beego: improve the RandomCreateBytes #620

when rand.Read is failed. will use the math/rand to generate the rand
bytes

@@ -8,19 +8,33 @@ package utils
 
 import (
 	"crypto/rand"
+	r "math/rand"
+	"time"
 )
 
 // RandomCreateBytes generate random []byte by specify chars.
 func RandomCreateBytes(n int, alphabets ...byte) []byte {
 	const alphanum = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 	var bytes = make([]byte, n)
-	rand.Read(bytes)
+	var randby bool
+	if num, err := rand.Read(bytes); num != n || err != nil {
+		r.Seed(time.Now().UnixNano())
+		randby = true
+	}
 	for i, b := range bytes {
 		if len(alphabets) == 0 {
+			if randby {
+				bytes[i] = alphanum[r.Intn(len(alphanum))]
+			} else {
 				bytes[i] = alphanum[b%byte(len(alphanum))]
+			}
+		} else {
+			if randby {
+				bytes[i] = alphabets[r.Intn(len(alphabets))]
 			} else {
 				bytes[i] = alphabets[b%byte(len(alphabets))]
 			}
 		}
+	}
 	return bytes
 }