[Python-checkins] bpo-44690: Adopt binacii.a2b_base64's strict mode in base64.b64decode (GH-27272)

[gpshead]

https://github.com/python/cpython/commit/fa6304a5225787054067bb56089632146d288b20
commit: fa6304a5225787054067bb56089632146d288b20
branch: main
author: Idan Moral <idan22moral at gmail.com>
committer: gpshead <greg at krypto.org>
date: 2021-08-23T16:44:28-07:00
summary:

bpo-44690: Adopt binacii.a2b_base64's strict mode in base64.b64decode (GH-27272)

* Use binascii.a2b_base64 to validate b64decode input.
   This change leads to exception messages changes (mostly).
* Added more information to docstring of b64decode
* Added a reference to binascii.a2b_base64 in the docs

files:
A Misc/NEWS.d/next/Library/2021-07-20-22-03-24.bpo-44690.tV7Zjg.rst
M Doc/library/base64.rst
M Lib/base64.py

diff --git a/Doc/library/base64.rst b/Doc/library/base64.rst
index f91547bd58403..29e52ad48e115 100644
--- a/Doc/library/base64.rst
+++ b/Doc/library/base64.rst
@@ -78,6 +78,8 @@ The modern interface provides:
    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`
+
 
 .. function:: standard_b64encode(s)
 
diff --git a/Lib/base64.py b/Lib/base64.py
index e1256ad9358e7..ffe2ce7332baa 100755
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -76,15 +76,16 @@ def b64decode(s, altchars=None, validate=False):
     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 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)
     if altchars is not None:
         altchars = _bytes_from_decode_data(altchars)
         assert len(altchars) == 2, repr(altchars)
         s = s.translate(bytes.maketrans(altchars, b'+/'))
-    if validate and not re.fullmatch(b'[A-Za-z0-9+/]*={0,2}', s):
-        raise binascii.Error('Non-base64 digit found')
-    return binascii.a2b_base64(s)
+    return binascii.a2b_base64(s, strict_mode=validate)
 
 
 def standard_b64encode(s):
diff --git a/Misc/NEWS.d/next/Library/2021-07-20-22-03-24.bpo-44690.tV7Zjg.rst b/Misc/NEWS.d/next/Library/2021-07-20-22-03-24.bpo-44690.tV7Zjg.rst
new file mode 100644
index 0000000000000..1d1184805471d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-07-20-22-03-24.bpo-44690.tV7Zjg.rst
@@ -0,0 +1 @@
+Adopt *binacii.a2b_base64*'s strict mode in *base64.b64decode*.
\ No newline at end of file