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>

heat/common/short_id.py

@@ -0,0 +1,58 @@
+# 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())

heat/tests/test_short_id.py

@@ -0,0 +1,76 @@
+# 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.
+
+
+import unittest
+from nose.plugins.attrib import attr
+
+from heat.common import short_id
+import uuid
+
+
+@attr(tag=['unit', 'short_id'])
+@attr(speed='fast')
+class ShortIdTest(unittest.TestCase):
+
+    def test_byte_string_8(self):
+        self.assertEqual(short_id._to_byte_string(0xab, 8), '\xab')
+        self.assertEqual(short_id._to_byte_string(0x05, 8), '\x05')
+
+    def test_byte_string_16(self):
+        self.assertEqual(short_id._to_byte_string(0xabcd, 16), '\xab\xcd')
+        self.assertEqual(short_id._to_byte_string(0xabc, 16), '\x0a\xbc')
+
+    def test_byte_string_12(self):
+        self.assertEqual(short_id._to_byte_string(0xabc, 12), '\xab\xc0')
+        self.assertEqual(short_id._to_byte_string(0x0ab, 12), '\x0a\xb0')
+
+    def test_byte_string_60(self):
+        val = 0x111111111111111
+        byte_string = short_id._to_byte_string(val, 60)
+        self.assertEqual(byte_string, '\x11\x11\x11\x11\x11\x11\x11\x10')
+
+    def test_get_id_string(self):
+        id = short_id.get_id('11111111-1111-4111-bfff-ffffffffffff')
+        self.assertEqual(id, 'ceirceirceir')
+
+    def test_get_id_uuid_1(self):
+        source = uuid.UUID('11111111-1111-4111-bfff-ffffffffffff')
+        self.assertEqual(source.time, 0x111111111111111)
+        self.assertEqual(short_id.get_id(source), 'ceirceirceir')
+
+    def test_get_id_uuid_f(self):
+        source = uuid.UUID('ffffffff-ffff-4fff-8000-000000000000')
+        self.assertEqual(short_id.get_id(source), '777777777777')
+
+    def test_get_id_uuid_0(self):
+        source = uuid.UUID('00000000-0000-4000-bfff-ffffffffffff')
+        self.assertEqual(short_id.get_id(source), 'aaaaaaaaaaaa')
+
+    def test_get_id_uuid_endianness(self):
+        source = uuid.UUID('ffffffff-00ff-4000-aaaa-aaaaaaaaaaaa')
+        self.assertEqual(short_id.get_id(source), 'aaaa77777777')
+
+    def test_get_id_uuid1(self):
+        source = uuid.uuid1()
+        self.assertRaises(ValueError, short_id.get_id, source)
+
+    def test_generate_ids(self):
+        allowed_chars = 'abcdefghijklmnopqrstuvwxyz234567'
+        ids = [short_id.generate_id() for i in range(25)]
+
+        for id in ids:
+            self.assertEqual(len(id), 12)
+            self.assertFalse(id.translate(None, allowed_chars))
+            self.assertEqual(ids.count(id), 1)