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