src/net/lookup_windows.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package net

 import (
 	"os"
 	"runtime"
 	"syscall"
 	"unsafe"
 )

 var (
 	lookupPort = oldLookupPort
 	lookupIP   = oldLookupIP
 )

 func getprotobyname(name string) (proto int, err error) {
 	p, err := syscall.GetProtoByName(name)
 	if err != nil {
 		return 0, os.NewSyscallError("GetProtoByName", err)
 	}
 	return int(p.Proto), nil
 }

 // lookupProtocol looks up IP protocol name and returns correspondent protocol number.
 func lookupProtocol(name string) (proto int, err error) {
 	// GetProtoByName return value is stored in thread local storage.
 	// Start new os thread before the call to prevent races.
 	type result struct {
 		proto int
 		err   error
 	}
 	ch := make(chan result)
 	go func() {
 		acquireThread()
 		defer releaseThread()
 		runtime.LockOSThread()
 		defer runtime.UnlockOSThread()
 		proto, err := getprotobyname(name)
 		ch <- result{proto: proto, err: err}
 	}()
 	r := <-ch
 	if r.err != nil {
 		if proto, ok := protocols[name]; ok {
 			return proto, nil
 		}
 	}
 	return r.proto, r.err
 }

 func lookupHost(name string) (addrs []string, err error) {
 	ips, err := LookupIP(name)
 	if err != nil {
 		return
 	}
 	addrs = make([]string, 0, len(ips))
 	for _, ip := range ips {
 		addrs = append(addrs, ip.String())
 	}
 	return
 }

 func gethostbyname(name string) (addrs []IP, err error) {
 	// caller already acquired thread
 	h, err := syscall.GetHostByName(name)
 	if err != nil {
 		return nil, os.NewSyscallError("GetHostByName", err)
 	}
 	switch h.AddrType {
 	case syscall.AF_INET:
 		i := 0
 		addrs = make([]IP, 100) // plenty of room to grow
 		for p := (*[100](*[4]byte))(unsafe.Pointer(h.AddrList)); i < cap(addrs) && p[i] != nil; i++ {
 			addrs[i] = IPv4(p[i][0], p[i][1], p[i][2], p[i][3])
 		}
 		addrs = addrs[0:i]
 	default: // TODO(vcc): Implement non IPv4 address lookups.
 		return nil, os.NewSyscallError("LookupIP", syscall.EWINDOWS)
 	}
 	return addrs, nil
 }

 func oldLookupIP(name string) (addrs []IP, err error) {
 	// GetHostByName return value is stored in thread local storage.
 	// Start new os thread before the call to prevent races.
 	type result struct {
 		addrs []IP
 		err   error
 	}
 	ch := make(chan result)
 	go func() {
 		acquireThread()
 		defer releaseThread()
 		runtime.LockOSThread()
 		defer runtime.UnlockOSThread()
 		addrs, err := gethostbyname(name)
 		ch <- result{addrs: addrs, err: err}
 	}()
 	r := <-ch
 	return r.addrs, r.err
 }

 func newLookupIP(name string) (addrs []IP, err error) {
 	acquireThread()
 	defer releaseThread()
 	hints := syscall.AddrinfoW{
 		Family:   syscall.AF_UNSPEC,
 		Socktype: syscall.SOCK_STREAM,
 		Protocol: syscall.IPPROTO_IP,
 	}
 	var result *syscall.AddrinfoW
 	e := syscall.GetAddrInfoW(syscall.StringToUTF16Ptr(name), nil, &hints, &result)
 	if e != nil {
 		return nil, os.NewSyscallError("GetAddrInfoW", e)
 	}
 	defer syscall.FreeAddrInfoW(result)
 	addrs = make([]IP, 0, 5)
 	for ; result != nil; result = result.Next {
 		addr := unsafe.Pointer(result.Addr)
 		switch result.Family {
 		case syscall.AF_INET:
 			a := (*syscall.RawSockaddrInet4)(addr).Addr
 			addrs = append(addrs, IPv4(a[0], a[1], a[2], a[3]))
 		case syscall.AF_INET6:
 			a := (*syscall.RawSockaddrInet6)(addr).Addr
 			addrs = append(addrs, IP{a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], a[13], a[14], a[15]})
 		default:
 			return nil, os.NewSyscallError("LookupIP", syscall.EWINDOWS)
 		}
 	}
 	return addrs, nil
 }

 func getservbyname(network, service string) (port int, err error) {
 	acquireThread()
 	defer releaseThread()
 	switch network {
 	case "tcp4", "tcp6":
 		network = "tcp"
 	case "udp4", "udp6":
 		network = "udp"
 	}
 	s, err := syscall.GetServByName(service, network)
 	if err != nil {
 		return 0, os.NewSyscallError("GetServByName", err)
 	}
 	return int(syscall.Ntohs(s.Port)), nil
 }

 func oldLookupPort(network, service string) (port int, err error) {
 	// GetServByName return value is stored in thread local storage.
 	// Start new os thread before the call to prevent races.
 	type result struct {
 		port int
 		err  error
 	}
 	ch := make(chan result)
 	go func() {
 		acquireThread()
 		defer releaseThread()
 		runtime.LockOSThread()
 		defer runtime.UnlockOSThread()
 		port, err := getservbyname(network, service)
 		ch <- result{port: port, err: err}
 	}()
 	r := <-ch
 	return r.port, r.err
 }

 func newLookupPort(network, service string) (port int, err error) {
 	acquireThread()
 	defer releaseThread()
 	var stype int32
 	switch network {
 	case "tcp4", "tcp6":
 		stype = syscall.SOCK_STREAM
 	case "udp4", "udp6":
 		stype = syscall.SOCK_DGRAM
 	}
 	hints := syscall.AddrinfoW{
 		Family:   syscall.AF_UNSPEC,
 		Socktype: stype,
 		Protocol: syscall.IPPROTO_IP,
 	}
 	var result *syscall.AddrinfoW
 	e := syscall.GetAddrInfoW(nil, syscall.StringToUTF16Ptr(service), &hints, &result)
 	if e != nil {
 		return 0, os.NewSyscallError("GetAddrInfoW", e)
 	}
 	defer syscall.FreeAddrInfoW(result)
 	if result == nil {
 		return 0, os.NewSyscallError("LookupPort", syscall.EINVAL)
 	}
 	addr := unsafe.Pointer(result.Addr)
 	switch result.Family {
 	case syscall.AF_INET:
 		a := (*syscall.RawSockaddrInet4)(addr)
 		return int(syscall.Ntohs(a.Port)), nil
 	case syscall.AF_INET6:
 		a := (*syscall.RawSockaddrInet6)(addr)
 		return int(syscall.Ntohs(a.Port)), nil
 	}
 	return 0, os.NewSyscallError("LookupPort", syscall.EINVAL)
 }

 func lookupCNAME(name string) (cname string, err error) {
 	acquireThread()
 	defer releaseThread()
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(name, syscall.DNS_TYPE_CNAME, 0, nil, &r, nil)
 	// windows returns DNS_INFO_NO_RECORDS if there are no CNAME-s
 	if errno, ok := e.(syscall.Errno); ok && errno == syscall.DNS_INFO_NO_RECORDS {
 		// if there are no aliases, the canonical name is the input name
 		if name == "" || name[len(name)-1] != '.' {
 			return name + ".", nil
 		}
 		return name, nil
 	}
 	if e != nil {
 		return "", os.NewSyscallError("LookupCNAME", e)
 	}
 	defer syscall.DnsRecordListFree(r, 1)

 	resolved := resolveCNAME(syscall.StringToUTF16Ptr(name), r)
 	cname = syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(resolved))[:]) + "."
 	return
 }

 func lookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
 	acquireThread()
 	defer releaseThread()
 	var target string
 	if service == "" && proto == "" {
 		target = name
 	} else {
 		target = "_" + service + "._" + proto + "." + name
 	}
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(target, syscall.DNS_TYPE_SRV, 0, nil, &r, nil)
 	if e != nil {
 		return "", nil, os.NewSyscallError("LookupSRV", e)
 	}
 	defer syscall.DnsRecordListFree(r, 1)

 	addrs = make([]*SRV, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_SRV, target) {
 		v := (*syscall.DNSSRVData)(unsafe.Pointer(&p.Data[0]))
 		addrs = append(addrs, &SRV{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Target))[:]), v.Port, v.Priority, v.Weight})
 	}
 	byPriorityWeight(addrs).sort()
 	return name, addrs, nil
 }

 func lookupMX(name string) (mx []*MX, err error) {
 	acquireThread()
 	defer releaseThread()
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(name, syscall.DNS_TYPE_MX, 0, nil, &r, nil)
 	if e != nil {
 		return nil, os.NewSyscallError("LookupMX", e)
 	}
 	defer syscall.DnsRecordListFree(r, 1)

 	mx = make([]*MX, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_MX, name) {
 		v := (*syscall.DNSMXData)(unsafe.Pointer(&p.Data[0]))
 		mx = append(mx, &MX{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.NameExchange))[:]) + ".", v.Preference})
 	}
 	byPref(mx).sort()
 	return mx, nil
 }

 func lookupNS(name string) (ns []*NS, err error) {
 	acquireThread()
 	defer releaseThread()
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(name, syscall.DNS_TYPE_NS, 0, nil, &r, nil)
 	if e != nil {
 		return nil, os.NewSyscallError("LookupNS", e)
 	}
 	defer syscall.DnsRecordListFree(r, 1)

 	ns = make([]*NS, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_NS, name) {
 		v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
 		ns = append(ns, &NS{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]) + "."})
 	}
 	return ns, nil
 }

 func lookupTXT(name string) (txt []string, err error) {
 	acquireThread()
 	defer releaseThread()
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(name, syscall.DNS_TYPE_TEXT, 0, nil, &r, nil)
 	if e != nil {
 		return nil, os.NewSyscallError("LookupTXT", e)
 	}
 	defer syscall.DnsRecordListFree(r, 1)

 	txt = make([]string, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_TEXT, name) {
 		d := (*syscall.DNSTXTData)(unsafe.Pointer(&p.Data[0]))
 		for _, v := range (*[1 << 10]*uint16)(unsafe.Pointer(&(d.StringArray[0])))[:d.StringCount] {
 			s := syscall.UTF16ToString((*[1 << 20]uint16)(unsafe.Pointer(v))[:])
 			txt = append(txt, s)
 		}
 	}
 	return
 }

 func lookupAddr(addr string) (name []string, err error) {
 	acquireThread()
 	defer releaseThread()
 	arpa, err := reverseaddr(addr)
 	if err != nil {
 		return nil, err
 	}
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(arpa, syscall.DNS_TYPE_PTR, 0, nil, &r, nil)
 	if e != nil {
 		return nil, os.NewSyscallError("LookupAddr", e)
 	}
 	defer syscall.DnsRecordListFree(r, 1)

 	name = make([]string, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_PTR, arpa) {
 		v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
 		name = append(name, syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]))
 	}
 	return name, nil
 }

 const dnsSectionMask = 0x0003

 // returns only results applicable to name and resolves CNAME entries
 func validRecs(r *syscall.DNSRecord, dnstype uint16, name string) []*syscall.DNSRecord {
 	cname := syscall.StringToUTF16Ptr(name)
 	if dnstype != syscall.DNS_TYPE_CNAME {
 		cname = resolveCNAME(cname, r)
 	}
 	rec := make([]*syscall.DNSRecord, 0, 10)
 	for p := r; p != nil; p = p.Next {
 		if p.Dw&dnsSectionMask != syscall.DnsSectionAnswer {
 			continue
 		}
 		if p.Type != dnstype {
 			continue
 		}
 		if !syscall.DnsNameCompare(cname, p.Name) {
 			continue
 		}
 		rec = append(rec, p)
 	}
 	return rec
 }

 // returns the last CNAME in chain
 func resolveCNAME(name *uint16, r *syscall.DNSRecord) *uint16 {
 	// limit cname resolving to 10 in case of a infinite CNAME loop
 Cname:
 	for cnameloop := 0; cnameloop < 10; cnameloop++ {
 		for p := r; p != nil; p = p.Next {
 			if p.Dw&dnsSectionMask != syscall.DnsSectionAnswer {
 				continue
 			}
 			if p.Type != syscall.DNS_TYPE_CNAME {
 				continue
 			}
 			if !syscall.DnsNameCompare(name, p.Name) {
 				continue
 			}
 			name = (*syscall.DNSPTRData)(unsafe.Pointer(&r.Data[0])).Host
 			continue Cname
 		}
 		break
 	}
 	return name
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package net

	import (
	"os"
	"runtime"
	"syscall"
	"unsafe"
	)

	var (
	lookupPort = oldLookupPort
	lookupIP = oldLookupIP
	)

	func getprotobyname(name string) (proto int, err error) {
	p, err := syscall.GetProtoByName(name)
	if err != nil {
	return 0, os.NewSyscallError("GetProtoByName", err)
	}
	return int(p.Proto), nil
	}

	// lookupProtocol looks up IP protocol name and returns correspondent protocol number.
	func lookupProtocol(name string) (proto int, err error) {
	// GetProtoByName return value is stored in thread local storage.
	// Start new os thread before the call to prevent races.
	type result struct {
	proto int
	err error
	}
	ch := make(chan result)
	go func() {
	acquireThread()
	defer releaseThread()
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()
	proto, err := getprotobyname(name)
	ch <- result{proto: proto, err: err}
	}()
	r := <-ch
	if r.err != nil {
	if proto, ok := protocols[name]; ok {
	return proto, nil
	}
	}
	return r.proto, r.err
	}

	func lookupHost(name string) (addrs []string, err error) {
	ips, err := LookupIP(name)
	if err != nil {
	return
	}
	addrs = make([]string, 0, len(ips))
	for _, ip := range ips {
	addrs = append(addrs, ip.String())
	}
	return
	}

	func gethostbyname(name string) (addrs []IP, err error) {
	// caller already acquired thread
	h, err := syscall.GetHostByName(name)
	if err != nil {
	return nil, os.NewSyscallError("GetHostByName", err)
	}
	switch h.AddrType {
	case syscall.AF_INET:
	i := 0
	addrs = make([]IP, 100) // plenty of room to grow
	for p := ([100]([4]byte))(unsafe.Pointer(h.AddrList)); i < cap(addrs) && p[i] != nil; i++ {
	addrs[i] = IPv4(p[i][0], p[i][1], p[i][2], p[i][3])
	}
	addrs = addrs[0:i]
	default: // TODO(vcc): Implement non IPv4 address lookups.
	return nil, os.NewSyscallError("LookupIP", syscall.EWINDOWS)
	}
	return addrs, nil
	}

	func oldLookupIP(name string) (addrs []IP, err error) {
	// GetHostByName return value is stored in thread local storage.
	// Start new os thread before the call to prevent races.
	type result struct {
	addrs []IP
	err error
	}
	ch := make(chan result)
	go func() {
	acquireThread()
	defer releaseThread()
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()
	addrs, err := gethostbyname(name)
	ch <- result{addrs: addrs, err: err}
	}()
	r := <-ch
	return r.addrs, r.err
	}

	func newLookupIP(name string) (addrs []IP, err error) {
	acquireThread()
	defer releaseThread()
	hints := syscall.AddrinfoW{
	Family: syscall.AF_UNSPEC,
	Socktype: syscall.SOCK_STREAM,
	Protocol: syscall.IPPROTO_IP,
	}
	var result *syscall.AddrinfoW
	e := syscall.GetAddrInfoW(syscall.StringToUTF16Ptr(name), nil, &hints, &result)
	if e != nil {
	return nil, os.NewSyscallError("GetAddrInfoW", e)
	}
	defer syscall.FreeAddrInfoW(result)
	addrs = make([]IP, 0, 5)
	for ; result != nil; result = result.Next {
	addr := unsafe.Pointer(result.Addr)
	switch result.Family {
	case syscall.AF_INET:
	a := (*syscall.RawSockaddrInet4)(addr).Addr
	addrs = append(addrs, IPv4(a[0], a[1], a[2], a[3]))
	case syscall.AF_INET6:
	a := (*syscall.RawSockaddrInet6)(addr).Addr
	addrs = append(addrs, IP{a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], a[13], a[14], a[15]})
	default:
	return nil, os.NewSyscallError("LookupIP", syscall.EWINDOWS)
	}
	}
	return addrs, nil
	}

	func getservbyname(network, service string) (port int, err error) {
	acquireThread()
	defer releaseThread()
	switch network {
	case "tcp4", "tcp6":
	network = "tcp"
	case "udp4", "udp6":
	network = "udp"
	}
	s, err := syscall.GetServByName(service, network)
	if err != nil {
	return 0, os.NewSyscallError("GetServByName", err)
	}
	return int(syscall.Ntohs(s.Port)), nil
	}

	func oldLookupPort(network, service string) (port int, err error) {
	// GetServByName return value is stored in thread local storage.
	// Start new os thread before the call to prevent races.
	type result struct {
	port int
	err error
	}
	ch := make(chan result)
	go func() {
	acquireThread()
	defer releaseThread()
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()
	port, err := getservbyname(network, service)
	ch <- result{port: port, err: err}
	}()
	r := <-ch
	return r.port, r.err
	}

	func newLookupPort(network, service string) (port int, err error) {
	acquireThread()
	defer releaseThread()
	var stype int32
	switch network {
	case "tcp4", "tcp6":
	stype = syscall.SOCK_STREAM
	case "udp4", "udp6":
	stype = syscall.SOCK_DGRAM
	}
	hints := syscall.AddrinfoW{
	Family: syscall.AF_UNSPEC,
	Socktype: stype,
	Protocol: syscall.IPPROTO_IP,
	}
	var result *syscall.AddrinfoW
	e := syscall.GetAddrInfoW(nil, syscall.StringToUTF16Ptr(service), &hints, &result)
	if e != nil {
	return 0, os.NewSyscallError("GetAddrInfoW", e)
	}
	defer syscall.FreeAddrInfoW(result)
	if result == nil {
	return 0, os.NewSyscallError("LookupPort", syscall.EINVAL)
	}
	addr := unsafe.Pointer(result.Addr)
	switch result.Family {
	case syscall.AF_INET:
	a := (*syscall.RawSockaddrInet4)(addr)
	return int(syscall.Ntohs(a.Port)), nil
	case syscall.AF_INET6:
	a := (*syscall.RawSockaddrInet6)(addr)
	return int(syscall.Ntohs(a.Port)), nil
	}
	return 0, os.NewSyscallError("LookupPort", syscall.EINVAL)
	}

	func lookupCNAME(name string) (cname string, err error) {
	acquireThread()
	defer releaseThread()
	var r *syscall.DNSRecord
	e := syscall.DnsQuery(name, syscall.DNS_TYPE_CNAME, 0, nil, &r, nil)
	// windows returns DNS_INFO_NO_RECORDS if there are no CNAME-s
	if errno, ok := e.(syscall.Errno); ok && errno == syscall.DNS_INFO_NO_RECORDS {
	// if there are no aliases, the canonical name is the input name
	if name == "" \|\| name[len(name)-1] != '.' {
	return name + ".", nil
	}
	return name, nil
	}
	if e != nil {
	return "", os.NewSyscallError("LookupCNAME", e)
	}
	defer syscall.DnsRecordListFree(r, 1)

	resolved := resolveCNAME(syscall.StringToUTF16Ptr(name), r)
	cname = syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(resolved))[:]) + "."
	return
	}

	func lookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
	acquireThread()
	defer releaseThread()
	var target string
	if service == "" && proto == "" {
	target = name
	} else {
	target = "_" + service + "._" + proto + "." + name
	}
	var r *syscall.DNSRecord
	e := syscall.DnsQuery(target, syscall.DNS_TYPE_SRV, 0, nil, &r, nil)
	if e != nil {
	return "", nil, os.NewSyscallError("LookupSRV", e)
	}
	defer syscall.DnsRecordListFree(r, 1)

	addrs = make([]*SRV, 0, 10)
	for _, p := range validRecs(r, syscall.DNS_TYPE_SRV, target) {
	v := (*syscall.DNSSRVData)(unsafe.Pointer(&p.Data[0]))
	addrs = append(addrs, &SRV{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Target))[:]), v.Port, v.Priority, v.Weight})
	}
	byPriorityWeight(addrs).sort()
	return name, addrs, nil
	}

	func lookupMX(name string) (mx []*MX, err error) {
	acquireThread()
	defer releaseThread()
	var r *syscall.DNSRecord
	e := syscall.DnsQuery(name, syscall.DNS_TYPE_MX, 0, nil, &r, nil)
	if e != nil {
	return nil, os.NewSyscallError("LookupMX", e)
	}
	defer syscall.DnsRecordListFree(r, 1)

	mx = make([]*MX, 0, 10)
	for _, p := range validRecs(r, syscall.DNS_TYPE_MX, name) {
	v := (*syscall.DNSMXData)(unsafe.Pointer(&p.Data[0]))
	mx = append(mx, &MX{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.NameExchange))[:]) + ".", v.Preference})
	}
	byPref(mx).sort()
	return mx, nil
	}

	func lookupNS(name string) (ns []*NS, err error) {
	acquireThread()
	defer releaseThread()
	var r *syscall.DNSRecord
	e := syscall.DnsQuery(name, syscall.DNS_TYPE_NS, 0, nil, &r, nil)
	if e != nil {
	return nil, os.NewSyscallError("LookupNS", e)
	}
	defer syscall.DnsRecordListFree(r, 1)

	ns = make([]*NS, 0, 10)
	for _, p := range validRecs(r, syscall.DNS_TYPE_NS, name) {
	v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
	ns = append(ns, &NS{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]) + "."})
	}
	return ns, nil
	}

	func lookupTXT(name string) (txt []string, err error) {
	acquireThread()
	defer releaseThread()
	var r *syscall.DNSRecord
	e := syscall.DnsQuery(name, syscall.DNS_TYPE_TEXT, 0, nil, &r, nil)
	if e != nil {
	return nil, os.NewSyscallError("LookupTXT", e)
	}
	defer syscall.DnsRecordListFree(r, 1)

	txt = make([]string, 0, 10)
	for _, p := range validRecs(r, syscall.DNS_TYPE_TEXT, name) {
	d := (*syscall.DNSTXTData)(unsafe.Pointer(&p.Data[0]))
	for _, v := range ([1 << 10]uint16)(unsafe.Pointer(&(d.StringArray[0])))[:d.StringCount] {
	s := syscall.UTF16ToString((*[1 << 20]uint16)(unsafe.Pointer(v))[:])
	txt = append(txt, s)
	}
	}
	return
	}

	func lookupAddr(addr string) (name []string, err error) {
	acquireThread()
	defer releaseThread()
	arpa, err := reverseaddr(addr)
	if err != nil {
	return nil, err
	}
	var r *syscall.DNSRecord
	e := syscall.DnsQuery(arpa, syscall.DNS_TYPE_PTR, 0, nil, &r, nil)
	if e != nil {
	return nil, os.NewSyscallError("LookupAddr", e)
	}
	defer syscall.DnsRecordListFree(r, 1)

	name = make([]string, 0, 10)
	for _, p := range validRecs(r, syscall.DNS_TYPE_PTR, arpa) {
	v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
	name = append(name, syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]))
	}
	return name, nil
	}

	const dnsSectionMask = 0x0003

	// returns only results applicable to name and resolves CNAME entries
	func validRecs(r syscall.DNSRecord, dnstype uint16, name string) []syscall.DNSRecord {
	cname := syscall.StringToUTF16Ptr(name)
	if dnstype != syscall.DNS_TYPE_CNAME {
	cname = resolveCNAME(cname, r)
	}
	rec := make([]*syscall.DNSRecord, 0, 10)
	for p := r; p != nil; p = p.Next {
	if p.Dw&dnsSectionMask != syscall.DnsSectionAnswer {
	continue
	}
	if p.Type != dnstype {
	continue
	}
	if !syscall.DnsNameCompare(cname, p.Name) {
	continue
	}
	rec = append(rec, p)
	}
	return rec
	}

	// returns the last CNAME in chain
	func resolveCNAME(name uint16, r syscall.DNSRecord) *uint16 {
	// limit cname resolving to 10 in case of a infinite CNAME loop
	Cname:
	for cnameloop := 0; cnameloop < 10; cnameloop++ {
	for p := r; p != nil; p = p.Next {
	if p.Dw&dnsSectionMask != syscall.DnsSectionAnswer {
	continue
	}
	if p.Type != syscall.DNS_TYPE_CNAME {
	continue
	}
	if !syscall.DnsNameCompare(name, p.Name) {
	continue
	}
	name = (*syscall.DNSPTRData)(unsafe.Pointer(&r.Data[0])).Host
	continue Cname
	}
	break
	}
	return name
	}