Improved the selectable prefixlengths in dropdown

Author: wouterhhuisman

src/custom-surf/components/inputForms/SplitPrefix.tsx

@@ -83,11 +83,19 @@ export default class SplitPrefix extends React.PureComponent<IProps> {
     };
 
     render() {
+        // IPv4 subnet size should be between /32 and /12
+        // IPv6 subnet size should be between /128 and /32
         const { id, name, subnet, prefixlen, prefixMin, selectedSubnet } = this.props;
         const version = subnet.indexOf(":") === -1 ? 4 : 6;
-        const max_for_version = version === 4 ? 32 : 64;
+        const minPrefixLength = version === 4 ? 12 : 32;
+        const minimalSelectablePrefixLength = minPrefixLength > prefixMin ? minPrefixLength : prefixMin;
+        const maximalSelectablePrefixLength = version === 4 ? 32 : minimalSelectablePrefixLength + 12;
+
         const { desiredPrefixlen } = this.state;
-        const prefixlengths = range(max_for_version - prefixMin + 1).map((x) => prefixMin + x);
+        const prefixlengths = range(maximalSelectablePrefixLength - minimalSelectablePrefixLength + 1).map(
+            (x) => minimalSelectablePrefixLength + x
+        );
+
         const length_options: Option<number>[] = prefixlengths.map((pl) => ({ value: pl, label: pl.toString() }));
         const length_value = length_options.find((option) => option.value === desiredPrefixlen);