anchor.diff:      {Reply, Req0, State}.
   
   
  --spec from_json(cowboy:req(), state()) ->
  -    {boolean(), cowboy:req(), state()}.
  +-spec from_json(cowboy_req:req(), state()) ->
  +    {boolean(), cowboy_req:req(), state()}.
   from_json(Req, #state{}) ->
       case get_vars_from_body(Req) of
           {ok, State, Req2} ->
  
positive.code:     end.
  
  %% internal function
  -spec get_vars_from_body(cowboy:req()) ->
      {ok | error, state() | bad_request, cowboy:req()}.
  get_vars_from_body(Req) ->
      {ok, Body, Req2} = cowboy_req:body(Req),
      try
  
negative.code: 
  -type state() :: #state{}.
  
  -spec trails() -> [trails:trail()] .
  trails() ->
      Metadata =
      #{get =>
  