Define constants for sign and revoke actions

datastructures/common.go

@@ -4,12 +4,20 @@ import "encoding/binary"
 
 type Action uint8
 
-const ActionNul = Action(0)
+const (
+	ActionNul = Action(0)
+	ActionSign = Action(1)
+	ActionRevoke = Action(2)
+)
 
 func (a Action) String() string {
 	switch a {
 	case ActionNul:
 		return "NUL"
+    case ActionSign:
+        return "SIGN"
+    case ActionRevoke:
+        return "REVOKE"
 	default:
 		return "unknown"
 	}