return nil, newDNSError(mapErr(ctx.Err()), name, "")
	}
}

func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
	if systemConf().mustUseGoResolver(r) {
		return lookupPortMap(network, service)
	}

	// TODO(bradfitz): finish ctx plumbing
	if err := acquireThread(ctx); err != nil {
		return 0, &DNSError{
			Name:      network + "/" + service,
			Err:       mapErr(err).Error(),

// "mobility-header", so we use that length, plus some slop in case
// something longer is added in the future.
const maxPortBufSize = len("mobility-header") + 10

func lookupPortMap(network, service string) (port int, error error) {
	switch network {
	case "ip": // no hints
		if p, err := lookupPortMapWithNetwork("tcp", "ip", service); err == nil {
			return p, nil
		}