deb-heat/heat/common/short_id.py
Zane Bitter ebcad29e1e Add a module for generating random short ID strings
These can be used to ensure uniqueness of names when creating resources in
OpenStack services.

Change-Id: Ifb048fd8ec676b7fd6a15c5d4a39bfc98f0aeca9
Signed-off-by: Zane Bitter <zbitter@redhat.com>
2013-02-25 10:51:41 +01:00

59 lines
1.9 KiB
Python

# vim: tabstop=4 shiftwidth=4 softtabstop=4
#
# 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.
'''
Utilities for creating short ID strings based on a random UUID. The IDs
each comprise 12 (lower-case) alphanumeric characters.
'''
import base64
import uuid
def _to_byte_string(value, num_bits):
'''
Convert an integer to a big-endian string of bytes, with any padding
required added at the end (i.e. after the least-significant bit).
'''
shifts = xrange(num_bits - 8, -8, -8)
byte_at = lambda off: (value >> off if off >= 0 else value << -off) & 0xff
return ''.join(chr(byte_at(offset)) for offset in shifts)
def get_id(source_uuid):
'''
Derive a short (12 character) id from a random UUID.
The supplied UUID must be a version 4 UUID object.
'''
if isinstance(source_uuid, basestring):
source_uuid = uuid.UUID(source_uuid)
if source_uuid.version != 4:
raise ValueError('Invalid UUID version (%d)' % source_uuid.version)
# The "time" field of a v4 UUID contains 60 random bits
# (see RFC4122, Section 4.4)
random_bytes = _to_byte_string(source_uuid.time, 60)
# The first 12 bytes (= 60 bits) of base32-encoded output is our data
encoded = base64.b32encode(random_bytes)[:12]
return encoded.lower()
def generate_id():
'''
Generate a short (12 character), random id.
'''
return get_id(uuid.uuid4())