//   IPv6 addresses.
			//
			// - When IP.To16() == nil and IP.To4() != nil,
			//   the raw connection consists of an IPv4
			//   socket using only IPv4 addresses.
			//
			// - Otherwise, the raw connection is a dual
			//   stack socket, an IPv6 socket using IPv6
			//   addresses including IPv4-mapped or
			//   IPv4-embedded IPv6 addresses.
			if addr.IP.To16() != nil && addr.IP.To4() == nil {

    InetAddress ipv4 = InetAddresses.forString("1.2.3.4");
    assertEquals(ipv4, InetAddresses.getEmbeddedIPv4ClientAddress(testIp));

    // Test 6to4 address.
    testIp = (Inet6Address) InetAddresses.forString("2002:0102:0304::1");
    assertTrue(InetAddresses.hasEmbeddedIPv4ClientAddress(testIp));
    ipv4 = InetAddresses.forString("1.2.3.4");
    assertEquals(ipv4, InetAddresses.getEmbeddedIPv4ClientAddress(testIp));

	}
	defer l.Close()
	if a := l.Addr(); isNotIPv4(a) {
		t.Errorf("address does not contain IPv4: %v", a)
	}
}

func TestUDP4ListenZero(t *testing.T) {
	c, err := ListenPacket("udp4", "0.0.0.0:0")
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()
	if a := c.LocalAddr(); isNotIPv4(a) {
		t.Errorf("address does not contain IPv4: %v", a)
	}

	network       string
	litAddrOrName string
	addr          *UDPAddr
	err           error
}

var resolveUDPAddrTests = []resolveUDPAddrTest{
	{"udp", "127.0.0.1:0", &UDPAddr{IP: IPv4(127, 0, 0, 1), Port: 0}, nil},
	{"udp4", "127.0.0.1:65535", &UDPAddr{IP: IPv4(127, 0, 0, 1), Port: 65535}, nil},

	{"udp", "[::1]:0", &UDPAddr{IP: ParseIP("::1"), Port: 0}, nil},
	{"udp6", "[::1]:65535", &UDPAddr{IP: ParseIP("::1"), Port: 65535}, nil},

		cidr  string
		addrs uint64
	}{
		{
			name:  "supported IPv4 cidr",
			cidr:  "192.168.1.0/24",
			addrs: 254,
		},
		{
			name:  "single IPv4 host",
			cidr:  "192.168.1.0/32",
			addrs: 0,
		},
		{
			name:  "small IPv4 cidr",
			cidr:  "192.168.1.0/31",
			addrs: 0,
		},
		{
			name:  "very large IPv4 cidr",
			cidr:  "0.0.0.0/1",
			addrs: math.MaxInt32 - 1,
		},

	"runtime"
	"sync"
	_ "unsafe" // for linkname
)

// BUG(rsc,mikio): On DragonFly BSD and OpenBSD, listening on the
// "tcp" and "udp" networks does not listen for both IPv4 and IPv6
// connections. This is due to the fact that IPv4 traffic will not be
// routed to an IPv6 socket - two separate sockets are required if
// both address families are to be supported.
// See inet6(4) for details.

			//   IPv6 addresses.
			//
			// - When IP.To16() == nil and IP.To4() != nil,
			//   the raw connection consists of an IPv4
			//   socket using only IPv4 addresses.
			//
			// - Otherwise, the raw connection is a dual
			//   stack socket, an IPv6 socket using IPv6
			//   addresses including IPv4-mapped or
			//   IPv4-embedded IPv6 addresses.
			if addr.IP.To16() != nil && addr.IP.To4() == nil {

		}
	}

	// Test functionality of IPv4 communication using AF_INET6
	// sockets.
	if !supportsIPv4map() && supportsIPv4() && (network == "tcp" || network == "udp" || network == "ip") && wildcard {
		// At this point, we prefer IPv4 when ip is nil.
		// See favoriteAddrFamily for further information.
		if ip.To16() != nil && ip.To4() == nil && cip.To4() != nil { // a pair of IPv6 server and IPv4 client
			return false
		}

		},

		// BAD VALUES WE CURRENTLY CONSIDER GOOD
		{
			name: "ipv4 with leading 0s",
			in:   "1.1.01.0/24",
		},
		{
			name: "ipv4-in-ipv6 with ipv4-sized prefix",
			in:   "::ffff:1.1.1.0/24",
		},
		{
			name: "ipv4-in-ipv6 with ipv6-sized prefix",
			in:   "::ffff:1.1.1.0/120",
		},
		{
			name: "ipv4 with bits past prefix",
			in:   "1.2.3.4/24",
		},
		{

package net

/*
#include <netdb.h>
*/
import "C"

// NOTE(rsc): In theory there are approximately balanced
// arguments for and against including AI_ADDRCONFIG
// in the flags (it includes IPv4 results only on IPv4 systems,
// and similarly for IPv6), but in practice setting it causes
// getaddrinfo to return the wrong canonical name on Linux.
// So definitely leave it out.