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gh-144156: Fix email header folding concatenating encoded words #144692

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Merged
bitdancer merged 14 commits into from
Feb 19, 2026
Merged

gh-144156: Fix email header folding concatenating encoded words #144692

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b5925e0
Fix email header wrapping omitting white space
robsdedude Feb 10, 2026
1a7824e
📜🤖 Added by blurb_it.
blurb-it[bot] Feb 10, 2026
fb23a6e
fixup! Fix email header wrapping omitting white space
robsdedude Feb 10, 2026
050491c
fixup! Fix email header wrapping omitting white space
robsdedude Feb 11, 2026
ed6f197
Formatting
robsdedude Feb 11, 2026
91b4b3b
Extend news fragment
robsdedude Feb 12, 2026
d5f5001
Formatting
robsdedude Feb 12, 2026
15e6618
Fix comment
robsdedude Feb 12, 2026
902ec59
Faster and more readable last_word_is_ew tracking
robsdedude Feb 12, 2026
a1cfe3c
Fix broken application of news fragment suggestion
robsdedude Feb 13, 2026
45022be
Simplify code
robsdedude Feb 13, 2026
ccf399d
Fix related WSP folding bug
robsdedude Feb 13, 2026
0d694d6
Inline helper function
robsdedude Feb 14, 2026
a433ab1
Flip case order for readability and brevity
robsdedude Feb 18, 2026
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Faster and more readable last_word_is_ew tracking
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@robsdedude
robsdedude committed Feb 12, 2026
commit 902ec59bd567b256ff974f5bbb982026612637f3
20 changes: 13 additions & 7 deletions Lib/email/_header_value_parser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -80,7 +80,8 @@
# Useful constants and functions
#

WSP = set(' \t')
_WSP = ' \t'
WSP = set(_WSP)
CFWS_LEADER = WSP | set('(')
SPECIALS = set(r'()<>@,:;.\"[]')
ATOM_ENDS = SPECIALS | WSP
Expand Down Expand Up @@ -2858,6 +2859,12 @@ def _steal_all_trailing_WSP_if_exists(lines):
return ''.join(wsp_lines)
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def _last_word_is_sill_ew(_last_word_is_ew, added_str):
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# If the last word is an encoded word, and the added string is all WSP,
# then (and only then) is the last word is still an encoded word.
return _last_word_is_ew and not bool(added_str.strip(_WSP))


def _refold_parse_tree(parse_tree, *, policy):
"""Return string of contents of parse_tree folded according to RFC rules.

Expand Down Expand Up @@ -2961,8 +2968,7 @@ def _refold_parse_tree(parse_tree, *, policy):

if len(tstr) <= maxlen - len(lines[-1]):
lines[-1] += tstr
if any(char not in WSP for char in tstr):
last_word_is_ew = False
last_word_is_ew = _last_word_is_sill_ew(last_word_is_ew, tstr)
continue

# This part is too long to fit. The RFC wants us to break at
Expand All @@ -2973,8 +2979,9 @@ def _refold_parse_tree(parse_tree, *, policy):
newline = _steal_trailing_WSP_if_exists(lines)
if newline or part.startswith_fws():
lines.append(newline + tstr)
if any(char not in WSP for char in lines[-1]):
last_word_is_ew = False
last_word_is_ew = _last_word_is_sill_ew(
last_word_is_ew, lines[-1]
)
last_ew = None
continue
if not hasattr(part, 'encode'):
Expand Down Expand Up @@ -3014,8 +3021,7 @@ def _refold_parse_tree(parse_tree, *, policy):
else:
# We can't fold it onto the next line either...
lines[-1] += tstr
if any(char not in WSP for char in tstr):
last_word_is_ew = False
last_word_is_ew = _last_word_is_sill_ew(last_word_is_ew, tstr)

return policy.linesep.join(lines) + policy.linesep

Expand Down
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