Class DnsNameResolver

core/src/main/java/io/grpc/internal/DnsNameResolver.java:65–709

A DNS-based NameResolver. Each A or AAAA record emits an EquivalentAddressGroup in the list passed to NameResolver.Listener2#onResult2(ResolutionResult). @see DnsNameResolverProvider

 * @see DnsNameResolverProvider
 */
public class DnsNameResolver extends NameResolver {

  private static final Logger logger = Logger.getLogger(DnsNameResolver.class.getName());

  private static final String SERVICE_CONFIG_CHOICE_CLIENT_LANGUAGE_KEY = "clientLanguage";
  private static final String SERVICE_CONFIG_CHOICE_PERCENTAGE_KEY = "percentage";
  private static final String SERVICE_CONFIG_CHOICE_CLIENT_HOSTNAME_KEY = "clientHostname";
  private static final String SERVICE_CONFIG_CHOICE_SERVICE_CONFIG_KEY = "serviceConfig";

  // From https://github.com/grpc/proposal/blob/master/A2-service-configs-in-dns.md
  static final String SERVICE_CONFIG_PREFIX = "grpc_config=";
  private static final Set<String> SERVICE_CONFIG_CHOICE_KEYS =
      Collections.unmodifiableSet(
          new HashSet<>(
              Arrays.asList(
                  SERVICE_CONFIG_CHOICE_CLIENT_LANGUAGE_KEY,
                  SERVICE_CONFIG_CHOICE_PERCENTAGE_KEY,
                  SERVICE_CONFIG_CHOICE_CLIENT_HOSTNAME_KEY,
                  SERVICE_CONFIG_CHOICE_SERVICE_CONFIG_KEY)));

  // From https://github.com/grpc/proposal/blob/master/A2-service-configs-in-dns.md
  private static final String SERVICE_CONFIG_NAME_PREFIX = "_grpc_config.";

  private static final String JNDI_PROPERTY =
      System.getProperty("io.grpc.internal.DnsNameResolverProvider.enable_jndi", "true");
  private static final String JNDI_LOCALHOST_PROPERTY =
      System.getProperty("io.grpc.internal.DnsNameResolverProvider.enable_jndi_localhost", "false");
  private static final String JNDI_TXT_PROPERTY =
      System.getProperty("io.grpc.internal.DnsNameResolverProvider.enable_service_config", "false");

  /**
   * Java networking system properties name for caching DNS result.
   *
   * <p>Default value is -1 (cache forever) if security manager is installed. If security manager is
   * not installed, the ttl value is {@code null} which falls back to {@link
   * #DEFAULT_NETWORK_CACHE_TTL_SECONDS gRPC default value}.
   *
   * <p>For android, gRPC uses a fixed value; this property value will be ignored.
   */
  @VisibleForTesting
  static final String NETWORKADDRESS_CACHE_TTL_PROPERTY = "networkaddress.cache.ttl";
  /** Default DNS cache duration if network cache ttl value is not specified ({@code null}). */
  @VisibleForTesting
  static final long DEFAULT_NETWORK_CACHE_TTL_SECONDS = 30;

  @VisibleForTesting
  static boolean enableJndi = Boolean.parseBoolean(JNDI_PROPERTY);
  @VisibleForTesting
  static boolean enableJndiLocalhost = Boolean.parseBoolean(JNDI_LOCALHOST_PROPERTY);
  @VisibleForTesting
  protected static boolean enableTxt = Boolean.parseBoolean(JNDI_TXT_PROPERTY);

  private static final ResourceResolverFactory resourceResolverFactory =
      getResourceResolverFactory(DnsNameResolver.class.getClassLoader());

  @VisibleForTesting
  final ProxyDetector proxyDetector;