fix: only output new headers instead of message in case decoding/enco…

…ding attachment errors (that customers emailed me about)

README.md

@@ -144,7 +144,7 @@ arcSign(message, selector, domain, privateKeyFile, srvId)
 })();
 ```
 
-The value of `result` is a String with the new message (with ARC signed headers added to the top).
+The value of `result` is a String with the new ARC headers to add to the top of the message (if any).
 
 
 ## Contributors

scripts/arcsign.py

@@ -70,7 +70,6 @@ def main():
                        srv_id, cv, linesep=dkim.util.get_linesep(message))
         for line in sig:
             sys.stdout.write(line)
-        sys.stdout.write(message)
     except Exception as e:
         print(e, file=sys.stderr, end = '')
         sys.stdout.write(message)

test/arc-sign.js

@@ -39,7 +39,6 @@ test('arc sign returns none', async (t) => {
   t.true(lines[0].startsWith('ARC-Seal'));
   t.true(lines[1].startsWith('ARC-Message-Signature'));
   t.true(lines[2].startsWith('ARC-Authentication-Results'));
-  t.is(none, lines.slice(3).join('\n'));
 });
 
 test('arc sign returns pass', async (t) => {
@@ -50,7 +49,7 @@ test('arc sign returns pass', async (t) => {
     key,
     'mx.google.com'
   );
-  t.is(result, pass);
+  t.is(result, '');
 });
 
 test('arc sign throws error with missing From header', async (t) => {