base64.b64decode() with validate=True does not raise for a trailing \n

[serhiy-storchaka]

BPO	39055
Nosy	@serhiy-storchaka, @miss-islington
PRs	bpo-39055: Reject a trailing \n in base64.b64decode() with validate=True. #17616 [3.8] bpo-39055: Reject a trailing \n in base64.b64decode() with validate=True. (GH-17616) #17833 [3.7] bpo-39055: Reject a trailing \n in base64.b64decode() with validate=True. (GH-17616) #17834

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-01-05.13:33:45.407>
created_at = <Date 2019-12-15.17:21:28.531>
labels = ['3.7', '3.8', 'type-bug', 'library', '3.9']
title = 'base64.b64decode() with validate=True does not raise for a trailing \\n'
updated_at = <Date 2020-01-05.13:33:45.406>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-01-05.13:33:45.406>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-01-05.13:33:45.407>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2019-12-15.17:21:28.531>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 39055
keywords = ['patch']
message_count = 4.0
messages = ['358438', '359334', '359337', '359340']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'miss-islington']
pr_nums = ['17616', '17833', '17834']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39055'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[serhiy-storchaka]

If validate=True is passed to base64.b64decode(), it should raise a binascii.Error if the input contains any character not from the acceptable alphabet.

But it does not raise if the input ends with a single \n. It raises if the input ends with a multiple \n or with any other whitespace character. Only a single \n is accepted.

This is an implementation artifact. A regular exception ending with $ is used to validate an input. But $ matches not only end of string. It matches also an empty string before the trailing \n.

Similar errors are also occurred in other sites. I'll open separate issues for different cases.

[serhiy-storchaka]

New changeset b19c0d7 by Serhiy Storchaka in branch 'master':
bpo-39055: Reject a trailing \n in base64.b64decode() with validate=True. (GH-17616)
b19c0d7

[miss-islington]

New changeset 3bdb2d9 by Miss Islington (bot) in branch '3.7':
bpo-39055: Reject a trailing \n in base64.b64decode() with validate=True. (GH-17616)
3bdb2d9

[miss-islington]

New changeset 34aa3e7 by Miss Islington (bot) in branch '3.8':
bpo-39055: Reject a trailing \n in base64.b64decode() with validate=True. (GH-17616)
34aa3e7