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gh-148016: Improve "Leading padding not allowed" error in Base32 and Base64 decoders #148017

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Merged
serhiy-storchaka merged 2 commits into from
Apr 4, 2026
+10 −6
Merged

gh-148016: Improve "Leading padding not allowed" error in Base32 and Base64 decoders #148017

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187ec60
gh-148016: Improve "Leading padding not allowed" error in Base32 and …
serhiy-storchaka Apr 2, 2026
cd62783
Merge branch 'main' into base32-base64-leading-padding-error
serhiy-storchaka Apr 4, 2026
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10 changes: 6 additions & 4 deletions Lib/test/test_binascii.py
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Original file line number Diff line number Diff line change
Expand Up @@ -171,8 +171,8 @@ def _assertRegexTemplate(assert_regex, data,
self.assertEqual(binascii.a2b_base64(data),
non_strict_mode_expected_result)

def assertLeadingPadding(*args):
_assertRegexTemplate(r'(?i)Leading padding', *args)
def assertLeadingPadding(*args, **kwargs):
_assertRegexTemplate(r'(?i)Leading padding', *args, **kwargs)

def assertDiscontinuousPadding(*args):
_assertRegexTemplate(r'(?i)Discontinuous padding', *args)
Expand Down Expand Up @@ -203,6 +203,7 @@ def assertInvalidLength(data, *args, length=None, **kwargs):
assertLeadingPadding(b'===abcd', b'i\xb7\x1d')
assertLeadingPadding(b'====abcd', b'i\xb7\x1d')
assertLeadingPadding(b'=====abcd', b'i\xb7\x1d')
assertLeadingPadding(b' =abcd', b'i\xb7\x1d', ignorechars=b' ')

assertInvalidLength(b'a=b==', b'i')
assertInvalidLength(b'a=bc=', b'i\xb7')
Expand Down Expand Up @@ -785,8 +786,8 @@ def assertExcessData(*args):
def assertExcessPadding(*args):
_assertRegexTemplate(r"(?i)Excess padding", *args)

def assertLeadingPadding(*args):
_assertRegexTemplate(r"(?i)Leading padding", *args)
def assertLeadingPadding(*args, **kwargs):
_assertRegexTemplate(r"(?i)Leading padding", *args, **kwargs)

def assertIncorrectPadding(*args):
_assertRegexTemplate(r"(?i)Incorrect padding", *args)
Expand Down Expand Up @@ -853,6 +854,7 @@ def assertInvalidLength(data, *args, length=None, **kwargs):
assertLeadingPadding(b"=======BEEFCAKE", b"\t\x08Q\x01D")
assertLeadingPadding(b"========BEEFCAKE", b"\t\x08Q\x01D")
assertLeadingPadding(b"=========BEEFCAKE", b"\t\x08Q\x01D")
assertLeadingPadding(b" =BEEFCAKE", ignorechars=b' ')

assertIncorrectPadding(b"AB")
assertIncorrectPadding(b"ABCD")
Expand Down
6 changes: 4 additions & 2 deletions Modules/binascii.c
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Original file line number Diff line number Diff line change
Expand Up @@ -816,8 +816,9 @@ binascii_a2b_base64_impl(PyObject *module, Py_buffer *data, int strict_mode,
}
state = get_binascii_state(module);
if (state) {
unsigned char *bin_data_start = PyBytesWriter_GetData(writer);
PyErr_SetString(state->Error,
(quad_pos == 0 && ascii_data == data->buf)
(quad_pos == 0 && bin_data == bin_data_start)
? "Leading padding not allowed"
: "Excess padding not allowed");
}
Expand Down Expand Up @@ -1601,8 +1602,9 @@ binascii_a2b_base32_impl(PyObject *module, Py_buffer *data,
}
state = get_binascii_state(module);
if (state) {
unsigned char *bin_data_start = PyBytesWriter_GetData(writer);
PyErr_SetString(state->Error,
(octa_pos == 0 && ascii_data == data->buf)
(octa_pos == 0 && bin_data == bin_data_start)
? "Leading padding not allowed"
: "Excess padding not allowed");
}
Expand Down
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