Fix 7bit/base64 content transfer encoding mismatch

Caused by picking the best transfer encoding twice in a row.

References #1128

Co-authored-by: Jeremy Daer <[email protected]>

CHANGELOG.rdoc

@@ -12,6 +12,7 @@ Performance:
 
 Bugs:
 * Fix transfer encoding when message encoding is blank. (jakubonty, saks)
+* Fix 7bit/base64 content transfer encoding mismatch. (ahorek)
 * Fix UTF-8 attachment filename quoting. (ahorek)
 
 

lib/mail/body.rb

@@ -154,7 +154,13 @@ def encoded(transfer_encoding = nil)
         ([preamble] + encoded_parts).join(crlf_boundary) + end_boundary + epilogue.to_s
       else
         dec = Mail::Encodings.get_encoding(encoding)
-        enc = negotiate_best_encoding(transfer_encoding)
+        enc =
+          if Utilities.blank?(transfer_encoding)
+            dec
+          else
+            negotiate_best_encoding(transfer_encoding)
+          end
+
         if dec.nil?
           # Cannot decode, so skip normalization
           raw_source

spec/mail/message_spec.rb

@@ -1405,6 +1405,25 @@ def message_headers_should_match(message, other)
 
       end
 
+      it "rfc2046 can be decoded" do
+        mail = Mail.new
+        mail.body << Mail::Part.new.tap do |part|
+          part.content_disposition = 'attachment; filename="test.eml"'
+          part.content_type = 'message/rfc822'
+          part.body = "This is NOT plain text ASCII　− かきくけこ" * 30
+        end
+
+        roundtripped = Mail.new(mail.encoded)
+        expect(roundtripped.content_transfer_encoding).to eq '7bit'
+        expect(roundtripped.parts.last.content_transfer_encoding).to eq ''
+
+        # Check that the part's transfer encoding isn't set to 7bit, causing
+        # the actual content to end up encoded with base64.
+        expect(roundtripped.encoded).to include('NOT plain')
+        expect(roundtripped.content_transfer_encoding).to eq '7bit'
+        expect(roundtripped.parts.last.content_transfer_encoding).to eq ''
+      end
+
       # https://www.ietf.org/rfc/rfc2046.txt
       # No encoding other than "7bit", "8bit", or "binary" is permitted for
       # the body of a "message/rfc822" entity.