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71 lines
2.2 KiB
71 lines
2.2 KiB
# Copyright 2016-2018 The NATS Authors
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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from __future__ import annotations
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from random import Random
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from secrets import randbelow, token_bytes
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from sys import maxsize as MaxInt
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DIGITS = b'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
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BASE = 62
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PREFIX_LENGTH = 12
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SEQ_LENGTH = 10
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MAX_SEQ = 839299365868340224 # BASE**10
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MIN_INC = 33
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MAX_INC = 333
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INC = MAX_INC - MIN_INC
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TOTAL_LENGTH = PREFIX_LENGTH + SEQ_LENGTH
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class NUID:
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"""
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NUID is an implementation of the approach for fast generation of
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unique identifiers used for inboxes in NATS.
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"""
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def __init__(self) -> None:
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self._prand = Random(randbelow(MaxInt))
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self._seq = self._prand.randint(0, MAX_SEQ)
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self._inc = MIN_INC + self._prand.randint(BASE + 1, INC)
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self._prefix = bytearray()
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self.randomize_prefix()
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def next(self) -> bytearray:
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"""
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next returns the next unique identifier.
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"""
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self._seq += self._inc
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if self._seq >= MAX_SEQ:
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self.randomize_prefix()
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self.reset_sequential()
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l = self._seq
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prefix = self._prefix[:]
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suffix = bytearray(SEQ_LENGTH)
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for i in reversed(range(SEQ_LENGTH)):
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suffix[i] = DIGITS[int(l) % BASE]
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l //= BASE
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prefix.extend(suffix)
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return prefix
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def randomize_prefix(self) -> None:
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random_bytes = token_bytes(PREFIX_LENGTH)
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self._prefix = bytearray(DIGITS[c % BASE] for c in random_bytes)
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def reset_sequential(self) -> None:
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self._seq = self._prand.randint(0, MAX_SEQ)
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self._inc = MIN_INC + self._prand.randint(0, INC)
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