Add random string

utils/string.go

@@ -0,0 +1,43 @@
+package utils
+
+import (
+	"math/rand"
+	"strings"
+	"time"
+	"unsafe"
+)
+
+var randSource rand.Source
+
+const (
+	bits     = 6
+	mask     = 1<<bits - 1
+	maxIndex = 63 / bits
+
+	characters = "abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ23456789"
+)
+
+func init() {
+	randSource = rand.NewSource(time.Now().UnixNano())
+}
+
+// RandString
+//   - param n: suggest at least 10 to avoid conflict
+//
+// referred to https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-go
+func RandString(n int) string {
+	b := make([]byte, n)
+	for i, cache, remain := n-1, randSource.Int63(), maxIndex; i >= 0; {
+		if remain == 0 {
+			cache, remain = randSource.Int63(), maxIndex
+		}
+		if idx := int(cache & mask); idx < len(characters) {
+			b[i] = characters[idx]
+			i--
+		}
+		cache >>= bits
+		remain--
+	}
+
+	return strings.ToLower(*(*string)(unsafe.Pointer(&b)))
+}

utils/string_test.go

@@ -0,0 +1,12 @@
+package utils
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRandString(t *testing.T) {
+	res := RandString(6)
+	assert.Equal(t, len(res), 6)
+}