| /* 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; |
| } |
| } |
| } |