anchor.diff:  %% Description: Handling call messages
   %% @hidden
   %%--------------------------------------------------------------------
  +handle_call(urls, _From, State) ->
  +    {reply, State#state.urls, State};
  +
   handle_call(_Msg, _From, State) ->
       {reply, {error, invalid_call}, State}.
   
  
positive.code: -export([start_link/0, init/1, handle_call/3, handle_cast/2, 
  	     handle_info/2, terminate/2, code_change/3]).
  
  -export([lookup/3, lookup_urls/0, list_diff/2, poll_shard_urls/0]).
  
  -include_lib("logplex.hrl").
  
  
negative.code:         {_RedisUrl, Pid} -> Pid;
          Other -> exit({shard_not_found, Other})
      end.
  
  urls() ->
      gen_server:call(?MODULE, urls).
  
  %%====================================================================
  %% gen_server callbacks
  