Merge pull request #8 from riskimidiw/feature/random-string

feature: create GenerateRandomAlphanumeric

CHANGELOG.md

@@ -1,5 +1,11 @@
 # go-utils
 
+<a name="v1.4.0"></a>
+## [v1.4.0] - 2020-06-11
+### New Features
+- create GenerateRandomAlphanumeric
+
+
 <a name="v1.3.1"></a>
 ## [v1.3.1] - 2020-04-02
 ### Fixes
@@ -33,7 +39,8 @@
 - init go-utils
 
 
-[Unreleased]: https://github.com/kumparan/kumnats/compare/v1.3.1...HEAD
+[Unreleased]: https://github.com/kumparan/kumnats/compare/v1.4.0...HEAD
+[v1.4.0]: https://github.com/kumparan/kumnats/compare/v1.3.1...v1.4.0
 [v1.3.1]: https://github.com/kumparan/kumnats/compare/v1.3.0...v1.3.1
 [v1.3.0]: https://github.com/kumparan/kumnats/compare/v1.2.0...v1.3.0
 [v1.2.0]: https://github.com/kumparan/kumnats/compare/v1.1.1...v1.2.0

rand.go

@@ -1,8 +1,22 @@
 package utils
 
 import (
-	"crypto/rand"
+	cryptoRand "crypto/rand"
 	"encoding/base64"
+	mathRand "math/rand"
+	"strings"
+	"time"
+)
+
+const (
+	letterBytes   = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	letterIdxBits = 6
+	letterIdxMask = 1<<letterIdxBits - 1
+	letterIdxMax  = 63 / letterIdxBits
+)
+
+var (
+	src = mathRand.NewSource(time.Now().UnixNano())
 )
 
 // GenerateRandomBytes adapted from https://elithrar.github.io/article/generating-secure-random-numbers-crypto-rand/
@@ -12,7 +26,7 @@ import (
 // case the caller should not continue.
 func GenerateRandomBytes(n int) ([]byte, error) {
 	b := make([]byte, n)
-	_, err := rand.Read(b)
+	_, err := cryptoRand.Read(b)
 	// Note that err == nil only if we read len(b) bytes.
 	if err != nil {
 		return nil, err
@@ -46,3 +60,23 @@ func GenerateRandomStringURLSafe(n int) (string, error) {
 	b, err := GenerateRandomBytes(n)
 	return base64.URLEncoding.EncodeToString(b), err
 }
+
+// GenerateRandomAlphanumeric Generate random alphanumeric character adapted from
+// https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-go
+func GenerateRandomAlphanumeric(n int) string {
+	sb := strings.Builder{}
+	sb.Grow(n)
+	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 < len(letterBytes) {
+			sb.WriteByte(letterBytes[idx])
+			i--
+		}
+		cache >>= letterIdxBits
+		remain--
+	}
+
+	return sb.String()
+}

rand_test.go

@@ -0,0 +1,21 @@
+package utils
+
+import "testing"
+
+func BenchmarkGenerateRandomString(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_, _ = GenerateRandomString(100)
+	}
+}
+
+func BenchmarkGenerateRandomAlphanumeric(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_ = GenerateRandomAlphanumeric(100)
+	}
+}
+
+func BenchmarkGenerateRandomStringURLSafe(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_, _ = GenerateRandomStringURLSafe(100)
+	}
+}