add IPVersion type to properly parse a 4 or 6

types/ip.go

@@ -5,6 +5,7 @@ import (
 	"database/sql/driver"
 	"fmt"
 	"net"
+	"strconv"
 )
 
 type (
@@ -12,6 +13,8 @@ type (
 	Subnet net.IPNet
 	// IP is used to parse an IP parameter.
 	IP net.IP
+	// IPVersion represents the two IP versions currently in use.
+	IPVersion int
 )
 
 // UnmarshalJSON parses a value into a subnet.
@@ -69,3 +72,16 @@ func (i *IP) UnmarshalJSON(in []byte) error {
 	*i = IP(ip)
 	return nil
 }
+
+// UnmarshalJSON parses the incoming version from json.
+func (v *IPVersion) UnmarshalJSON(in []byte) error {
+	raw, err := strconv.Atoi(string(in))
+	if err != nil {
+		return fmt.Errorf("can't parse ip version: %#v", err)
+	}
+	if raw != 4 && raw != 6 {
+		return fmt.Errorf("only version 4 and 6 are supported")
+	}
+	*v = IPVersion(raw)
+	return nil
+}