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Correctly fold unknown-8bit originating from encoded words. #142517

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Correctly fold unknown-8bit originating from encoded words. #142517

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ee40a0c
Correctly fold unknown-8bit originating from encoded words.
bitdancer Dec 10, 2025
1bba134
News entry.
bitdancer Dec 10, 2025
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Correctly fold unknown-8bit originating from encoded words. 
The unknown-8bit trick was designed to deal with unknown bytes in an
ASCII message, and it works fine for that.  However, I also tried to
extend it to handle bytes that can't be decoded using the charset
specified in an encoded word, and there it fails because there can be
other non-ASCII characters that were *successfully* decoded.  The fix is
simple: do the unknown-8bit encoding using the utf-8 codec.  This is
especially appropriate since anyone trying to do recovery on an unknown
byte string will probably attempt utf-8 first.
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@bitdancer
bitdancer committed Dec 10, 2025
commit ee40a0c8d946d3c3fd553734004f580fb315feed
2 changes: 1 addition & 1 deletion Lib/email/_encoded_words.py
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Original file line number Diff line number Diff line change
Expand Up @@ -219,7 +219,7 @@ def encode(string, charset='utf-8', encoding=None, lang=''):

"""
if charset == 'unknown-8bit':
bstring = string.encode('ascii', 'surrogateescape')
bstring = string.encode('utf-8', 'surrogateescape')
else:
bstring = string.encode(charset)
if encoding is None:
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8 changes: 8 additions & 0 deletions Lib/test/test_email/test__header_value_parser.py
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Expand Up @@ -3265,5 +3265,13 @@ def test_fold_unfoldable_element_stealing_whitespace(self):
token = parser.get_address_list(text)[0]
self._test(token, expected, policy=policy)

def test_encoded_word_with_undecodable_bytes(self):
self._test(parser.get_address_list(
' =?utf-8?Q?=E5=AE=A2=E6=88=B6=E6=AD=A3=E8=A6=8F=E4=BA=A4=E7?='
)[0],
' =?unknown-8bit?b?5a6i5oi25q2j6KaP5Lqk5w==?=\n',
)


if __name__ == '__main__':
unittest.main()