content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 com.datastax.oss.driver.internal.core.addresstranslation;
  
  import com.datastax.oss.driver.api.core.addresstranslation.AddressTranslator;
  import com.datastax.oss.driver.api.core.context.DriverContext;
  import com.datastax.oss.driver.internal.core.util.Loggers;
  import com.datastax.oss.driver.shaded.guava.common.annotations.VisibleForTesting;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import java.net.InetAddress;
  import java.net.InetSocketAddress;
  import java.util.Enumeration;
  import java.util.Hashtable;
  import javax.naming.Context;
  import javax.naming.NamingEnumeration;
  import javax.naming.NamingException;
  import javax.naming.directory.Attribute;
  import javax.naming.directory.Attributes;
  import javax.naming.directory.DirContext;
  import javax.naming.directory.InitialDirContext;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * {@link AddressTranslator} implementation for a multi-region EC2 deployment <b>where clients are
   * also deployed in EC2</b>.
   *
   * <p>Its distinctive feature is that it translates addresses according to the location of the
   * Cassandra host:
   *
   * <ul>
   *   <li>addresses in different EC2 regions (than the client) are unchanged;
   *   <li>addresses in the same EC2 region are <b>translated to private IPs</b>.
   * </ul>
   *
   * This optimizes network costs, because Amazon charges more for communication over public IPs.
   *
   * <p>Implementation note: this class performs a reverse DNS lookup of the origin address, to find
   * the domain name of the target instance. Then it performs a forward DNS lookup of the domain name;
   * the EC2 DNS does the private/public switch automatically based on location.
   */
  public class Ec2MultiRegionAddressTranslator implements AddressTranslator {
  
    private static final Logger LOG = LoggerFactory.getLogger(Ec2MultiRegionAddressTranslator.class);
  
    private final DirContext ctx;
    private final String logPrefix;
  
    public Ec2MultiRegionAddressTranslator(
        @SuppressWarnings("unused") @NonNull DriverContext context) {
      this.logPrefix = context.getSessionName();
      @SuppressWarnings("JdkObsolete")
      Hashtable<Object, Object> env = new Hashtable<>();
      env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
      try {
        ctx = new InitialDirContext(env);
      } catch (NamingException e) {
        throw new RuntimeException("Could not create translator", e);
      }
    }
  
    @VisibleForTesting
    Ec2MultiRegionAddressTranslator(@NonNull DirContext ctx) {
      this.logPrefix = "test";
      this.ctx = ctx;
    }
  
    @NonNull
    @Override
    public InetSocketAddress translate(@NonNull InetSocketAddress socketAddress) {
      InetAddress address = socketAddress.getAddress();
      try {
        // InetAddress#getHostName() is supposed to perform a reverse DNS lookup, but for some reason
        // it doesn't work within the same EC2 region (it returns the IP address itself).
        // We use an alternate implementation:
        String domainName = lookupPtrRecord(reverse(address));
        if (domainName == null) {
          LOG.warn("[{}] Found no domain name for {}, returning it as-is", logPrefix, address);
          return socketAddress;
        }
  
        InetAddress translatedAddress = InetAddress.getByName(domainName);
        LOG.debug("[{}] Resolved {} to {}", logPrefix, address, translatedAddress);
        return new InetSocketAddress(translatedAddress, socketAddress.getPort());
      } catch (Exception e) {
        Loggers.warnWithException(
            LOG, "[{}] Error resolving {}, returning it as-is", logPrefix, address, e);
        return socketAddress;
      }
    }
  
    private String lookupPtrRecord(String reversedDomain) throws Exception {
      Attributes attrs = ctx.getAttributes(reversedDomain, new String[] {"PTR"});
      for (NamingEnumeration ae = attrs.getAll(); ae.hasMoreElements(); ) {
        Attribute attr = (Attribute) ae.next();
        Enumeration<?> vals = attr.getAll();
        if (vals.hasMoreElements()) {
          return vals.nextElement().toString();
        }
      }
      return null;
    }
  
    @Override
    public void close() {
      try {
        ctx.close();
      } catch (NamingException e) {
        Loggers.warnWithException(LOG, "Error closing translator", e);
      }
    }
  
    // Builds the "reversed" domain name in the ARPA domain to perform the reverse lookup
    @VisibleForTesting
    static String reverse(InetAddress address) {
      byte[] bytes = address.getAddress();
      if (bytes.length == 4) return reverseIpv4(bytes);
      else return reverseIpv6(bytes);
    }
  
    private static String reverseIpv4(byte[] bytes) {
      StringBuilder builder = new StringBuilder();
      for (int i = bytes.length - 1; i >= 0; i--) {
        builder.append(bytes[i] & 0xFF).append('.');
      }
      builder.append("in-addr.arpa");
      return builder.toString();
    }
  
    private static String reverseIpv6(byte[] bytes) {
      StringBuilder builder = new StringBuilder();
      for (int i = bytes.length - 1; i >= 0; i--) {
        byte b = bytes[i];
        int lowNibble = b & 0x0F;
        int highNibble = b >> 4 & 0x0F;
        builder
            .append(Integer.toHexString(lowNibble))
            .append('.')
            .append(Integer.toHexString(highNibble))
            .append('.');
      }
      builder.append("ip6.arpa");
      return builder.toString();
    }
  }
  