net: make Dial and Listen behavior consistent across over platforms

This CL changes the behavior of Dial and Listen API family.

Previous Dial and Listen allow a combo of "tcp6" and IPv4 or IPv6
IPv4-mapped address as its argument, but it also makes slightly
different behaviors between Linux and other platforms. This CL fixes
such differences across over platforms by tweaking IP-level socket
option IPV6_V6ONLY. Consequently new Dial and Listen API family will
reject arguments consists of "tcp6" and IPv4 or IPv6 IPv4-mapped
address.

This CL also adds a bit clarified unicast listener tests.

Fixes #2581.

R=rsc, minux.ma
CC=golang-dev
https://golang.org/cl/5677086

src/pkg/net/file_test.go

@@ -60,12 +60,7 @@ func TestFileListener(t *testing.T) {
 		return
 	}
 	testFileListener(t, "tcp", "127.0.0.1")
-	testFileListener(t, "tcp", "127.0.0.1")
+	testFileListener(t, "tcp", "[::ffff:127.0.0.1]")
-	if supportsIPv6 && supportsIPv4map {
-		testFileListener(t, "tcp", "[::ffff:127.0.0.1]")
-		testFileListener(t, "tcp", "127.0.0.1")
-		testFileListener(t, "tcp", "[::ffff:127.0.0.1]")
-	}
 	if runtime.GOOS == "linux" {
 		testFileListener(t, "unix", "@gotest/net")
 		testFileListener(t, "unixpacket", "@gotest/net")
@@ -125,12 +120,10 @@ func TestFilePacketConn(t *testing.T) {
 	}
 	testFilePacketConnListen(t, "udp", "127.0.0.1:0")
 	testFilePacketConnDial(t, "udp", "127.0.0.1:12345")
+	testFilePacketConnDial(t, "udp", "[::ffff:127.0.0.1]:12345")
 	if supportsIPv6 {
 		testFilePacketConnListen(t, "udp", "[::1]:0")
 	}
-	if supportsIPv6 && supportsIPv4map {
-		testFilePacketConnDial(t, "udp", "[::ffff:127.0.0.1]:12345")
-	}
 	if runtime.GOOS == "linux" {
 		testFilePacketConnListen(t, "unixgram", "@gotest1/net")
 	}

src/pkg/net/iprawsock_posix.go

@@ -34,6 +34,13 @@ func (a *IPAddr) family() int {
 	return syscall.AF_INET6
 }
 
+func (a *IPAddr) isWildcard() bool {
+	if a == nil || a.IP == nil {
+		return true
+	}
+	return a.IP.IsUnspecified()
+}
+
 func (a *IPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	return ipToSockaddr(family, a.IP, 0)
 }

src/pkg/net/ipsock_posix.go

@@ -38,6 +38,7 @@ func probeIPv6Stack() (supportsIPv6, supportsIPv4map bool) {
 			continue
 		}
 		defer closesocket(s)
+		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
 		sa, err := probes[i].la.toAddr().sockaddr(syscall.AF_INET6)
 		if err != nil {
 			continue
@@ -55,58 +56,75 @@ func probeIPv6Stack() (supportsIPv6, supportsIPv4map bool) {
 // favoriteAddrFamily returns the appropriate address family to
 // the given net, laddr, raddr and mode.  At first it figures
 // address family out from the net.  If mode indicates "listen"
-// and laddr.(type).IP is nil, it assumes that the user wants to
+// and laddr is a wildcard, it assumes that the user wants to
-// make a passive connection with wildcard address family, both
+// make a passive connection with a wildcard address family, both
-// INET and INET6, and wildcard address.  Otherwise guess: if the
+// AF_INET and AF_INET6, and a wildcard address like following:
-// addresses are IPv4 then returns INET, or else returns INET6.
+//
-func favoriteAddrFamily(net string, laddr, raddr sockaddr, mode string) int {
+//	1. A wild-wild listen, "tcp" + ""
+//	If the platform supports both IPv6 and IPv6 IPv4-mapping
+//	capabilities, we assume that the user want to listen on
+//	both IPv4 and IPv6 wildcard address over an AF_INET6
+//	socket with IPV6_V6ONLY=0.  Otherwise we prefer an IPv4
+//	wildcard address listen over an AF_INET socket.
+//
+//	2. A wild-ipv4wild listen, "tcp" + "0.0.0.0"
+//	Same as 1.
+//
+//	3. A wild-ipv6wild listen, "tcp" + "[::]"
+//	Almost same as 1 but we prefer an IPv6 wildcard address
+//	listen over an AF_INET6 socket with IPV6_V6ONLY=0 when
+//	the platform supports IPv6 capability but not IPv6 IPv4-
+//	mapping capability.
+//
+//	4. A ipv4-ipv4wild listen, "tcp4" + "" or "0.0.0.0"
+//	We use an IPv4 (AF_INET) wildcard address listen.
+//
+//	5. A ipv6-ipv6wild listen, "tcp6" + "" or "[::]"
+//	We use an IPv6 (AF_INET6, IPV6_V6ONLY=1) wildcard address
+//	listen.
+//
+// Otherwise guess: if the addresses are IPv4 then returns AF_INET,
+// or else returns AF_INET6.  It also returns a boolean value what
+// designates IPV6_V6ONLY option.
+//
+// Note that OpenBSD allows neither "net.inet6.ip6.v6only=1" change
+// nor IPPROTO_IPV6 level IPV6_V6ONLY socket option setting.
+func favoriteAddrFamily(net string, laddr, raddr sockaddr, mode string) (family int, ipv6only bool) {
 	switch net[len(net)-1] {
 	case '4':
-		return syscall.AF_INET
+		return syscall.AF_INET, false
 	case '6':
-		return syscall.AF_INET6
+		return syscall.AF_INET6, true
 	}
 
-	if mode == "listen" {
+	if mode == "listen" && laddr.isWildcard() {
-		// Note that OpenBSD allows neither "net.inet6.ip6.v6only"
+		if supportsIPv4map {
-		// change nor IPPROTO_IPV6 level IPV6_V6ONLY socket option
+			return syscall.AF_INET6, false
-		// setting.
-		switch a := laddr.(type) {
-		case *TCPAddr:
-			if a.IP == nil && supportsIPv6 && supportsIPv4map {
-				return syscall.AF_INET6
-			}
-		case *UDPAddr:
-			if a.IP == nil && supportsIPv6 && supportsIPv4map {
-				return syscall.AF_INET6
-			}
-		case *IPAddr:
-			if a.IP == nil && supportsIPv6 && supportsIPv4map {
-				return syscall.AF_INET6
-			}
 		}
+		return laddr.family(), false
 	}
 
 	if (laddr == nil || laddr.family() == syscall.AF_INET) &&
 		(raddr == nil || raddr.family() == syscall.AF_INET) {
-		return syscall.AF_INET
+		return syscall.AF_INET, false
 	}
-	return syscall.AF_INET6
+	return syscall.AF_INET6, false
 }
 
-// Internet sockets (TCP, UDP)
+// Internet sockets (TCP, UDP, IP)
 
-// A sockaddr represents a TCP or UDP network address that can
+// A sockaddr represents a TCP, UDP or IP network address that can
 // be converted into a syscall.Sockaddr.
 type sockaddr interface {
 	Addr
-	sockaddr(family int) (syscall.Sockaddr, error)
 	family() int
+	isWildcard() bool
+	sockaddr(family int) (syscall.Sockaddr, error)
 }
 
 func internetSocket(net string, laddr, raddr sockaddr, sotype, proto int, mode string, toAddr func(syscall.Sockaddr) Addr) (fd *netFD, err error) {
 	var la, ra syscall.Sockaddr
-	family := favoriteAddrFamily(net, laddr, raddr, mode)
+	family, ipv6only := favoriteAddrFamily(net, laddr, raddr, mode)
 	if laddr != nil {
 		if la, err = laddr.sockaddr(family); err != nil {
 			goto Error
@@ -117,7 +135,7 @@ func internetSocket(net string, laddr, raddr sockaddr, sotype, proto int, mode s
 			goto Error
 		}
 	}
-	fd, err = socket(net, family, sotype, proto, la, ra, toAddr)
+	fd, err = socket(net, family, sotype, proto, ipv6only, la, ra, toAddr)
 	if err != nil {
 		goto Error
 	}
@@ -152,7 +170,7 @@ func ipToSockaddr(family int, ip IP, port int) (syscall.Sockaddr, error) {
 		}
 		// IPv4 callers use 0.0.0.0 to mean "announce on any available address".
 		// In IPv6 mode, Linux treats that as meaning "announce on 0.0.0.0",
-		// which it refuses to do.  Rewrite to the IPv6 all zeros.
+		// which it refuses to do.  Rewrite to the IPv6 unspecified address.
 		if ip.Equal(IPv4zero) {
 			ip = IPv6zero
 		}

src/pkg/net/net_test.go

@@ -11,6 +11,14 @@ import (
 	"time"
 )
 
+// avoidOSXFirewallDialogPopup avoids OS X, former konwn as MacOS X,
+// firewall dialog popups during tests.  It looks like OS X checks
+// wildcard listens by default for security reasons.  A listen with
+// specific address doesn't make dialog popups for now.
+var avoidOSXFirewallDialogPopup = func() bool {
+	return testing.Short() && runtime.GOOS == "darwin"
+}
+
 func TestShutdown(t *testing.T) {
 	if runtime.GOOS == "plan9" {
 		return

src/pkg/net/server_test.go

@@ -128,19 +128,14 @@ func TestTCPServer(t *testing.T) {
 		doTest(t, "tcp6", "[::]", "[::1]")
 		doTest(t, "tcp6", "[::1]", "[::1]")
 	}
-	if supportsIPv6 && supportsIPv4map {
+	if supportsIPv4map {
 		doTest(t, "tcp", "[::ffff:0.0.0.0]", "127.0.0.1")
 		doTest(t, "tcp", "[::]", "127.0.0.1")
 		doTest(t, "tcp4", "[::ffff:0.0.0.0]", "127.0.0.1")
-		doTest(t, "tcp6", "", "127.0.0.1")
-		doTest(t, "tcp6", "[::ffff:0.0.0.0]", "127.0.0.1")
-		doTest(t, "tcp6", "[::]", "127.0.0.1")
 		doTest(t, "tcp", "127.0.0.1", "[::ffff:127.0.0.1]")
 		doTest(t, "tcp", "[::ffff:127.0.0.1]", "127.0.0.1")
 		doTest(t, "tcp4", "127.0.0.1", "[::ffff:127.0.0.1]")
 		doTest(t, "tcp4", "[::ffff:127.0.0.1]", "127.0.0.1")
-		doTest(t, "tcp6", "127.0.0.1", "[::ffff:127.0.0.1]")
-		doTest(t, "tcp6", "[::ffff:127.0.0.1]", "127.0.0.1")
 	}
 }
 
@@ -215,7 +210,7 @@ func TestUDPServer(t *testing.T) {
 	for _, isEmpty := range []bool{false, true} {
 		doTestPacket(t, "udp", "0.0.0.0", "127.0.0.1", isEmpty)
 		doTestPacket(t, "udp", "", "127.0.0.1", isEmpty)
-		if supportsIPv6 && supportsIPv4map {
+		if supportsIPv4map {
 			doTestPacket(t, "udp", "[::]", "[::ffff:127.0.0.1]", isEmpty)
 			doTestPacket(t, "udp", "[::]", "127.0.0.1", isEmpty)
 			doTestPacket(t, "udp", "0.0.0.0", "[::ffff:127.0.0.1]", isEmpty)

src/pkg/net/sock.go

@@ -16,7 +16,7 @@ import (
 var listenerBacklog = maxListenerBacklog()
 
 // Generic socket creation.
-func socket(net string, f, t, p int, la, ra syscall.Sockaddr, toAddr func(syscall.Sockaddr) Addr) (fd *netFD, err error) {
+func socket(net string, f, t, p int, ipv6only bool, la, ra syscall.Sockaddr, toAddr func(syscall.Sockaddr) Addr) (fd *netFD, err error) {
 	// See ../syscall/exec.go for description of ForkLock.
 	syscall.ForkLock.RLock()
 	s, err := syscall.Socket(f, t, p)
@@ -27,7 +27,7 @@ func socket(net string, f, t, p int, la, ra syscall.Sockaddr, toAddr func(syscal
 	syscall.CloseOnExec(s)
 	syscall.ForkLock.RUnlock()
 
-	err = setDefaultSockopts(s, f, t)
+	err = setDefaultSockopts(s, f, t, ipv6only)
 	if err != nil {
 		closesocket(s)
 		return nil, err

src/pkg/net/sockopt_bsd.go

@@ -13,12 +13,17 @@ import (
 	"syscall"
 )
 
-func setDefaultSockopts(s, f, t int) error {
+func setDefaultSockopts(s, f, t int, ipv6only bool) error {
 	switch f {
 	case syscall.AF_INET6:
-		// Allow both IP versions even if the OS default is otherwise.
+		if ipv6only {
-		// Note that some operating systems never admit this option.
+			syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 1)
-		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+		} else {
+			// Allow both IP versions even if the OS default
+			// is otherwise.  Note that some operating systems
+			// never admit this option.
+			syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+		}
 	}
 	// Allow broadcast.
 	err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)

src/pkg/net/sockopt_linux.go

@@ -11,12 +11,17 @@ import (
 	"syscall"
 )
 
-func setDefaultSockopts(s, f, t int) error {
+func setDefaultSockopts(s, f, t int, ipv6only bool) error {
 	switch f {
 	case syscall.AF_INET6:
-		// Allow both IP versions even if the OS default is otherwise.
+		if ipv6only {
-		// Note that some operating systems never admit this option.
+			syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 1)
-		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+		} else {
+			// Allow both IP versions even if the OS default
+			// is otherwise.  Note that some operating systems
+			// never admit this option.
+			syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+		}
 	}
 	// Allow broadcast.
 	err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)

src/pkg/net/sockopt_windows.go

@@ -11,12 +11,17 @@ import (
 	"syscall"
 )
 
-func setDefaultSockopts(s syscall.Handle, f, t int) error {
+func setDefaultSockopts(s syscall.Handle, f, t int, ipv6only bool) error {
 	switch f {
 	case syscall.AF_INET6:
-		// Allow both IP versions even if the OS default is otherwise.
+		if ipv6only {
-		// Note that some operating systems never admit this option.
+			syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 1)
-		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+		} else {
+			// Allow both IP versions even if the OS default
+			// is otherwise.  Note that some operating systems
+			// never admit this option.
+			syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+		}
 	}
 	// Allow broadcast.
 	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)

src/pkg/net/tcpsock_posix.go

@@ -46,6 +46,13 @@ func (a *TCPAddr) family() int {
 	return syscall.AF_INET6
 }
 
+func (a *TCPAddr) isWildcard() bool {
+	if a == nil || a.IP == nil {
+		return true
+	}
+	return a.IP.IsUnspecified()
+}
+
 func (a *TCPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	return ipToSockaddr(family, a.IP, a.Port)
 }

src/pkg/net/udpsock_posix.go

@@ -37,6 +37,13 @@ func (a *UDPAddr) family() int {
 	return syscall.AF_INET6
 }
 
+func (a *UDPAddr) isWildcard() bool {
+	if a == nil || a.IP == nil {
+		return true
+	}
+	return a.IP.IsUnspecified()
+}
+
 func (a *UDPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	return ipToSockaddr(family, a.IP, a.Port)
 }

src/pkg/net/unicast_test.go

@@ -7,81 +7,484 @@ package net
 import (
 	"io"
 	"runtime"
+	"syscall"
 	"testing"
 )
 
-var unicastTests = []struct {
+var listenerTests = []struct {
-	net    string
+	net      string
-	laddr  string
+	laddr    string
-	ipv6   bool
+	ipv6     bool // test with underlying AF_INET6 socket
-	packet bool
+	wildcard bool // test with wildcard address
 }{
-	{net: "tcp4", laddr: "127.0.0.1:0"},
+	{net: "tcp", laddr: "", wildcard: true},
-	{net: "tcp4", laddr: "previous"},
+	{net: "tcp", laddr: "0.0.0.0", wildcard: true},
-	{net: "tcp6", laddr: "[::1]:0", ipv6: true},
+	{net: "tcp", laddr: "[::ffff:0.0.0.0]", wildcard: true},
-	{net: "tcp6", laddr: "previous", ipv6: true},
+	{net: "tcp", laddr: "[::]", ipv6: true, wildcard: true},
-	{net: "udp4", laddr: "127.0.0.1:0", packet: true},
+
-	{net: "udp6", laddr: "[::1]:0", ipv6: true, packet: true},
+	{net: "tcp", laddr: "127.0.0.1"},
+	{net: "tcp", laddr: "[::ffff:127.0.0.1]"},
+	{net: "tcp", laddr: "[::1]", ipv6: true},
+
+	{net: "tcp4", laddr: "", wildcard: true},
+	{net: "tcp4", laddr: "0.0.0.0", wildcard: true},
+	{net: "tcp4", laddr: "[::ffff:0.0.0.0]", wildcard: true},
+
+	{net: "tcp4", laddr: "127.0.0.1"},
+	{net: "tcp4", laddr: "[::ffff:127.0.0.1]"},
+
+	{net: "tcp6", laddr: "", ipv6: true, wildcard: true},
+	{net: "tcp6", laddr: "[::]", ipv6: true, wildcard: true},
+
+	{net: "tcp6", laddr: "[::1]", ipv6: true},
 }
 
-func TestUnicastTCPAndUDP(t *testing.T) {
+// TestTCPListener tests both single and double listen to a test
-	if runtime.GOOS == "plan9" || runtime.GOOS == "windows" {
+// listener with same address family, same listening address and
+// same port.
+func TestTCPListener(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9", "windows":
 		return
 	}
 
-	prevladdr := ""
+	for _, tt := range listenerTests {
-	for _, tt := range unicastTests {
+		if tt.wildcard && avoidOSXFirewallDialogPopup() {
+			continue
+		}
 		if tt.ipv6 && !supportsIPv6 {
 			continue
 		}
-		var (
+		port := usableLocalPort(t, tt.net, tt.laddr)
-			fd     *netFD
+		l1, err := Listen(tt.net, tt.laddr+":"+port)
-			closer io.Closer
+		if err != nil {
-		)
+			t.Fatalf("First Listen(%q, %q) failed: %v", tt.net, tt.laddr+":"+port, err)
-		if !tt.packet {
-			if tt.laddr == "previous" {
-				tt.laddr = prevladdr
-			}
-			l, err := Listen(tt.net, tt.laddr)
-			if err != nil {
-				t.Fatalf("Listen failed: %v", err)
-			}
-			prevladdr = l.Addr().String()
-			closer = l
-			fd = l.(*TCPListener).fd
-		} else {
-			c, err := ListenPacket(tt.net, tt.laddr)
-			if err != nil {
-				t.Fatalf("ListenPacket failed: %v", err)
-			}
-			closer = c
-			fd = c.(*UDPConn).fd
 		}
-		if !tt.ipv6 {
+		checkFirstListener(t, tt.net, tt.laddr+":"+port, l1)
+		l2, err := Listen(tt.net, tt.laddr+":"+port)
+		checkSecondListener(t, tt.net, tt.laddr+":"+port, err, l2)
+		fd := l1.(*TCPListener).fd
+		switch fd.family {
+		case syscall.AF_INET:
 			testIPv4UnicastSocketOptions(t, fd)
-		} else {
+		case syscall.AF_INET6:
 			testIPv6UnicastSocketOptions(t, fd)
 		}
-		closer.Close()
+		l1.(io.Closer).Close()
+	}
+}
+
+// TestUDPListener tests both single and double listen to a test
+// listener with same address family, same listening address and
+// same port.
+func TestUDPListener(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9", "windows":
+		return
+	}
+
+	toudpnet := func(net string) string {
+		switch net {
+		case "tcp":
+			return "udp"
+		case "tcp4":
+			return "udp4"
+		case "tcp6":
+			return "udp6"
+		}
+		return "<nil>"
+	}
+
+	for _, tt := range listenerTests {
+		if tt.wildcard && avoidOSXFirewallDialogPopup() {
+			continue
+		}
+		if tt.ipv6 && !supportsIPv6 {
+			continue
+		}
+		tt.net = toudpnet(tt.net)
+		port := usableLocalPort(t, tt.net, tt.laddr)
+		l1, err := ListenPacket(tt.net, tt.laddr+":"+port)
+		if err != nil {
+			t.Fatalf("First ListenPacket(%q, %q) failed: %v", tt.net, tt.laddr+":"+port, err)
+		}
+		checkFirstListener(t, tt.net, tt.laddr+":"+port, l1)
+		l2, err := ListenPacket(tt.net, tt.laddr+":"+port)
+		checkSecondListener(t, tt.net, tt.laddr+":"+port, err, l2)
+		fd := l1.(*UDPConn).fd
+		switch fd.family {
+		case syscall.AF_INET:
+			testIPv4UnicastSocketOptions(t, fd)
+		case syscall.AF_INET6:
+			testIPv6UnicastSocketOptions(t, fd)
+		}
+		l1.(io.Closer).Close()
+	}
+}
+
+func TestSimpleTCPListener(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9":
+		return
+	}
+
+	for _, tt := range listenerTests {
+		if tt.wildcard && avoidOSXFirewallDialogPopup() {
+			continue
+		}
+		if tt.ipv6 {
+			continue
+		}
+		port := usableLocalPort(t, tt.net, tt.laddr)
+		l1, err := Listen(tt.net, tt.laddr+":"+port)
+		if err != nil {
+			t.Fatalf("First Listen(%q, %q) failed: %v", tt.net, tt.laddr+":"+port, err)
+		}
+		checkFirstListener(t, tt.net, tt.laddr+":"+port, l1)
+		l2, err := Listen(tt.net, tt.laddr+":"+port)
+		checkSecondListener(t, tt.net, tt.laddr+":"+port, err, l2)
+		l1.(io.Closer).Close()
+	}
+}
+
+func TestSimpleUDPListener(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9":
+		return
+	}
+
+	toudpnet := func(net string) string {
+		switch net {
+		case "tcp":
+			return "udp"
+		case "tcp4":
+			return "udp4"
+		case "tcp6":
+			return "udp6"
+		}
+		return "<nil>"
+	}
+
+	for _, tt := range listenerTests {
+		if tt.wildcard && avoidOSXFirewallDialogPopup() {
+			continue
+		}
+		if tt.ipv6 {
+			continue
+		}
+		tt.net = toudpnet(tt.net)
+		port := usableLocalPort(t, tt.net, tt.laddr)
+		l1, err := ListenPacket(tt.net, tt.laddr+":"+port)
+		if err != nil {
+			t.Fatalf("First ListenPacket(%q, %q) failed: %v", tt.net, tt.laddr+":"+port, err)
+		}
+		checkFirstListener(t, tt.net, tt.laddr+":"+port, l1)
+		l2, err := ListenPacket(tt.net, tt.laddr+":"+port)
+		checkSecondListener(t, tt.net, tt.laddr+":"+port, err, l2)
+		l1.(io.Closer).Close()
+	}
+}
+
+var dualStackListenerTests = []struct {
+	net1     string // first listener
+	laddr1   string
+	net2     string // second listener
+	laddr2   string
+	wildcard bool  // test with wildcard address
+	xerr     error // expected error value, nil or other
+}{
+	// Test cases and expected results for the attemping 2nd listen on the same port
+	// 1st listen                2nd listen                 darwin  freebsd  linux  openbsd
+	// ------------------------------------------------------------------------------------
+	// "tcp"  ""                 "tcp"  ""                    -        -       -       - 
+	// "tcp"  ""                 "tcp"  "0.0.0.0"             -        -       -       - 
+	// "tcp"  "0.0.0.0"          "tcp"  ""                    -        -       -       - 
+	// ------------------------------------------------------------------------------------
+	// "tcp"  ""                 "tcp"  "[::]"                -        -       -       ok
+	// "tcp"  "[::]"             "tcp"  ""                    -        -       -       ok
+	// "tcp"  "0.0.0.0"          "tcp"  "[::]"                -        -       -       ok
+	// "tcp"  "[::]"             "tcp"  "0.0.0.0"             -        -       -       ok
+	// "tcp"  "[::ffff:0.0.0.0]" "tcp"  "[::]"                -        -       -       ok
+	// "tcp"  "[::]"             "tcp"  "[::ffff:0.0.0.0]"    -        -       -       ok
+	// ------------------------------------------------------------------------------------
+	// "tcp4" ""                 "tcp6" ""                    ok       ok      ok      ok
+	// "tcp6" ""                 "tcp4" ""                    ok       ok      ok      ok
+	// "tcp4" "0.0.0.0"          "tcp6" "[::]"                ok       ok      ok      ok
+	// "tcp6" "[::]"             "tcp4" "0.0.0.0"             ok       ok      ok      ok
+	// ------------------------------------------------------------------------------------
+	// "tcp"  "127.0.0.1"        "tcp"  "[::1]"               ok       ok      ok      ok
+	// "tcp"  "[::1]"            "tcp"  "127.0.0.1"           ok       ok      ok      ok
+	// "tcp4" "127.0.0.1"        "tcp6" "[::1]"               ok       ok      ok      ok
+	// "tcp6" "[::1]"            "tcp4" "127.0.0.1"           ok       ok      ok      ok
+	//
+	// Platform default configurations:
+	// darwin, kernel version 11.3.0
+	//	net.inet6.ip6.v6only=0 (overridable by sysctl or IPV6_V6ONLY option)
+	// freebsd, kernel version 8.2
+	//	net.inet6.ip6.v6only=1 (overridable by sysctl or IPV6_V6ONLY option)
+	// linux, kernel version 3.0.0
+	//	net.ipv6.bindv6only=0 (overridable by sysctl or IPV6_V6ONLY option)
+	// openbsd, kernel version 5.0
+	//	net.inet6.ip6.v6only=1 (overriding is prohibited)
+
+	{net1: "tcp", laddr1: "", net2: "tcp", laddr2: "", wildcard: true, xerr: syscall.EADDRINUSE},
+	{net1: "tcp", laddr1: "", net2: "tcp", laddr2: "0.0.0.0", wildcard: true, xerr: syscall.EADDRINUSE},
+	{net1: "tcp", laddr1: "0.0.0.0", net2: "tcp", laddr2: "", wildcard: true, xerr: syscall.EADDRINUSE},
+
+	{net1: "tcp", laddr1: "", net2: "tcp", laddr2: "[::]", wildcard: true, xerr: syscall.EADDRINUSE},
+	{net1: "tcp", laddr1: "[::]", net2: "tcp", laddr2: "", wildcard: true, xerr: syscall.EADDRINUSE},
+	{net1: "tcp", laddr1: "0.0.0.0", net2: "tcp", laddr2: "[::]", wildcard: true, xerr: syscall.EADDRINUSE},
+	{net1: "tcp", laddr1: "[::]", net2: "tcp", laddr2: "0.0.0.0", wildcard: true, xerr: syscall.EADDRINUSE},
+	{net1: "tcp", laddr1: "[::ffff:0.0.0.0]", net2: "tcp", laddr2: "[::]", wildcard: true, xerr: syscall.EADDRINUSE},
+	{net1: "tcp", laddr1: "[::]", net2: "tcp", laddr2: "[::ffff:0.0.0.0]", wildcard: true, xerr: syscall.EADDRINUSE},
+
+	{net1: "tcp4", laddr1: "", net2: "tcp6", laddr2: "", wildcard: true},
+	{net1: "tcp6", laddr1: "", net2: "tcp4", laddr2: "", wildcard: true},
+	{net1: "tcp4", laddr1: "0.0.0.0", net2: "tcp6", laddr2: "[::]", wildcard: true},
+	{net1: "tcp6", laddr1: "[::]", net2: "tcp4", laddr2: "0.0.0.0", wildcard: true},
+
+	{net1: "tcp", laddr1: "127.0.0.1", net2: "tcp", laddr2: "[::1]"},
+	{net1: "tcp", laddr1: "[::1]", net2: "tcp", laddr2: "127.0.0.1"},
+	{net1: "tcp4", laddr1: "127.0.0.1", net2: "tcp6", laddr2: "[::1]"},
+	{net1: "tcp6", laddr1: "[::1]", net2: "tcp4", laddr2: "127.0.0.1"},
+}
+
+// TestDualStackTCPListener tests both single and double listen
+// to a test listener with various address families, differnet
+// listening address and same port.
+func TestDualStackTCPListener(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9":
+		return
+	}
+	if !supportsIPv6 {
+		return
+	}
+
+	for _, tt := range dualStackListenerTests {
+		if tt.wildcard && avoidOSXFirewallDialogPopup() {
+			continue
+		}
+		switch runtime.GOOS {
+		case "openbsd":
+			if tt.wildcard && differentWildcardAddr(tt.laddr1, tt.laddr2) {
+				tt.xerr = nil
+			}
+		}
+		port := usableLocalPort(t, tt.net1, tt.laddr1)
+		laddr := tt.laddr1 + ":" + port
+		l1, err := Listen(tt.net1, laddr)
+		if err != nil {
+			t.Fatalf("First Listen(%q, %q) failed: %v", tt.net1, laddr, err)
+		}
+		checkFirstListener(t, tt.net1, laddr, l1)
+		laddr = tt.laddr2 + ":" + port
+		l2, err := Listen(tt.net2, laddr)
+		checkDualStackSecondListener(t, tt.net2, laddr, tt.xerr, err, l2)
+		l1.Close()
+	}
+}
+
+// TestDualStackUDPListener tests both single and double listen
+// to a test listener with various address families, differnet
+// listening address and same port.
+func TestDualStackUDPListener(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9":
+		return
+	}
+	if !supportsIPv6 {
+		return
+	}
+
+	toudpnet := func(net string) string {
+		switch net {
+		case "tcp":
+			return "udp"
+		case "tcp4":
+			return "udp4"
+		case "tcp6":
+			return "udp6"
+		}
+		return "<nil>"
+	}
+
+	for _, tt := range dualStackListenerTests {
+		if tt.wildcard && avoidOSXFirewallDialogPopup() {
+			continue
+		}
+		tt.net1 = toudpnet(tt.net1)
+		tt.net2 = toudpnet(tt.net2)
+		switch runtime.GOOS {
+		case "openbsd":
+			if tt.wildcard && differentWildcardAddr(tt.laddr1, tt.laddr2) {
+				tt.xerr = nil
+			}
+		}
+		port := usableLocalPort(t, tt.net1, tt.laddr1)
+		laddr := tt.laddr1 + ":" + port
+		l1, err := ListenPacket(tt.net1, laddr)
+		if err != nil {
+			t.Fatalf("First ListenPacket(%q, %q) failed: %v", tt.net1, laddr, err)
+		}
+		checkFirstListener(t, tt.net1, laddr, l1)
+		laddr = tt.laddr2 + ":" + port
+		l2, err := ListenPacket(tt.net2, laddr)
+		checkDualStackSecondListener(t, tt.net2, laddr, tt.xerr, err, l2)
+		l1.Close()
+	}
+}
+
+func usableLocalPort(t *testing.T, net, laddr string) string {
+	var nladdr string
+	switch net {
+	case "tcp", "tcp4", "tcp6":
+		l, err := Listen(net, laddr+":0")
+		if err != nil {
+			t.Fatalf("Probe Listen(%q, %q) failed: %v", net, laddr, err)
+		}
+		defer l.Close()
+		nladdr = l.(*TCPListener).Addr().String()
+	case "udp", "udp4", "udp6":
+		c, err := ListenPacket(net, laddr+":0")
+		if err != nil {
+			t.Fatalf("Probe ListenPacket(%q, %q) failed: %v", net, laddr, err)
+		}
+		defer c.Close()
+		nladdr = c.(*UDPConn).LocalAddr().String()
+	}
+	_, port, err := SplitHostPort(nladdr)
+	if err != nil {
+		t.Fatalf("SplitHostPort failed: %v", err)
+	}
+	return port
+}
+
+func differentWildcardAddr(i, j string) bool {
+	if (i == "" || i == "0.0.0.0" || i == "::ffff:0.0.0.0") && (j == "" || j == "0.0.0.0" || j == "::ffff:0.0.0.0") {
+		return false
+	}
+	if i == "[::]" && j == "[::]" {
+		return false
+	}
+	return true
+}
+
+func checkFirstListener(t *testing.T, net, laddr string, l interface{}) {
+	switch net {
+	case "tcp":
+		fd := l.(*TCPListener).fd
+		checkDualStackAddrFamily(t, net, laddr, fd)
+	case "tcp4":
+		fd := l.(*TCPListener).fd
+		if fd.family != syscall.AF_INET {
+			t.Fatalf("First Listen(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, syscall.AF_INET)
+		}
+	case "tcp6":
+		fd := l.(*TCPListener).fd
+		if fd.family != syscall.AF_INET6 {
+			t.Fatalf("First Listen(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, syscall.AF_INET6)
+		}
+	case "udp":
+		fd := l.(*UDPConn).fd
+		checkDualStackAddrFamily(t, net, laddr, fd)
+	case "udp4":
+		fd := l.(*UDPConn).fd
+		if fd.family != syscall.AF_INET {
+			t.Fatalf("First ListenPacket(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, syscall.AF_INET)
+		}
+	case "udp6":
+		fd := l.(*UDPConn).fd
+		if fd.family != syscall.AF_INET6 {
+			t.Fatalf("First ListenPacket(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, syscall.AF_INET6)
+		}
+	default:
+		t.Fatalf("Unexpected network: %q", net)
+	}
+}
+
+func checkSecondListener(t *testing.T, net, laddr string, err error, l interface{}) {
+	switch net {
+	case "tcp", "tcp4", "tcp6":
+		if err == nil {
+			l.(*TCPListener).Close()
+			t.Fatalf("Second Listen(%q, %q) should fail", net, laddr)
+		}
+	case "udp", "udp4", "udp6":
+		if err == nil {
+			l.(*UDPConn).Close()
+			t.Fatalf("Second ListenPacket(%q, %q) should fail", net, laddr)
+		}
+	default:
+		t.Fatalf("Unexpected network: %q", net)
+	}
+}
+
+func checkDualStackSecondListener(t *testing.T, net, laddr string, xerr, err error, l interface{}) {
+	switch net {
+	case "tcp", "tcp4", "tcp6":
+		if xerr == nil && err != nil || xerr != nil && err == nil {
+			t.Fatalf("Second Listen(%q, %q) returns %v, expected %v", net, laddr, err, xerr)
+		}
+		l.(*TCPListener).Close()
+	case "udp", "udp4", "udp6":
+		if xerr == nil && err != nil || xerr != nil && err == nil {
+			t.Fatalf("Second ListenPacket(%q, %q) returns %v, expected %v", net, laddr, err, xerr)
+		}
+		l.(*UDPConn).Close()
+	default:
+		t.Fatalf("Unexpected network: %q", net)
+	}
+}
+
+func checkDualStackAddrFamily(t *testing.T, net, laddr string, fd *netFD) {
+	switch a := fd.laddr.(type) {
+	case *TCPAddr:
+		// If a node under test supports both IPv6 capability
+		// and IPv6 IPv4-mapping capability, we can assume
+		// that the node listens on a wildcard address with an
+		// AF_INET6 socket.
+		if supportsIPv4map && fd.laddr.(*TCPAddr).isWildcard() {
+			if fd.family != syscall.AF_INET6 {
+				t.Fatalf("Listen(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, syscall.AF_INET6)
+			}
+		} else {
+			if fd.family != a.family() {
+				t.Fatalf("Listen(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, a.family())
+			}
+		}
+	case *UDPAddr:
+		// If a node under test supports both IPv6 capability
+		// and IPv6 IPv4-mapping capability, we can assume
+		// that the node listens on a wildcard address with an
+		// AF_INET6 socket.
+		if supportsIPv4map && fd.laddr.(*UDPAddr).isWildcard() {
+			if fd.family != syscall.AF_INET6 {
+				t.Fatalf("ListenPacket(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, syscall.AF_INET6)
+			}
+		} else {
+			if fd.family != a.family() {
+				t.Fatalf("ListenPacket(%q, %q) returns address family %v, expected %v", net, laddr, fd.family, a.family())
+			}
+		}
+	default:
+		t.Fatalf("Unexpected protocol address type: %T", a)
 	}
 }
 
 func testIPv4UnicastSocketOptions(t *testing.T, fd *netFD) {
-	tos, err := ipv4TOS(fd)
+	_, err := ipv4TOS(fd)
 	if err != nil {
 		t.Fatalf("ipv4TOS failed: %v", err)
 	}
-	t.Logf("IPv4 TOS: %v", tos)
 	err = setIPv4TOS(fd, 1)
 	if err != nil {
 		t.Fatalf("setIPv4TOS failed: %v", err)
 	}
-
+	_, err = ipv4TTL(fd)
-	ttl, err := ipv4TTL(fd)
 	if err != nil {
 		t.Fatalf("ipv4TTL failed: %v", err)
 	}
-	t.Logf("IPv4 TTL: %v", ttl)
 	err = setIPv4TTL(fd, 1)
 	if err != nil {
 		t.Fatalf("setIPv4TTL failed: %v", err)
@@ -89,23 +492,53 @@ func testIPv4UnicastSocketOptions(t *testing.T, fd *netFD) {
 }
 
 func testIPv6UnicastSocketOptions(t *testing.T, fd *netFD) {
-	tos, err := ipv6TrafficClass(fd)
+	_, err := ipv6TrafficClass(fd)
 	if err != nil {
 		t.Fatalf("ipv6TrafficClass failed: %v", err)
 	}
-	t.Logf("IPv6 TrafficClass: %v", tos)
 	err = setIPv6TrafficClass(fd, 1)
 	if err != nil {
 		t.Fatalf("setIPv6TrafficClass failed: %v", err)
 	}
-
+	_, err = ipv6HopLimit(fd)
-	hoplim, err := ipv6HopLimit(fd)
 	if err != nil {
 		t.Fatalf("ipv6HopLimit failed: %v", err)
 	}
-	t.Logf("IPv6 HopLimit: %v", hoplim)
 	err = setIPv6HopLimit(fd, 1)
 	if err != nil {
 		t.Fatalf("setIPv6HopLimit failed: %v", err)
 	}
 }
+
+var prohibitionaryDialArgTests = []struct {
+	net  string
+	addr string
+}{
+	{"tcp6", "127.0.0.1"},
+	{"tcp6", "[::ffff:127.0.0.1]"},
+}
+
+func TestProhibitionaryDialArgs(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9":
+		return
+	}
+	// This test requires both IPv6 and IPv6 IPv4-mapping functionality.
+	if !supportsIPv4map || avoidOSXFirewallDialogPopup() {
+		return
+	}
+
+	port := usableLocalPort(t, "tcp", "[::]")
+	l, err := Listen("tcp", "[::]"+":"+port)
+	if err != nil {
+		t.Fatalf("Listen failed: %v", err)
+	}
+	defer l.Close()
+
+	for _, tt := range prohibitionaryDialArgTests {
+		_, err = Dial(tt.net, tt.addr+":"+port)
+		if err == nil {
+			t.Fatal("Dial(%q, %q) should fail", tt.net, tt.addr)
+		}
+	}
+}

src/pkg/net/unixsock_posix.go

@@ -59,7 +59,7 @@ func unixSocket(net string, laddr, raddr *UnixAddr, mode string) (fd *netFD, err
 		f = sockaddrToUnixpacket
 	}
 
-	fd, err = socket(net, syscall.AF_UNIX, sotype, 0, la, ra, f)
+	fd, err = socket(net, syscall.AF_UNIX, sotype, 0, false, la, ra, f)
 	if err != nil {
 		goto Error
 	}