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* Add randomness pool mode for V4 UUID

Adds an optional randomness pool mode for Random (Version 4)
UUID generation. The pool contains random bytes read from
the random number generator on demand in batches. Enabling
the pool may improve the UUID generation throughput
significantly.

Since the pool is stored on the Go heap, this feature may
be a bad fit for security sensitive applications. That's
why it's implemented as an opt-in feature.

* fixup! document thread-safety aspects
11 contributors

Users who have contributed to this file

@bmatsuo @pborman @martinlindhe @shawnps @charlielukman @OrlovEvgeny @KonstantinCodes @joewreschnig @loderunner @puzpuzpuz @johejo
// Copyright 2018 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 (
"bytes"
"crypto/rand"
"encoding/hex"
"errors"
"fmt"
"io"
"strings"
"sync"
)
// A UUID is a 128 bit (16 byte) Universal Unique IDentifier as defined in RFC
// 4122.
type UUID [16]byte
// A Version represents a UUID's version.
type Version byte
// A Variant represents a UUID's variant.
type Variant byte
// Constants returned by Variant.
const (
Invalid = Variant(iota) // Invalid UUID
RFC4122 // The variant specified in RFC4122
Reserved // Reserved, NCS backward compatibility.
Microsoft // Reserved, Microsoft Corporation backward compatibility.
Future // Reserved for future definition.
)
const randPoolSize = 16 * 16
var (
rander = rand.Reader // random function
poolEnabled = false
poolMu sync.Mutex
poolPos = randPoolSize // protected with poolMu
pool [randPoolSize]byte // protected with poolMu
)
type invalidLengthError struct{ len int }
func (err invalidLengthError) Error() string {
return fmt.Sprintf("invalid UUID length: %d", err.len)
}
// IsInvalidLengthError is matcher function for custom error invalidLengthError
func IsInvalidLengthError(err error) bool {
_, ok := err.(invalidLengthError)
return ok
}
// Parse decodes s into a UUID or returns an error. Both the standard UUID
// forms of xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx and
// urn:uuid:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx are decoded as well as the
// Microsoft encoding {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} and the raw hex
// encoding: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.
func Parse(s string) (UUID, error) {
var uuid UUID
switch len(s) {
// xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
case 36:
// urn:uuid:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
case 36 + 9:
if strings.ToLower(s[:9]) != "urn:uuid:" {
return uuid, fmt.Errorf("invalid urn prefix: %q", s[:9])
}
s = s[9:]
// {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}
case 36 + 2:
s = s[1:]
// xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
case 32:
var ok bool
for i := range uuid {
uuid[i], ok = xtob(s[i*2], s[i*2+1])
if !ok {
return uuid, errors.New("invalid UUID format")
}
}
return uuid, nil
default:
return uuid, invalidLengthError{len(s)}
}
// s is now at least 36 bytes long
// it must be of the form xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
if s[8] != '-' || s[13] != '-' || s[18] != '-' || s[23] != '-' {
return uuid, errors.New("invalid UUID format")
}
for i, x := range [16]int{
0, 2, 4, 6,
9, 11,
14, 16,
19, 21,
24, 26, 28, 30, 32, 34} {
v, ok := xtob(s[x], s[x+1])
if !ok {
return uuid, errors.New("invalid UUID format")
}
uuid[i] = v
}
return uuid, nil
}
// ParseBytes is like Parse, except it parses a byte slice instead of a string.
func ParseBytes(b []byte) (UUID, error) {
var uuid UUID
switch len(b) {
case 36: // xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
case 36 + 9: // urn:uuid:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
if !bytes.Equal(bytes.ToLower(b[:9]), []byte("urn:uuid:")) {
return uuid, fmt.Errorf("invalid urn prefix: %q", b[:9])
}
b = b[9:]
case 36 + 2: // {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}
b = b[1:]
case 32: // xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
var ok bool
for i := 0; i < 32; i += 2 {
uuid[i/2], ok = xtob(b[i], b[i+1])
if !ok {
return uuid, errors.New("invalid UUID format")
}
}
return uuid, nil
default:
return uuid, invalidLengthError{len(b)}
}
// s is now at least 36 bytes long
// it must be of the form xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
if b[8] != '-' || b[13] != '-' || b[18] != '-' || b[23] != '-' {
return uuid, errors.New("invalid UUID format")
}
for i, x := range [16]int{
0, 2, 4, 6,
9, 11,
14, 16,
19, 21,
24, 26, 28, 30, 32, 34} {
v, ok := xtob(b[x], b[x+1])
if !ok {
return uuid, errors.New("invalid UUID format")
}
uuid[i] = v
}
return uuid, nil
}
// MustParse is like Parse but panics if the string cannot be parsed.
// It simplifies safe initialization of global variables holding compiled UUIDs.
func MustParse(s string) UUID {
uuid, err := Parse(s)
if err != nil {
panic(`uuid: Parse(` + s + `): ` + err.Error())
}
return uuid
}
// FromBytes creates a new UUID from a byte slice. Returns an error if the slice
// does not have a length of 16. The bytes are copied from the slice.
func FromBytes(b []byte) (uuid UUID, err error) {
err = uuid.UnmarshalBinary(b)
return uuid, err
}
// Must returns uuid if err is nil and panics otherwise.
func Must(uuid UUID, err error) UUID {
if err != nil {
panic(err)
}
return uuid
}
// String returns the string form of uuid, xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
// , or "" if uuid is invalid.
func (uuid UUID) String() string {
var buf [36]byte
encodeHex(buf[:], uuid)
return string(buf[:])
}
// URN returns the RFC 2141 URN form of uuid,
// urn:uuid:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, or "" if uuid is invalid.
func (uuid UUID) URN() string {
var buf [36 + 9]byte
copy(buf[:], "urn:uuid:")
encodeHex(buf[9:], uuid)
return string(buf[:])
}
func encodeHex(dst []byte, uuid UUID) {
hex.Encode(dst, uuid[:4])
dst[8] = '-'
hex.Encode(dst[9:13], uuid[4:6])
dst[13] = '-'
hex.Encode(dst[14:18], uuid[6:8])
dst[18] = '-'
hex.Encode(dst[19:23], uuid[8:10])
dst[23] = '-'
hex.Encode(dst[24:], uuid[10:])
}
// Variant returns the variant encoded in uuid.
func (uuid UUID) Variant() Variant {
switch {
case (uuid[8] & 0xc0) == 0x80:
return RFC4122
case (uuid[8] & 0xe0) == 0xc0:
return Microsoft
case (uuid[8] & 0xe0) == 0xe0:
return Future
default:
return Reserved
}
}
// Version returns the version of uuid.
func (uuid UUID) Version() Version {
return Version(uuid[6] >> 4)
}
func (v Version) String() string {
if v > 15 {
return fmt.Sprintf("BAD_VERSION_%d", v)
}
return fmt.Sprintf("VERSION_%d", v)
}
func (v Variant) String() string {
switch v {
case RFC4122:
return "RFC4122"
case Reserved:
return "Reserved"
case Microsoft:
return "Microsoft"
case Future:
return "Future"
case Invalid:
return "Invalid"
}
return fmt.Sprintf("BadVariant%d", int(v))
}
// SetRand sets the random number generator to r, which implements io.Reader.
// If r.Read returns an error when the package requests random data then
// a panic will be issued.
//
// Calling SetRand with nil sets the random number generator to the default
// generator.
func SetRand(r io.Reader) {
if r == nil {
rander = rand.Reader
return
}
rander = r
}
// EnableRandPool enables internal randomness pool used for Random
// (Version 4) UUID generation. The pool contains random bytes read from
// the random number generator on demand in batches. Enabling the pool
// may improve the UUID generation throughput significantly.
//
// Since the pool is stored on the Go heap, this feature may be a bad fit
// for security sensitive applications.
//
// Both EnableRandPool and DisableRandPool are not thread-safe and should
// only be called when there is no possibility that New or any other
// UUID Version 4 generation function will be called concurrently.
func EnableRandPool() {
poolEnabled = true
}
// DisableRandPool disables the randomness pool if it was previously
// enabled with EnableRandPool.
//
// Both EnableRandPool and DisableRandPool are not thread-safe and should
// only be called when there is no possibility that New or any other
// UUID Version 4 generation function will be called concurrently.
func DisableRandPool() {
poolEnabled = false
defer poolMu.Unlock()
poolMu.Lock()
poolPos = randPoolSize
}