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// Copyright 2016 Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package uuid
import (
"encoding/binary"
"sync"
"time"
)
// A Time represents a time as the number of 100's of nanoseconds since 15 Oct
// 1582.
type Time int64
const (
lillian = 2299160 // Julian day of 15 Oct 1582
unix = 2440587 // Julian day of 1 Jan 1970
epoch = unix - lillian // Days between epochs
g1582 = epoch * 86400 // seconds between epochs
g1582ns100 = g1582 * 10000000 // 100s of a nanoseconds between epochs
)
var (
timeMu sync.Mutex
lasttime uint64 // last time we returned
clockSeq uint16 // clock sequence for this run
timeNow = time.Now // for testing
)
// UnixTime converts t the number of seconds and nanoseconds using the Unix
// epoch of 1 Jan 1970.
func (t Time) UnixTime() (sec, nsec int64) {
sec = int64(t - g1582ns100)
nsec = (sec % 10000000) * 100
sec /= 10000000
return sec, nsec
}
// GetTime returns the current Time (100s of nanoseconds since 15 Oct 1582) and
// clock sequence as well as adjusting the clock sequence as needed. An error
// is returned if the current time cannot be determined.
func GetTime() (Time, uint16, error) {
defer timeMu.Unlock()
timeMu.Lock()
return getTime()
}
func getTime() (Time, uint16, error) {
t := timeNow()
// If we don't have a clock sequence already, set one.
if clockSeq == 0 {
setClockSequence(-1)
}
now := uint64(t.UnixNano()/100) + g1582ns100
// If time has gone backwards with this clock sequence then we
// increment the clock sequence
if now <= lasttime {
clockSeq = ((clockSeq + 1) & 0x3fff) | 0x8000
}
lasttime = now
return Time(now), clockSeq, nil
}
// ClockSequence returns the current clock sequence, generating one if not
// already set. The clock sequence is only used for Version 1 UUIDs.
//
// The uuid package does not use global static storage for the clock sequence or
// the last time a UUID was generated. Unless SetClockSequence is used, a new
// random clock sequence is generated the first time a clock sequence is
// requested by ClockSequence, GetTime, or NewUUID. (section 4.2.1.1)
func ClockSequence() int {
defer timeMu.Unlock()
timeMu.Lock()
return clockSequence()
}
func clockSequence() int {
if clockSeq == 0 {
setClockSequence(-1)
}
return int(clockSeq & 0x3fff)
}
// SetClockSequence sets the clock sequence to the lower 14 bits of seq. Setting to
// -1 causes a new sequence to be generated.
func SetClockSequence(seq int) {
defer timeMu.Unlock()
timeMu.Lock()
setClockSequence(seq)
}
func setClockSequence(seq int) {
if seq == -1 {
var b [2]byte
randomBits(b[:]) // clock sequence
seq = int(b[0])<<8 | int(b[1])
}
oldSeq := clockSeq
clockSeq = uint16(seq&0x3fff) | 0x8000 // Set our variant
if oldSeq != clockSeq {
lasttime = 0
}
}
// Time returns the time in 100s of nanoseconds since 15 Oct 1582 encoded in
// uuid. The time is only defined for version 1, 2, 6 and 7 UUIDs.
func (uuid UUID) Time() Time {
var t Time
switch uuid.Version() {
case 6:
time := binary.BigEndian.Uint64(uuid[:8]) // Ignore uuid[6] version b0110
t = Time(time)
case 7:
time := binary.BigEndian.Uint64(uuid[:8])
t = Time((time>>16)*10000 + g1582ns100)
default: // forward compatible
time := int64(binary.BigEndian.Uint32(uuid[0:4]))
time |= int64(binary.BigEndian.Uint16(uuid[4:6])) << 32
time |= int64(binary.BigEndian.Uint16(uuid[6:8])&0xfff) << 48
t = Time(time)
}
return t
}
// ClockSequence returns the clock sequence encoded in uuid.
// The clock sequence is only well defined for version 1 and 2 UUIDs.
func (uuid UUID) ClockSequence() int {
return int(binary.BigEndian.Uint16(uuid[8:10])) & 0x3fff
}
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