libgo/go/net/cgo_unix.go - gofrontend - Git at Google

 // Copyright 2011 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.

 // +build cgo,!netgo
 // +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris

 package net

 /*
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netdb.h>
 #include <unistd.h>
 #include <string.h>

 // If nothing else defined EAI_OVERFLOW, make sure it has a value.
 #ifndef EAI_OVERFLOW
 #define EAI_OVERFLOW -12
 #endif
 */

 import (
 	"context"
 	"syscall"
 	"unsafe"
 )

 //extern getaddrinfo
 func libc_getaddrinfo(node *byte, service *byte, hints *syscall.Addrinfo, res **syscall.Addrinfo) int32

 //extern freeaddrinfo
 func libc_freeaddrinfo(res *syscall.Addrinfo)

 //extern gai_strerror
 func libc_gai_strerror(errcode int) *byte

 // bytePtrToString takes a NUL-terminated array of bytes and convert
 // it to a Go string.
 func bytePtrToString(p *byte) string {
 	a := (*[10000]byte)(unsafe.Pointer(p))
 	i := 0
 	for a[i] != 0 {
 		i++
 	}
 	return string(a[:i])
 }

 // An addrinfoErrno represents a getaddrinfo, getnameinfo-specific
 // error number. It's a signed number and a zero value is a non-error
 // by convention.
 type addrinfoErrno int

 func (eai addrinfoErrno) Error() string   { return bytePtrToString(libc_gai_strerror(int(eai))) }
 func (eai addrinfoErrno) Temporary() bool { return eai == syscall.EAI_AGAIN }
 func (eai addrinfoErrno) Timeout() bool   { return false }

 type portLookupResult struct {
 	port int
 	err  error
 }

 type ipLookupResult struct {
 	addrs []IPAddr
 	cname string
 	err   error
 }

 type reverseLookupResult struct {
 	names []string
 	err   error
 }

 func cgoLookupHost(ctx context.Context, name string) (hosts []string, err error, completed bool) {
 	addrs, err, completed := cgoLookupIP(ctx, "ip", name)
 	for _, addr := range addrs {
 		hosts = append(hosts, addr.String())
 	}
 	return
 }

 func cgoLookupPort(ctx context.Context, network, service string) (port int, err error, completed bool) {
 	var hints syscall.Addrinfo
 	switch network {
 	case "": // no hints
 	case "tcp", "tcp4", "tcp6":
 		hints.Ai_socktype = syscall.SOCK_STREAM
 		hints.Ai_protocol = syscall.IPPROTO_TCP
 	case "udp", "udp4", "udp6":
 		hints.Ai_socktype = syscall.SOCK_DGRAM
 		hints.Ai_protocol = syscall.IPPROTO_UDP
 	default:
 		return 0, &DNSError{Err: "unknown network", Name: network + "/" + service}, true
 	}
 	switch ipVersion(network) {
 	case '4':
 		hints.Ai_family = syscall.AF_INET
 	case '6':
 		hints.Ai_family = syscall.AF_INET6
 	}
 	if ctx.Done() == nil {
 		port, err := cgoLookupServicePort(&hints, network, service)
 		return port, err, true
 	}
 	result := make(chan portLookupResult, 1)
 	go cgoPortLookup(result, &hints, network, service)
 	select {
 	case r := <-result:
 		return r.port, r.err, true
 	case <-ctx.Done():
 		// Since there isn't a portable way to cancel the lookup,
 		// we just let it finish and write to the buffered channel.
 		return 0, mapErr(ctx.Err()), false
 	}
 }

 func cgoLookupServicePort(hints *syscall.Addrinfo, network, service string) (port int, err error) {
 	s, err := syscall.BytePtrFromString(service)
 	if err != nil {
 		return 0, err
 	}
 	// Lowercase the service name in the memory passed to C.
 	for i := 0; i < len(service); i++ {
 		bp := (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(s)) + uintptr(i)))
 		*bp = lowerASCII(*bp)
 	}
 	var res *syscall.Addrinfo
 	syscall.Entersyscall()
 	gerrno := libc_getaddrinfo(nil, s, hints, &res)
 	syscall.Exitsyscall()
 	if gerrno != 0 {
 		isTemporary := false
 		switch gerrno {
 		case syscall.EAI_SYSTEM:
 			errno := syscall.GetErrno()
 			if errno == 0 { // see golang.org/issue/6232
 				errno = syscall.EMFILE
 			}
 			err = errno
 		default:
 			err = addrinfoErrno(gerrno)
 			isTemporary = addrinfoErrno(gerrno).Temporary()
 		}
 		return 0, &DNSError{Err: err.Error(), Name: network + "/" + service, IsTemporary: isTemporary}
 	}
 	defer libc_freeaddrinfo(res)

 	for r := res; r != nil; r = r.Ai_next {
 		switch r.Ai_family {
 		case syscall.AF_INET:
 			sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.Ai_addr))
 			p := (*[2]byte)(unsafe.Pointer(&sa.Port))
 			return int(p[0])<<8 | int(p[1]), nil
 		case syscall.AF_INET6:
 			sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.Ai_addr))
 			p := (*[2]byte)(unsafe.Pointer(&sa.Port))
 			return int(p[0])<<8 | int(p[1]), nil
 		}
 	}
 	return 0, &DNSError{Err: "unknown port", Name: network + "/" + service}
 }

 func cgoPortLookup(result chan<- portLookupResult, hints *syscall.Addrinfo, network, service string) {
 	port, err := cgoLookupServicePort(hints, network, service)
 	result <- portLookupResult{port, err}
 }

 func cgoLookupIPCNAME(network, name string) (addrs []IPAddr, cname string, err error) {
 	acquireThread()
 	defer releaseThread()

 	var hints syscall.Addrinfo
 	hints.Ai_flags = int32(cgoAddrInfoFlags)
 	hints.Ai_socktype = syscall.SOCK_STREAM
 	hints.Ai_family = syscall.AF_UNSPEC
 	switch ipVersion(network) {
 	case '4':
 		hints.Ai_family = syscall.AF_INET
 	case '6':
 		hints.Ai_family = syscall.AF_INET6
 	}

 	h := syscall.StringBytePtr(name)
 	var res *syscall.Addrinfo
 	syscall.Entersyscall()
 	gerrno := libc_getaddrinfo(h, nil, &hints, &res)
 	syscall.Exitsyscall()
 	if gerrno != 0 {
 		isErrorNoSuchHost := false
 		isTemporary := false
 		switch gerrno {
 		case syscall.EAI_SYSTEM:
 			errno := syscall.GetErrno()
 			if errno == 0 {
 				// err should not be nil, but sometimes getaddrinfo returns
 				// gerrno == C.EAI_SYSTEM with err == nil on Linux.
 				// The report claims that it happens when we have too many
 				// open files, so use syscall.EMFILE (too many open files in system).
 				// Most system calls would return ENFILE (too many open files),
 				// so at the least EMFILE should be easy to recognize if this
 				// comes up again. golang.org/issue/6232.
 				errno = syscall.EMFILE
 			}
 			err = errno
 		case syscall.EAI_NONAME:
 			err = errNoSuchHost
 			isErrorNoSuchHost = true
 		default:
 			err = addrinfoErrno(gerrno)
 			isTemporary = addrinfoErrno(gerrno).Temporary()
 		}

 		return nil, "", &DNSError{Err: err.Error(), Name: name, IsNotFound: isErrorNoSuchHost, IsTemporary: isTemporary}
 	}
 	defer libc_freeaddrinfo(res)

 	if res != nil {
 		cname = bytePtrToString((*byte)(unsafe.Pointer(res.Ai_canonname)))
 		if cname == "" {
 			cname = name
 		}
 		if len(cname) > 0 && cname[len(cname)-1] != '.' {
 			cname += "."
 		}
 	}
 	for r := res; r != nil; r = r.Ai_next {
 		// We only asked for SOCK_STREAM, but check anyhow.
 		if r.Ai_socktype != syscall.SOCK_STREAM {
 			continue
 		}
 		switch r.Ai_family {
 		case syscall.AF_INET:
 			sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.Ai_addr))
 			addr := IPAddr{IP: copyIP(sa.Addr[:])}
 			addrs = append(addrs, addr)
 		case syscall.AF_INET6:
 			sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.Ai_addr))
 			addr := IPAddr{IP: copyIP(sa.Addr[:]), Zone: zoneCache.name(int(sa.Scope_id))}
 			addrs = append(addrs, addr)
 		}
 	}
 	return addrs, cname, nil
 }

 func cgoIPLookup(result chan<- ipLookupResult, network, name string) {
 	addrs, cname, err := cgoLookupIPCNAME(network, name)
 	result <- ipLookupResult{addrs, cname, err}
 }

 func cgoLookupIP(ctx context.Context, network, name string) (addrs []IPAddr, err error, completed bool) {
 	if ctx.Done() == nil {
 		addrs, _, err = cgoLookupIPCNAME(network, name)
 		return addrs, err, true
 	}
 	result := make(chan ipLookupResult, 1)
 	go cgoIPLookup(result, network, name)
 	select {
 	case r := <-result:
 		return r.addrs, r.err, true
 	case <-ctx.Done():
 		return nil, mapErr(ctx.Err()), false
 	}
 }

 func cgoLookupCNAME(ctx context.Context, name string) (cname string, err error, completed bool) {
 	if ctx.Done() == nil {
 		_, cname, err = cgoLookupIPCNAME("ip", name)
 		return cname, err, true
 	}
 	result := make(chan ipLookupResult, 1)
 	go cgoIPLookup(result, "ip", name)
 	select {
 	case r := <-result:
 		return r.cname, r.err, true
 	case <-ctx.Done():
 		return "", mapErr(ctx.Err()), false
 	}
 }

 // These are roughly enough for the following:
 //
 // Source		Encoding			Maximum length of single name entry
 // Unicast DNS		ASCII or			<=253 + a NUL terminator
 //			Unicode in RFC 5892		252 * total number of labels + delimiters + a NUL terminator
 // Multicast DNS	UTF-8 in RFC 5198 or		<=253 + a NUL terminator
 //			the same as unicast DNS ASCII	<=253 + a NUL terminator
 // Local database	various				depends on implementation
 const (
 	nameinfoLen    = 64
 	maxNameinfoLen = 4096
 )

 func cgoLookupPTR(ctx context.Context, addr string) (names []string, err error, completed bool) {
 	var zone string
 	ip := parseIPv4(addr)
 	if ip == nil {
 		ip, zone = parseIPv6Zone(addr)
 	}
 	if ip == nil {
 		return nil, &DNSError{Err: "invalid address", Name: addr}, true
 	}
 	sa, salen := cgoSockaddr(ip, zone)
 	if sa == nil {
 		return nil, &DNSError{Err: "invalid address " + ip.String(), Name: addr}, true
 	}
 	if ctx.Done() == nil {
 		names, err := cgoLookupAddrPTR(addr, sa, salen)
 		return names, err, true
 	}
 	result := make(chan reverseLookupResult, 1)
 	go cgoReverseLookup(result, addr, sa, salen)
 	select {
 	case r := <-result:
 		return r.names, r.err, true
 	case <-ctx.Done():
 		return nil, mapErr(ctx.Err()), false
 	}
 }

 func cgoLookupAddrPTR(addr string, sa *syscall.RawSockaddr, salen syscall.Socklen_t) (names []string, err error) {
 	acquireThread()
 	defer releaseThread()

 	var gerrno int
 	var b []byte
 	for l := nameinfoLen; l <= maxNameinfoLen; l *= 2 {
 		b = make([]byte, l)
 		gerrno, err = cgoNameinfoPTR(b, sa, salen)
 		if gerrno == 0 || gerrno != syscall.EAI_OVERFLOW {
 			break
 		}
 	}
 	if gerrno != 0 {
 		isTemporary := false
 		switch gerrno {
 		case syscall.EAI_SYSTEM:
 			if err == nil { // see golang.org/issue/6232
 				err = syscall.EMFILE
 			}
 		default:
 			err = addrinfoErrno(gerrno)
 			isTemporary = addrinfoErrno(gerrno).Temporary()
 		}
 		return nil, &DNSError{Err: err.Error(), Name: addr, IsTemporary: isTemporary}
 	}
 	for i := 0; i < len(b); i++ {
 		if b[i] == 0 {
 			b = b[:i]
 			break
 		}
 	}
 	return []string{absDomainName(b)}, nil
 }

 func cgoReverseLookup(result chan<- reverseLookupResult, addr string, sa *syscall.RawSockaddr, salen syscall.Socklen_t) {
 	names, err := cgoLookupAddrPTR(addr, sa, salen)
 	result <- reverseLookupResult{names, err}
 }

 func cgoSockaddr(ip IP, zone string) (*syscall.RawSockaddr, syscall.Socklen_t) {
 	if ip4 := ip.To4(); ip4 != nil {
 		return cgoSockaddrInet4(ip4), syscall.Socklen_t(syscall.SizeofSockaddrInet4)
 	}
 	if ip6 := ip.To16(); ip6 != nil {
 		return cgoSockaddrInet6(ip6, zoneCache.index(zone)), syscall.Socklen_t(syscall.SizeofSockaddrInet6)
 	}
 	return nil, 0
 }

 func copyIP(x IP) IP {
 	if len(x) < 16 {
 		return x.To16()
 	}
 	y := make(IP, len(x))
 	copy(y, x)
 	return y
 }
	// Copyright 2011 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.

	// +build cgo,!netgo
	// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris

	package net

	/*
	#include <sys/types.h>
	#include <sys/socket.h>
	#include <netinet/in.h>
	#include <netdb.h>
	#include <unistd.h>
	#include <string.h>

	// If nothing else defined EAI_OVERFLOW, make sure it has a value.
	#ifndef EAI_OVERFLOW
	#define EAI_OVERFLOW -12
	#endif
	*/

	import (
	"context"
	"syscall"
	"unsafe"
	)

	//extern getaddrinfo
	func libc_getaddrinfo(node byte, service byte, hints syscall.Addrinfo, res *syscall.Addrinfo) int32

	//extern freeaddrinfo
	func libc_freeaddrinfo(res *syscall.Addrinfo)

	//extern gai_strerror
	func libc_gai_strerror(errcode int) *byte

	// bytePtrToString takes a NUL-terminated array of bytes and convert
	// it to a Go string.
	func bytePtrToString(p *byte) string {
	a := (*[10000]byte)(unsafe.Pointer(p))
	i := 0
	for a[i] != 0 {
	i++
	}
	return string(a[:i])
	}

	// An addrinfoErrno represents a getaddrinfo, getnameinfo-specific
	// error number. It's a signed number and a zero value is a non-error
	// by convention.
	type addrinfoErrno int

	func (eai addrinfoErrno) Error() string { return bytePtrToString(libc_gai_strerror(int(eai))) }
	func (eai addrinfoErrno) Temporary() bool { return eai == syscall.EAI_AGAIN }
	func (eai addrinfoErrno) Timeout() bool { return false }

	type portLookupResult struct {
	port int
	err error
	}

	type ipLookupResult struct {
	addrs []IPAddr
	cname string
	err error
	}

	type reverseLookupResult struct {
	names []string
	err error
	}

	func cgoLookupHost(ctx context.Context, name string) (hosts []string, err error, completed bool) {
	addrs, err, completed := cgoLookupIP(ctx, "ip", name)
	for _, addr := range addrs {
	hosts = append(hosts, addr.String())
	}
	return
	}

	func cgoLookupPort(ctx context.Context, network, service string) (port int, err error, completed bool) {
	var hints syscall.Addrinfo
	switch network {
	case "": // no hints
	case "tcp", "tcp4", "tcp6":
	hints.Ai_socktype = syscall.SOCK_STREAM
	hints.Ai_protocol = syscall.IPPROTO_TCP
	case "udp", "udp4", "udp6":
	hints.Ai_socktype = syscall.SOCK_DGRAM
	hints.Ai_protocol = syscall.IPPROTO_UDP
	default:
	return 0, &DNSError{Err: "unknown network", Name: network + "/" + service}, true
	}
	switch ipVersion(network) {
	case '4':
	hints.Ai_family = syscall.AF_INET
	case '6':
	hints.Ai_family = syscall.AF_INET6
	}
	if ctx.Done() == nil {
	port, err := cgoLookupServicePort(&hints, network, service)
	return port, err, true
	}
	result := make(chan portLookupResult, 1)
	go cgoPortLookup(result, &hints, network, service)
	select {
	case r := <-result:
	return r.port, r.err, true
	case <-ctx.Done():
	// Since there isn't a portable way to cancel the lookup,
	// we just let it finish and write to the buffered channel.
	return 0, mapErr(ctx.Err()), false
	}
	}

	func cgoLookupServicePort(hints *syscall.Addrinfo, network, service string) (port int, err error) {
	s, err := syscall.BytePtrFromString(service)
	if err != nil {
	return 0, err
	}
	// Lowercase the service name in the memory passed to C.
	for i := 0; i < len(service); i++ {
	bp := (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(s)) + uintptr(i)))
	bp = lowerASCII(bp)
	}
	var res *syscall.Addrinfo
	syscall.Entersyscall()
	gerrno := libc_getaddrinfo(nil, s, hints, &res)
	syscall.Exitsyscall()
	if gerrno != 0 {
	isTemporary := false
	switch gerrno {
	case syscall.EAI_SYSTEM:
	errno := syscall.GetErrno()
	if errno == 0 { // see golang.org/issue/6232
	errno = syscall.EMFILE
	}
	err = errno
	default:
	err = addrinfoErrno(gerrno)
	isTemporary = addrinfoErrno(gerrno).Temporary()
	}
	return 0, &DNSError{Err: err.Error(), Name: network + "/" + service, IsTemporary: isTemporary}
	}
	defer libc_freeaddrinfo(res)

	for r := res; r != nil; r = r.Ai_next {
	switch r.Ai_family {
	case syscall.AF_INET:
	sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.Ai_addr))
	p := (*[2]byte)(unsafe.Pointer(&sa.Port))
	return int(p[0])<<8 \| int(p[1]), nil
	case syscall.AF_INET6:
	sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.Ai_addr))
	p := (*[2]byte)(unsafe.Pointer(&sa.Port))
	return int(p[0])<<8 \| int(p[1]), nil
	}
	}
	return 0, &DNSError{Err: "unknown port", Name: network + "/" + service}
	}

	func cgoPortLookup(result chan<- portLookupResult, hints *syscall.Addrinfo, network, service string) {
	port, err := cgoLookupServicePort(hints, network, service)
	result <- portLookupResult{port, err}
	}

	func cgoLookupIPCNAME(network, name string) (addrs []IPAddr, cname string, err error) {
	acquireThread()
	defer releaseThread()

	var hints syscall.Addrinfo
	hints.Ai_flags = int32(cgoAddrInfoFlags)
	hints.Ai_socktype = syscall.SOCK_STREAM
	hints.Ai_family = syscall.AF_UNSPEC
	switch ipVersion(network) {
	case '4':
	hints.Ai_family = syscall.AF_INET
	case '6':
	hints.Ai_family = syscall.AF_INET6
	}

	h := syscall.StringBytePtr(name)
	var res *syscall.Addrinfo
	syscall.Entersyscall()
	gerrno := libc_getaddrinfo(h, nil, &hints, &res)
	syscall.Exitsyscall()
	if gerrno != 0 {
	isErrorNoSuchHost := false
	isTemporary := false
	switch gerrno {
	case syscall.EAI_SYSTEM:
	errno := syscall.GetErrno()
	if errno == 0 {
	// err should not be nil, but sometimes getaddrinfo returns
	// gerrno == C.EAI_SYSTEM with err == nil on Linux.
	// The report claims that it happens when we have too many
	// open files, so use syscall.EMFILE (too many open files in system).
	// Most system calls would return ENFILE (too many open files),
	// so at the least EMFILE should be easy to recognize if this
	// comes up again. golang.org/issue/6232.
	errno = syscall.EMFILE
	}
	err = errno
	case syscall.EAI_NONAME:
	err = errNoSuchHost
	isErrorNoSuchHost = true
	default:
	err = addrinfoErrno(gerrno)
	isTemporary = addrinfoErrno(gerrno).Temporary()
	}

	return nil, "", &DNSError{Err: err.Error(), Name: name, IsNotFound: isErrorNoSuchHost, IsTemporary: isTemporary}
	}
	defer libc_freeaddrinfo(res)

	if res != nil {
	cname = bytePtrToString((*byte)(unsafe.Pointer(res.Ai_canonname)))
	if cname == "" {
	cname = name
	}
	if len(cname) > 0 && cname[len(cname)-1] != '.' {
	cname += "."
	}
	}
	for r := res; r != nil; r = r.Ai_next {
	// We only asked for SOCK_STREAM, but check anyhow.
	if r.Ai_socktype != syscall.SOCK_STREAM {
	continue
	}
	switch r.Ai_family {
	case syscall.AF_INET:
	sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.Ai_addr))
	addr := IPAddr{IP: copyIP(sa.Addr[:])}
	addrs = append(addrs, addr)
	case syscall.AF_INET6:
	sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.Ai_addr))
	addr := IPAddr{IP: copyIP(sa.Addr[:]), Zone: zoneCache.name(int(sa.Scope_id))}
	addrs = append(addrs, addr)
	}
	}
	return addrs, cname, nil
	}

	func cgoIPLookup(result chan<- ipLookupResult, network, name string) {
	addrs, cname, err := cgoLookupIPCNAME(network, name)
	result <- ipLookupResult{addrs, cname, err}
	}

	func cgoLookupIP(ctx context.Context, network, name string) (addrs []IPAddr, err error, completed bool) {
	if ctx.Done() == nil {
	addrs, _, err = cgoLookupIPCNAME(network, name)
	return addrs, err, true
	}
	result := make(chan ipLookupResult, 1)
	go cgoIPLookup(result, network, name)
	select {
	case r := <-result:
	return r.addrs, r.err, true
	case <-ctx.Done():
	return nil, mapErr(ctx.Err()), false
	}
	}

	func cgoLookupCNAME(ctx context.Context, name string) (cname string, err error, completed bool) {
	if ctx.Done() == nil {
	_, cname, err = cgoLookupIPCNAME("ip", name)
	return cname, err, true
	}
	result := make(chan ipLookupResult, 1)
	go cgoIPLookup(result, "ip", name)
	select {
	case r := <-result:
	return r.cname, r.err, true
	case <-ctx.Done():
	return "", mapErr(ctx.Err()), false
	}
	}

	// These are roughly enough for the following:
	//
	// Source Encoding Maximum length of single name entry
	// Unicast DNS ASCII or <=253 + a NUL terminator
	// Unicode in RFC 5892 252 * total number of labels + delimiters + a NUL terminator
	// Multicast DNS UTF-8 in RFC 5198 or <=253 + a NUL terminator
	// the same as unicast DNS ASCII <=253 + a NUL terminator
	// Local database various depends on implementation
	const (
	nameinfoLen = 64
	maxNameinfoLen = 4096
	)

	func cgoLookupPTR(ctx context.Context, addr string) (names []string, err error, completed bool) {
	var zone string
	ip := parseIPv4(addr)
	if ip == nil {
	ip, zone = parseIPv6Zone(addr)
	}
	if ip == nil {
	return nil, &DNSError{Err: "invalid address", Name: addr}, true
	}
	sa, salen := cgoSockaddr(ip, zone)
	if sa == nil {
	return nil, &DNSError{Err: "invalid address " + ip.String(), Name: addr}, true
	}
	if ctx.Done() == nil {
	names, err := cgoLookupAddrPTR(addr, sa, salen)
	return names, err, true
	}
	result := make(chan reverseLookupResult, 1)
	go cgoReverseLookup(result, addr, sa, salen)
	select {
	case r := <-result:
	return r.names, r.err, true
	case <-ctx.Done():
	return nil, mapErr(ctx.Err()), false
	}
	}

	func cgoLookupAddrPTR(addr string, sa *syscall.RawSockaddr, salen syscall.Socklen_t) (names []string, err error) {
	acquireThread()
	defer releaseThread()

	var gerrno int
	var b []byte
	for l := nameinfoLen; l <= maxNameinfoLen; l *= 2 {
	b = make([]byte, l)
	gerrno, err = cgoNameinfoPTR(b, sa, salen)
	if gerrno == 0 \|\| gerrno != syscall.EAI_OVERFLOW {
	break
	}
	}
	if gerrno != 0 {
	isTemporary := false
	switch gerrno {
	case syscall.EAI_SYSTEM:
	if err == nil { // see golang.org/issue/6232
	err = syscall.EMFILE
	}
	default:
	err = addrinfoErrno(gerrno)
	isTemporary = addrinfoErrno(gerrno).Temporary()
	}
	return nil, &DNSError{Err: err.Error(), Name: addr, IsTemporary: isTemporary}
	}
	for i := 0; i < len(b); i++ {
	if b[i] == 0 {
	b = b[:i]
	break
	}
	}
	return []string{absDomainName(b)}, nil
	}

	func cgoReverseLookup(result chan<- reverseLookupResult, addr string, sa *syscall.RawSockaddr, salen syscall.Socklen_t) {
	names, err := cgoLookupAddrPTR(addr, sa, salen)
	result <- reverseLookupResult{names, err}
	}

	func cgoSockaddr(ip IP, zone string) (*syscall.RawSockaddr, syscall.Socklen_t) {
	if ip4 := ip.To4(); ip4 != nil {
	return cgoSockaddrInet4(ip4), syscall.Socklen_t(syscall.SizeofSockaddrInet4)
	}
	if ip6 := ip.To16(); ip6 != nil {
	return cgoSockaddrInet6(ip6, zoneCache.index(zone)), syscall.Socklen_t(syscall.SizeofSockaddrInet6)
	}
	return nil, 0
	}

	func copyIP(x IP) IP {
	if len(x) < 16 {
	return x.To16()
	}
	y := make(IP, len(x))
	copy(y, x)
	return y
	}