Requiem.handle_call

You're seeing just the callback handle_call, go back to Requiem module for more information.
Link to this callback

handle_call(request, from, conn, state)

Specs

handle_call(
  request :: term(),
  from :: pid(),
  conn :: Requiem.ConnectionState.t(),
  state :: any()
) ::
  {:noreply, Requiem.ConnectionState.t(), any()}
  | {:noreply, Requiem.ConnectionState.t(), any(), timeout() | :hibernate}
  | {:reply, any(), Requiem.ConnectionState.t(), any()}
  | {:reply, any(), Requiem.ConnectionState.t(), any(), timeout() | :hibernate}
  | {:stop, non_neg_integer(), atom()}