105 lines
3.3 KiB
Go
105 lines
3.3 KiB
Go
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// Copyright 2023 Google Inc. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package uuid
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import (
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"io"
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)
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// UUID version 7 features a time-ordered value field derived from the widely
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// implemented and well known Unix Epoch timestamp source,
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// the number of milliseconds seconds since midnight 1 Jan 1970 UTC, leap seconds excluded.
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// As well as improved entropy characteristics over versions 1 or 6.
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//
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// see https://datatracker.ietf.org/doc/html/draft-peabody-dispatch-new-uuid-format-03#name-uuid-version-7
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//
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// Implementations SHOULD utilize UUID version 7 over UUID version 1 and 6 if possible.
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//
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// NewV7 returns a Version 7 UUID based on the current time(Unix Epoch).
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// Uses the randomness pool if it was enabled with EnableRandPool.
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// On error, NewV7 returns Nil and an error
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func NewV7() (UUID, error) {
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uuid, err := NewRandom()
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if err != nil {
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return uuid, err
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}
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makeV7(uuid[:])
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return uuid, nil
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}
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// NewV7FromReader returns a Version 7 UUID based on the current time(Unix Epoch).
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// it use NewRandomFromReader fill random bits.
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// On error, NewV7FromReader returns Nil and an error.
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func NewV7FromReader(r io.Reader) (UUID, error) {
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uuid, err := NewRandomFromReader(r)
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if err != nil {
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return uuid, err
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}
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makeV7(uuid[:])
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return uuid, nil
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}
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// makeV7 fill 48 bits time (uuid[0] - uuid[5]), set version b0111 (uuid[6])
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// uuid[8] already has the right version number (Variant is 10)
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// see function NewV7 and NewV7FromReader
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func makeV7(uuid []byte) {
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/*
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| unix_ts_ms |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| unix_ts_ms | ver | rand_a (12 bit seq) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|var| rand_b |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| rand_b |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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_ = uuid[15] // bounds check
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t, s := getV7Time()
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uuid[0] = byte(t >> 40)
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uuid[1] = byte(t >> 32)
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uuid[2] = byte(t >> 24)
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uuid[3] = byte(t >> 16)
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uuid[4] = byte(t >> 8)
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uuid[5] = byte(t)
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uuid[6] = 0x70 | (0x0F & byte(s>>8))
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uuid[7] = byte(s)
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}
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// lastV7time is the last time we returned stored as:
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//
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// 52 bits of time in milliseconds since epoch
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// 12 bits of (fractional nanoseconds) >> 8
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var lastV7time int64
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const nanoPerMilli = 1000000
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// getV7Time returns the time in milliseconds and nanoseconds / 256.
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// The returned (milli << 12 + seq) is guarenteed to be greater than
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// (milli << 12 + seq) returned by any previous call to getV7Time.
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func getV7Time() (milli, seq int64) {
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timeMu.Lock()
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defer timeMu.Unlock()
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nano := timeNow().UnixNano()
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milli = nano / nanoPerMilli
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// Sequence number is between 0 and 3906 (nanoPerMilli>>8)
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seq = (nano - milli*nanoPerMilli) >> 8
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now := milli<<12 + seq
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if now <= lastV7time {
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now = lastV7time + 1
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milli = now >> 12
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seq = now & 0xfff
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}
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lastV7time = now
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return milli, seq
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}
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