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
 5package uuid
 6
 7import "io"
 8
 9// New creates a new random UUID or panics.  New is equivalent to
10// the expression
11//
12//    uuid.Must(uuid.NewRandom())
13func 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()
21func 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.
39func 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.
47func 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
58func 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}