Don't mutate raw_source in mailer preview interceptor

The raw_source method is documented as returning the exact value that
was used to create the body; mutating it breaks that contract.

Additionally, if the value used to create the body is blank, raw_source
returns a frozen string which causes the interceptor to raise an error.

1 files changed, 1 insertions, 5 deletions

diff --git a/actionmailer/lib/action_mailer/inline_preview_interceptor.rb b/actionmailer/lib/action_mailer/inline_preview_interceptor.rb
index 9087d335fa..980415afe0 100644
--- a/actionmailer/lib/action_mailer/inline_preview_interceptor.rb
+++ b/actionmailer/lib/action_mailer/inline_preview_interceptor.rb
@@ -26,7 +26,7 @@ module ActionMailer
     def transform! #:nodoc:
       return message if html_part.blank?
 
-      html_source.gsub!(PATTERN) do |match|
+      html_part.body = html_part.decoded.gsub(PATTERN) do |match|
         if part = find_part(match[9..-2])
           %[src="#{data_url(part)}"]
         else
@@ -46,10 +46,6 @@ module ActionMailer
         @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