1 // Copyright 2016 Google Inc. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 package uuid
6 7 import "io"
8 9 // New creates a new random UUID or panics. New is equivalent to
10 // the expression
11 //
12 // uuid.Must(uuid.NewRandom())
13 func New() UUID {
14 return Must(NewRandom())
15 }
16 17 // NewString creates a new random UUID and returns it as a string or panics.
18 // NewString is equivalent to the expression
19 //
20 // uuid.New().String()
21 func NewString() string {
22 return Must(NewRandom()).String()
23 }
24 25 // NewRandom returns a Random (Version 4) UUID.
26 //
27 // The strength of the UUIDs is based on the strength of the crypto/rand
28 // package.
29 //
30 // Uses the randomness pool if it was enabled with EnableRandPool.
31 //
32 // A note about uniqueness derived from the UUID Wikipedia entry:
33 //
34 // Randomly generated UUIDs have 122 random bits. One's annual risk of being
35 // hit by a meteorite is estimated to be one chance in 17 billion, that
36 // means the probability is about 0.00000000006 (6 × 10−11),
37 // equivalent to the odds of creating a few tens of trillions of UUIDs in a
38 // year and having one duplicate.
39 func NewRandom() (UUID, error) {
40 if !poolEnabled {
41 return NewRandomFromReader(rander)
42 }
43 return newRandomFromPool()
44 }
45 46 // NewRandomFromReader returns a UUID based on bytes read from a given io.Reader.
47 func NewRandomFromReader(r io.Reader) (UUID, error) {
48 var uuid UUID
49 _, err := io.ReadFull(r, uuid[:])
50 if err != nil {
51 return Nil, err
52 }
53 uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
54 uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
55 return uuid, nil
56 }
57 58 func newRandomFromPool() (UUID, error) {
59 var uuid UUID
60 poolMu.Lock()
61 if poolPos == randPoolSize {
62 _, err := io.ReadFull(rander, pool[:])
63 if err != nil {
64 poolMu.Unlock()
65 return Nil, err
66 }
67 poolPos = 0
68 }
69 copy(uuid[:], pool[poolPos:(poolPos+16)])
70 poolPos += 16
71 poolMu.Unlock()
72 73 uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
74 uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
75 return uuid, nil
76 }
77