anchor.diff:  -export([get_id_pids/1, send/2, send/3]).
   -export([get_listening/2, get_listening/3, is_local/1, is_local/2, is_local_ip/1]).
   -export([get_nkport/1, get_local/1, get_remote/1, get_remote_bin/1, get_local_bin/1,
  -         get_external_url/1]).
  +         get_external_url/1, get_debug/1]).
   -export([get_class/1, get_id/1, get_user_state/1]).
   
   -export_type([id/0, class/0, transport/0, protocol/0, nkport/0, nkconn/0]).
  
positive.code:     {ok, maps:get(external_url, Opts, undefined)};
  get_external_url(Id) ->
      apply_nkport(Id, fun get_external_url/1).
  
  
  %% @private Finds a listening transport of Proto.
  
negative.code:     end.
  
  
  %% @doc Gets the current pids for a listener or connection
  -spec get_id_pids(id()|nkport()|pid()) ->
      [pid()].
  