class Rack::Session::Abstract::Persisted

def prepare_session(req)
  session_was               = req.get_header RACK_SESSION
  session                   = session_class.new(self, req)
  req.set_header RACK_SESSION, session
  req.set_header RACK_SESSION_OPTIONS, @default_options.dup
  session.merge! session_was if session_was
end