method private make_filter acl_fqp =
       let filter = Hashtbl.create 16 in
       try 
         let acl_file = open_in acl_fqp in
         let rec read_acl cur_filter = 
           let next_item = 
             try Some(input_line acl_file)
             with _ -> None
           in
             match next_item with
               | None -> close_in acl_file;cur_filter
               | Some(item) -> 
                   Hashtbl.add cur_filter item true;
                   read_acl cur_filter
         in
           Some(read_acl filter)
       with _ ->
         None