net: make use of IPv4 for parsing routing information on windows

In general the package net deals IPv4 addresses as IPv6 IPv4-mapped
addresses internally for the dual stack era, when we need to support
various techniques on IPv4/IPv6 translation.

This change makes windows implementation follow the same pattern which
BSD variants and Linux do.

Updates #13544.

Also fixes an unintentionally formatted line by accident by gofmt.

Change-Id: I4953796e751fd8050c73094468a0d7b0d33f5516
Reviewed-on: https://go-review.googlesource.com/17992Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/net/interface_test.go

@@ -185,6 +185,10 @@ func testAddrs(t *testing.T, ifat []Addr) (naf4, naf6 int) {
 				t.Errorf("unexpected value: %#v", ifa)
 				continue
 			}
+			if len(ifa.IP) != IPv6len {
+				t.Errorf("should be internal representation either IPv6 or IPv6 IPv4-mapped address: %#v", ifa)
+				continue
+			}
 			prefixLen, maxPrefixLen := ifa.Mask.Size()
 			if ifa.IP.To4() != nil {
 				if 0 >= prefixLen || prefixLen > 8*IPv4len || maxPrefixLen != 8*IPv4len {
@@ -211,7 +215,11 @@ func testAddrs(t *testing.T, ifat []Addr) (naf4, naf6 int) {
 			t.Logf("interface address %q", ifa.String())
 		case *IPAddr:
 			if ifa == nil || ifa.IP == nil || ifa.IP.IsUnspecified() || ifa.IP.IsMulticast() {
-				t.Errorf("unexpected value: %+v", ifa)
+				t.Errorf("unexpected value: %#v", ifa)
+				continue
+			}
+			if len(ifa.IP) != IPv6len {
+				t.Errorf("should be internal representation either IPv6 or IPv6 IPv4-mapped address: %#v", ifa)
 				continue
 			}
 			if ifa.IP.To4() != nil {
@@ -233,7 +241,11 @@ func testMulticastAddrs(t *testing.T, ifmat []Addr) (nmaf4, nmaf6 int) {
 		switch ifma := ifma.(type) {
 		case *IPAddr:
 			if ifma == nil || ifma.IP == nil || ifma.IP.IsUnspecified() || !ifma.IP.IsMulticast() {
-				t.Errorf("unexpected value: %#v", ifma)
+				t.Errorf("unexpected value: %+v", ifma)
+				continue
+			}
+			if len(ifma.IP) != IPv6len {
+				t.Errorf("should be internal representation either IPv6 or IPv6 IPv4-mapped address: %#v", ifma)
 				continue
 			}
 			if ifma.IP.To4() != nil {

src/net/interface_windows.go

@@ -95,9 +95,7 @@ func interfaceTable(ifindex int) ([]Interface, error) {
 			case windows.IF_TYPE_SOFTWARE_LOOPBACK:
 				ifi.Flags |= FlagLoopback | FlagMulticast
 			case windows.IF_TYPE_ATM:
-				ifi.Flags |= FlagBroadcast |
-					FlagPointToPoint |
-					FlagMulticast // assume all services available; LANE, point-to-point and point-to-multipoint
+				ifi.Flags |= FlagBroadcast | FlagPointToPoint | FlagMulticast // assume all services available; LANE, point-to-point and point-to-multipoint
 			}
 			if aa.Mtu == 0xffffffff {
 				ifi.MTU = -1
@@ -152,9 +150,7 @@ func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
 					} else {
 						l = addrPrefixLen(pfx4, IP(sa.Addr[:]))
 					}
-					ifa := &IPNet{IP: make(IP, IPv4len), Mask: CIDRMask(l, 8*IPv4len)}
-					copy(ifa.IP, sa.Addr[:])
-					ifat = append(ifat, ifa)
+					ifat = append(ifat, &IPNet{IP: IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3]), Mask: CIDRMask(l, 8*IPv4len)})
 				case *syscall.SockaddrInet6:
 					if supportsVistaIP {
 						l = int(puni.OnLinkPrefixLength)
@@ -173,9 +169,7 @@ func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
 				}
 				switch sa := sa.(type) {
 				case *syscall.SockaddrInet4:
-					ifa := &IPAddr{IP: make(IP, IPv4len)}
-					copy(ifa.IP, sa.Addr[:])
-					ifat = append(ifat, ifa)
+					ifat = append(ifat, &IPAddr{IP: IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])})
 				case *syscall.SockaddrInet6:
 					ifa := &IPAddr{IP: make(IP, IPv6len)}
 					copy(ifa.IP, sa.Addr[:])
@@ -261,9 +255,7 @@ func interfaceMulticastAddrTable(ifi *Interface) ([]Addr, error) {
 				}
 				switch sa := sa.(type) {
 				case *syscall.SockaddrInet4:
-					ifa := &IPAddr{IP: make(IP, IPv4len)}
-					copy(ifa.IP, sa.Addr[:])
-					ifat = append(ifat, ifa)
+					ifat = append(ifat, &IPAddr{IP: IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])})
 				case *syscall.SockaddrInet6:
 					ifa := &IPAddr{IP: make(IP, IPv6len)}
 					copy(ifa.IP, sa.Addr[:])