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gh-135854: Fix function email.message.Message.get_boundary strips boundaries twice #135891

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gh-135854: Fix function email.message.Message.get_boundary strips boundaries twice #135891

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00bc8b5
Fix email.parser stripping boudaries twice
tanloong Jun 24, 2025
d3c93ea
blurb add
tanloong Jun 24, 2025
e9cfcc9
improve news entry
tanloong Jun 24, 2025
7f410eb
indent multiline string
tanloong Jun 25, 2025
46021ac
Merge branch 'main' into fix-duplicate-boundary-stripping
tanloong Aug 9, 2025
a481b91
Merge branch 'main' into fix-duplicate-boundary-stripping
tanloong May 2, 2026
2e660ff
Merge branch 'fix-duplicate-boundary-stripping' of https://github.com…
tanloong May 2, 2026
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2 changes: 1 addition & 1 deletion Lib/email/message.py
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Original file line number Diff line number Diff line change
Expand Up @@ -870,7 +870,7 @@ def get_boundary(self, failobj=None):
parameter, and it is unquoted.
"""
missing = object()
boundary = self.get_param('boundary', missing)
boundary = self.get_param('boundary', missing, unquote=False)
if boundary is missing:
return failobj
# RFC 2046 says that boundaries may begin but not end in w/s
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36 changes: 36 additions & 0 deletions Lib/test/test_email/test_email.py
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Expand Up @@ -2231,6 +2231,42 @@ def test_boundary_with_leading_space(self):
eq(msg.get_boundary(), ' XXXX')
eq(len(msg.get_payload()), 2)

def test_boundary_stripped_only_once(self):
eq = self.assertEqual
msg = email.message_from_string(textwrap.dedent('''\
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="<>"

--<>
Content-Type: text/plain


--<>
Content-Type: text/plain

--<>--
'''))
self.assertTrue(msg.is_multipart())
eq(msg.get_boundary(), '<>')
eq(len(msg.get_payload()), 2)

msg = email.message_from_string(textwrap.dedent('''\
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary=<"">

@bitdancer bitdancer Aug 19, 2026

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Unfortunately, this is not a valid parameter value. Technically this should in fact fail to be recognized as a multipart. Per rfc 2045, <> characters must be inside quotes to be valid. Any idea what other email programs do with this kind of broken value?

I'm reluctant to apply the proposed fix since it would make valid a boundary specification that is not in fact valid. See my comments on the issue for more.


--""
Content-Type: text/plain


--""
Content-Type: text/plain

--""--
'''))
self.assertTrue(msg.is_multipart())
eq(msg.get_boundary(), '""')
eq(len(msg.get_payload()), 2)

def test_boundary_without_trailing_newline(self):
m = Parser().parsestr("""\
Content-Type: multipart/mixed; boundary="===============0012394164=="
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2025-06-24-21-08-26.gh-issue-135854.j0WMfD.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix :func:`email.message.Message.get_boundary` strips boundaries twice.
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