Too long line in part with `Content-Transfer-Encoding: base64` in notification mail

[Jun Omae]

unit-test with r17497 fails on my environment.

======================================================================
FAIL: test_mimebody_b64 (trac.ticket.tests.notification.NotificationTestCase)
MIME Base64/utf-8 encoding
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/jun66j5/src/tracdev/git/trac/ticket/tests/notification.py", line 721, in test_mimebody_b64
    ticket, True)
  File "/home/jun66j5/src/tracdev/git/trac/ticket/tests/notification.py", line 848, in _validate_mimebody
    self.assertTrue(len(line) <= MAXBODYWIDTH)
AssertionError: False is not true

----------------------------------------------------------------------

I applied the following changes to investigate the failure.

trac/ticket/tests/notification.py

@@ -844 +844 @@
         self.assertEqual(mime_charset, charset)
         self.assertEqual(headers['Content-Transfer-Encoding'], mime_name)
         # checks the width of each body line
-        for line in body.splitlines():
-            self.assertTrue(len(line) <= MAXBODYWIDTH)
+        for idx, line in enumerate(body.splitlines()):
+            self.assertTrue(len(line) <= MAXBODYWIDTH,
+                            'Line %d too long (%d > %d, %r)' %
+                            (idx + 1, len(line), MAXBODYWIDTH, line))
         # attempts to decode the body, following the specified MIME encoding
         # and charset
         try:

After the changes, I get the following message. Body encoded with base64 has line exceeded 76 characters. That's weird.

======================================================================
FAIL: test_mimebody_b64 (trac.ticket.tests.notification.NotificationTestCase)
MIME Base64/utf-8 encoding
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/jun66j5/src/tracdev/git/trac/ticket/tests/notification.py", line 721, in test_mimebody_b64
    ticket, True)
  File "/home/jun66j5/src/tracdev/git/trac/ticket/tests/notification.py", line 850, in _validate_mimebody
    (idx + 1, len(line), MAXBODYWIDTH, line))
AssertionError: False is not true : Line 1 too long (80 > 76, 'IzE6IFRoaXMgaXMgYSBsb25nIGVub3VnaCBzdW1tYXJ5IHRvIGNhdXNlIFRyYWMgdG8gZ2VuZXJhdA==')

----------------------------------------------------------------------

[Jun Omae]

It is able to reproduce with small code:

from email.message import EmailMessage
m = EmailMessage()
m.set_content('あ' * 20, subtype='plain', cte='base64')
print(m)

Output:

Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: base64
MIME-Version: 1.0

44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC44GC4w==
gYIK

I noticed it occurs only with Python 3.5.2 (Ubuntu 16.04LTS). It doesn't occur with Python 3.6.12, 3.7.9, 3.8.7, 3.9.1 and 3.10.0a3.

Investigating, I found ​https://bugs.python.org/issue28047 related to the issue and it has been fixed in ​https://hg.python.org/cpython/rev/99db6a25444b (Python 3.5.3). I confirmed fixed with Python 3.5.4 on Windows.

Going to close as cantfix….