generator.go

/**
  Copyright (C) 2013-2018 by Maxim Bublis <b@codemonkey.ru>

  Permission is hereby granted, free of charge, to any person obtaining
  a copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be
  included in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
**/

package uuid

import (
	"crypto/md5"
	"crypto/rand"
	"crypto/sha1"
	"encoding/binary"
	"fmt"
	"hash"
	"io"
	"net"
	"os"
	"sync"
	"time"
)

// 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()

var (
	posixUID = uint32(os.Getuid())
	posixGID = uint32(os.Getgid())
)

// NewV1 returns a UUID based on the current timestamp and MAC address.
func NewV1() (UUID, error) {
	return DefaultGenerator.NewV1()
}

// NewV2 returns a DCE Security UUID based on the POSIX UID/GID.
func NewV2(domain byte) (UUID, error) {
	return DefaultGenerator.NewV2(domain)
}

// 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)
	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.
func NewGen() *Gen {
	return NewGenWithHWAF(defaultHWAddrFunc)
}

// 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
}

// NewV2 returns a DCE Security UUID based on the POSIX UID/GID.
func (g *Gen) NewV2(domain byte) (UUID, error) {
	u, err := g.NewV1()
	if err != nil {
		return Nil, err
	}

	switch domain {
	case DomainPerson:
		binary.BigEndian.PutUint32(u[:], posixUID)
	case DomainGroup:
		binary.BigEndian.PutUint32(u[:], posixGID)
	}

	u[9] = domain

	u.SetVersion(V2)
	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 _, err := io.ReadFull(g.rand, u[:]); err != nil {
		return Nil, err
	}
	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{}
	h.Write(ns[:])
	h.Write([]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")
}