code review fixes

Author: jfbus

src/net/dnsclient_unix.go

@@ -26,6 +26,12 @@ import (
 	"golang.org/x/net/dns/dnsmessage"
 )
 
+const (
+	// to be used as a useTCP parameter to exchange
+	useTCPOnly  = true
+	useUDPOrTCP = false
+)
+
 var (
 	errLameReferral              = errors.New("lame referral")
 	errCannotUnmarshalDNSMessage = errors.New("cannot unmarshal DNS message")
@@ -131,14 +137,14 @@ func dnsStreamRoundTrip(c Conn, id uint16, query dnsmessage.Question, b []byte)
 }
 
 // exchange sends a query on the connection and hopes for a response.
-func (r *Resolver) exchange(ctx context.Context, server string, q dnsmessage.Question, timeout time.Duration, usetcp bool) (dnsmessage.Parser, dnsmessage.Header, error) {
+func (r *Resolver) exchange(ctx context.Context, server string, q dnsmessage.Question, timeout time.Duration, useTCP bool) (dnsmessage.Parser, dnsmessage.Header, error) {
 	q.Class = dnsmessage.ClassINET
 	id, udpReq, tcpReq, err := newRequest(q)
 	if err != nil {
 		return dnsmessage.Parser{}, dnsmessage.Header{}, errCannotMarshalDNSMessage
 	}
 	var networks []string
-	if usetcp {
+	if useTCP {
 		networks = []string{"tcp"}
 	} else {
 		networks = []string{"udp", "tcp"}
@@ -247,7 +253,7 @@ func (r *Resolver) tryOneName(ctx context.Context, cfg *dnsConfig, name string,
 		for j := uint32(0); j < sLen; j++ {
 			server := cfg.servers[(serverOffset+j)%sLen]
 
-			p, h, err := r.exchange(ctx, server, q, cfg.timeout, cfg.usetcp)
+			p, h, err := r.exchange(ctx, server, q, cfg.timeout, cfg.useTCP)
 			if err != nil {
 				dnsErr := &DNSError{
 					Err:    err.Error(),

src/net/dnsclient_unix_test.go

@@ -81,7 +81,7 @@ func TestDNSTransportFallback(t *testing.T) {
 	for _, tt := range dnsTransportFallbackTests {
 		ctx, cancel := context.WithCancel(context.Background())
 		defer cancel()
-		_, h, err := r.exchange(ctx, tt.server, tt.question, time.Second, false)
+		_, h, err := r.exchange(ctx, tt.server, tt.question, time.Second, useUDPOrTCP)
 		if err != nil {
 			t.Error(err)
 			continue
@@ -137,7 +137,7 @@ func TestSpecialDomainName(t *testing.T) {
 	for _, tt := range specialDomainNameTests {
 		ctx, cancel := context.WithCancel(context.Background())
 		defer cancel()
-		_, h, err := r.exchange(ctx, server, tt.question, 3*time.Second, false)
+		_, h, err := r.exchange(ctx, server, tt.question, 3*time.Second, useUDPOrTCP)
 		if err != nil {
 			t.Error(err)
 			continue
@@ -1564,7 +1564,7 @@ func TestDNSDialTCP(t *testing.T) {
 	}
 	r := Resolver{PreferGo: true, Dial: fake.DialContext}
 	ctx := context.Background()
-	_, _, err := r.exchange(ctx, "0.0.0.0", mustQuestion("com.", dnsmessage.TypeALL, dnsmessage.ClassINET), time.Second, false)
+	_, _, err := r.exchange(ctx, "0.0.0.0", mustQuestion("com.", dnsmessage.TypeALL, dnsmessage.ClassINET), time.Second, useUDPOrTCP)
 	if err != nil {
 		t.Fatal("exhange failed:", err)
 	}
@@ -1717,7 +1717,7 @@ func TestDNSUseTCP(t *testing.T) {
 	r := Resolver{PreferGo: true, Dial: fake.DialContext}
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
-	_, _, err := r.exchange(ctx, "0.0.0.0", mustQuestion("com.", dnsmessage.TypeALL, dnsmessage.ClassINET), time.Second, true)
+	_, _, err := r.exchange(ctx, "0.0.0.0", mustQuestion("com.", dnsmessage.TypeALL, dnsmessage.ClassINET), time.Second, useTCPOnly)
 	if err != nil {
 		t.Fatal("exchange failed:", err)
 	}

src/net/dnsconfig_unix.go

@@ -33,7 +33,7 @@ type dnsConfig struct {
 	mtime         time.Time     // time of resolv.conf modification
 	soffset       uint32        // used by serverOffset
 	singleRequest bool          // use sequential A and AAAA queries instead of parallel queries
-	usetcp        bool          // force usage of TCP for DNS resolutions
+	useTCP        bool          // force usage of TCP for DNS resolutions
 }
 
 // See resolv.conf(5) on a Linux machine.
@@ -125,7 +125,11 @@ func dnsReadConfig(filename string) *dnsConfig {
 					//  perform the IPv6 and IPv4 requests sequentially."
 					conf.singleRequest = true
 				case s == "use-vc":
-					conf.usetcp = true
+					// Linux glibc option:
+					// http://man7.org/linux/man-pages/man5/resolv.conf.5.html
+					// "Sets RES_USEVC in _res.options.
+					//  This option forces the use of TCP for DNS resolutions."
+					conf.useTCP = true
 				default:
 					conf.unknownOpt = true
 				}

src/net/dnsconfig_unix_test.go

@@ -129,7 +129,7 @@ var dnsReadConfigTests = []struct {
 		want: &dnsConfig{
 			servers:  defaultNS,
 			ndots:    1,
-			usetcp:   true,
+			useTCP:   true,
 			timeout:  5 * time.Second,
 			attempts: 2,
 			search:   []string{"domain.local."},