net: return rooted DNS names on windows

This CL also changes windows LookupSRV to return
_xmpp-server._tcp.google.com. as cname instead of google.com
similar to linux. Otherwise TestLookupDots still fails.

Updates #12193 (with plan9 still to do)

Change-Id: Id225e15bee95037cdb4226803506cce690c5d341
Reviewed-on: https://go-review.googlesource.com/13887
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/lookup_windows.go

@@ -213,6 +213,17 @@ func newLookupPort(network, service string) (int, error) {
 	return 0, &DNSError{Err: syscall.EINVAL.Error(), Name: network + "/" + service}
 }
 
+// ensureEndDot adds '.' at the end of name unless it is already there.
+func ensureEndDot(name string) string {
+	if name == "" {
+		return "."
+	}
+	if name[len(name)-1] == '.' {
+		return name
+	}
+	return name + "."
+}
+
 func lookupCNAME(name string) (string, error) {
 	acquireThread()
 	defer releaseThread()
@@ -221,10 +232,7 @@ func lookupCNAME(name string) (string, error) {
 	// 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
+		return ensureEndDot(name), nil
 	}
 	if e != nil {
 		return "", &DNSError{Err: os.NewSyscallError("dnsquery", e).Error(), Name: name}
@@ -232,8 +240,8 @@ func lookupCNAME(name string) (string, error) {
 	defer syscall.DnsRecordListFree(r, 1)
 
 	resolved := resolveCNAME(syscall.StringToUTF16Ptr(name), r)
-	cname := syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(resolved))[:]) + "."
-	return cname, nil
+	cname := syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(resolved))[:])
+	return ensureEndDot(cname), nil
 }
 
 func lookupSRV(service, proto, name string) (string, []*SRV, error) {
@@ -255,10 +263,10 @@ func lookupSRV(service, proto, name string) (string, []*SRV, error) {
 	srvs := make([]*SRV, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_SRV, target) {
 		v := (*syscall.DNSSRVData)(unsafe.Pointer(&p.Data[0]))
-		srvs = append(srvs, &SRV{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Target))[:]), v.Port, v.Priority, v.Weight})
+		srvs = append(srvs, &SRV{ensureEndDot(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Target))[:])), v.Port, v.Priority, v.Weight})
 	}
 	byPriorityWeight(srvs).sort()
-	return name, srvs, nil
+	return ensureEndDot(target), srvs, nil
 }
 
 func lookupMX(name string) ([]*MX, error) {
@@ -274,7 +282,7 @@ func lookupMX(name string) ([]*MX, error) {
 	mxs := make([]*MX, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_MX, name) {
 		v := (*syscall.DNSMXData)(unsafe.Pointer(&p.Data[0]))
-		mxs = append(mxs, &MX{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.NameExchange))[:]) + ".", v.Preference})
+		mxs = append(mxs, &MX{ensureEndDot(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.NameExchange))[:])), v.Preference})
 	}
 	byPref(mxs).sort()
 	return mxs, nil
@@ -293,7 +301,7 @@ func lookupNS(name string) ([]*NS, error) {
 	nss := make([]*NS, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_NS, name) {
 		v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
-		nss = append(nss, &NS{syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]) + "."})
+		nss = append(nss, &NS{ensureEndDot(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]))})
 	}
 	return nss, nil
 }
@@ -336,7 +344,7 @@ func lookupAddr(addr string) ([]string, error) {
 	ptrs := make([]string, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_PTR, arpa) {
 		v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
-		ptrs = append(ptrs, syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]))
+		ptrs = append(ptrs, ensureEndDot(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:])))
 	}
 	return ptrs, nil
 }

src/net/lookup_windows_test.go

@@ -148,13 +148,6 @@ func (s byHost) Len() int           { return len(s) }
 func (s byHost) Less(i, j int) bool { return s[i].Host < s[j].Host }
 func (s byHost) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
 
-func fqdn(s string) string {
-	if len(s) == 0 || s[len(s)-1] != '.' {
-		return s + "."
-	}
-	return s
-}
-
 func nslookup(qtype, name string) (string, error) {
 	var out bytes.Buffer
 	var err bytes.Buffer
@@ -184,14 +177,14 @@ func nslookupMX(name string) (mx []*MX, err error) {
 	rx := regexp.MustCompile(`(?m)^([a-z0-9.\-]+)\s+mail exchanger\s*=\s*([0-9]+)\s*([a-z0-9.\-]+)$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
 		pref, _, _ := dtoi(ans[2], 0)
-		mx = append(mx, &MX{fqdn(ans[3]), uint16(pref)})
+		mx = append(mx, &MX{ensureEndDot(ans[3]), uint16(pref)})
 	}
 	// windows nslookup syntax
 	// gmail.com       MX preference = 30, mail exchanger = alt3.gmail-smtp-in.l.google.com
 	rx = regexp.MustCompile(`(?m)^([a-z0-9.\-]+)\s+MX preference\s*=\s*([0-9]+)\s*,\s*mail exchanger\s*=\s*([a-z0-9.\-]+)$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
 		pref, _, _ := dtoi(ans[2], 0)
-		mx = append(mx, &MX{fqdn(ans[3]), uint16(pref)})
+		mx = append(mx, &MX{ensureEndDot(ans[3]), uint16(pref)})
 	}
 	return
 }
@@ -205,7 +198,7 @@ func nslookupNS(name string) (ns []*NS, err error) {
 	// golang.org      nameserver = ns1.google.com.
 	rx := regexp.MustCompile(`(?m)^([a-z0-9.\-]+)\s+nameserver\s*=\s*([a-z0-9.\-]+)$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
-		ns = append(ns, &NS{fqdn(ans[2])})
+		ns = append(ns, &NS{ensureEndDot(ans[2])})
 	}
 	return
 }
@@ -222,7 +215,7 @@ func nslookupCNAME(name string) (cname string, err error) {
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
 		last = ans[2]
 	}
-	return fqdn(last), nil
+	return ensureEndDot(last), nil
 }
 
 func nslookupTXT(name string) (txt []string, err error) {