diff --git a/Doc/library/base64.rst b/Doc/library/base64.rst index 4876117f6403b2..3e7884debd5948 100644 --- a/Doc/library/base64.rst +++ b/Doc/library/base64.rst @@ -84,15 +84,20 @@ POST request. A :exc:`binascii.Error` exception is raised if *s* is incorrectly padded. - If *validate* is ``False`` (the default), characters that are neither + If *validate* is false (the default), characters that are neither in the normal base-64 alphabet nor the alternative alphabet are - discarded prior to the padding check. If *validate* is ``True``, - these non-alphabet characters in the input result in a - :exc:`binascii.Error`. + 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). + If *validate* is true, these non-alphabet characters in the input + result in a :exc:`binascii.Error`. For more information about the strict base64 check, see :func:`binascii.a2b_base64` - May assert or raise a :exc:`ValueError` if the length of *altchars* is not 2. + .. deprecated:: next + Accepting the ``+`` and ``/`` characters with an alternative alphabet + is now deprecated. + .. function:: standard_b64encode(s) @@ -123,6 +128,9 @@ POST request. ``/`` in the standard Base64 alphabet, and return the decoded :class:`bytes`. + .. deprecated:: next + Accepting the ``+`` and ``/`` characters is now deprecated. + .. function:: b32encode(s) diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst index b7a27d5db63875..0e3e0c49bfc579 100644 --- a/Doc/whatsnew/3.15.rst +++ b/Doc/whatsnew/3.15.rst @@ -1143,6 +1143,15 @@ Deprecated New deprecations ---------------- +* :mod:`base64`: + + * Accepting the ``+`` and ``/`` characters with an alternative alphabet in + :func:`~base64.b64decode` and :func:`~base64.urlsafe_b64decode` is now + deprecated. + In future Python versions they will be errors in the strict mode and + discarded in the non-strict mode. + (Contributed by Serhiy Storchaka in :gh:`125346`.) + * CLI: * Deprecate :option:`-b` and :option:`!-bb` command-line options diff --git a/Lib/base64.py b/Lib/base64.py index e62ae6aff580fa..6e0da16b23ce99 100644 --- a/Lib/base64.py +++ b/Lib/base64.py @@ -72,20 +72,39 @@ def b64decode(s, altchars=None, validate=False): The result is returned as a bytes object. A binascii.Error is raised if s is incorrectly padded. - If validate is False (the default), characters that are neither in the + If validate is false (the default), characters that are neither in the normal base-64 alphabet nor the alternative alphabet are discarded prior - to the padding check. If validate is True, these non-alphabet characters + to the padding check. If validate is true, these non-alphabet characters in the input result in a binascii.Error. For more information about the strict base64 check, see: https://docs.python.org/3.11/library/binascii.html#binascii.a2b_base64 """ s = _bytes_from_decode_data(s) + badchar = None if altchars is not None: altchars = _bytes_from_decode_data(altchars) - assert len(altchars) == 2, repr(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: + badchar = b + break s = s.translate(bytes.maketrans(altchars, b'+/')) - return binascii.a2b_base64(s, strict_mode=validate) + result = binascii.a2b_base64(s, strict_mode=validate) + if badchar is not None: + import warnings + 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: + 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 def standard_b64encode(s): @@ -130,8 +149,19 @@ def urlsafe_b64decode(s): The alphabet uses '-' instead of '+' and '_' instead of '/'. """ s = _bytes_from_decode_data(s) + badchar = None + for b in b'+/': + if b in s: + badchar = b + break s = s.translate(_urlsafe_decode_translation) - return b64decode(s) + result = binascii.a2b_base64(s, strict_mode=False) + if badchar is not None: + import warnings + warnings.warn(f'invalid character {chr(badchar)!a} in URL-safe Base64 data ' + f'will be discarded in future Python versions', + FutureWarning, stacklevel=2) + return result diff --git a/Lib/test/test_base64.py b/Lib/test/test_base64.py index 120c5824a42a40..d02992903f15a7 100644 --- a/Lib/test/test_base64.py +++ b/Lib/test/test_base64.py @@ -292,6 +292,11 @@ def test_b64decode_altchars(self): eq(base64.b64decode(data, altchars=altchars_str), res) eq(base64.b64decode(data_str, altchars=altchars_str), res) + self.assertRaises(ValueError, base64.b64decode, b'', altchars=b'+') + self.assertRaises(ValueError, base64.b64decode, b'', altchars=b'+/-') + self.assertRaises(ValueError, base64.b64decode, '', altchars='+') + self.assertRaises(ValueError, base64.b64decode, '', altchars='+/-') + def test_b64decode_padding_error(self): self.assertRaises(binascii.Error, base64.b64decode, b'abc') self.assertRaises(binascii.Error, base64.b64decode, 'abc') @@ -323,13 +328,25 @@ def test_b64decode_invalid_chars(self): with self.assertRaises(binascii.Error): base64.b64decode(bstr.decode('ascii'), validate=True) - # Normal alphabet characters not discarded when alternative given - res = b'\xfb\xef\xff' - self.assertEqual(base64.b64decode(b'++//', validate=True), res) - self.assertEqual(base64.b64decode(b'++//', '-_', validate=True), res) - self.assertEqual(base64.b64decode(b'--__', '-_', validate=True), res) - self.assertEqual(base64.urlsafe_b64decode(b'++//'), res) - self.assertEqual(base64.urlsafe_b64decode(b'--__'), res) + # Normal alphabet characters will be discarded when alternative given + with self.assertWarns(FutureWarning): + self.assertEqual(base64.b64decode(b'++++', altchars=b'-_'), + b'\xfb\xef\xbe') + with self.assertWarns(FutureWarning): + self.assertEqual(base64.b64decode(b'////', altchars=b'-_'), + b'\xff\xff\xff') + with self.assertWarns(DeprecationWarning): + self.assertEqual(base64.b64decode(b'++++', altchars=b'-_', validate=True), + b'\xfb\xef\xbe') + with self.assertWarns(DeprecationWarning): + self.assertEqual(base64.b64decode(b'////', altchars=b'-_', validate=True), + b'\xff\xff\xff') + with self.assertWarns(FutureWarning): + self.assertEqual(base64.urlsafe_b64decode(b'++++'), b'\xfb\xef\xbe') + with self.assertWarns(FutureWarning): + self.assertEqual(base64.urlsafe_b64decode(b'////'), b'\xff\xff\xff') + with self.assertRaises(binascii.Error): + base64.b64decode(b'+/!', altchars=b'-_') def _altchars_strategy(): """Generate 'altchars' for base64 encoding.""" diff --git a/Misc/NEWS.d/next/Library/2025-11-06-12-03-29.gh-issue-125346.7Gfpgw.rst b/Misc/NEWS.d/next/Library/2025-11-06-12-03-29.gh-issue-125346.7Gfpgw.rst new file mode 100644 index 00000000000000..187a6ebbe79b26 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2025-11-06-12-03-29.gh-issue-125346.7Gfpgw.rst @@ -0,0 +1,5 @@ +Accepting ``+`` and ``/`` characters with an alternative alphabet in +:func:`base64.b64decode` and :func:`base64.urlsafe_b64decode` is now +deprecated. +In future Python versions they will be errors in the strict mode and +discarded in the non-strict mode.