Document inline image mailer preview interceptor

Explain what the interceptor is used for and how to remove it.

5 files changed, 83 insertions, 56 deletions

diff --git a/actionmailer/lib/action_mailer.rb b/actionmailer/lib/action_mailer.rb
index 17d8dcc208..291a8c1e34 100644
--- a/actionmailer/lib/action_mailer.rb
+++ b/actionmailer/lib/action_mailer.rb
@@ -40,6 +40,7 @@ module ActionMailer
 
   autoload :Base
   autoload :DeliveryMethods
+  autoload :InlinePreviewInterceptor
   autoload :MailHelper
   autoload :Preview
   autoload :Previews, 'action_mailer/preview'
diff --git a/actionmailer/lib/action_mailer/inline_preview_interceptor.rb b/actionmailer/lib/action_mailer/inline_preview_interceptor.rb
new file mode 100644
index 0000000000..dea5e52f0c
--- /dev/null
+++ b/actionmailer/lib/action_mailer/inline_preview_interceptor.rb
@@ -0,0 +1,61 @@
+require 'base64'
+
+module ActionMailer
+  # Implements a mailer preview interceptor that converts image tag src attributes
+  # that use inline cid: style urls to data: style urls so that they are visible
+  # when previewing a HTML email in a web browser.
+  #
+  # This interceptor is enabled by default, to remove it delete it from the
+  # <tt>ActionMailer::Base.preview_interceptors</tt> array:
+  #
+  #   ActionMailer::Base.preview_interceptors.delete(ActionMailer::InlinePreviewInterceptor)
+  #
+  class InlinePreviewInterceptor
+    PATTERN  = /src=(?:"cid:[^"]+"|'cid:[^']+')/i
+
+    include Base64
+
+    def self.previewing_email(message) #:nodoc:
+      new(message).transform!
+    end
+
+    def initialize(message) #:nodoc:
+      @message = message
+    end
+
+    def transform! #:nodoc:
+      return message if html_part.blank?
+
+      html_source.gsub!(PATTERN) do |match|
+        if part = find_part(match[9..-2])
+          %[src="#{data_url(part)}"]
+        else
+          match
+        end
+      end
+
+      message
+    end
+
+    private
+      def message
+        @message
+      end
+
+      def html_part
+        @html_part ||= message.html_part
+      end
+
+      def html_source
+        html_part.body.raw_source
+      end
+
+      def data_url(part)
+        "data:#{part.mime_type};base64,#{strict_encode64(part.body.raw_source)}"
+      end
+
+      def find_part(cid)
+        message.all_parts.find{ |p| p.attachment? && p.cid == cid }
+      end
+  end
+end
diff --git a/actionmailer/lib/action_mailer/preview.rb b/actionmailer/lib/action_mailer/preview.rb
index 4888eac345..25ad7ee721 100644
--- a/actionmailer/lib/action_mailer/preview.rb
+++ b/actionmailer/lib/action_mailer/preview.rb
@@ -1,57 +1,9 @@
 require 'active_support/descendants_tracker'
-require 'base64'
 
 module ActionMailer
   module Previews #:nodoc:
     extend ActiveSupport::Concern
 
-    class InlineAttachments #:nodoc:
-      PATTERN  = /src=(?:"cid:[^"]+"|'cid:[^']+')/i
-
-      include Base64
-
-      attr_reader :message
-
-      def self.previewing_email(message)
-        new(message).transform!
-      end
-
-      def initialize(message)
-        @message = message
-      end
-
-      def transform!
-        return message if html_part.blank?
-
-        html_source.gsub!(PATTERN) do |match|
-          if part = find_part(match[9..-2])
-            %[src="#{data_url(part)}"]
-          else
-            match
-          end
-        end
-
-        message
-      end
-
-      private
-        def html_part
-          @html_part ||= message.html_part
-        end
-
-        def html_source
-          html_part.body.raw_source
-        end
-
-        def data_url(part)
-          "data:#{part.mime_type};base64,#{urlsafe_encode64(part.body.raw_source)}"
-        end
-
-        def find_part(cid)
-          message.all_parts.find{ |p| p.attachment? && p.cid == cid }
-        end
-    end
-
     included do
       # Set the location of mailer previews through app configuration:
       #
@@ -69,7 +21,7 @@ module ActionMailer
 
       # :nodoc:
       mattr_accessor :preview_interceptors, instance_writer: false
-      self.preview_interceptors = [ActionMailer::Previews::InlineAttachments]
+      self.preview_interceptors = [ActionMailer::InlinePreviewInterceptor]
     end
 
     module ClassMethods
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 14912326fc..38516a1c1a 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -690,7 +690,7 @@ module ApplicationTests
 
       _ = ActionMailer::Base
 
-      assert_equal [ActionMailer::Previews::InlineAttachments, ::MyPreviewMailInterceptor], ActionMailer::Base.preview_interceptors
+      assert_equal [ActionMailer::InlinePreviewInterceptor, ::MyPreviewMailInterceptor], ActionMailer::Base.preview_interceptors
     end
 
     test "registers multiple preview interceptors with ActionMailer" do
@@ -703,7 +703,20 @@ module ApplicationTests
 
       _ = ActionMailer::Base
 
-      assert_equal [ActionMailer::Previews::InlineAttachments, MyPreviewMailInterceptor, MyOtherPreviewMailInterceptor], ActionMailer::Base.preview_interceptors
+      assert_equal [ActionMailer::InlinePreviewInterceptor, MyPreviewMailInterceptor, MyOtherPreviewMailInterceptor], ActionMailer::Base.preview_interceptors
+    end
+
+    test "default preview interceptor can be removed" do
+      app_file 'config/initializers/preview_interceptors.rb', <<-RUBY
+        ActionMailer::Base.preview_interceptors.delete(ActionMailer::InlinePreviewInterceptor)
+      RUBY
+
+      require "#{app_path}/config/environment"
+      require "mail"
+
+      _ = ActionMailer::Base
+
+      assert_equal [], ActionMailer::Base.preview_interceptors
     end
 
     test "registers observers with ActionMailer" do
diff --git a/railties/test/application/mailer_previews_test.rb b/railties/test/application/mailer_previews_test.rb
index 3c9de0115f..e462d2c15e 100644
--- a/railties/test/application/mailer_previews_test.rb
+++ b/railties/test/application/mailer_previews_test.rb
@@ -487,7 +487,7 @@ module ApplicationTests
     end
 
     test "plain text mailer preview with attachment" do
-      image_file "pixel.png", "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca_JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="
+      image_file "pixel.png", "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca/JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="
 
       mailer 'notifier', <<-RUBY
         class Notifier < ActionMailer::Base
@@ -524,7 +524,7 @@ module ApplicationTests
     end
 
     test "multipart mailer preview with attachment" do
-      image_file "pixel.png", "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca_JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="
+      image_file "pixel.png", "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca/JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="
 
       mailer 'notifier', <<-RUBY
         class Notifier < ActionMailer::Base
@@ -569,7 +569,7 @@ module ApplicationTests
     end
 
     test "multipart mailer preview with inline attachment" do
-      image_file "pixel.png", "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca_JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="
+      image_file "pixel.png", "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca/JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="
 
       mailer 'notifier', <<-RUBY
         class Notifier < ActionMailer::Base
@@ -612,7 +612,7 @@ module ApplicationTests
       get "/rails/mailers/notifier/foo?part=text/html"
       assert_equal 200, last_response.status
       assert_match %r[<p>Hello, World!</p>], last_response.body
-      assert_match %r[src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca_JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="], last_response.body
+      assert_match %r[src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca/JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="], last_response.body
     end
 
     test "multipart mailer preview with attached email" do
@@ -695,7 +695,7 @@ module ApplicationTests
       end
 
       def image_file(name, contents)
-        app_file("public/images/#{name}", Base64.urlsafe_decode64(contents), 'wb')
+        app_file("public/images/#{name}", Base64.strict_decode64(contents), 'wb')
       end
   end
 end