net: implement LookupTXT for windows

R=rsc
CC=golang-dev
https://golang.org/cl/5318056

src/pkg/net/lookup_test.go

@@ -52,10 +52,6 @@ func TestGmailMX(t *testing.T) {
 }
 
 func TestGmailTXT(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Logf("LookupTXT is not implemented on Windows")
-		return
-	}
 	if testing.Short() || avoidMacFirewall {
 		t.Logf("skipping test to avoid external network")
 		return

src/pkg/net/lookup_windows.go

@@ -5,7 +5,6 @@
 package net
 
 import (
-	"errors"
 	"syscall"
 	"unsafe"
 	"os"
@@ -81,7 +80,7 @@ func LookupPort(network, service string) (port int, err error) {
 func LookupCNAME(name string) (cname string, err error) {
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(name, syscall.DNS_TYPE_CNAME, 0, nil, &r, nil)
-	if int(e) != 0 {
+	if e != 0 {
 		return "", os.NewSyscallError("LookupCNAME", int(e))
 	}
 	defer syscall.DnsRecordListFree(r, 1)
@@ -110,7 +109,7 @@ func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err err
 	}
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(target, syscall.DNS_TYPE_SRV, 0, nil, &r, nil)
-	if int(e) != 0 {
+	if e != 0 {
 		return "", nil, os.NewSyscallError("LookupSRV", int(e))
 	}
 	defer syscall.DnsRecordListFree(r, 1)
@@ -126,7 +125,7 @@ func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err err
 func LookupMX(name string) (mx []*MX, err error) {
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(name, syscall.DNS_TYPE_MX, 0, nil, &r, nil)
-	if int(e) != 0 {
+	if e != 0 {
 		return nil, os.NewSyscallError("LookupMX", int(e))
 	}
 	defer syscall.DnsRecordListFree(r, 1)
@@ -140,7 +139,21 @@ func LookupMX(name string) (mx []*MX, err error) {
 }
 
 func LookupTXT(name string) (txt []string, err error) {
-	return nil, errors.New("net.LookupTXT is not implemented on Windows")
+	var r *syscall.DNSRecord
+	e := syscall.DnsQuery(name, syscall.DNS_TYPE_TEXT, 0, nil, &r, nil)
+	if e != 0 {
+		return nil, os.NewSyscallError("LookupTXT", int(e))
+	}
+	defer syscall.DnsRecordListFree(r, 1)
+	txt = make([]string, 0, 10)
+	if r != nil && r.Type == syscall.DNS_TYPE_TEXT {
+		d := (*syscall.DNSTXTData)(unsafe.Pointer(&r.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) {
@@ -150,7 +163,7 @@ func LookupAddr(addr string) (name []string, err error) {
 	}
 	var r *syscall.DNSRecord
 	e := syscall.DnsQuery(arpa, syscall.DNS_TYPE_PTR, 0, nil, &r, nil)
-	if int(e) != 0 {
+	if e != 0 {
 		return nil, os.NewSyscallError("LookupAddr", int(e))
 	}
 	defer syscall.DnsRecordListFree(r, 1)

src/pkg/syscall/ztypes_windows.go

@@ -530,6 +530,11 @@ type DNSMXData struct {
 	Pad          uint16
 }
 
+type DNSTXTData struct {
+	StringCount uint16
+	StringArray [1]*uint16
+}
+
 type DNSRecord struct {
 	Next     *DNSRecord
 	Name     *uint16