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gh-135307: Fix email error when policy max_line_length is set to 0 or None #135367

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gh-135307: Fix email error when policy max_line_length is set to 0 or None #135367

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a210d49
Merge pull request #169 from python/main
zangjiucheng Jun 8, 2025
e9de710
enhance email content handling: allow infinite line length in encoding
zangjiucheng Jun 10, 2025
0a5f379
Fix lint
zangjiucheng Jun 10, 2025
d0dc3c0
fix: correct formatting in email test cases and NEWS entry
zangjiucheng Jun 10, 2025
77ea798
Update NEWS entry, test case enhance, lint code
zangjiucheng Jun 19, 2025
52e590c
resort import; restructure testcase
zangjiucheng Jun 19, 2025
603ff74
tiny enhance varaible
zangjiucheng Jun 19, 2025
38e6381
Tiny update for test case for better readability
zangjiucheng Jun 21, 2025
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12 changes: 7 additions & 5 deletions Lib/email/contentmanager.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
import email.charset
import email.message
import email.errors
import sys
from email import quoprimime

class ContentManager:
Expand Down Expand Up @@ -142,22 +143,23 @@ def _encode_base64(data, max_line_length):


def _encode_text(string, charset, cte, policy):
# max_line_length 0/None means no limit, ie: infinitely long.
maxlen = policy.max_line_length or sys.maxsize
lines = string.encode(charset).splitlines()
linesep = policy.linesep.encode('ascii')
def embedded_body(lines): return linesep.join(lines) + linesep
def normal_body(lines): return b'\n'.join(lines) + b'\n'
if cte is None:
# Use heuristics to decide on the "best" encoding.
if max((len(x) for x in lines), default=0) <= policy.max_line_length:
if max((len(x) for x in lines), default=0) <= maxlen:
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We can use: max(map(len, lines), default=0), though I'm not sure which is the fastest and which is the most "readable".

@bitdancer What is the style you'd recommend in general in the email package? would you rather for readability, succintness, or performance?

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Just my comment: we're not required to take the fastest route here, since we may not have a heavy load on the email module. Still wish to hear more comments before we resolve this :)

try:
return '7bit', normal_body(lines).decode('ascii')
except UnicodeDecodeError:
pass
if policy.cte_type == '8bit':
return '8bit', normal_body(lines).decode('ascii', 'surrogateescape')
sniff = embedded_body(lines[:10])
sniff_qp = quoprimime.body_encode(sniff.decode('latin-1'),
policy.max_line_length)
sniff_qp = quoprimime.body_encode(sniff.decode('latin-1'), maxlen)
sniff_base64 = binascii.b2a_base64(sniff)
# This is a little unfair to qp; it includes lineseps, base64 doesn't.
if len(sniff_qp) > len(sniff_base64):
Expand All @@ -172,9 +174,9 @@ def normal_body(lines): return b'\n'.join(lines) + b'\n'
data = normal_body(lines).decode('ascii', 'surrogateescape')
elif cte == 'quoted-printable':
data = quoprimime.body_encode(normal_body(lines).decode('latin-1'),
policy.max_line_length)
maxlen)
elif cte == 'base64':
data = _encode_base64(embedded_body(lines), policy.max_line_length)
data = _encode_base64(embedded_body(lines), maxlen)
else:
raise ValueError("Unknown content transfer encoding {}".format(cte))
return cte, data
Expand Down
26 changes: 26 additions & 0 deletions Lib/test/test_email/test_message.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1004,6 +1004,32 @@ def test_folding_with_long_nospace_http_policy_1(self):
parsed_msg = message_from_bytes(m.as_bytes(), policy=policy.default)
self.assertEqual(parsed_msg['Message-ID'], m['Message-ID'])

def test_no_wrapping_max_line_length(self):
# Test that falsey 'max_line_length' are converted to sys.maxsize.
for n in [0, None]:
with self.subTest(max_line_length=n):
self.do_test_no_wrapping_max_line_length(n)

def do_test_no_wrapping_max_line_length(self, falsey):
self.assertFalse(falsey)
pol = policy.default.clone(max_line_length=falsey)
subj = "S" * 100
body = "B" * 100
msg = EmailMessage(policy=pol)
msg["From"] = "[email protected]"
msg["To"] = "[email protected]"
msg["Subject"] = subj
msg.set_content(body)

raw = msg.as_bytes()
self.assertNotIn(b"\r\n ", raw,
"Found fold indicator; wrapping not disabled")

parsed = message_from_bytes(raw, policy=policy.default)
self.assertEqual(parsed["Subject"], subj)
parsed_body = parsed.get_body().get_content().rstrip('\n')
self.assertEqual(parsed_body, body)

def test_invalid_header_names(self):
invalid_headers = [
('Invalid Header', 'contains space'),
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-06-10-18-02-29.gh-issue-135307.fXGrcK.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
:mod:`email`: Ensure policy accepts unlimited line lengths by
treating falsey values as :data:`sys.maxsize`.
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