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generator.go
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generator.go
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// Copyright 2023 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Copyright 2019 The Cockroach Authors.
//
// Use of this software is governed by the Business Source License
// included in the file licenses/BSL.txt.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0, included in the file
// licenses/APL.txt.
// Copyright (C) 2013-2018 by Maxim Bublis <b@codemonkey.ru>
// Use of this source code is governed by a MIT-style
// license that can be found in licenses/MIT-gofrs.txt.
// This code originated in github.com/gofrs/uuid.
package uuid
import (
"crypto/md5"
"crypto/rand"
"crypto/sha1"
"encoding/binary"
"fmt"
"hash"
"io"
"net"
"sync"
"time"
"github.com/cockroachdb/errors"
)
// Difference in 100-nanosecond intervals between
// UUID epoch (October 15, 1582) and Unix epoch (January 1, 1970).
const epochStart = 122192928000000000
type epochFunc func() time.Time
// HWAddrFunc is the function type used to provide hardware (MAC) addresses.
type HWAddrFunc func() (net.HardwareAddr, error)
// DefaultGenerator is the default UUID Generator used by this package.
var DefaultGenerator Generator = NewGen()
// NewV1 returns a UUID based on the current timestamp and MAC address.
func NewV1() (UUID, error) {
return DefaultGenerator.NewV1()
}
// NewV3 returns a UUID based on the MD5 hash of the namespace UUID and name.
func NewV3(ns UUID, name string) UUID {
return DefaultGenerator.NewV3(ns, name)
}
// NewV4 returns a randomly generated UUID.
func NewV4() (UUID, error) {
return DefaultGenerator.NewV4()
}
// NewV5 returns a UUID based on SHA-1 hash of the namespace UUID and name.
func NewV5(ns UUID, name string) UUID {
return DefaultGenerator.NewV5(ns, name)
}
// Generator provides an interface for generating UUIDs.
type Generator interface {
NewV1() (UUID, error)
// NewV2(domain byte) (UUID, error) // CRL: Removed support for V2.
NewV3(ns UUID, name string) UUID
NewV4() (UUID, error)
NewV5(ns UUID, name string) UUID
}
// Gen is a reference UUID generator based on the specifications laid out in
// RFC-4122 and DCE 1.1: Authentication and Security Services. This type
// satisfies the Generator interface as defined in this package.
//
// For consumers who are generating V1 UUIDs, but don't want to expose the MAC
// address of the node generating the UUIDs, the NewGenWithHWAF() function has been
// provided as a convenience. See the function's documentation for more info.
//
// The authors of this package do not feel that the majority of users will need
// to obfuscate their MAC address, and so we recommend using NewGen() to create
// a new generator.
type Gen struct {
clockSequenceOnce sync.Once
hardwareAddrOnce sync.Once
storageMutex sync.Mutex
rand io.Reader
epochFunc epochFunc
hwAddrFunc HWAddrFunc
lastTime uint64
clockSequence uint16
hardwareAddr [6]byte
}
// interface check -- build will fail if *Gen doesn't satisfy Generator
var _ Generator = (*Gen)(nil)
// NewGen returns a new instance of Gen with some default values set. Most
// people should use this.
// NewGen by default uses crypto/rand.Reader as its source of randomness.
func NewGen() *Gen {
return NewGenWithHWAF(defaultHWAddrFunc)
}
// NewGenWithReader returns a new instance of gen which uses r as its source of
// randomness.
func NewGenWithReader(r io.Reader) *Gen {
g := NewGen()
g.rand = r
return g
}
// NewGenWithHWAF builds a new UUID generator with the HWAddrFunc provided. Most
// consumers should use NewGen() instead.
//
// This is used so that consumers can generate their own MAC addresses, for use
// in the generated UUIDs, if there is some concern about exposing the physical
// address of the machine generating the UUID.
//
// The Gen generator will only invoke the HWAddrFunc once, and cache that MAC
// address for all the future UUIDs generated by it. If you'd like to switch the
// MAC address being used, you'll need to create a new generator using this
// function.
func NewGenWithHWAF(hwaf HWAddrFunc) *Gen {
return &Gen{
epochFunc: time.Now,
hwAddrFunc: hwaf,
rand: rand.Reader,
}
}
// NewV1 returns a UUID based on the current timestamp and MAC address.
func (g *Gen) NewV1() (UUID, error) {
u := UUID{}
timeNow, clockSeq, err := g.getClockSequence()
if err != nil {
return Nil, err
}
binary.BigEndian.PutUint32(u[0:], uint32(timeNow))
binary.BigEndian.PutUint16(u[4:], uint16(timeNow>>32))
binary.BigEndian.PutUint16(u[6:], uint16(timeNow>>48))
binary.BigEndian.PutUint16(u[8:], clockSeq)
hardwareAddr, err := g.getHardwareAddr()
if err != nil {
return Nil, err
}
copy(u[10:], hardwareAddr)
u.SetVersion(V1)
u.SetVariant(VariantRFC4122)
return u, nil
}
// NewV3 returns a UUID based on the MD5 hash of the namespace UUID and name.
func (g *Gen) NewV3(ns UUID, name string) UUID {
u := newFromHash(md5.New(), ns, name)
u.SetVersion(V3)
u.SetVariant(VariantRFC4122)
return u
}
// NewV4 returns a randomly generated UUID.
func (g *Gen) NewV4() (UUID, error) {
u := UUID{}
if r, ok := g.rand.(defaultRandReader); ok {
if n, err := r.Read(u[:]); n != len(u) {
panic("math/rand.Read always returns len(p)")
} else if err != nil {
panic("math/rand.Read always returns a nil error")
}
} else {
willEscape := UUID{}
if _, err := io.ReadFull(g.rand, willEscape[:]); err != nil {
return Nil, err
}
u = willEscape
}
u.SetVersion(V4)
u.SetVariant(VariantRFC4122)
return u, nil
}
// NewV5 returns a UUID based on SHA-1 hash of the namespace UUID and name.
func (g *Gen) NewV5(ns UUID, name string) UUID {
u := newFromHash(sha1.New(), ns, name)
u.SetVersion(V5)
u.SetVariant(VariantRFC4122)
return u
}
// Returns the epoch and clock sequence.
func (g *Gen) getClockSequence() (uint64, uint16, error) {
var err error
g.clockSequenceOnce.Do(func() {
buf := make([]byte, 2)
if _, err = io.ReadFull(g.rand, buf); err != nil {
return
}
g.clockSequence = binary.BigEndian.Uint16(buf)
})
if err != nil {
return 0, 0, err
}
g.storageMutex.Lock()
defer g.storageMutex.Unlock()
timeNow := g.getEpoch()
// Clock didn't change since last UUID generation.
// Should increase clock sequence.
if timeNow <= g.lastTime {
g.clockSequence++
}
g.lastTime = timeNow
return timeNow, g.clockSequence, nil
}
// Returns the hardware address.
func (g *Gen) getHardwareAddr() ([]byte, error) {
var err error
g.hardwareAddrOnce.Do(func() {
var hwAddr net.HardwareAddr
if hwAddr, err = g.hwAddrFunc(); err == nil {
copy(g.hardwareAddr[:], hwAddr)
return
}
// Initialize hardwareAddr randomly in case
// of real network interfaces absence.
if _, err = io.ReadFull(g.rand, g.hardwareAddr[:]); err != nil {
return
}
// Set multicast bit as recommended by RFC-4122
g.hardwareAddr[0] |= 0x01
})
if err != nil {
return []byte{}, err
}
return g.hardwareAddr[:], nil
}
// Returns the difference between UUID epoch (October 15, 1582)
// and current time in 100-nanosecond intervals.
func (g *Gen) getEpoch() uint64 {
return epochStart + uint64(g.epochFunc().UnixNano()/100)
}
// Returns the UUID based on the hashing of the namespace UUID and name.
func newFromHash(h hash.Hash, ns UUID, name string) UUID {
u := UUID{}
mustWrite := func(data []byte) {
if _, err := h.Write(data); err != nil {
panic(errors.Wrap(err, "failed to write to hash"))
}
}
mustWrite(ns[:])
mustWrite([]byte(name))
copy(u[:], h.Sum(nil))
return u
}
// Returns the hardware address.
func defaultHWAddrFunc() (net.HardwareAddr, error) {
ifaces, err := net.Interfaces()
if err != nil {
return []byte{}, err
}
for _, iface := range ifaces {
if len(iface.HardwareAddr) >= 6 {
return iface.HardwareAddr, nil
}
}
return []byte{}, fmt.Errorf("uuid: no HW address found")
}