@Nullable
    static byte[] ipv6ToIpv4Address(Inet6Address address) {
        final byte[] addr = address.getAddress();
        assert addr.length == 16
                : "the length of " + address.getClass().getSimpleName() + ": " + addr.length;
        // The first 10 bytes should be 0.
        for (int i = 0; i < 10; i++) {
            if (addr[i] != 0x00) {
                return null;
            }
        }

        if (addr[10] == 0x00 && addr[11] == 0x00) {
            if (addr[12] == 0x00 && addr[13] == 0x00 && addr[14] == 0x00 && addr[15] == 0x01) {
                return localhost;
            }
            return new byte[] { addr[12], addr[13], addr[14], addr[15] };
        }

        if (addr[10] == (byte) 0xFF && addr[11] == (byte) 0xFF) {
            return new byte[] { addr[12], addr[13], addr[14], addr[15] };
        }

        return null;
    }
Returns IPv4 byte representation of the specified {@link Inet6Address}. {@code null} is returned
if the specified {@link Inet6Address} is not able to be converted to IPv4.
core/src/main/java/com/linecorp/armeria/common/util/Inet4AddressBlock.java