policy.max_line_length is incorrectly assumed to never be None

[equaeghe]

BPO	41585
Nosy	@warsaw, @bitdancer, @maxking, @websurfer5, @iritkatriel, @Foxyblue, @akulakov
PRs	bpo-41585 When max-line-length is None default to 0 #21955

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-08-18.20:47:21.272>
labels = ['type-bug', 'expert-email', '3.10']
title = 'policy.max_line_length is incorrectly assumed to never be None'
updated_at = <Date 2021-12-29.03:47:26.359>
user = 'https://bugs.python.org/equaeghe'

bugs.python.org fields:

activity = <Date 2021-12-29.03:47:26.359>
actor = 'andrei.avk'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['email']
creation = <Date 2020-08-18.20:47:21.272>
creator = 'equaeghe'
dependencies = []
files = []
hgrepos = []
issue_num = 41585
keywords = ['patch']
message_count = 4.0
messages = ['375625', '375653', '375691', '409280']
nosy_count = 8.0
nosy_names = ['barry', 'r.david.murray', 'maxking', 'equaeghe', 'Jeffrey.Kintscher', 'iritkatriel', 's.williams-wynn', 'andrei.avk']
pr_nums = ['21955']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41585'
versions = ['Python 3.10']

[equaeghe]

I got the following error (Python 3.7.8):

Traceback (most recent call last):
  File "/home/equaeghe/.local/bin/html2alternative.py", line 68, in <module>
    replaceable.add_alternative(plain)
  File "/usr/lib/python3.7/email/message.py", line 1153, in add_alternative
    self._add_multipart('alternative', *args, **kw)
  File "/usr/lib/python3.7/email/message.py", line 1144, in _add_multipart
    part.set_content(*args, **kw)
  File "/usr/lib/python3.7/email/message.py", line 1171, in set_content
    super().set_content(*args, **kw)
  File "/usr/lib/python3.7/email/message.py", line 1101, in set_content
    content_manager.set_content(self, *args, **kw)
  File "/usr/lib/python3.7/email/contentmanager.py", line 37, in set_content
    handler(msg, obj, *args, **kw)
  File "/usr/lib/python3.7/email/contentmanager.py", line 185, in set_text_content
    cte, payload = _encode_text(string, charset, cte, msg.policy)
  File "/usr/lib/python3.7/email/contentmanager.py", line 154, in _encode_text
    max(len(x) for x in lines) <= policy.max_line_length):
TypeError: '<=' not supported between instances of 'int' and 'NoneType'

This is triggered because it is incorrectly assumed that policy.max_line_length cannot be None. This issue is still present in current master:

cpython/Lib/email/contentmanager.py

Line 149 in c3dd7e4

if max((len(x) for x in lines), default=0) <= policy.max_line_length:

[iritkatriel]

Are you able to post a script that reproduces the issue?

[equaeghe]

The script that triggered the issue can be found at

https://github.com/equaeghe/mailfilters/blob/master/html2alternative.py

You'll have to remove ", cte='8bit'" on line 68 to expose the bug (that was added as a workaround for this bug).

I was consistently able to trigger the bug when applying it to a mail with a multipart/alternative with text and html parts already present. It should replace that html part by a (nested) multipart/alternative part, but it crashes unless you keep the workaround.

[akulakov]

Seems to be a duplicate of bpo-34800