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#
# Copyright (C) 2018 Codethink Limited
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
# Authors:
# Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
import hashlib
import ujson
# Internal record of the size of a cache key
_CACHEKEY_SIZE = len(hashlib.sha256().hexdigest())
# Hex digits
_HEX_DIGITS = "0123456789abcdef"
# is_key()
#
# Check if the passed in string *could be* a cache key. This basically checks
# that the length matches a sha256 hex digest, and that the string does not
# contain any non-hex characters and is fully lower case.
#
# Args:
# key (str): The string to check
#
# Returns:
# (bool): Whether or not `key` could be a cache key
#
def is_key(key):
if len(key) != _CACHEKEY_SIZE:
return False
return not any(ch not in _HEX_DIGITS for ch in key)
# generate_key()
#
# Generate an sha256 hex digest from the given value. The value
# can be a simple value or recursive dictionary with lists etc,
# anything simple enough to serialize.
#
# Args:
# value: A value to get a key for
#
# Returns:
# (str): An sha256 hex digest of the given value
#
def generate_key(value):
ustring = ujson.dumps(value, sort_keys=True, escape_forward_slashes=False).encode("utf-8")
return hashlib.sha256(ustring).hexdigest()
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