progress on server refactor

server/internal/utils/uid.go

@@ -0,0 +1,98 @@
+package utils
+
+import (
+	"crypto/rand"
+	"fmt"
+	"math"
+)
+
+const (
+	defaultAlphabet = "_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" // len=64
+	defaultSize     = 21
+	defaultMaskSize = 5
+)
+
+// Generator function
+type Generator func([]byte) (int, error)
+
+// BytesGenerator is the default bytes generator
+var BytesGenerator Generator = rand.Read
+
+func initMasks(params ...int) []uint {
+	var size int
+	if len(params) == 0 {
+		size = defaultMaskSize
+	} else {
+		size = params[0]
+	}
+	masks := make([]uint, size)
+	for i := 0; i < size; i++ {
+		shift := 3 + i
+		masks[i] = (2 << uint(shift)) - 1
+	}
+	return masks
+}
+
+func getMask(alphabet string, masks []uint) int {
+	for i := 0; i < len(masks); i++ {
+		curr := int(masks[i])
+		if curr >= len(alphabet)-1 {
+			return curr
+		}
+	}
+	return 0
+}
+
+// GenerateUID is a low-level function to change alphabet and ID size.
+func GenerateUID(alphabet string, size int) (string, error) {
+	if len(alphabet) == 0 || len(alphabet) > 255 {
+		return "", fmt.Errorf("alphabet must not empty and contain no more than 255 chars. Current len is %d", len(alphabet))
+	}
+	if size <= 0 {
+		return "", fmt.Errorf("size must be positive integer")
+	}
+
+	masks := initMasks(size)
+	mask := getMask(alphabet, masks)
+	ceilArg := 1.6 * float64(mask*size) / float64(len(alphabet))
+	step := int(math.Ceil(ceilArg))
+
+	id := make([]byte, size)
+	bytes := make([]byte, step)
+	for j := 0; ; {
+		_, err := BytesGenerator(bytes)
+		if err != nil {
+			return "", err
+		}
+		for i := 0; i < step; i++ {
+			currByte := bytes[i] & byte(mask)
+			if currByte < byte(len(alphabet)) {
+				id[j] = alphabet[currByte]
+				j++
+				if j == size {
+					return string(id[:size]), nil
+				}
+			}
+		}
+	}
+}
+
+// NewUID generates secure URL-friendly unique ID.
+func NewUID(param ...int) (string, error) {
+	var size int
+	if len(param) == 0 {
+		size = defaultSize
+	} else {
+		size = param[0]
+	}
+	bytes := make([]byte, size)
+	_, err := BytesGenerator(bytes)
+	if err != nil {
+		return "", err
+	}
+	id := make([]byte, size)
+	for i := 0; i < size; i++ {
+		id[i] = defaultAlphabet[bytes[i]&63]
+	}
+	return string(id[:size]), nil
+}