_base64.py

# Copyright 2019 PrivateStorage.io, LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
This module implements base64 encoding-related functionality.
"""

from __future__ import (
    absolute_import,
)

from re import (
    compile as _compile,
)

from binascii import (
    Error,
)

from base64 import (
    b64decode as _b64decode,
)

_b64decode_validator = _compile(b'^[A-Za-z0-9-_]*={0,2}$')

def urlsafe_b64decode(s):
    """
    Like ``base64.b64decode`` but with validation.
    """
    if not _b64decode_validator.match(s):
        raise Error('Non-base64 digit found')
    return _b64decode(s, altchars=b"-_")