Merge pull request #1506 from mikel/regression/preserve-message-level…

…-multipart-backport

Regression/preserve message level multipart backport

lib/mail/message.rb

@@ -2066,7 +2066,11 @@ def add_multipart_alternate_header
 
     def add_boundary
       unless body.boundary && boundary
-        header['content-type'] = 'multipart/mixed' unless header['content-type']
+        unless header['content-type']
+          _charset = charset
+          header['content-type'] = 'multipart/mixed'
+          header['content-type'].parameters[:charset] = _charset
+        end
         header['content-type'].parameters[:boundary] = ContentTypeField.generate_boundary
         body.boundary = boundary
       end

spec/mail/message_spec.rb

@@ -1989,6 +1989,24 @@ def self.delivering_email(mail)
     end
   end
 
+  describe "adding parts should preserve the charset of the mail" do
+    charsets = ['UTF-8', 'ISO-8859-1', nil]
+    charsets.each do |mail_charset|
+      charsets.each do |part_charset|
+        it "when #{mail_charset || 'nil'} vs #{part_charset || 'nil'}" do
+          mail = Mail.new
+          mail['charset'] = mail_charset
+          expect(mail.charset).to eq mail_charset
+          p = Mail::Part.new(:content_type => 'text/html', :body => 'HTML TEXT', :charset => part_charset)
+          expect(p.charset).to eq part_charset
+          mail.add_part(p)
+          expect(mail.charset).to eq mail_charset
+          expect(p.charset).to eq part_charset
+        end
+      end
+    end
+  end
+
   describe "ordering messages" do
     it "should put all attachments as the last item" do
       mail = Mail.new