.

vendor/git.antanst.com/antanst/uid/README.md

@@ -0,0 +1,5 @@
+# UID
+
+This project generates a reasonably secure and convenient UID.
+
+Borrows code from https://github.com/matoous/go-nanoid

vendor/git.antanst.com/antanst/uid/uid.go

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+package uid
+
+import (
+	"crypto/rand"
+	"errors"
+	"math"
+)
+
+// UID is a high level function that returns a reasonably secure UID.
+// Only alphanumeric characters except 'o','O' and 'l'
+func UID() string {
+	id, err := Generate("abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ0123456789", 20)
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
+
+// Generate is a low-level function to change alphabet and ID size.
+// Taken from go-nanoid project
+func Generate(alphabet string, size int) (string, error) {
+	chars := []rune(alphabet)
+
+	if len(alphabet) == 0 || len(alphabet) > 255 {
+		return "", errors.New("alphabet must not be empty and contain no more than 255 chars")
+	}
+	if size <= 0 {
+		return "", errors.New("size must be positive integer")
+	}
+
+	mask := getMask(len(chars))
+	// estimate how many random bytes we will need for the ID, we might actually need more but this is tradeoff
+	// between average case and worst case
+	ceilArg := 1.6 * float64(mask*size) / float64(len(alphabet))
+	step := int(math.Ceil(ceilArg))
+
+	id := make([]rune, size)
+	bytes := make([]byte, step)
+	for j := 0; ; {
+		_, err := rand.Read(bytes)
+		if err != nil {
+			return "", err
+		}
+		for i := 0; i < step; i++ {
+			currByte := bytes[i] & byte(mask)
+			if currByte < byte(len(chars)) {
+				id[j] = chars[currByte]
+				j++
+				if j == size {
+					return string(id[:size]), nil
+				}
+			}
+		}
+	}
+}
+
+// getMask generates bit mask used to obtain bits from the random bytes that are used to get index of random character
+// from the alphabet. Example: if the alphabet has 6 = (110)_2 characters it is sufficient to use mask 7 = (111)_2
+// Taken from go-nanoid project
+func getMask(alphabetSize int) int {
+	for i := 1; i <= 8; i++ {
+		mask := (2 << uint(i)) - 1
+		if mask >= alphabetSize-1 {
+			return mask
+		}
+	}
+	return 0
+}