anchor.diff:                  grpc_metadata :: map() | undefined,
                   endpoints :: [uri_string:uri_map()]}).
   
  +%% @doc Initialize the exporter based on the provided configuration.
   init(Opts0) ->
       Opts1 = merge_with_environment(Opts0),
       Endpoints = endpoints(maps:get(endpoints, Opts1, ?DEFAULT_ENDPOINTS)),
  
positive.code:                         protocol=http_json}}
      end.
  
  export(_Tab, _Resource, #state{protocol=http_json}) ->
      {error, unimplemented};
  export(Tab, Resource, #state{protocol=http_protobuf,
  
negative.code:             error
      end.
  
  %% @doc Shutdown the exporter.
  shutdown(#state{channel_pid=undefined}) ->
      ok;
  shutdown(#state{channel_pid=Pid}) ->
  