code: func SpecificDC(dc string, tlsWrap DCWrapper) Wrapper {
  	if tlsWrap == nil {
  		return nil
  	}
  	return func(conn net.Conn) (net.Conn, error) {
  		return tlsWrap(dc, conn)
  	}
  }
docs: // SpecificDC is used to invoke a static datacenter
  // and turns a DCWrapper into a Wrapper type.