Skip to content

gh-144001: Simplify Base64 decoding with altchars and ignorechars specified #144324

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
serhiy-storchaka wants to merge 1 commit into
base: main
Choose a base branch
from
+41 −50
Open

gh-144001: Simplify Base64 decoding with altchars and ignorechars specified #144324

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
10 changes: 5 additions & 5 deletions Doc/library/base64.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -91,7 +91,8 @@ POST request.
``False`` otherwise.

If *validate* is false, characters that are neither
in the normal base-64 alphabet nor the alternative alphabet are
in the normal base-64 alphabet nor (if *ignorechars* is not specified)
the alternative alphabet are
discarded prior to the padding check, but the ``+`` and ``/`` characters
keep their meaning if they are not in *altchars* (they will be discarded
in future Python versions).
Expand All @@ -101,15 +102,14 @@ POST request.

For more information about the strict base64 check, see :func:`binascii.a2b_base64`

.. versionchanged:: next
Added the *ignorechars* parameter.

.. deprecated:: next
Accepting the ``+`` and ``/`` characters with an alternative alphabet
is now deprecated.


.. versionchanged:: next
Added the *ignorechars* parameter.


.. function:: standard_b64encode(s)

Encode :term:`bytes-like object` *s* using the standard Base64 alphabet
Expand Down
42 changes: 15 additions & 27 deletions Lib/base64.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -89,49 +89,37 @@ def b64decode(s, altchars=None, validate=_NOT_SPECIFIED, *, ignorechars=_NOT_SPE
s = _bytes_from_decode_data(s)
if validate is _NOT_SPECIFIED:
validate = ignorechars is not _NOT_SPECIFIED
if ignorechars is _NOT_SPECIFIED:
ignorechars = b''
badchar = None
badchar_strict = False
if altchars is not None:
altchars = _bytes_from_decode_data(altchars)
if len(altchars) != 2:
raise ValueError(f'invalid altchars: {altchars!r}')
for b in b'+/':
if b not in altchars and b in s:
if badchar is None:
badchar = b
if not validate:
break
if not isinstance(ignorechars, (bytes, bytearray)):
ignorechars = memoryview(ignorechars).cast('B')
if b not in ignorechars:
badchar_strict = True
if ignorechars is _NOT_SPECIFIED:
for b in b'+/':
if b not in altchars and b in s:
badchar = b
break
s = s.translate(bytes.maketrans(altchars, b'+/'))
s = s.translate(bytes.maketrans(altchars, b'+/'))
else:
trans = bytes.maketrans(b'+/' + altchars, altchars + b'+/')
s = s.translate(trans)
ignorechars = ignorechars.translate(trans)
if ignorechars is _NOT_SPECIFIED:
ignorechars = b''
result = binascii.a2b_base64(s, strict_mode=validate,
ignorechars=ignorechars)
if badchar is not None:
import warnings
if badchar_strict:
if validate:
warnings.warn(f'invalid character {chr(badchar)!a} in Base64 data '
f'with altchars={altchars!r} and validate=True '
f'will be an error in future Python versions',
DeprecationWarning, stacklevel=2)
else:
ignorechars = bytes(ignorechars)
if ignorechars:
warnings.warn(f'invalid character {chr(badchar)!a} in Base64 data '
f'with altchars={altchars!r} '
f'and ignorechars={ignorechars!r} '
f'will be discarded in future Python versions',
FutureWarning, stacklevel=2)
else:
warnings.warn(f'invalid character {chr(badchar)!a} in Base64 data '
f'with altchars={altchars!r} and validate=False '
f'will be discarded in future Python versions',
FutureWarning, stacklevel=2)
warnings.warn(f'invalid character {chr(badchar)!a} in Base64 data '
f'with altchars={altchars!r} and validate=False '
f'will be discarded in future Python versions',
FutureWarning, stacklevel=2)
return result


Expand Down
39 changes: 21 additions & 18 deletions Lib/test/test_base64.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -291,6 +291,7 @@ def test_b64decode_altchars(self):
eq(base64.b64decode(data_str, altchars=altchars), res)
eq(base64.b64decode(data, altchars=altchars_str), res)
eq(base64.b64decode(data_str, altchars=altchars_str), res)
eq(base64.b64decode(data, altchars=altchars, ignorechars=b'\n'), res)

self.assertRaises(ValueError, base64.b64decode, b'', altchars=b'+')
self.assertRaises(ValueError, base64.b64decode, b'', altchars=b'+/-')
Expand Down Expand Up @@ -370,26 +371,28 @@ def test_b64decode_invalid_chars(self):
self.assertEqual(r, b'\xff\xff\xff')
self.assertEqual(str(cm.warning),
error % ('/', "altchars=b'-_' and validate=True"))
with self.assertWarns(FutureWarning) as cm:
r = base64.b64decode(b'++++', altchars=b'-_', ignorechars=b'+')
self.assertEqual(r, b'\xfb\xef\xbe')
self.assertEqual(str(cm.warning),
discarded % ('+', "altchars=b'-_' and ignorechars=b'+'"))
with self.assertWarns(FutureWarning) as cm:
r = base64.b64decode(b'////', altchars=b'-_', ignorechars=b'/')
self.assertEqual(r, b'\xff\xff\xff')
self.assertEqual(str(cm.warning),
discarded % ('/', "altchars=b'-_' and ignorechars=b'/'"))
with self.assertWarns(DeprecationWarning) as cm:
r = base64.b64decode(b'++++////', altchars=b'-_', ignorechars=b'+')
r = base64.b64decode(b'++++', altchars=b'-_', ignorechars=b'+')
self.assertEqual(r, b'')
r = base64.b64decode(b'////', altchars=b'-_', ignorechars=b'/')
self.assertEqual(r, b'')
r = base64.b64decode(b'++++////', altchars=b'-_', validate=False, ignorechars=b'')
self.assertEqual(r, b'')
with self.assertRaisesRegex(binascii.Error, 'Only base64 data is allowed'):
base64.b64decode(b'////', altchars=b'-_', ignorechars=b'')
with self.assertRaisesRegex(binascii.Error, 'Only base64 data is allowed'):
base64.b64decode(b'++++', altchars=b'-_', ignorechars=b'')
r = base64.b64decode(b'++++YWJj----____', altchars=b'-_', ignorechars=b'+')
self.assertEqual(r, b'abc\xfb\xef\xbe\xff\xff\xff')
r = base64.b64decode(b'////YWJj----____', altchars=b'-_', ignorechars=b'/')
self.assertEqual(r, b'abc\xfb\xef\xbe\xff\xff\xff')
r = base64.b64decode(b'++++,,,,', altchars=b'+,', ignorechars=b'+')
self.assertEqual(r, b'\xfb\xef\xbe\xff\xff\xff')
self.assertEqual(str(cm.warning),
error % ('/', "altchars=b'-_' and validate=True"))
with self.assertWarns(DeprecationWarning) as cm:
r = base64.b64decode(b'++++////', altchars=b'-_', ignorechars=b'/')
r = base64.b64decode(b'////YWJj++++,,,,', altchars=b'+,', ignorechars=b'/')
self.assertEqual(r, b'abc\xfb\xef\xbe\xff\xff\xff')
r = base64.b64decode(b'----////', altchars=b'-/', ignorechars=b'/')
self.assertEqual(r, b'\xfb\xef\xbe\xff\xff\xff')
self.assertEqual(str(cm.warning),
error % ('+', "altchars=b'-_' and validate=True"))
r = base64.b64decode(b'++++YWJj----////', altchars=b'-/', ignorechars=b'+')
self.assertEqual(r, b'abc\xfb\xef\xbe\xff\xff\xff')

with self.assertWarns(FutureWarning) as cm:
self.assertEqual(base64.urlsafe_b64decode(b'++++'), b'\xfb\xef\xbe')
Expand Down
Loading