-
Notifications
You must be signed in to change notification settings - Fork 1
/
uid.go
43 lines (37 loc) · 1.32 KB
/
uid.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
package secrets
import (
"math/rand"
"time"
)
const (
letterBytes = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
letterIdxBits = 6 // 6 bits to represent a letter index
letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
letterIdxMax = 63 / letterIdxBits // # of letter indices fitting in 63 bits
UniqueIdentifierCharacterSet = "abcdefghijklmnopqrstuvwxyz" +
"ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
VisuallyUnambiguousLowerCaseCharacterSet = `abcdefhijkmnoprstwxy34`
VisuallyUnambiguousCharacterSet = VisuallyUnambiguousLowerCaseCharacterSet + `ABCDEFHIJKMNOPRSTWXY`
)
var src = rand.NewSource(time.Now().UnixNano())
// FastRandom is inspired by Ketan Parmar's work:
//
// - https://github.com/kpbird/golang_random_string/blob/master/main.go
// - https://kpbird.medium.com/golang-generate-fixed-size-random-string-dd6dbd5e63c0
func NewID(n int) []byte {
b := make([]byte, n)
l := len(letterBytes)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = src.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < l {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return b
}