class Protobuf::Rpc::Connectors::EventMachine

don't want to swallow the black holes.
otherwise implement one here that simply throws an exception, since we
If a failure callback was set, just use that as a direct assignment

Returns a callable that ensures any errors will be returned to the client

def ensure_cb
  @ensure_cb ||= (@failure_cb || lambda { |error| raise "#{error.code.name}: #{error.message}" })
end