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gh-130110: Support hyphens in RFC 2231 continuation parameter names #153536

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gh-130110: Support hyphens in RFC 2231 continuation parameter names #153536

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gh-130110: Support hyphens in RFC 2231 continuation parameter names
Phantom-d-e-v Jul 10, 2026
5fa95ba
Add NEWS entry for gh-130110
Phantom-d-e-v Jul 10, 2026
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2 changes: 1 addition & 1 deletion Lib/email/utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -399,7 +399,7 @@ def encode_rfc2231(s, charset=None, language=None):
return "%s'%s'%s" % (charset, language, s)


rfc2231_continuation = re.compile(r'^(?P<name>\w+)\*((?P<num>[0-9]+)\*?)?$',
rfc2231_continuation = re.compile(r'^(?P<name>[\w-]+)\*((?P<num>[0-9]+)\*?)?$',

@bitdancer bitdancer Jul 11, 2026

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If we're going to go to the trouble of fixing this, we should make it conform fully to the RFC. Are there any printable characters other than - that are not in specials and also not in \w? Hopefully there aren't any characters recognized by \w that shouldn't be valid in parameter names, because changing that would be backward incompatible.

re.ASCII)

def decode_params(params):
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12 changes: 12 additions & 0 deletions Lib/test/test_email/test_email.py
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Expand Up @@ -400,6 +400,18 @@ def test_continuation_sorting_part_order(self):
filename = msg.get_filename()
self.assertEqual(filename, 'foo bar.txt')

def test_continuation_with_hyphenated_name(self):
# gh-130110: parameter names containing hyphens were not recognized
# as RFC 2231 continuations and were left undecoded.
msg = email.message_from_string(
"Content-Disposition: attachment; "
"file-name*0*=\"utf-8''start\"; "
"file-name*1*=\"-middle-\"; "
"file-name*2*=\"end\"\n"
)
value = msg.get_param('file-name', header='content-disposition')
self.assertEqual(value, ('utf-8', '', 'start-middle-end'))

def test_sorting_no_continuations(self):
msg = email.message_from_string(
"Content-Disposition: attachment; "
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-10-23-32-52.gh-issue-130110.R7xQz2.rst
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@@ -0,0 +1,3 @@
:meth:`email.utils.decode_params` (and the parameter parsing it backs) now
correctly decodes :rfc:`2231` continuation parameter names that contain
hyphens, such as ``file-name*0*``.
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