anchor.diff:      {ok, maps:get(external_url, Opts, undefined)};
   get_external_url(Id) ->
       apply_nkport(Id, fun get_external_url/1).
  +
  +%% @doc
  +-spec get_debug(id()|pid()|nkport()) ->
  +    {ok, boolean()} | error.
  +
  +get_debug(#nkport{opts=Opts}) ->
  +    {ok, maps:get(debug, Opts, false)};
  +get_debug(Id) ->
  +    apply_nkport(Id, fun get_debug/1).
   
   
   %% @private Finds a listening transport of Proto.
  
positive.code: get_id(#nkport{id=Id, class=Class}) ->
      {ok, Class, Id};
  get_id(Id) ->
      apply_nkport(Id, fun get_user_state/1).
  
  
  %% @doc
  
negative.code:     end.
  
  
  %% @doc Gets the current pids for a listener or connection
  -spec get_id_pids(id()|nkport()|pid()) ->
      [pid()].
  