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   /*
    * Copyright 2015 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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.netty.resolver.dns;
  
  import io.netty.util.NetUtil;
  import io.netty.util.collection.IntObjectHashMap;
  import io.netty.util.collection.IntObjectMap;
  
  import java.net.Inet4Address;
  import java.net.Inet6Address;
  import java.net.InetAddress;
  import java.net.InetSocketAddress;
  import java.net.UnknownHostException;
  import java.util.HashMap;
  import java.util.Map;
  
  final class DnsQueryContextManager {
  
      /**
       * A map whose key is the DNS server address and value is the map of the DNS query ID and its corresponding
       * {@link DnsQueryContext}.
       */
      private final Map<InetSocketAddress, DnsQueryContextMap> map =
              new HashMap<InetSocketAddress, DnsQueryContextMap>();
  
      /**
       * Add {@link DnsQueryContext} to the context manager and return the ID that should be used for the query.
       * This method will return {@code -1} if an ID could not be generated and the context was not stored.
       *
       * @param nameServerAddr    The {@link InetSocketAddress} of the nameserver to query.
       * @param qCtx              The {@link {@link DnsQueryContext} to store.
       * @return                  the ID that should be used or {@code -1} if none could be generated.
       */
      int add(InetSocketAddress nameServerAddr, DnsQueryContext qCtx) {
          final DnsQueryContextMap contexts = getOrCreateContextMap(nameServerAddr);
          return contexts.add(qCtx);
      }
  
      /**
       * Return the {@link DnsQueryContext} for the given {@link InetSocketAddress} and id or {@code null} if
       * none could be found.
       *
       * @param nameServerAddr    The {@link InetSocketAddress} of the nameserver.
       * @param id                The id that identifies the {@link DnsQueryContext} and was used for the query.
       * @return                  The context or {@code null} if none could be found.
       */
      DnsQueryContext get(InetSocketAddress nameServerAddr, int id) {
          final DnsQueryContextMap contexts = getContextMap(nameServerAddr);
          if (contexts == null) {
              return null;
          }
          return contexts.get(id);
      }
  
      /**
       * Remove the {@link DnsQueryContext} for the given {@link InetSocketAddress} and id or {@code null} if
       * none could be found.
       *
       * @param nameServerAddr    The {@link InetSocketAddress} of the nameserver.
       * @param id                The id that identifies the {@link DnsQueryContext} and was used for the query.
       * @return                  The context or {@code null} if none could be removed.
       */
      DnsQueryContext remove(InetSocketAddress nameServerAddr, int id) {
          final DnsQueryContextMap contexts = getContextMap(nameServerAddr);
          if (contexts == null) {
              return null;
          }
          return contexts.remove(id);
      }
  
      private DnsQueryContextMap getContextMap(InetSocketAddress nameServerAddr) {
          synchronized (map) {
              return map.get(nameServerAddr);
          }
      }
  
      private DnsQueryContextMap getOrCreateContextMap(InetSocketAddress nameServerAddr) {
          synchronized (map) {
              final DnsQueryContextMap contexts = map.get(nameServerAddr);
              if (contexts != null) {
                  return contexts;
              }
  
              final DnsQueryContextMap newContexts = new DnsQueryContextMap();
              final InetAddress a = nameServerAddr.getAddress();
             final int port = nameServerAddr.getPort();
             DnsQueryContextMap old = map.put(nameServerAddr, newContexts);
             // Assert that we didn't replace an existing mapping.
             assert old == null : "DnsQueryContextMap already exists for " + nameServerAddr;
 
             InetSocketAddress extraAddress = null;
             if (a instanceof Inet4Address) {
                 // Also add the mapping for the IPv4-compatible IPv6 address.
                 final Inet4Address a4 = (Inet4Address) a;
                 if (a4.isLoopbackAddress()) {
                     extraAddress = new InetSocketAddress(NetUtil.LOCALHOST6, port);
                 } else {
                     extraAddress = new InetSocketAddress(toCompactAddress(a4), port);
                 }
             } else if (a instanceof Inet6Address) {
                 // Also add the mapping for the IPv4 address if this IPv6 address is compatible.
                 final Inet6Address a6 = (Inet6Address) a;
                 if (a6.isLoopbackAddress()) {
                     extraAddress = new InetSocketAddress(NetUtil.LOCALHOST4, port);
                 } else if (a6.isIPv4CompatibleAddress()) {
                     extraAddress = new InetSocketAddress(toIPv4Address(a6), port);
                 }
             }
             if (extraAddress != null) {
                 old = map.put(extraAddress, newContexts);
                 // Assert that we didn't replace an existing mapping.
                 assert old == null : "DnsQueryContextMap already exists for " + extraAddress;
             }
 
             return newContexts;
         }
     }
 
     private static Inet6Address toCompactAddress(Inet4Address a4) {
         byte[] b4 = a4.getAddress();
         byte[] b6 = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, b4[0], b4[1], b4[2], b4[3] };
         try {
             return (Inet6Address) InetAddress.getByAddress(b6);
         } catch (UnknownHostException e) {
             throw new Error(e);
         }
     }
 
     private static Inet4Address toIPv4Address(Inet6Address a6) {
         assert a6.isIPv4CompatibleAddress();
 
         byte[] b6 = a6.getAddress();
         byte[] b4 = { b6[12], b6[13], b6[14], b6[15] };
         try {
             return (Inet4Address) InetAddress.getByAddress(b4);
         } catch (UnknownHostException e) {
             throw new Error(e);
         }
     }
 
     private static final class DnsQueryContextMap {
 
         private final DnsQueryIdSpace idSpace = new DnsQueryIdSpace();
 
         // We increment on every usage so start with -1, this will ensure we start with 0 as first id.
         private final IntObjectMap<DnsQueryContext> map = new IntObjectHashMap<DnsQueryContext>();
 
         synchronized int add(DnsQueryContext ctx) {
             int id = idSpace.nextId();
             DnsQueryContext oldCtx = map.put(id, ctx);
             assert oldCtx == null;
             return id;
         }
 
         synchronized DnsQueryContext get(int id) {
             return map.get(id);
         }
 
         synchronized DnsQueryContext remove(int id) {
             idSpace.pushId(id);
             return map.remove(id);
         }
     }
 }