1package rand
2
3import (
4 "encoding/hex"
5 "io"
6)
7
8const dash byte = '-'
9
10// UUIDIdempotencyToken provides a utility to get idempotency tokens in the
11// UUID format.
12type 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.
18func NewUUIDIdempotencyToken(r io.Reader) *UUIDIdempotencyToken {
19 return &UUIDIdempotencyToken{uuid: NewUUID(r)}
20}
21
22// GetIdempotencyToken returns a random UUID value for Idempotency token.
23func (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.
29type 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.
35func 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.
41func (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.
52func (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
61func (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
71func 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}