DnsNameResolver Class — netty Architecture

Source Code

resolver-dns/src/main/java/io/netty/resolver/dns/DnsNameResolver.java lines 96–1608

public class DnsNameResolver extends InetNameResolver {
    /**
     * An attribute used to mark all channels created by the {@link DnsNameResolver}.
     */
    public static final AttributeKey<Boolean> DNS_PIPELINE_ATTRIBUTE =
            AttributeKey.newInstance("io.netty.resolver.dns.pipeline");

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(DnsNameResolver.class);
    private static final String LOCALHOST = "localhost";
    private static final String WINDOWS_HOST_NAME;
    private static final InetAddress LOCALHOST_ADDRESS;
    private static final DnsRecord[] EMPTY_ADDITIONALS = new DnsRecord[0];
    private static final DnsRecordType[] IPV4_ONLY_RESOLVED_RECORD_TYPES =
            {DnsRecordType.A};
    private static final SocketProtocolFamily[] IPV4_ONLY_RESOLVED_PROTOCOL_FAMILIES =
            {SocketProtocolFamily.INET};
    private static final DnsRecordType[] IPV4_PREFERRED_RESOLVED_RECORD_TYPES =
            {DnsRecordType.A, DnsRecordType.AAAA};
    private static final SocketProtocolFamily[] IPV4_PREFERRED_RESOLVED_PROTOCOL_FAMILIES =
            {SocketProtocolFamily.INET, SocketProtocolFamily.INET6};
    private static final DnsRecordType[] IPV6_ONLY_RESOLVED_RECORD_TYPES =
            {DnsRecordType.AAAA};
    private static final SocketProtocolFamily[] IPV6_ONLY_RESOLVED_PROTOCOL_FAMILIES =
            {SocketProtocolFamily.INET6};
    private static final DnsRecordType[] IPV6_PREFERRED_RESOLVED_RECORD_TYPES =
            {DnsRecordType.AAAA, DnsRecordType.A};
    private static final SocketProtocolFamily[] IPV6_PREFERRED_RESOLVED_PROTOCOL_FAMILIES =
            {SocketProtocolFamily.INET6, SocketProtocolFamily.INET};

    private static final ChannelHandler NOOP_HANDLER = new ChannelHandlerAdapter() {
        @Override
        public boolean isSharable() {
            return true;
        }
    };

    static final ResolvedAddressTypes DEFAULT_RESOLVE_ADDRESS_TYPES;
    static final String[] DEFAULT_SEARCH_DOMAINS;
    private static final UnixResolverOptions DEFAULT_OPTIONS;

    static {
        if (NetUtil.isIpV4StackPreferred() || !anyInterfaceSupportsIpV6()) {
            DEFAULT_RESOLVE_ADDRESS_TYPES = ResolvedAddressTypes.IPV4_ONLY;
            LOCALHOST_ADDRESS = NetUtil.LOCALHOST4;
        } else {
            if (NetUtil.isIpV6AddressesPreferred()) {
                DEFAULT_RESOLVE_ADDRESS_TYPES = ResolvedAddressTypes.IPV6_PREFERRED;
                LOCALHOST_ADDRESS = NetUtil.LOCALHOST6;
            } else {
                DEFAULT_RESOLVE_ADDRESS_TYPES = ResolvedAddressTypes.IPV4_PREFERRED;
                LOCALHOST_ADDRESS = NetUtil.LOCALHOST4;
            }
        }
        logger.debug("Default ResolvedAddressTypes: {}", DEFAULT_RESOLVE_ADDRESS_TYPES);
        logger.debug("Localhost address: {}", LOCALHOST_ADDRESS);

        String hostName;
        try {
            hostName = PlatformDependent.isWindows() ? InetAddress.getLocalHost().getHostName() : null;
        } catch (Exception ignore) {
            hostName = null;
        }
        WINDOWS_HOST_NAME = hostName;
        logger.debug("Windows hostname: {}", WINDOWS_HOST_NAME);

        String[] searchDomains;
        try {
            List<String> list = PlatformDependent.isWindows()
                    ? getSearchDomainsHack()
                    : UnixResolverDnsServerAddressStreamProvider.parseEtcResolverSearchDomains();
            searchDomains = list.toArray(EmptyArrays.EMPTY_STRINGS);
        } catch (Exception ignore) {
            // Failed to get the system name search domain list.
            searchDomains = EmptyArrays.EMPTY_STRINGS;
        }
        DEFAULT_SEARCH_DOMAINS = searchDomains;
        logger.debug("Default search domains: {}", Arrays.toString(DEFAULT_SEARCH_DOMAINS));

        UnixResolverOptions options;
        try {
            options = UnixResolverDnsServerAddressStreamProvider.parseEtcResolverOptions();