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+// Copyright (C) 2013-2018 by Maxim Bublis <b@codemonkey.ru>
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+//
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+// Permission is hereby granted, free of charge, to any person obtaining
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+// a copy of this software and associated documentation files (the
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+// "Software"), to deal in the Software without restriction, including
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+// without limitation the rights to use, copy, modify, merge, publish,
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+// distribute, sublicense, and/or sell copies of the Software, and to
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+// permit persons to whom the Software is furnished to do so, subject to
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+// the following conditions:
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+//
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+// The above copyright notice and this permission notice shall be
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+// included in all copies or substantial portions of the Software.
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+//
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+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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+// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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+// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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+// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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+
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+package uuid
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+
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+import (
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+ "crypto/md5"
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+ "crypto/rand"
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+ "crypto/sha1"
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+ "encoding/binary"
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+ "hash"
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+ "net"
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+ "os"
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+ "sync"
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+ "time"
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+)
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+
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+// Difference in 100-nanosecond intervals between
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+// UUID epoch (October 15, 1582) and Unix epoch (January 1, 1970).
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+const epochStart = 122192928000000000
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+
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+var (
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+ global = newDefaultGenerator()
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+
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+ epochFunc = unixTimeFunc
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+ posixUID = uint32(os.Getuid())
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+ posixGID = uint32(os.Getgid())
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+)
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+
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+// NewV1 returns UUID based on current timestamp and MAC address.
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+func NewV1() UUID {
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+ return global.NewV1()
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+}
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+
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+// NewV2 returns DCE Security UUID based on POSIX UID/GID.
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+func NewV2(domain byte) UUID {
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+ return global.NewV2(domain)
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+}
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+
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+// NewV3 returns UUID based on MD5 hash of namespace UUID and name.
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+func NewV3(ns UUID, name string) UUID {
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+ return global.NewV3(ns, name)
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+}
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+
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+// NewV4 returns random generated UUID.
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+func NewV4() UUID {
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+ return global.NewV4()
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+}
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+
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+// NewV5 returns UUID based on SHA-1 hash of namespace UUID and name.
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+func NewV5(ns UUID, name string) UUID {
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+ return global.NewV5(ns, name)
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+}
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+
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+// Generator provides interface for generating UUIDs.
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+type Generator interface {
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+ NewV1() UUID
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+ NewV2(domain byte) UUID
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+ NewV3(ns UUID, name string) UUID
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+ NewV4() UUID
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+ NewV5(ns UUID, name string) UUID
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+}
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+
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+// Default generator implementation.
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+type generator struct {
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+ storageOnce sync.Once
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+ storageMutex sync.Mutex
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+
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+ lastTime uint64
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+ clockSequence uint16
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+ hardwareAddr [6]byte
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+}
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+
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+func newDefaultGenerator() Generator {
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+ return &generator{}
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+}
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+
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+// NewV1 returns UUID based on current timestamp and MAC address.
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+func (g *generator) NewV1() UUID {
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+ u := UUID{}
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+
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+ timeNow, clockSeq, hardwareAddr := g.getStorage()
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+
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+ binary.BigEndian.PutUint32(u[0:], uint32(timeNow))
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+ binary.BigEndian.PutUint16(u[4:], uint16(timeNow>>32))
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+ binary.BigEndian.PutUint16(u[6:], uint16(timeNow>>48))
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+ binary.BigEndian.PutUint16(u[8:], clockSeq)
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+
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+ copy(u[10:], hardwareAddr)
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+
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+ u.SetVersion(V1)
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+ u.SetVariant(VariantRFC4122)
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+
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+ return u
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+}
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+
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+// NewV2 returns DCE Security UUID based on POSIX UID/GID.
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+func (g *generator) NewV2(domain byte) UUID {
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+ u := UUID{}
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+
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+ timeNow, clockSeq, hardwareAddr := g.getStorage()
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+
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+ switch domain {
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+ case DomainPerson:
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+ binary.BigEndian.PutUint32(u[0:], posixUID)
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+ case DomainGroup:
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+ binary.BigEndian.PutUint32(u[0:], posixGID)
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+ }
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+
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+ binary.BigEndian.PutUint16(u[4:], uint16(timeNow>>32))
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+ binary.BigEndian.PutUint16(u[6:], uint16(timeNow>>48))
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+ binary.BigEndian.PutUint16(u[8:], clockSeq)
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+ u[9] = domain
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+
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+ copy(u[10:], hardwareAddr)
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+
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+ u.SetVersion(V2)
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+ u.SetVariant(VariantRFC4122)
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+
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+ return u
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+}
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+
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+// NewV3 returns UUID based on MD5 hash of namespace UUID and name.
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+func (g *generator) NewV3(ns UUID, name string) UUID {
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+ u := newFromHash(md5.New(), ns, name)
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+ u.SetVersion(V3)
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+ u.SetVariant(VariantRFC4122)
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+
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+ return u
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+}
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+
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+// NewV4 returns random generated UUID.
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+func (g *generator) NewV4() UUID {
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+ u := UUID{}
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+ g.safeRandom(u[:])
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+ u.SetVersion(V4)
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+ u.SetVariant(VariantRFC4122)
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+
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+ return u
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+}
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+
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+// NewV5 returns UUID based on SHA-1 hash of namespace UUID and name.
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+func (g *generator) NewV5(ns UUID, name string) UUID {
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+ u := newFromHash(sha1.New(), ns, name)
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+ u.SetVersion(V5)
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+ u.SetVariant(VariantRFC4122)
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+
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+ return u
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+}
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+
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+func (g *generator) initStorage() {
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+ g.initClockSequence()
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+ g.initHardwareAddr()
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+}
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+
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+func (g *generator) initClockSequence() {
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+ buf := make([]byte, 2)
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+ g.safeRandom(buf)
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+ g.clockSequence = binary.BigEndian.Uint16(buf)
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+}
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+
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+func (g *generator) initHardwareAddr() {
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+ interfaces, err := net.Interfaces()
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+ if err == nil {
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+ for _, iface := range interfaces {
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+ if len(iface.HardwareAddr) >= 6 {
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+ copy(g.hardwareAddr[:], iface.HardwareAddr)
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+ return
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+ }
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+ }
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+ }
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+
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+ // Initialize hardwareAddr randomly in case
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+ // of real network interfaces absence
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+ g.safeRandom(g.hardwareAddr[:])
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+
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+ // Set multicast bit as recommended in RFC 4122
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+ g.hardwareAddr[0] |= 0x01
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+}
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+
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+func (g *generator) safeRandom(dest []byte) {
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+ if _, err := rand.Read(dest); err != nil {
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+ panic(err)
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+ }
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+}
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+
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+// Returns UUID v1/v2 storage state.
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+// Returns epoch timestamp, clock sequence, and hardware address.
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+func (g *generator) getStorage() (uint64, uint16, []byte) {
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+ g.storageOnce.Do(g.initStorage)
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+
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+ g.storageMutex.Lock()
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+ defer g.storageMutex.Unlock()
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+
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+ timeNow := epochFunc()
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+ // Clock changed backwards since last UUID generation.
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+ // Should increase clock sequence.
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+ if timeNow <= g.lastTime {
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+ g.clockSequence++
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+ }
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+ g.lastTime = timeNow
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+
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+ return timeNow, g.clockSequence, g.hardwareAddr[:]
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+}
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+
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+// Returns difference in 100-nanosecond intervals between
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+// UUID epoch (October 15, 1582) and current time.
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+// This is default epoch calculation function.
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+func unixTimeFunc() uint64 {
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+ return epochStart + uint64(time.Now().UnixNano()/100)
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+}
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+
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+// Returns UUID based on hashing of namespace UUID and name.
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+func newFromHash(h hash.Hash, ns UUID, name string) UUID {
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+ u := UUID{}
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+ h.Write(ns[:])
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+ h.Write([]byte(name))
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+ copy(u[:], h.Sum(nil))
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+
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+ return u
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+}
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