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version7.go (3371B)

      1 // Copyright 2023 Google Inc.  All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 package uuid
      6 
      7 import (
      8 	"io"
      9 )
     10 
     11 // UUID version 7 features a time-ordered value field derived from the widely
     12 // implemented and well known Unix Epoch timestamp source,
     13 // the number of milliseconds seconds since midnight 1 Jan 1970 UTC, leap seconds excluded.
     14 // As well as improved entropy characteristics over versions 1 or 6.
     15 //
     16 // see https://datatracker.ietf.org/doc/html/draft-peabody-dispatch-new-uuid-format-03#name-uuid-version-7
     17 //
     18 // Implementations SHOULD utilize UUID version 7 over UUID version 1 and 6 if possible.
     19 //
     20 // NewV7 returns a Version 7 UUID based on the current time(Unix Epoch).
     21 // Uses the randomness pool if it was enabled with EnableRandPool.
     22 // On error, NewV7 returns Nil and an error
     23 func NewV7() (UUID, error) {
     24 	uuid, err := NewRandom()
     25 	if err != nil {
     26 		return uuid, err
     27 	}
     28 	makeV7(uuid[:])
     29 	return uuid, nil
     30 }
     31 
     32 // NewV7FromReader returns a Version 7 UUID based on the current time(Unix Epoch).
     33 // it use NewRandomFromReader fill random bits.
     34 // On error, NewV7FromReader returns Nil and an error.
     35 func NewV7FromReader(r io.Reader) (UUID, error) {
     36 	uuid, err := NewRandomFromReader(r)
     37 	if err != nil {
     38 		return uuid, err
     39 	}
     40 
     41 	makeV7(uuid[:])
     42 	return uuid, nil
     43 }
     44 
     45 // makeV7 fill 48 bits time (uuid[0] - uuid[5]), set version b0111 (uuid[6])
     46 // uuid[8] already has the right version number (Variant is 10)
     47 // see function NewV7 and NewV7FromReader
     48 func makeV7(uuid []byte) {
     49 	/*
     50 		 0                   1                   2                   3
     51 		 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
     52 		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     53 		|                           unix_ts_ms                          |
     54 		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     55 		|          unix_ts_ms           |  ver  |  rand_a (12 bit seq)  |
     56 		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     57 		|var|                        rand_b                             |
     58 		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     59 		|                            rand_b                             |
     60 		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     61 	*/
     62 	_ = uuid[15] // bounds check
     63 
     64 	t, s := getV7Time()
     65 
     66 	uuid[0] = byte(t >> 40)
     67 	uuid[1] = byte(t >> 32)
     68 	uuid[2] = byte(t >> 24)
     69 	uuid[3] = byte(t >> 16)
     70 	uuid[4] = byte(t >> 8)
     71 	uuid[5] = byte(t)
     72 
     73 	uuid[6] = 0x70 | (0x0F & byte(s>>8))
     74 	uuid[7] = byte(s)
     75 }
     76 
     77 // lastV7time is the last time we returned stored as:
     78 //
     79 //	52 bits of time in milliseconds since epoch
     80 //	12 bits of (fractional nanoseconds) >> 8
     81 var lastV7time int64
     82 
     83 const nanoPerMilli = 1000000
     84 
     85 // getV7Time returns the time in milliseconds and nanoseconds / 256.
     86 // The returned (milli << 12 + seq) is guarenteed to be greater than
     87 // (milli << 12 + seq) returned by any previous call to getV7Time.
     88 func getV7Time() (milli, seq int64) {
     89 	timeMu.Lock()
     90 	defer timeMu.Unlock()
     91 
     92 	nano := timeNow().UnixNano()
     93 	milli = nano / nanoPerMilli
     94 	// Sequence number is between 0 and 3906 (nanoPerMilli>>8)
     95 	seq = (nano - milli*nanoPerMilli) >> 8
     96 	now := milli<<12 + seq
     97 	if now <= lastV7time {
     98 		now = lastV7time + 1
     99 		milli = now >> 12
    100 		seq = now & 0xfff
    101 	}
    102 	lastV7time = now
    103 	return milli, seq
    104 }