path: root/core/src/main/java/io/grpc/internal/DnsNameResolver.java

/*
 * Copyright 2015 The gRPC Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.grpc.internal;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.common.base.Stopwatch;
import com.google.common.base.Verify;
import io.grpc.Attributes;
import io.grpc.EquivalentAddressGroup;
import io.grpc.NameResolver;
import io.grpc.Status;
import io.grpc.internal.SharedResourceHolder.Resource;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.URI;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;

/**
 * A DNS-based {@link NameResolver}.
 *
 * <p>Each {@code A} or {@code AAAA} record emits an {@link EquivalentAddressGroup} in the list
 * passed to {@link NameResolver.Listener#onAddresses(List, Attributes)}
 *
 * @see DnsNameResolverProvider
 */
final 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<String>(
              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.";
  // From https://github.com/grpc/proposal/blob/master/A5-grpclb-in-dns.md
  private static final String GRPCLB_NAME_PREFIX = "_grpclb._tcp.";

  private static final String JNDI_PROPERTY =
      System.getProperty("io.grpc.internal.DnsNameResolverProvider.enable_jndi", "true");
  private static final String JNDI_SRV_PROPERTY =
      System.getProperty("io.grpc.internal.DnsNameResolverProvider.enable_grpclb", "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}.
   */
  @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 enableSrv = Boolean.parseBoolean(JNDI_SRV_PROPERTY);
  @VisibleForTesting
  static boolean enableTxt = Boolean.parseBoolean(JNDI_TXT_PROPERTY);


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

  @VisibleForTesting
  final ProxyDetector proxyDetector;

  /** Access through {@link #getLocalHostname}. */
  private static String localHostname;

  private final Random random = new Random();

  private volatile AddressResolver addressResolver = JdkAddressResolver.INSTANCE;
  private final AtomicReference<ResourceResolver> resourceResolver =
      new AtomicReference<ResourceResolver>();

  private final String authority;
  private final String host;
  private final int port;
  private final Resource<ExecutorService> executorResource;
  private final long networkAddressCacheTtlNanos;
  private final Stopwatch stopwatch;
  @GuardedBy("this")
  private boolean shutdown;
  @GuardedBy("this")
  private ExecutorService executor;
  @GuardedBy("this")
  private boolean resolving;
  @GuardedBy("this")
  private Listener listener;
  private ResolutionResults cachedResolutionResults;

  DnsNameResolver(@Nullable String nsAuthority, String name, Attributes params,
      Resource<ExecutorService> executorResource, ProxyDetector proxyDetector,
      Stopwatch stopwatch) {
    // TODO: if a DNS server is provided as nsAuthority, use it.
    // https://www.captechconsulting.com/blogs/accessing-the-dusty-corners-of-dns-with-java
    this.executorResource = executorResource;
    // Must prepend a "//" to the name when constructing a URI, otherwise it will be treated as an
    // opaque URI, thus the authority and host of the resulted URI would be null.
    URI nameUri = URI.create("//" + checkNotNull(name, "name"));
    Preconditions.checkArgument(nameUri.getHost() != null, "Invalid DNS name: %s", name);
    authority = Preconditions.checkNotNull(nameUri.getAuthority(),
        "nameUri (%s) doesn't have an authority", nameUri);
    host = nameUri.getHost();
    if (nameUri.getPort() == -1) {
      Integer defaultPort = params.get(NameResolver.Factory.PARAMS_DEFAULT_PORT);
      if (defaultPort != null) {
        port = defaultPort;
      } else {
        throw new IllegalArgumentException(
            "name '" + name + "' doesn't contain a port, and default port is not set in params");
      }
    } else {
      port = nameUri.getPort();
    }
    this.proxyDetector = proxyDetector;
    this.stopwatch = Preconditions.checkNotNull(stopwatch, "stopwatch");
    this.networkAddressCacheTtlNanos = getNetworkAddressCacheTtlNanos();
  }

  @Override
  public final String getServiceAuthority() {
    return authority;
  }

  @Override
  public final synchronized void start(Listener listener) {
    Preconditions.checkState(this.listener == null, "already started");
    executor = SharedResourceHolder.get(executorResource);
    this.listener = Preconditions.checkNotNull(listener, "listener");
    resolve();
  }

  @Override
  public final synchronized void refresh() {
    Preconditions.checkState(listener != null, "not started");
    resolve();
  }

  private final Runnable resolutionRunnable = new Runnable() {
      @Override
      public void run() {
        Listener savedListener;
        synchronized (DnsNameResolver.this) {
          if (shutdown) {
            return;
          }
          boolean resourceRefreshRequired = cachedResolutionResults == null
              || networkAddressCacheTtlNanos == 0
              || (networkAddressCacheTtlNanos > 0
                  && stopwatch.elapsed(TimeUnit.NANOSECONDS) > networkAddressCacheTtlNanos);
          if (!resourceRefreshRequired) {
            return;
          }
          savedListener = listener;
          resolving = true;
        }
        try {
          InetSocketAddress destination = InetSocketAddress.createUnresolved(host, port);
          ProxyParameters proxy;
          try {
            proxy = proxyDetector.proxyFor(destination);
          } catch (IOException e) {
            savedListener.onError(
                Status.UNAVAILABLE.withDescription("Unable to resolve host " + host).withCause(e));
            return;
          }
          if (proxy != null) {
            EquivalentAddressGroup server =
                new EquivalentAddressGroup(
                    new ProxySocketAddress(destination, proxy));
            savedListener.onAddresses(Collections.singletonList(server), Attributes.EMPTY);
            return;
          }

          ResolutionResults resolutionResults;
          try {
            ResourceResolver resourceResolver = null;
            if (enableJndi) {
              resourceResolver = getResourceResolver();
            }
            resolutionResults =
                resolveAll(addressResolver, resourceResolver, enableSrv, enableTxt, host);
            cachedResolutionResults = resolutionResults;
            if (networkAddressCacheTtlNanos > 0) {
              stopwatch.reset().start();
            }
          } catch (Exception e) {
            savedListener.onError(
                Status.UNAVAILABLE.withDescription("Unable to resolve host " + host).withCause(e));
            return;
          }
          // Each address forms an EAG
          List<EquivalentAddressGroup> servers = new ArrayList<EquivalentAddressGroup>();
          for (InetAddress inetAddr : resolutionResults.addresses) {
            servers.add(new EquivalentAddressGroup(new InetSocketAddress(inetAddr, port)));
          }
          servers.addAll(resolutionResults.balancerAddresses);

          Attributes.Builder attrs = Attributes.newBuilder();
          if (!resolutionResults.txtRecords.isEmpty()) {
            Map<String, Object> serviceConfig = null;
            try {
              for (Map<String, Object> possibleConfig :
                  parseTxtResults(resolutionResults.txtRecords)) {
                try {
                  serviceConfig =
                      maybeChooseServiceConfig(possibleConfig, random, getLocalHostname());
                } catch (RuntimeException e) {
                  logger.log(Level.WARNING, "Bad service config choice " + possibleConfig, e);
                }
                if (serviceConfig != null) {
                  break;
                }
              }
            } catch (RuntimeException e) {
              logger.log(Level.WARNING, "Can't parse service Configs", e);
            }
            if (serviceConfig != null) {
              attrs.set(GrpcAttributes.NAME_RESOLVER_SERVICE_CONFIG, serviceConfig);
            }
          } else {
            logger.log(Level.FINE, "No TXT records found for {0}", new Object[]{host});
          }
          savedListener.onAddresses(servers, attrs.build());
        } finally {
          synchronized (DnsNameResolver.this) {
            resolving = false;
          }
        }
      }
    };

  /** Returns value of network address cache ttl property. */
  private static long getNetworkAddressCacheTtlNanos() {
    String cacheTtlPropertyValue = System.getProperty(NETWORKADDRESS_CACHE_TTL_PROPERTY);
    long cacheTtl = DEFAULT_NETWORK_CACHE_TTL_SECONDS;
    if (cacheTtlPropertyValue != null) {
      try {
        cacheTtl = Long.parseLong(cacheTtlPropertyValue);
      } catch (NumberFormatException e) {
        logger.log(
            Level.WARNING,
            "Property({0}) valid is not valid number format({1}), fall back to default({2})",
            new Object[] {NETWORKADDRESS_CACHE_TTL_PROPERTY, cacheTtlPropertyValue, cacheTtl});
      }
    }
    return cacheTtl > 0 ? TimeUnit.SECONDS.toNanos(cacheTtl) : cacheTtl;
  }

  @GuardedBy("this")
  private void resolve() {
    if (resolving || shutdown) {
      return;
    }
    executor.execute(resolutionRunnable);
  }

  @Override
  public final synchronized void shutdown() {
    if (shutdown) {
      return;
    }
    shutdown = true;
    if (executor != null) {
      executor = SharedResourceHolder.release(executorResource, executor);
    }
  }

  final int getPort() {
    return port;
  }

  @VisibleForTesting
  static ResolutionResults resolveAll(
      AddressResolver addressResolver,
      @Nullable ResourceResolver resourceResolver,
      boolean requestSrvRecords,
      boolean requestTxtRecords,
      String name) {
    List<? extends InetAddress> addresses = Collections.emptyList();
    Exception addressesException = null;
    List<EquivalentAddressGroup> balancerAddresses = Collections.emptyList();
    Exception balancerAddressesException = null;
    List<String> txtRecords = Collections.emptyList();
    Exception txtRecordsException = null;

    try {
      addresses = addressResolver.resolveAddress(name);
    } catch (Exception e) {
      addressesException = e;
    }
    if (resourceResolver != null) {
      if (requestSrvRecords) {
        try {
          balancerAddresses =
              resourceResolver.resolveSrv(addressResolver, GRPCLB_NAME_PREFIX + name);
        } catch (Exception e) {
          balancerAddressesException = e;
        }
      }
      if (requestTxtRecords) {
        boolean balancerLookupFailedOrNotAttempted =
            !requestSrvRecords || balancerAddressesException != null;
        boolean dontResolveTxt =
            (addressesException != null) && balancerLookupFailedOrNotAttempted;
        // Only do the TXT record lookup if one of the above address resolutions succeeded.
        if (!dontResolveTxt) {
          try {
            txtRecords = resourceResolver.resolveTxt(SERVICE_CONFIG_NAME_PREFIX + name);
          } catch (Exception e) {
            txtRecordsException = e;
          }
        }
      }
    }
    try {
      if (addressesException != null && balancerAddressesException != null) {
        throw new RuntimeException(addressesException);
      }
    } finally {
      if (addressesException != null) {
        logger.log(Level.FINE, "Address resolution failure", addressesException);
      }
      if (balancerAddressesException != null) {
        logger.log(Level.FINE, "Balancer resolution failure", balancerAddressesException);
      }
      if (txtRecordsException != null) {
        logger.log(Level.FINE, "ServiceConfig resolution failure", txtRecordsException);
      }
    }
    return new ResolutionResults(addresses, txtRecords, balancerAddresses);
  }

  @SuppressWarnings("unchecked")
  @VisibleForTesting
  static List<Map<String, Object>> parseTxtResults(List<String> txtRecords) {
    List<Map<String, Object>> serviceConfigs = new ArrayList<Map<String, Object>>();
    for (String txtRecord : txtRecords) {
      if (txtRecord.startsWith(SERVICE_CONFIG_PREFIX)) {
        List<Map<String, Object>> choices;
        try {
          Object rawChoices = JsonParser.parse(txtRecord.substring(SERVICE_CONFIG_PREFIX.length()));
          if (!(rawChoices instanceof List)) {
            throw new IOException("wrong type " + rawChoices);
          }
          List<Object> listChoices = (List<Object>) rawChoices;
          for (Object obj : listChoices) {
            if (!(obj instanceof Map)) {
              throw new IOException("wrong element type " + rawChoices);
            }
          }
          choices = (List<Map<String, Object>>) (List<?>) listChoices;
        } catch (IOException e) {
          logger.log(Level.WARNING, "Bad service config: " + txtRecord, e);
          continue;
        }
        serviceConfigs.addAll(choices);
      } else {
        logger.log(Level.FINE, "Ignoring non service config {0}", new Object[]{txtRecord});
      }
    }
    return serviceConfigs;
  }

  @Nullable
  private static final Double getPercentageFromChoice(
      Map<String, Object> serviceConfigChoice) {
    if (!serviceConfigChoice.containsKey(SERVICE_CONFIG_CHOICE_PERCENTAGE_KEY)) {
      return null;
    }
    return ServiceConfigUtil.getDouble(serviceConfigChoice, SERVICE_CONFIG_CHOICE_PERCENTAGE_KEY);
  }

  @Nullable
  private static final List<String> getClientLanguagesFromChoice(
      Map<String, Object> serviceConfigChoice) {
    if (!serviceConfigChoice.containsKey(SERVICE_CONFIG_CHOICE_CLIENT_LANGUAGE_KEY)) {
      return null;
    }
    return ServiceConfigUtil.checkStringList(
        ServiceConfigUtil.getList(serviceConfigChoice, SERVICE_CONFIG_CHOICE_CLIENT_LANGUAGE_KEY));
  }

  @Nullable
  private static final List<String> getHostnamesFromChoice(
      Map<String, Object> serviceConfigChoice) {
    if (!serviceConfigChoice.containsKey(SERVICE_CONFIG_CHOICE_CLIENT_HOSTNAME_KEY)) {
      return null;
    }
    return ServiceConfigUtil.checkStringList(
        ServiceConfigUtil.getList(serviceConfigChoice, SERVICE_CONFIG_CHOICE_CLIENT_HOSTNAME_KEY));
  }

  /**
   * Determines if a given Service Config choice applies, and if so, returns it.
   *
   * @see <a href="https://github.com/grpc/proposal/blob/master/A2-service-configs-in-dns.md">
   *   Service Config in DNS</a>
   * @param choice The service config choice.
   * @return The service config object or {@code null} if this choice does not apply.
   */
  @Nullable
  @SuppressWarnings("BetaApi") // Verify isn't all that beta
  @VisibleForTesting
  static Map<String, Object> maybeChooseServiceConfig(
      Map<String, Object> choice, Random random, String hostname) {
    for (Entry<String, ?> entry : choice.entrySet()) {
      Verify.verify(SERVICE_CONFIG_CHOICE_KEYS.contains(entry.getKey()), "Bad key: %s", entry);
    }

    List<String> clientLanguages = getClientLanguagesFromChoice(choice);
    if (clientLanguages != null && !clientLanguages.isEmpty()) {
      boolean javaPresent = false;
      for (String lang : clientLanguages) {
        if ("java".equalsIgnoreCase(lang)) {
          javaPresent = true;
          break;
        }
      }
      if (!javaPresent) {
        return null;
      }
    }
    Double percentage = getPercentageFromChoice(choice);
    if (percentage != null) {
      int pct = percentage.intValue();
      Verify.verify(pct >= 0 && pct <= 100, "Bad percentage: %s", percentage);
      if (random.nextInt(100) >= pct) {
        return null;
      }
    }
    List<String> clientHostnames = getHostnamesFromChoice(choice);
    if (clientHostnames != null && !clientHostnames.isEmpty()) {
      boolean hostnamePresent = false;
      for (String clientHostname : clientHostnames) {
        if (clientHostname.equals(hostname)) {
          hostnamePresent = true;
          break;
        }
      }
      if (!hostnamePresent) {
        return null;
      }
    }
    return ServiceConfigUtil.getObject(choice, SERVICE_CONFIG_CHOICE_SERVICE_CONFIG_KEY);
  }

  /**
   * Describes the results from a DNS query.
   */
  @VisibleForTesting
  static final class ResolutionResults {
    final List<? extends InetAddress> addresses;
    final List<String> txtRecords;
    final List<EquivalentAddressGroup> balancerAddresses;

    ResolutionResults(
        List<? extends InetAddress> addresses,
        List<String> txtRecords,
        List<EquivalentAddressGroup> balancerAddresses) {
      this.addresses = Collections.unmodifiableList(checkNotNull(addresses, "addresses"));
      this.txtRecords = Collections.unmodifiableList(checkNotNull(txtRecords, "txtRecords"));
      this.balancerAddresses =
          Collections.unmodifiableList(checkNotNull(balancerAddresses, "balancerAddresses"));
    }
  }

  @VisibleForTesting
  void setAddressResolver(AddressResolver addressResolver) {
    this.addressResolver = addressResolver;
  }

  /**
   * {@link ResourceResolverFactory} is a factory for making resource resolvers.  It supports
   * optionally checking if the factory is available.
   */
  interface ResourceResolverFactory {

    /**
     * Creates a new resource resolver.  The return value is {@code null} iff
     * {@link #unavailabilityCause()} is not null;
     */
    @Nullable ResourceResolver newResourceResolver();

    /**
     * Returns the reason why the resource resolver cannot be created.  The return value is
     * {@code null} if {@link #newResourceResolver()} is suitable for use.
     */
    @Nullable Throwable unavailabilityCause();
  }

  /**
   * AddressResolver resolves a hostname into a list of addresses.
   */
  interface AddressResolver {
    List<InetAddress> resolveAddress(String host) throws Exception;
  }

  private enum JdkAddressResolver implements AddressResolver {
    INSTANCE;

    @Override
    public List<InetAddress> resolveAddress(String host) throws UnknownHostException {
      return Collections.unmodifiableList(Arrays.asList(InetAddress.getAllByName(host)));
    }
  }

  /**
   * {@link ResourceResolver} is a Dns ResourceRecord resolver.
   */
  interface ResourceResolver {
    List<String> resolveTxt(String host) throws Exception;

    List<EquivalentAddressGroup> resolveSrv(
        AddressResolver addressResolver, String host) throws Exception;
  }

  @Nullable
  private ResourceResolver getResourceResolver() {
    ResourceResolver rr;
    if ((rr = resourceResolver.get()) == null) {
      if (resourceResolverFactory != null) {
        assert resourceResolverFactory.unavailabilityCause() == null;
        rr = resourceResolverFactory.newResourceResolver();
      }
    }
    return rr;
  }

  @Nullable
  @VisibleForTesting
  static ResourceResolverFactory getResourceResolverFactory(ClassLoader loader) {
    Class<? extends ResourceResolverFactory> jndiClazz;
    try {
      jndiClazz =
          Class.forName("io.grpc.internal.JndiResourceResolverFactory", true, loader)
              .asSubclass(ResourceResolverFactory.class);
    } catch (ClassNotFoundException e) {
      logger.log(Level.FINE, "Unable to find JndiResourceResolverFactory, skipping.", e);
      return null;
    }
    Constructor<? extends ResourceResolverFactory> jndiCtor;
    try {
      jndiCtor = jndiClazz.getConstructor();
    } catch (Exception e) {
      logger.log(Level.FINE, "Can't find JndiResourceResolverFactory ctor, skipping.", e);
      return null;
    }
    ResourceResolverFactory rrf;
    try {
      rrf = jndiCtor.newInstance();
    } catch (Exception e) {
      logger.log(Level.FINE, "Can't construct JndiResourceResolverFactory, skipping.", e);
      return null;
    }
    if (rrf.unavailabilityCause() != null) {
      logger.log(
          Level.FINE,
          "JndiResourceResolverFactory not available, skipping.",
          rrf.unavailabilityCause());
    }
    return rrf;
  }

  private static String getLocalHostname() {
    if (localHostname == null) {
      try {
        localHostname = InetAddress.getLocalHost().getHostName();
      } catch (UnknownHostException e) {
        throw new RuntimeException(e);
      }
    }
    return localHostname;
  }
}