net: add a LookupTXT function.

This CL only supports Unix, not Plan 9 or Windows.

R=rsc
CC=golang-dev
https://golang.org/cl/4996048

src/pkg/net/lookup_plan9.go

@@ -204,6 +204,11 @@ func LookupMX(name string) (mx []*MX, err os.Error) {
 	return
 }
 
+// LookupTXT returns the DNS TXT records for the given domain name.
+func LookupTXT(name string) (txt []string, err os.Error) {
+	return nil, os.NewError("net.LookupTXT is not implemented on Plan 9")
+}
+
 // LookupAddr performs a reverse lookup for the given address, returning a list
 // of names mapping to that address.
 func LookupAddr(addr string) (name []string, err os.Error) {

src/pkg/net/lookup_test.go

@@ -42,6 +42,24 @@ func TestGmailMX(t *testing.T) {
 	}
 }
 
+func TestGmailTXT(t *testing.T) {
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		t.Logf("LookupTXT is not implemented on Windows or Plan 9")
+		return
+	}
+	if testing.Short() || avoidMacFirewall {
+		t.Logf("skipping test to avoid external network")
+		return
+	}
+	txt, err := LookupTXT("gmail.com")
+	if err != nil {
+		t.Errorf("failed: %s", err)
+	}
+	if len(txt) == 0 || len(txt[0]) == 0 {
+		t.Errorf("no results")
+	}
+}
+
 func TestGoogleDNSAddr(t *testing.T) {
 	if testing.Short() || avoidMacFirewall {
 		t.Logf("skipping test to avoid external network")

src/pkg/net/lookup_unix.go

@@ -72,19 +72,32 @@ func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err os.
 
 // LookupMX returns the DNS MX records for the given domain name sorted by preference.
 func LookupMX(name string) (mx []*MX, err os.Error) {
-	_, rr, err := lookup(name, dnsTypeMX)
+	_, records, err := lookup(name, dnsTypeMX)
 	if err != nil {
 		return
 	}
-	mx = make([]*MX, len(rr))
-	for i := range rr {
-		r := rr[i].(*dnsRR_MX)
+	mx = make([]*MX, len(records))
+	for i, rr := range records {
+		r := rr.(*dnsRR_MX)
 		mx[i] = &MX{r.Mx, r.Pref}
 	}
 	byPref(mx).sort()
 	return
 }
 
+// LookupTXT returns the DNS TXT records for the given domain name.
+func LookupTXT(name string) (txt []string, err os.Error) {
+	_, records, err := lookup(name, dnsTypeTXT)
+	if err != nil {
+		return
+	}
+	txt = make([]string, len(records))
+	for i, r := range records {
+		txt[i] = r.(*dnsRR_TXT).Txt
+	}
+	return
+}
+
 // LookupAddr performs a reverse lookup for the given address, returning a list
 // of names mapping to that address.
 func LookupAddr(addr string) (name []string, err os.Error) {

src/pkg/net/lookup_windows.go

@@ -110,6 +110,10 @@ func LookupMX(name string) (mx []*MX, err os.Error) {
 	return mx, nil
 }
 
+func LookupTXT(name string) (txt []string, err os.Error) {
+	return nil, os.NewError("net.LookupTXT is not implemented on Windows")
+}
+
 func LookupAddr(addr string) (name []string, err os.Error) {
 	arpa, err := reverseaddr(addr)
 	if err != nil {