'Generate a response for the given name containing the given result
records, or a failure if there are no result records.
@param name: The DNS name the response is for.
@type name: C{str}
@param records: A tuple of L{dns.RRHeader} instances giving the results
that will go into the response.
@return: A L{Deferred} which will fire with a three-tuple of result
records, authority records, and additional records, or which will
fail with L{dns.DomainError} if there are no result records.'

def _respond(self, name, records):

    if records:
        return defer.succeed((records, (), ()))
    return defer.fail(failure.Failure(dns.DomainError(name)))
