From 4db4680452edea5cfbfa4c6ee86346d11f6a57ef Mon Sep 17 00:00:00 2001
From: "maximilian.schubert@telekom.de" <maximilian.schubert@telekom.de>
Date: Wed, 16 Nov 2022 12:14:05 +0100
Subject: [PATCH] new rand token func with crypto/rand + test

---
 helper/helper.go      | 30 ++++++++++++++++++------------
 helper/helper_test.go | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 12 deletions(-)
 create mode 100644 helper/helper_test.go

diff --git a/helper/helper.go b/helper/helper.go
index 81fe065..135f735 100644
--- a/helper/helper.go
+++ b/helper/helper.go
@@ -22,6 +22,7 @@
 package helper
 
 import (
+	"crypto/rand"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/base64"
@@ -30,10 +31,9 @@ import (
 	"hash/fnv"
 	"io/ioutil"
 	"log"
-	"math/rand"
+	"math/big"
 	"net"
 	"regexp"
-	"time"
 
 	"google.golang.org/grpc/credentials"
 )
@@ -117,19 +117,25 @@ const charset = "abcdefghijklmnopqrstuvwxyz" +
 	"ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
 	"0123456789"
 
-var seededRand *rand.Rand = rand.New(
-	rand.NewSource(time.Now().UnixNano()))
-
-func stringWithCharset(length int, charset string) string {
-	b := make([]byte, length)
-	for i := range b {
-		b[i] = charset[seededRand.Intn(len(charset))]
+func stringWithCharset(n int64, chars string) (string, error) {
+	ret := make([]byte, n)
+	for i := int64(0); i < n; i++ {
+		num, err := rand.Int(rand.Reader, big.NewInt(int64(len(chars))))
+		if err != nil {
+			return "", err
+		}
+		ret[i] = chars[num.Int64()]
 	}
-	return string(b)
+
+	return string(ret), nil
 }
 
-func GenerateRandomToken(length int) string {
-	return stringWithCharset(length, charset)
+func GenerateRandomToken(length int64) string {
+	token, err := stringWithCharset(length, charset)
+	if err != nil {
+		panic("Could not generate a random token, please check func GenerateRandomToken")
+	}
+	return token
 }
 
 //------------------
diff --git a/helper/helper_test.go b/helper/helper_test.go
new file mode 100644
index 0000000..43f505d
--- /dev/null
+++ b/helper/helper_test.go
@@ -0,0 +1,43 @@
+package helper
+
+import (
+	"fmt"
+	"testing"
+)
+
+func Test_stringWithCharset(t *testing.T) {
+	tests := []struct {
+		name    string
+		length  int64
+		charset string
+	}{
+		{
+			name:    "normal string",
+			length:  32,
+			charset: charset,
+		},
+		{
+			name:    "0 string",
+			length:  0,
+			charset: charset,
+		},
+		{
+			name:    "0 charset",
+			length:  32,
+			charset: "1",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			str, err := stringWithCharset(tt.length, tt.charset)
+			fmt.Printf("%v\n", str)
+			if err != nil {
+				t.Error("stringWithCharset with errors")
+			}
+			if len(str) != int(tt.length) {
+				t.Errorf("Length of string is not as eypexted: %v != %v", len(str), tt.length)
+			}
+		})
+	}
+}