fix occasional panic on registration

GenerateRandomStringDNSSafe will panic occasionally if the random base64
string contains too many - and _ due to the replacement. Fix by looping.

utils.go

@@ -325,11 +325,17 @@ func GenerateRandomStringURLSafe(n int) (string, error) {
 // number generator fails to function correctly, in which
 // case the caller should not continue.
 func GenerateRandomStringDNSSafe(n int) (string, error) {
-	str, err := GenerateRandomStringURLSafe(n)
-
+	var str string
+	var err error
+	for len(str) < n {
+		str, err = GenerateRandomStringURLSafe(n)
+		if err != nil {
+			return "", err
+		}
 		str = strings.ToLower(strings.ReplaceAll(strings.ReplaceAll(str, "_", ""), "-", ""))
+	}
 
-	return str[:n], err
+	return str[:n], nil
 }
 
 func IsStringInSlice(slice []string, str string) bool {

utils_test.go

@@ -185,3 +185,15 @@ func (s *Suite) TestGetAvailableIpMachineWithoutIP(c *check.C) {
 	c.Assert(len(ips2), check.Equals, 1)
 	c.Assert(ips2[0].String(), check.Equals, expected.String())
 }
+
+func (s *Suite) TestGenerateRandomStringDNSSafe(c *check.C) {
+	for i := 0; i < 100000; i++ {
+		str, err := GenerateRandomStringDNSSafe(8)
+		if err != nil {
+			c.Error(err)
+		}
+		if len(str) != 8 {
+			c.Error("invalid length", len(str), str)
+		}
+	}
+}