1 package rand
2 3 import (
4 "encoding/hex"
5 "io"
6 )
7 8 const dash byte = '-'
9 10 // UUIDIdempotencyToken provides a utility to get idempotency tokens in the
11 // UUID format.
12 type UUIDIdempotencyToken struct {
13 uuid *UUID
14 }
15 16 // NewUUIDIdempotencyToken returns a idempotency token provider returning
17 // tokens in the UUID random format using the reader provided.
18 func NewUUIDIdempotencyToken(r io.Reader) *UUIDIdempotencyToken {
19 return &UUIDIdempotencyToken{uuid: NewUUID(r)}
20 }
21 22 // GetIdempotencyToken returns a random UUID value for Idempotency token.
23 func (u UUIDIdempotencyToken) GetIdempotencyToken() (string, error) {
24 return u.uuid.GetUUID()
25 }
26 27 // UUID provides computing random UUID version 4 values from a random source
28 // reader.
29 type UUID struct {
30 randSrc io.Reader
31 }
32 33 // NewUUID returns an initialized UUID value that can be used to retrieve
34 // random UUID version 4 values.
35 func NewUUID(r io.Reader) *UUID {
36 return &UUID{randSrc: r}
37 }
38 39 // GetUUID returns a random UUID version 4 string representation sourced from the random reader the
40 // UUID was created with. Returns an error if unable to compute the UUID.
41 func (r *UUID) GetUUID() (string, error) {
42 var b [16]byte
43 if _, err := io.ReadFull(r.randSrc, b[:]); err != nil {
44 return "", err
45 }
46 r.makeUUIDv4(b[:])
47 return format(b), nil
48 }
49 50 // GetBytes returns a byte slice containing a random UUID version 4 sourced from the random reader the
51 // UUID was created with. Returns an error if unable to compute the UUID.
52 func (r *UUID) GetBytes() (u []byte, err error) {
53 u = make([]byte, 16)
54 if _, err = io.ReadFull(r.randSrc, u); err != nil {
55 return u, err
56 }
57 r.makeUUIDv4(u)
58 return u, nil
59 }
60 61 func (r *UUID) makeUUIDv4(u []byte) {
62 // 13th character is "4"
63 u[6] = (u[6] & 0x0f) | 0x40 // Version 4
64 // 17th character is "8", "9", "a", or "b"
65 u[8] = (u[8] & 0x3f) | 0x80 // Variant most significant bits are 10x where x can be either 1 or 0
66 }
67 68 // Format returns the canonical text representation of a UUID.
69 // This implementation is optimized to not use fmt.
70 // Example: 82e42f16-b6cc-4d5b-95f5-d403c4befd3d
71 func format(u [16]byte) string {
72 // https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29
73 74 var scratch [36]byte
75 76 hex.Encode(scratch[:8], u[0:4])
77 scratch[8] = dash
78 hex.Encode(scratch[9:13], u[4:6])
79 scratch[13] = dash
80 hex.Encode(scratch[14:18], u[6:8])
81 scratch[18] = dash
82 hex.Encode(scratch[19:23], u[8:10])
83 scratch[23] = dash
84 hex.Encode(scratch[24:], u[10:])
85 86 return string(scratch[:])
87 }
88