Smtp, ActionMailer::Base.delivery_method
   end
 end
 
@@ -35,7 +50,7 @@ class DefaultDeliveryMethodMailer_delivery_method_Test < Test::Unit::TestCase
   end
   
   def test_should_be_the_default_smtp
-    assert_equal :smtp, DefaultDeliveryMethodMailer.delivery_method
+    assert_instance_of ActionMailer::DeliveryMethod::Smtp, DefaultDeliveryMethodMailer.delivery_method
   end
 end
 
@@ -49,7 +64,7 @@ class NonDefaultDeliveryMethodMailer_delivery_method_Test < Test::Unit::TestCase
   end
 
   def test_should_be_the_set_delivery_method
-    assert_equal :sendmail, NonDefaultDeliveryMethodMailer.delivery_method
+    assert_instance_of ActionMailer::DeliveryMethod::Sendmail, NonDefaultDeliveryMethodMailer.delivery_method
   end
 end
 
@@ -63,7 +78,7 @@ class FileDeliveryMethodMailer_delivery_method_Test < Test::Unit::TestCase
   end
 
   def test_should_be_the_set_delivery_method
-    assert_equal :file, FileDeliveryMethodMailer.delivery_method
+    assert_instance_of ActionMailer::DeliveryMethod::File, FileDeliveryMethodMailer.delivery_method
   end
 
   def test_should_default_location_to_the_tmpdir
@@ -71,3 +86,16 @@ class FileDeliveryMethodMailer_delivery_method_Test < Test::Unit::TestCase
   end
 end
 
+class CustomDeliveryMethodMailer_delivery_method_Test < Test::Unit::TestCase
+  def setup
+    set_delivery_method :smtp
+  end
+
+  def teardown
+    restore_delivery_method
+  end
+
+  def test_should_be_the_set_delivery_method
+    assert_instance_of CustomDeliveryMethod, CustomerDeliveryMailer.delivery_method
+  end
+end

actionmailer/test/mail_service_test.rb

@@ -554,7 +554,7 @@ class ActionMailerTest < Test::Unit::TestCase
 
   def test_doesnt_raise_errors_when_raise_delivery_errors_is_false
     ActionMailer::Base.raise_delivery_errors = false
-    TestMailer.any_instance.expects(:perform_delivery_test).raises(Exception)
+    TestMailer.delivery_method.expects(:perform_delivery).raises(Exception)
     assert_nothing_raised { TestMailer.deliver_signed_up(@recipient) }
   end
 

actionmailer/test/test_helper_test.rb

@@ -10,7 +10,7 @@ end
 
 class TestHelperMailerTest < ActionMailer::TestCase
   def test_setup_sets_right_action_mailer_options
-    assert_equal :test, ActionMailer::Base.delivery_method
+    assert_instance_of ActionMailer::DeliveryMethod::Test, ActionMailer::Base.delivery_method
     assert ActionMailer::Base.perform_deliveries
     assert_equal [], ActionMailer::Base.deliveries
   end