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diff --git a/java/net/ResolverCache.java b/java/net/ResolverCache.java
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+/* ResolverCache.java -- A cache of resolver lookups for InetAddress.
+   Copyright (C) 2006 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package java.net;
+
+import java.security.Security;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedList;
+
+/**
+ * This class provides a cache of name service resolutions.  By
+ * default successful resolutions are cached forever to guard
+ * against DNS spoofing attacks and failed resolutions are cached
+ * for 10 seconds to improve performance.  The length of time that
+ * results remain in the cache is determined by the following
+ * security properties:
+ * <dl>
+ *   <dt><code>networkaddress.cache.ttl</code></dt>
+ *   <dd>
+ *     This property specifies the length of time in seconds that
+ *     successful resolutions remain in the cache.  The default is
+ *     -1, indicating to cache forever.
+ *   </dd>
+ *   <dt><code>networkaddress.cache.negative.ttl</code></dt>
+ *   <dd>
+ *     This property specifies the length of time in seconds that
+ *     unsuccessful resolutions remain in the cache.  The default
+ *     is 10, indicating to cache for 10 seconds.
+ *   </dd>
+ * In both cases, a value of -1 indicates to cache forever and a
+ * value of 0 indicates not to cache.
+ *
+ * @author Gary Benson (gbenson@redhat.com)
+ */
+class ResolverCache
+{
+  /**
+   * The time in seconds for which successful lookups are cached.
+   */
+  private static final int POSITIVE_TTL =
+    getTTL("networkaddress.cache.ttl", -1);
+
+  /**
+   * The time in seconds for which unsuccessful lookups are cached.
+   */
+  private static final int NEGATIVE_TTL =
+    getTTL("networkaddress.cache.negative.ttl", 10);
+
+  /**
+   * Helper function to set the TTLs.
+   */
+  private static int getTTL(String propName, int defaultValue)
+  {
+    String propValue = Security.getProperty(propName);
+    if (propValue == null)
+      return defaultValue;
+
+    return Integer.parseInt(propValue);
+  }
+
+  /**
+   * The cache itself.
+   */
+  private static HashMap cache = new HashMap();
+
+  /**
+   * List of entries which may expire.
+   */
+  private static LinkedList killqueue = new LinkedList();
+
+  /**
+   * Return the hostname for the specified IP address.
+   *
+   * @param ip The IP address as a byte array
+   *
+   * @return The hostname
+   *
+   * @exception UnknownHostException If the reverse lookup fails
+   */
+  public static String getHostByAddr(byte[] addr) throws UnknownHostException
+  {
+    Object key = makeHashableAddress(addr);
+    Entry entry = (Entry) get(key);
+    if (entry != null)
+      {
+	if (entry.value == null)
+	  throw new UnknownHostException();
+	return (String) entry.value;
+      }
+
+    try
+      {
+	String hostname = VMInetAddress.getHostByAddr(addr);
+	put(new Entry(key, hostname));
+	return hostname;
+      }
+    catch (UnknownHostException e)
+      {
+	put(new Entry(key, null));
+	throw e;
+      }
+  }
+
+  /**
+   * Return a list of all IP addresses for the specified hostname.
+   *
+   * @param hostname The hostname
+   *
+   * @return An list of IP addresses as byte arrays
+   *
+   * @exception UnknownHostException If the lookup fails
+   */
+  public static byte[][] getHostByName(String hostname)
+    throws UnknownHostException
+  {
+    Entry entry = (Entry) get(hostname);
+    if (entry != null)
+      {
+	if (entry.value == null)
+	  throw new UnknownHostException();
+	return (byte[][]) entry.value;
+      }
+
+    try
+      {
+	byte[][] addrs = VMInetAddress.getHostByName(hostname);
+	put(new Entry(hostname, addrs));
+	return addrs;
+      }
+    catch (UnknownHostException e)
+      {
+	put(new Entry(hostname, null));
+	throw e;
+      }
+  }
+
+  /**
+   * Convert an IP address expressed as a byte array into something
+   * we can use as a hashtable key.
+   */
+  private static Object makeHashableAddress(byte[] addr)
+  {
+    char[] chars = new char[addr.length];
+    for (int i = 0; i < addr.length; i++)
+      chars[i] = (char) addr[i];
+    return new String(chars);
+  }
+
+  /**
+   * Return the entry in the cache associated with the supplied key,
+   * or <code>null</code> if the cache does not contain an entry
+   * associated with this key.
+   */
+  private static synchronized Entry get(Object key)
+  {
+    reap();
+    return (Entry) cache.get(key);
+  }
+
+  /**
+   * Insert the supplied entry into the cache.
+   */
+  private static synchronized void put(Entry entry)
+  {
+    reap();
+    if (entry.expires != 0)
+      {
+	if (entry.expires != -1)
+	  killqueue.add(entry);
+	cache.put(entry.key, entry);
+      }
+  }
+
+  /**
+   * Clear expired entries.  This method is not synchronized, so
+   * it must only be called by methods that are.
+   */
+  private static void reap()
+  {
+    if (!killqueue.isEmpty())
+      {
+	long now = System.currentTimeMillis();
+
+	Iterator iter = killqueue.iterator();
+	while (iter.hasNext())
+	  {
+	    Entry entry = (Entry) iter.next();
+	    if (entry.expires > now)
+	      break;
+	    cache.remove(entry.key);
+	    iter.remove();
+	  }
+      }
+  }
+  
+  /**
+   * An entry in the cache.
+   */
+  private static class Entry
+  {
+    /**
+     * The key by which this entry is referenced.
+     */
+    public final Object key;
+
+    /**
+     * The entry itself.  A null value indicates a failed lookup.
+     */
+    public final Object value;
+    
+    /**
+     * The time when this cache entry expires.  If set to -1 then
+     * this entry will never expire.  If set to 0 then this entry
+     * expires immediately and will not be inserted into the cache.
+     */
+    public final long expires;
+
+    /**
+     * Constructor.
+     */
+    public Entry(Object key, Object value)
+    {
+      this.key = key;
+      this.value = value;
+
+      int ttl = value != null ? POSITIVE_TTL : NEGATIVE_TTL;
+      if (ttl < 1)
+	expires = ttl;
+      else
+	expires = System.currentTimeMillis() + ttl * 1000;
+    }
+  }
+}