1 // Copyright 2016 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 "encoding/binary"
9 "sync"
10 "time"
11 )
12 13 // A Time represents a time as the number of 100's of nanoseconds since 15 Oct
14 // 1582.
15 type Time int64
16 17 const (
18 lillian = 2299160 // Julian day of 15 Oct 1582
19 unix = 2440587 // Julian day of 1 Jan 1970
20 epoch = unix - lillian // Days between epochs
21 g1582 = epoch * 86400 // seconds between epochs
22 g1582ns100 = g1582 * 10000000 // 100s of a nanoseconds between epochs
23 )
24 25 var (
26 timeMu sync.Mutex
27 lasttime uint64 // last time we returned
28 clockSeq uint16 // clock sequence for this run
29 30 timeNow = time.Now // for testing
31 )
32 33 // UnixTime converts t the number of seconds and nanoseconds using the Unix
34 // epoch of 1 Jan 1970.
35 func (t Time) UnixTime() (sec, nsec int64) {
36 sec = int64(t - g1582ns100)
37 nsec = (sec % 10000000) * 100
38 sec /= 10000000
39 return sec, nsec
40 }
41 42 // GetTime returns the current Time (100s of nanoseconds since 15 Oct 1582) and
43 // clock sequence as well as adjusting the clock sequence as needed. An error
44 // is returned if the current time cannot be determined.
45 func GetTime() (Time, uint16, error) {
46 defer timeMu.Unlock()
47 timeMu.Lock()
48 return getTime()
49 }
50 51 func getTime() (Time, uint16, error) {
52 t := timeNow()
53 54 // If we don't have a clock sequence already, set one.
55 if clockSeq == 0 {
56 setClockSequence(-1)
57 }
58 now := uint64(t.UnixNano()/100) + g1582ns100
59 60 // If time has gone backwards with this clock sequence then we
61 // increment the clock sequence
62 if now <= lasttime {
63 clockSeq = ((clockSeq + 1) & 0x3fff) | 0x8000
64 }
65 lasttime = now
66 return Time(now), clockSeq, nil
67 }
68 69 // ClockSequence returns the current clock sequence, generating one if not
70 // already set. The clock sequence is only used for Version 1 UUIDs.
71 //
72 // The uuid package does not use global static storage for the clock sequence or
73 // the last time a UUID was generated. Unless SetClockSequence is used, a new
74 // random clock sequence is generated the first time a clock sequence is
75 // requested by ClockSequence, GetTime, or NewUUID. (section 4.2.1.1)
76 func ClockSequence() int {
77 defer timeMu.Unlock()
78 timeMu.Lock()
79 return clockSequence()
80 }
81 82 func clockSequence() int {
83 if clockSeq == 0 {
84 setClockSequence(-1)
85 }
86 return int(clockSeq & 0x3fff)
87 }
88 89 // SetClockSequence sets the clock sequence to the lower 14 bits of seq. Setting to
90 // -1 causes a new sequence to be generated.
91 func SetClockSequence(seq int) {
92 defer timeMu.Unlock()
93 timeMu.Lock()
94 setClockSequence(seq)
95 }
96 97 func setClockSequence(seq int) {
98 if seq == -1 {
99 var b [2]byte
100 randomBits(b[:]) // clock sequence
101 seq = int(b[0])<<8 | int(b[1])
102 }
103 oldSeq := clockSeq
104 clockSeq = uint16(seq&0x3fff) | 0x8000 // Set our variant
105 if oldSeq != clockSeq {
106 lasttime = 0
107 }
108 }
109 110 // Time returns the time in 100s of nanoseconds since 15 Oct 1582 encoded in
111 // uuid. The time is only defined for version 1, 2, 6 and 7 UUIDs.
112 func (uuid UUID) Time() Time {
113 var t Time
114 switch uuid.Version() {
115 case 6:
116 time := binary.BigEndian.Uint64(uuid[:8]) // Ignore uuid[6] version b0110
117 t = Time(time)
118 case 7:
119 time := binary.BigEndian.Uint64(uuid[:8])
120 t = Time((time>>16)*10000 + g1582ns100)
121 default: // forward compatible
122 time := int64(binary.BigEndian.Uint32(uuid[0:4]))
123 time |= int64(binary.BigEndian.Uint16(uuid[4:6])) << 32
124 time |= int64(binary.BigEndian.Uint16(uuid[6:8])&0xfff) << 48
125 t = Time(time)
126 }
127 return t
128 }
129 130 // ClockSequence returns the clock sequence encoded in uuid.
131 // The clock sequence is only well defined for version 1 and 2 UUIDs.
132 func (uuid UUID) ClockSequence() int {
133 return int(binary.BigEndian.Uint16(uuid[8:10])) & 0x3fff
134 }
135