net: protocol family adaptive address family selection

This CL will help to make an adaptive address family
selection possible when an any address family, vague
network string such as "ip", "tcp" or "udp" is passed
to Dial and Listen API.

Fixes #1769.

R=bradfitz, rsc
CC=golang-dev
https://golang.org/cl/4438066

src/pkg/net/dial.go

@@ -60,7 +60,7 @@ func Dial(net, addr string) (c Conn, err os.Error) {
 		return c, nil
 	case "ip", "ip4", "ip6":
 		var ra *IPAddr
-		if ra, err = ResolveIPAddr(raddr); err != nil {
+		if ra, err = ResolveIPAddr(net, raddr); err != nil {
 			goto Error
 		}
 		c, err := DialIP(net, nil, ra)
@@ -139,12 +139,13 @@ func ListenPacket(net, laddr string) (c PacketConn, err os.Error) {
 		return c, nil
 	}
 
-	if i := last(net, ':'); i > 0 {
-		switch net[0:i] {
+	var rawnet string
+	if rawnet, _, err = splitNetProto(net); err != nil {
+		switch rawnet {
 		case "ip", "ip4", "ip6":
 			var la *IPAddr
 			if laddr != "" {
-				if la, err = ResolveIPAddr(laddr); err != nil {
+				if la, err = ResolveIPAddr(rawnet, laddr); err != nil {
 					return nil, err
 				}
 			}

src/pkg/net/dialgoogle_test.go

@@ -105,14 +105,12 @@ func TestDialGoogleIPv4(t *testing.T) {
 		doDial(t, "tcp", addr)
 		if addr[0] != '[' {
 			doDial(t, "tcp4", addr)
-			if !preferIPv4 {
-				// make sure preferIPv4 flag works.
-				preferIPv4 = true
+			if supportsIPv6 {
+				// make sure syscall.SocketDisableIPv6 flag works.
 				syscall.SocketDisableIPv6 = true
 				doDial(t, "tcp", addr)
 				doDial(t, "tcp4", addr)
 				syscall.SocketDisableIPv6 = false
-				preferIPv4 = false
 			}
 		}
 	}
@@ -132,7 +130,7 @@ func TestDialGoogleIPv6(t *testing.T) {
 		return
 	}
 	// Only run tcp6 if the kernel will take it.
-	if !*ipv6 || !kernelSupportsIPv6() {
+	if !*ipv6 || !supportsIPv6 {
 		return
 	}
 

src/pkg/net/file_test.go

@@ -62,7 +62,7 @@ func TestFileListener(t *testing.T) {
 	}
 	testFileListener(t, "tcp", "127.0.0.1")
 	testFileListener(t, "tcp", "127.0.0.1")
-	if kernelSupportsIPv6() {
+	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]")
@@ -121,8 +121,10 @@ func TestFilePacketConn(t *testing.T) {
 	}
 	testFilePacketConnListen(t, "udp", "127.0.0.1:0")
 	testFilePacketConnDial(t, "udp", "127.0.0.1:12345")
-	if kernelSupportsIPv6() {
+	if supportsIPv6 {
 		testFilePacketConnListen(t, "udp", "[::1]:0")
+	}
+	if supportsIPv6 && supportsIPv4map {
 		testFilePacketConnDial(t, "udp", "[::ffff:127.0.0.1]:12345")
 	}
 	if syscall.OS == "linux" {

src/pkg/net/ip.go

@@ -75,8 +75,12 @@ var (
 
 // Well-known IPv6 addresses
 var (
-	IPzero       = make(IP, IPv6len) // all zeros
-	IPv6loopback = IP([]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1})
+	IPv6zero                   = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+	IPv6unspecified            = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+	IPv6loopback               = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}
+	IPv6interfacelocalallnodes = IP{0xff, 0x01, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
+	IPv6linklocalallnodes      = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
+	IPv6linklocalallrouters    = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x02}
 )
 
 // Is p all zeros?

src/pkg/net/ip_test.go

@@ -143,3 +143,36 @@ func TestJoinHostPort(t *testing.T) {
 		}
 	}
 }
+
+var ipaftests = []struct {
+	in  IP
+	af4 bool
+	af6 bool
+}{
+	{IPv4bcast, true, false},
+	{IPv4allsys, true, false},
+	{IPv4allrouter, true, false},
+	{IPv4zero, true, false},
+	{IPv4(224, 0, 0, 1), true, false},
+	{IPv4(127, 0, 0, 1), true, false},
+	{IPv4(240, 0, 0, 1), true, false},
+	{IPv6unspecified, false, true},
+	{IPv6loopback, false, true},
+	{IPv6interfacelocalallnodes, false, true},
+	{IPv6linklocalallnodes, false, true},
+	{IPv6linklocalallrouters, false, true},
+	{ParseIP("ff05::a:b:c:d"), false, true},
+	{ParseIP("fe80::1:2:3:4"), false, true},
+	{ParseIP("2001:db8::123:12:1"), false, true},
+}
+
+func TestIPAddrFamily(t *testing.T) {
+	for _, tt := range ipaftests {
+		if af := tt.in.To4() != nil; af != tt.af4 {
+			t.Errorf("verifying IPv4 address family for %#q = %v, want %v", tt.in, af, tt.af4)
+		}
+		if af := len(tt.in) == IPv6len && tt.in.To4() == nil; af != tt.af6 {
+			t.Errorf("verifying IPv6 address family for %#q = %v, want %v", tt.in, af, tt.af6)
+		}
+	}
+}

src/pkg/net/ipraw_test.go

@@ -75,15 +75,15 @@ func TestICMP(t *testing.T) {
 		err   os.Error
 	)
 	if *srchost != "" {
-		laddr, err = ResolveIPAddr(*srchost)
+		laddr, err = ResolveIPAddr("ip4", *srchost)
 		if err != nil {
-			t.Fatalf(`net.ResolveIPAddr("%v") = %v, %v`, *srchost, laddr, err)
+			t.Fatalf(`net.ResolveIPAddr("ip4", %v") = %v, %v`, *srchost, laddr, err)
 		}
 	}
 
-	raddr, err := ResolveIPAddr(*dsthost)
+	raddr, err := ResolveIPAddr("ip4", *dsthost)
 	if err != nil {
-		t.Fatalf(`net.ResolveIPAddr("%v") = %v, %v`, *dsthost, raddr, err)
+		t.Fatalf(`net.ResolveIPAddr("ip4", %v") = %v, %v`, *dsthost, raddr, err)
 	}
 
 	c, err := ListenIP("ip4:icmp", laddr)

src/pkg/net/iprawsock.go

@@ -43,7 +43,7 @@ func (a *IPAddr) family() int {
 	if a == nil || len(a.IP) <= 4 {
 		return syscall.AF_INET
 	}
-	if ip := a.IP.To4(); ip != nil {
+	if a.IP.To4() != nil {
 		return syscall.AF_INET
 	}
 	return syscall.AF_INET6
@@ -61,10 +61,11 @@ func (a *IPAddr) toAddr() sockaddr {
 }
 
 // ResolveIPAddr parses addr as a IP address and resolves domain
-// names to numeric addresses.  A literal IPv6 host address must be
+// names to numeric addresses on the network net, which must be
+// "ip", "ip4" or "ip6".  A literal IPv6 host address must be
 // enclosed in square brackets, as in "[::]".
-func ResolveIPAddr(addr string) (*IPAddr, os.Error) {
-	ip, err := hostToIP(addr)
+func ResolveIPAddr(net, addr string) (*IPAddr, os.Error) {
+	ip, err := hostToIP(net, addr)
 	if err != nil {
 		return nil, err
 	}
@@ -234,32 +235,36 @@ func (c *IPConn) WriteTo(b []byte, addr Addr) (n int, err os.Error) {
 }
 
 // Convert "host" into IP address.
-func hostToIP(host string) (ip IP, err os.Error) {
+func hostToIP(net, host string) (ip IP, err os.Error) {
 	var addr IP
 	// Try as an IP address.
 	addr = ParseIP(host)
 	if addr == nil {
+		filter := anyaddr
+		if net != "" && net[len(net)-1] == '4' {
+			filter = ipv4only
+		}
+		if net != "" && net[len(net)-1] == '6' {
+			filter = ipv6only
+		}
 		// Not an IP address.  Try as a DNS name.
 		addrs, err1 := LookupHost(host)
 		if err1 != nil {
 			err = err1
 			goto Error
 		}
-		addr = firstSupportedAddr(anyaddr, addrs)
+		addr = firstFavoriteAddr(filter, addrs)
 		if addr == nil {
 			// should not happen
-			err = &AddrError{"LookupHost returned invalid address", addrs[0]}
+			err = &AddrError{"LookupHost returned no suitable address", addrs[0]}
 			goto Error
 		}
 	}
-
 	return addr, nil
-
 Error:
 	return nil, err
 }
 
-
 var protocols map[string]int
 
 func readProtocols() {
@@ -285,7 +290,7 @@ func readProtocols() {
 	}
 }
 
-func netProtoSplit(netProto string) (net string, proto int, err os.Error) {
+func splitNetProto(netProto string) (net string, proto int, err os.Error) {
 	onceReadProtocols.Do(readProtocols)
 	i := last(netProto, ':')
 	if i < 0 { // no colon
@@ -307,7 +312,7 @@ func netProtoSplit(netProto string) (net string, proto int, err os.Error) {
 // DialIP connects to the remote address raddr on the network net,
 // which must be "ip", "ip4", or "ip6".
 func DialIP(netProto string, laddr, raddr *IPAddr) (c *IPConn, err os.Error) {
-	net, proto, err := netProtoSplit(netProto)
+	net, proto, err := splitNetProto(netProto)
 	if err != nil {
 		return
 	}
@@ -331,7 +336,7 @@ func DialIP(netProto string, laddr, raddr *IPAddr) (c *IPConn, err os.Error) {
 // and WriteTo methods can be used to receive and send IP
 // packets with per-packet addressing.
 func ListenIP(netProto string, laddr *IPAddr) (c *IPConn, err os.Error) {
-	net, proto, err := netProtoSplit(netProto)
+	net, proto, err := splitNetProto(netProto)
 	if err != nil {
 		return
 	}

src/pkg/net/ipsock.go

@@ -15,25 +15,86 @@ import (
 // only dealing with IPv4 sockets?  As long as the host system
 // understands IPv6, it's okay to pass IPv4 addresses to the IPv6
 // interface.  That simplifies our code and is most general.
-// Unfortunately, we need to run on kernels built without IPv6 support too.
-// So probe the kernel to figure it out.
-func kernelSupportsIPv6() bool {
-	s, err := syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
-	if err != 0 {
-		return false
+// Unfortunately, we need to run on kernels built without IPv6
+// support too.  So probe the kernel to figure it out.
+//
+// probeIPv6Stack probes both basic IPv6 capability and IPv6 IPv4-
+// mapping capability which is controlled by IPV6_V6ONLY socket
+// option and/or kernel state "net.inet6.ip6.v6only".
+// It returns two boolean values.  If the first boolean value is
+// true, kernel supports basic IPv6 functionality.  If the second
+// boolean value is true, kernel supports IPv6 IPv4-mapping.
+func probeIPv6Stack() (supportsIPv6, supportsIPv4map bool) {
+	var probes = []struct {
+		s  int
+		la TCPAddr
+		ok bool
+	}{
+		// IPv6 communication capability
+		{-1, TCPAddr{IP: ParseIP("::1")}, false},
+		// IPv6 IPv4-mapped address communication capability
+		{-1, TCPAddr{IP: IPv4(127, 0, 0, 1)}, false},
 	}
-	defer closesocket(s)
+	var errno int
 
-	la := &TCPAddr{IP: IPv4(127, 0, 0, 1)}
-	sa, oserr := la.toAddr().sockaddr(syscall.AF_INET6)
-	if oserr != nil {
-		return false
+	for i := range probes {
+		probes[i].s, errno = syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
+		if errno != 0 {
+			continue
+		}
+		defer closesocket(probes[i].s)
+		sa, err := probes[i].la.toAddr().sockaddr(syscall.AF_INET6)
+		if err != nil {
+			continue
+		}
+		errno = syscall.Bind(probes[i].s, sa)
+		if errno != 0 {
+			continue
+		}
+		probes[i].ok = true
 	}
 
-	return syscall.Bind(s, sa) == 0
+	return probes[0].ok, probes[1].ok
+}
+
+var supportsIPv6, supportsIPv4map = probeIPv6Stack()
+
+func favoriteAddrFamily(net string, raddr, laddr sockaddr) (family int) {
+	// Figure out IP version.
+	// If network has a suffix like "tcp4", obey it.
+	family = syscall.AF_INET6
+	switch net[len(net)-1] {
+	case '4':
+		family = syscall.AF_INET
+	case '6':
+		// nothing to do
+	default:
+		// Otherwise, guess.
+		// If the addresses are IPv4, use 4; else 6.
+		if (laddr == nil || laddr.family() == syscall.AF_INET) &&
+			(raddr == nil || raddr.family() == syscall.AF_INET) {
+			family = syscall.AF_INET
+		}
+	}
+	return
 }
 
-var preferIPv4 = !kernelSupportsIPv6()
+func firstFavoriteAddr(filter func(IP) IP, addrs []string) (addr IP) {
+	if filter == anyaddr {
+		// We'll take any IP address, but since the dialing code
+		// does not yet try multiple addresses, prefer to use
+		// an IPv4 address if possible.  This is especially relevant
+		// if localhost resolves to [ipv6-localhost, ipv4-localhost].
+		// Too much code assumes localhost == ipv4-localhost.
+		addr = firstSupportedAddr(ipv4only, addrs)
+		if addr == nil {
+			addr = firstSupportedAddr(anyaddr, addrs)
+		}
+	} else {
+		addr = firstSupportedAddr(filter, addrs)
+	}
+	return
+}
 
 func firstSupportedAddr(filter func(IP) IP, addrs []string) IP {
 	for _, s := range addrs {
@@ -44,19 +105,25 @@ func firstSupportedAddr(filter func(IP) IP, addrs []string) IP {
 	return nil
 }
 
-func anyaddr(x IP) IP  { return x }
+func anyaddr(x IP) IP {
+	if x4 := x.To4(); x4 != nil {
+		return x4
+	}
+	if supportsIPv6 {
+		return x
+	}
+	return nil
+}
+
 func ipv4only(x IP) IP { return x.To4() }
 
 func ipv6only(x IP) IP {
 	// Only return addresses that we can use
 	// with the kernel's IPv6 addressing modes.
-	// If preferIPv4 is set, it means the IPv6 stack
-	// cannot take IPv4 addresses directly (we prefer
-	// to use the IPv4 stack) so reject IPv4 addresses.
-	if x.To4() != nil && preferIPv4 {
-		return nil
+	if len(x) == IPv6len && x.To4() == nil && supportsIPv6 {
+		return x
 	}
-	return x
+	return nil
 }
 
 // TODO(rsc): if syscall.OS == "linux", we're supposd to read
@@ -78,23 +145,8 @@ func internetSocket(net string, laddr, raddr sockaddr, socktype, proto int, mode
 	// Figure out IP version.
 	// If network has a suffix like "tcp4", obey it.
 	var oserr os.Error
-	family := syscall.AF_INET6
-	switch net[len(net)-1] {
-	case '4':
-		family = syscall.AF_INET
-	case '6':
-		// nothing to do
-	default:
-		// Otherwise, guess.
-		// If the addresses are IPv4 and we prefer IPv4, use 4; else 6.
-		if preferIPv4 &&
-			(laddr == nil || laddr.family() == syscall.AF_INET) &&
-			(raddr == nil || raddr.family() == syscall.AF_INET) {
-			family = syscall.AF_INET
-		}
-	}
-
 	var la, ra syscall.Sockaddr
+	family := favoriteAddrFamily(net, raddr, laddr)
 	if laddr != nil {
 		if la, oserr = laddr.sockaddr(family); oserr != nil {
 			goto Error
@@ -142,13 +194,13 @@ func ipToSockaddr(family int, ip IP, port int) (syscall.Sockaddr, os.Error) {
 		return s, nil
 	case syscall.AF_INET6:
 		if len(ip) == 0 {
-			ip = IPzero
+			ip = IPv6zero
 		}
 		// 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.
-		if p4 := ip.To4(); p4 != nil && p4[0] == 0 && p4[1] == 0 && p4[2] == 0 && p4[3] == 0 {
-			ip = IPzero
+		if ip.Equal(IPv4zero) {
+			ip = IPv6zero
 		}
 		if ip = ip.To16(); ip == nil {
 			return nil, InvalidAddrError("non-IPv6 address")
@@ -212,9 +264,10 @@ func hostPortToIP(net, hostport string) (ip IP, iport int, err os.Error) {
 		addr = ParseIP(host)
 		if addr == nil {
 			filter := anyaddr
-			if len(net) >= 4 && net[3] == '4' {
+			if net != "" && net[len(net)-1] == '4' {
 				filter = ipv4only
-			} else if len(net) >= 4 && net[3] == '6' {
+			}
+			if net != "" && net[len(net)-1] == '6' {
 				filter = ipv6only
 			}
 			// Not an IP address.  Try as a DNS name.
@@ -223,22 +276,10 @@ func hostPortToIP(net, hostport string) (ip IP, iport int, err os.Error) {
 				err = err1
 				goto Error
 			}
-			if filter == anyaddr {
-				// We'll take any IP address, but since the dialing code
-				// does not yet try multiple addresses, prefer to use
-				// an IPv4 address if possible.  This is especially relevant
-				// if localhost resolves to [ipv6-localhost, ipv4-localhost].
-				// Too much code assumes localhost == ipv4-localhost.
-				addr = firstSupportedAddr(ipv4only, addrs)
-				if addr == nil {
-					addr = firstSupportedAddr(anyaddr, addrs)
-				}
-			} else {
-				addr = firstSupportedAddr(filter, addrs)
-			}
+			addr = firstFavoriteAddr(filter, addrs)
 			if addr == nil {
 				// should not happen
-				err = &AddrError{"LookupHost returned invalid address", addrs[0]}
+				err = &AddrError{"LookupHost returned no suitable address", addrs[0]}
 				goto Error
 			}
 		}

src/pkg/net/server_test.go

@@ -109,8 +109,10 @@ func doTest(t *testing.T, network, listenaddr, dialaddr string) {
 
 func TestTCPServer(t *testing.T) {
 	doTest(t, "tcp", "127.0.0.1", "127.0.0.1")
-	if kernelSupportsIPv6() {
+	if supportsIPv6 {
 		doTest(t, "tcp", "[::1]", "[::1]")
+	}
+	if supportsIPv6 && supportsIPv4map {
 		doTest(t, "tcp", "127.0.0.1", "[::ffff:127.0.0.1]")
 	}
 }
@@ -186,7 +188,7 @@ 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 kernelSupportsIPv6() {
+		if supportsIPv6 && 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/tcpsock.go

@@ -41,7 +41,7 @@ func (a *TCPAddr) family() int {
 	if a == nil || len(a.IP) <= 4 {
 		return syscall.AF_INET
 	}
-	if ip := a.IP.To4(); ip != nil {
+	if a.IP.To4() != nil {
 		return syscall.AF_INET
 	}
 	return syscall.AF_INET6
@@ -60,10 +60,11 @@ func (a *TCPAddr) toAddr() sockaddr {
 
 // ResolveTCPAddr parses addr as a TCP address of the form
 // host:port and resolves domain names or port names to
-// numeric addresses.  A literal IPv6 host address must be
+// numeric addresses on the network net, which must be "tcp",
+// "tcp4" or "tcp6".  A literal IPv6 host address must be
 // enclosed in square brackets, as in "[::]:80".
-func ResolveTCPAddr(network, addr string) (*TCPAddr, os.Error) {
-	ip, port, err := hostPortToIP(network, addr)
+func ResolveTCPAddr(net, addr string) (*TCPAddr, os.Error) {
+	ip, port, err := hostPortToIP(net, addr)
 	if err != nil {
 		return nil, err
 	}

src/pkg/net/udpsock.go

@@ -41,7 +41,7 @@ func (a *UDPAddr) family() int {
 	if a == nil || len(a.IP) <= 4 {
 		return syscall.AF_INET
 	}
-	if ip := a.IP.To4(); ip != nil {
+	if a.IP.To4() != nil {
 		return syscall.AF_INET
 	}
 	return syscall.AF_INET6
@@ -60,10 +60,11 @@ func (a *UDPAddr) toAddr() sockaddr {
 
 // ResolveUDPAddr parses addr as a UDP address of the form
 // host:port and resolves domain names or port names to
-// numeric addresses.  A literal IPv6 host address must be
+// numeric addresses on the network net, which must be "udp",
+// "udp4" or "udp6".  A literal IPv6 host address must be
 // enclosed in square brackets, as in "[::]:80".
-func ResolveUDPAddr(network, addr string) (*UDPAddr, os.Error) {
-	ip, port, err := hostPortToIP(network, addr)
+func ResolveUDPAddr(net, addr string) (*UDPAddr, os.Error) {
+	ip, port, err := hostPortToIP(net, addr)
 	if err != nil {
 		return nil, err
 	}