bpo-34222: Lib/email: Fix infinite loop when folding #8990
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Currently when folding headers with length > maxlen, _fold_as_ew tries to split the to_encode into multiple parts to fulfill the maxlen limit, in an inapropriate way. If a long header has non-ascii characters, in some situations (e.g. a Subject: with full of CJK chars), it will split the to_encode into ["", to_encode], entering an infinite loop. This commit fixes this by introducing a smarter way to split. Besides, when an header needs to be folded now, every non-last line will try its best to reach the maxlen, in O(log N) time. Also, apply missing charset= parameter for _ew.encode. The bug is introduced in commit 85d5c18
| if len(ew) > remaining_space: | ||
| # Find the longest first_part | ||
| # since len(_ew.encode(to_encode[:x])) is a non-linear | ||
| # monotonically increasing function, and calculating the |
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_ew.encode is biased towards the 'q' encoding. This might violate the assumption of a monotonically increasing function for some corner cases. (This was already the case for the old code.)
I hope to find the time to write a test case for this.
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Thank you for the contribution. This was fixed in GH-12020, so I'm closing this as a duplicate. |
Currently when folding headers with length > maxlen, _fold_as_ew tries
to split the to_encode into multiple parts to fulfill the maxlen limit,
in an inapropriate way.
If a long header has non-ascii characters, in some situations (e.g. a
Subject: with full of CJK chars), it will split the to_encode into
["", to_encode], entering an infinite loop.
This commit fixes this by introduce a smarter way to split.
Besides, when an header needs to be folded now, every non-last line will
try its best to reach the maxlen, in O(log N) time.
Also, apply missing charset= parameter for _ew.encode.
The bug is introduced in commit 85d5c18
https://bugs.python.org/issue34222