From ab474ea06350ce43d7621bb92f824df8ea0c29bf Mon Sep 17 00:00:00 2001
From: Matt Tucker <matt@jivesoftware.com>
Date: Sat, 17 Sep 2005 22:01:24 +0000
Subject: [PATCH] Added DNS SRV support (SMACK-29).

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@2832 b35dd754-fafc-0310-a699-88a17e54d16e
---
 build/projects/Smack.iml                      |   9 +
 build/projects/Smack.ipr                      |  13 +-
 .../jivesoftware/smack/XMPPConnection.java    |  54 +-
 source/org/jivesoftware/smack/util/Cache.java | 628 ++++++++++++++++++
 .../org/jivesoftware/smack/util/DNSUtil.java  | 219 ++++++
 .../jivesoftware/smack/util/CacheTest.java    |  77 +++
 6 files changed, 993 insertions(+), 7 deletions(-)
 create mode 100644 source/org/jivesoftware/smack/util/Cache.java
 create mode 100644 source/org/jivesoftware/smack/util/DNSUtil.java
 create mode 100644 test/org/jivesoftware/smack/util/CacheTest.java

diff --git a/build/projects/Smack.iml b/build/projects/Smack.iml
index 9fe263f33..c13e5eec3 100644
--- a/build/projects/Smack.iml
+++ b/build/projects/Smack.iml
@@ -74,6 +74,15 @@
         <SOURCES />
       </library>
     </orderEntry>
+    <orderEntry type="module-library">
+      <library>
+        <CLASSES>
+          <root url="file://$MODULE_DIR$/../resources" />
+        </CLASSES>
+        <JAVADOC />
+        <SOURCES />
+      </library>
+    </orderEntry>
     <orderEntryProperties />
   </component>
 </module>
diff --git a/build/projects/Smack.ipr b/build/projects/Smack.ipr
index 87af33d40..cf93dbc34 100644
--- a/build/projects/Smack.ipr
+++ b/build/projects/Smack.ipr
@@ -33,6 +33,17 @@
       <entry name=".+\.(properties|xml|html|dtd|tld)" />
       <entry name=".+\.(gif|png|jpeg|jpg)" />
     </resourceExtensions>
+    <wildcardResourcePatterns>
+      <entry name="?*.properties" />
+      <entry name="?*.xml" />
+      <entry name="?*.html" />
+      <entry name="?*.dtd" />
+      <entry name="?*.tld" />
+      <entry name="?*.gif" />
+      <entry name="?*.png" />
+      <entry name="?*.jpeg" />
+      <entry name="?*.jpg" />
+    </wildcardResourcePatterns>
   </component>
   <component name="DataSourceManagerImpl" />
   <component name="DependenciesAnalyzeManager">
@@ -188,7 +199,7 @@
       <module fileurl="file://$PROJECT_DIR$/Smack.iml" filepath="$PROJECT_DIR$/Smack.iml" />
     </modules>
   </component>
-  <component name="ProjectRootManager" version="2" assert-keyword="false" jdk-15="false" project-jdk-name="JDK 1.4.2" />
+  <component name="ProjectRootManager" version="2" assert-keyword="true" jdk-15="false" project-jdk-name="JDK 1.4.2" />
   <component name="RmicSettings">
     <option name="IS_EANABLED" value="false" />
     <option name="DEBUGGING_INFO" value="true" />
diff --git a/source/org/jivesoftware/smack/XMPPConnection.java b/source/org/jivesoftware/smack/XMPPConnection.java
index e8d920188..afa354174 100644
--- a/source/org/jivesoftware/smack/XMPPConnection.java
+++ b/source/org/jivesoftware/smack/XMPPConnection.java
@@ -28,6 +28,7 @@ import org.jivesoftware.smack.packet.Packet;
 import org.jivesoftware.smack.packet.Presence;
 import org.jivesoftware.smack.packet.XMPPError;
 import org.jivesoftware.smack.util.StringUtils;
+import org.jivesoftware.smack.util.DNSUtil;
 
 import javax.net.SocketFactory;
 import javax.net.ssl.SSLContext;
@@ -132,8 +133,11 @@ public class XMPPConnection {
     Map chats = new HashMap();
 
     /**
-     * Creates a new connection to the specified XMPP server. The default port of 5222 will
-     * be used. The IP address of the server is assumed to match the service name.
+     * Creates a new connection to the specified XMPP server. A DNS SRV lookup will be
+     * performed to try to determine the IP address and port corresponding to the
+     * serviceName; if that lookup fails, it's assumed that server resides at serviceName
+     * with the default port of 5222. This is the preferred constructor for connecting
+     * to an XMPP server.
      *
      * @param serviceName the name of the XMPP server to connect to; e.g. <tt>jivesoftware.com</tt>.
      * @throws XMPPException if an error occurs while trying to establish the connection.
@@ -143,7 +147,27 @@ public class XMPPConnection {
      *      appropiate error messages to end-users.
      */
     public XMPPConnection(String serviceName) throws XMPPException {
-        this(serviceName, 5222, serviceName);
+        DNSUtil.HostAddress address = DNSUtil.resolveXMPPDomain(serviceName);
+
+        this.host = address.getHost();
+        this.port = address.getPort();
+        try {
+            this.socket = new Socket(host, port);
+        }
+        catch (UnknownHostException uhe) {
+            throw new XMPPException(
+                "Could not connect to " + host + ":" + port + ".",
+                new XMPPError(504),
+                uhe);
+        }
+        catch (IOException ioe) {
+            throw new XMPPException(
+                "XMPPError connecting to " + host + ":" + port + ".",
+                new XMPPError(502),
+                ioe);
+        }
+        this.serviceName = serviceName;
+        init();
     }
 
     /**
@@ -159,7 +183,25 @@ public class XMPPConnection {
      *      appropiate error messages to end-users.
      */
     public XMPPConnection(String host, int port) throws XMPPException {
-        this(host, port, host);
+        this.host = host;
+        this.port = port;
+        try {
+            this.socket = new Socket(host, port);
+        }
+        catch (UnknownHostException uhe) {
+            throw new XMPPException(
+                "Could not connect to " + host + ":" + port + ".",
+                new XMPPError(504),
+                uhe);
+        }
+        catch (IOException ioe) {
+            throw new XMPPException(
+                "XMPPError connecting to " + host + ":" + port + ".",
+                new XMPPError(502),
+                ioe);
+        }
+        this.serviceName = host;
+        init();
     }
 
     /**
@@ -216,7 +258,8 @@ public class XMPPConnection {
      *      appropiate error messages to end-users.
      */
     public XMPPConnection(String host, int port, String serviceName, SocketFactory socketFactory)
-            throws XMPPException {
+            throws XMPPException
+    {
         this.host = host;
         this.port = port;
         try {
@@ -994,5 +1037,4 @@ public class XMPPConnection {
         // Send a new opening stream to the server
         packetWriter.openStream();
     }
-
 }
\ No newline at end of file
diff --git a/source/org/jivesoftware/smack/util/Cache.java b/source/org/jivesoftware/smack/util/Cache.java
new file mode 100644
index 000000000..ec282c054
--- /dev/null
+++ b/source/org/jivesoftware/smack/util/Cache.java
@@ -0,0 +1,628 @@
+/**
+ * $Revision: 1456 $
+ * $Date: 2005-06-01 22:04:54 -0700 (Wed, 01 Jun 2005) $
+ *
+ * Copyright 2003-2005 Jive Software.
+ *
+ * All rights reserved. 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 org.jivesoftware.smack.util;
+
+import java.util.*;
+
+/**
+ * A specialized Map that is size-limited (using an LRU algorithm) and
+ * has an optional expiration time for cache items. The Map is thread-safe.<p>
+ *
+ * The algorithm for cache is as follows: a HashMap is maintained for fast
+ * object lookup. Two linked lists are maintained: one keeps objects in the
+ * order they are accessed from cache, the other keeps objects in the order
+ * they were originally added to cache. When objects are added to cache, they
+ * are first wrapped by a CacheObject which maintains the following pieces
+ * of information:<ul>
+ * <li> A pointer to the node in the linked list that maintains accessed
+ * order for the object. Keeping a reference to the node lets us avoid
+ * linear scans of the linked list.
+ * <li> A pointer to the node in the linked list that maintains the age
+ * of the object in cache. Keeping a reference to the node lets us avoid
+ * linear scans of the linked list.</ul>
+ * <p/>
+ * To get an object from cache, a hash lookup is performed to get a reference
+ * to the CacheObject that wraps the real object we are looking for.
+ * The object is subsequently moved to the front of the accessed linked list
+ * and any necessary cache cleanups are performed. Cache deletion and expiration
+ * is performed as needed.
+ *
+ * @author Matt Tucker
+ */
+class Cache implements Map {
+
+    /**
+     * The map the keys and values are stored in.
+     */
+    protected Map map;
+
+    /**
+     * Linked list to maintain order that cache objects are accessed
+     * in, most used to least used.
+     */
+    protected LinkedList lastAccessedList;
+
+    /**
+     * Linked list to maintain time that cache objects were initially added
+     * to the cache, most recently added to oldest added.
+     */
+    protected LinkedList ageList;
+
+    /**
+     * Maximum number of items the cache will hold.
+     */
+    protected int maxCacheSize;
+
+    /**
+     * Maximum length of time objects can exist in cache before expiring.
+     */
+    protected long maxLifetime;
+
+    /**
+     * Maintain the number of cache hits and misses. A cache hit occurs every
+     * time the get method is called and the cache contains the requested
+     * object. A cache miss represents the opposite occurence.<p>
+     *
+     * Keeping track of cache hits and misses lets one measure how efficient
+     * the cache is; the higher the percentage of hits, the more efficient.
+     */
+    protected long cacheHits, cacheMisses = 0L;
+
+    /**
+     * Create a new cache and specify the maximum size of for the cache in
+     * bytes, and the maximum lifetime of objects.
+     *
+     * @param maxSize the maximum number of objects the cache will hold. -1
+     *      means the cache has no max size.
+     * @param maxLifetime the maximum amount of time (in ms) objects can exist in
+     *      cache before being deleted. -1 means objects never expire.
+     */
+    public Cache(int maxSize, long maxLifetime) {
+        if (maxSize == 0) {
+            throw new IllegalArgumentException("Max cache size cannot be 0.");
+        }
+        this.maxCacheSize = maxSize;
+        this.maxLifetime = maxLifetime;
+
+        // Our primary data structure is a hash map. The default capacity of 11
+        // is too small in almost all cases, so we set it bigger.
+        map = new HashMap(103);
+
+        lastAccessedList = new LinkedList();
+        ageList = new LinkedList();
+    }
+
+    public synchronized Object put(Object key, Object value) {
+        Object oldValue = null;
+        // Delete an old entry if it exists.
+        if (map.containsKey(key)) {
+            oldValue = remove(key, true);
+        }
+
+        CacheObject cacheObject = new CacheObject(value);
+        map.put(key, cacheObject);
+        // Make an entry into the cache order list.
+        // Store the cache order list entry so that we can get back to it
+        // during later lookups.
+        cacheObject.lastAccessedListNode = lastAccessedList.addFirst(key);
+        // Add the object to the age list
+        LinkedListNode ageNode = ageList.addFirst(key);
+        ageNode.timestamp = System.currentTimeMillis();
+        cacheObject.ageListNode = ageNode;
+
+        // If cache is too full, remove least used cache entries until it is not too full.
+        cullCache();
+
+        return oldValue;
+    }
+
+    public synchronized Object get(Object key) {
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        CacheObject cacheObject = (CacheObject) map.get(key);
+        if (cacheObject == null) {
+            // The object didn't exist in cache, so increment cache misses.
+            cacheMisses++;
+            return null;
+        }
+        // Remove the object from it's current place in the cache order list,
+        // and re-insert it at the front of the list.
+        cacheObject.lastAccessedListNode.remove();
+        lastAccessedList.addFirst(cacheObject.lastAccessedListNode);
+
+        // The object exists in cache, so increment cache hits. Also, increment
+        // the object's read count.
+        cacheHits++;
+        cacheObject.readCount++;
+
+        return cacheObject.object;
+    }
+
+    public synchronized Object remove(Object key) {
+        return remove(key, false);
+    }
+
+    /*
+     * Remove operation with a flag so we can tell coherence if the remove was
+     * caused by cache internal processing such as eviction or loading
+     */
+    public synchronized Object remove(Object key, boolean internal) {
+        CacheObject cacheObject = (CacheObject) map.remove(key);
+        // If the object is not in cache, stop trying to remove it.
+        if (cacheObject == null) {
+            return null;
+        }
+        // Remove from the cache order list
+        cacheObject.lastAccessedListNode.remove();
+        cacheObject.ageListNode.remove();
+        // Remove references to linked list nodes
+        cacheObject.ageListNode = null;
+        cacheObject.lastAccessedListNode = null;
+
+        return cacheObject.object;
+    }
+
+    public synchronized void clear() {
+        Object[] keys = map.keySet().toArray();
+        for (int i = 0; i < keys.length; i++) {
+            remove(keys[i]);
+        }
+
+        // Now, reset all containers.
+        map.clear();
+        lastAccessedList.clear();
+        ageList.clear();
+
+        cacheHits = 0;
+        cacheMisses = 0;
+    }
+
+    public synchronized int size() {
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        return map.size();
+    }
+
+    public synchronized boolean isEmpty() {
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        return map.isEmpty();
+    }
+
+    public synchronized Collection values() {
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        Object[] cacheObjects = map.values().toArray();
+        Object[] values = new Object[cacheObjects.length];
+        for (int i = 0; i < cacheObjects.length; i++) {
+            values[i] = ((CacheObject) cacheObjects[i]).object;
+        }
+        return Collections.unmodifiableList(Arrays.asList(values));
+    }
+
+    public synchronized boolean containsKey(Object key) {
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        return map.containsKey(key);
+    }
+
+    public void putAll(Map map) {
+        for (Iterator i = map.entrySet().iterator(); i.hasNext();) {
+            Map.Entry entry = (Map.Entry) i.next();
+            Object value = entry.getValue();
+            // If the map is another DefaultCache instance than the
+            // entry values will be CacheObject instances that need
+            // to be converted to the normal object form.
+            if (value instanceof CacheObject) {
+                value = ((CacheObject) value).object;
+            }
+            put(entry.getKey(), value);
+        }
+    }
+
+    public synchronized boolean containsValue(Object value) {
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        CacheObject cacheObject = new CacheObject(value);
+
+        return map.containsValue(cacheObject);
+    }
+
+    public synchronized Set entrySet() {
+        // Warning -- this method returns CacheObject instances and not Objects
+        // in the same form they were put into cache.
+
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        return Collections.unmodifiableSet(map.entrySet());
+    }
+
+    public synchronized Set keySet() {
+        // First, clear all entries that have been in cache longer than the
+        // maximum defined age.
+        deleteExpiredEntries();
+
+        return Collections.unmodifiableSet(map.keySet());
+    }
+
+    public long getCacheHits() {
+        return cacheHits;
+    }
+
+    public long getCacheMisses() {
+        return cacheMisses;
+    }
+
+    public int getMaxCacheSize() {
+        return maxCacheSize;
+    }
+
+    public synchronized void setMaxCacheSize(int maxCacheSize) {
+        this.maxCacheSize = maxCacheSize;
+        // It's possible that the new max size is smaller than our current cache
+        // size. If so, we need to delete infrequently used items.
+        cullCache();
+    }
+
+    public long getMaxLifetime() {
+        return maxLifetime;
+    }
+
+    public void setMaxLifetime(long maxLifetime) {
+        this.maxLifetime = maxLifetime;
+    }
+
+    /**
+     * Clears all entries out of cache where the entries are older than the
+     * maximum defined age.
+     */
+    protected synchronized void deleteExpiredEntries() {
+        // Check if expiration is turned on.
+        if (maxLifetime <= 0) {
+            return;
+        }
+
+        // Remove all old entries. To do this, we remove objects from the end
+        // of the linked list until they are no longer too old. We get to avoid
+        // any hash lookups or looking at any more objects than is strictly
+        // neccessary.
+        LinkedListNode node = ageList.getLast();
+        // If there are no entries in the age list, return.
+        if (node == null) {
+            return;
+        }
+
+        // Determine the expireTime, which is the moment in time that elements
+        // should expire from cache. Then, we can do an easy check to see
+        // if the expire time is greater than the expire time.
+        long expireTime = System.currentTimeMillis() - maxLifetime;
+
+        while (expireTime > node.timestamp) {
+            if (remove(node.object, true) == null) {
+                System.err.println("Error attempting to remove(" + node.object.toString() +
+                ") - cacheObject not found in cache!");
+                // remove from the ageList
+                node.remove();
+            }
+
+            // Get the next node.
+            node = ageList.getLast();
+            // If there are no more entries in the age list, return.
+            if (node == null) {
+                return;
+            }
+        }
+    }
+
+    /**
+     * Removes the least recently used elements if the cache size is greater than
+     * or equal to the maximum allowed size until the cache is at least 10% empty.
+     */
+    protected synchronized void cullCache() {
+        // Check if a max cache size is defined.
+        if (maxCacheSize < 0) {
+            return;
+        }
+
+        // See if the cache is too big. If so, clean out cache until it's 10% free.
+        if (map.size() > maxCacheSize) {
+            // First, delete any old entries to see how much memory that frees.
+            deleteExpiredEntries();
+            // Next, delete the least recently used elements until 10% of the cache
+            // has been freed.
+            int desiredSize = (int) (maxCacheSize * .90);
+            for (int i=map.size(); i>desiredSize; i--) {
+                // Get the key and invoke the remove method on it.
+                if (remove(lastAccessedList.getLast().object, true) == null) {
+                    System.err.println("Error attempting to cullCache with remove(" +
+                            lastAccessedList.getLast().object.toString() + ") - " +
+                            "cacheObject not found in cache!");
+                    lastAccessedList.getLast().remove();
+                }
+            }
+        }
+    }
+
+    /**
+     * Wrapper for all objects put into cache. It's primary purpose is to maintain
+     * references to the linked lists that maintain the creation time of the object
+     * and the ordering of the most used objects.
+     *
+     * This class is optimized for speed rather than strictly correct encapsulation.
+     */
+    private static class CacheObject {
+
+       /**
+        * Underlying object wrapped by the CacheObject.
+        */
+        public Object object;
+
+        /**
+         * A reference to the node in the cache order list. We keep the reference
+         * here to avoid linear scans of the list. Every time the object is
+         * accessed, the node is removed from its current spot in the list and
+         * moved to the front.
+         */
+        public LinkedListNode lastAccessedListNode;
+
+        /**
+         * A reference to the node in the age order list. We keep the reference
+         * here to avoid linear scans of the list. The reference is used if the
+         * object has to be deleted from the list.
+         */
+        public LinkedListNode ageListNode;
+
+        /**
+         * A count of the number of times the object has been read from cache.
+         */
+        public int readCount = 0;
+
+        /**
+         * Creates a new cache object wrapper.
+         *
+         * @param object the underlying Object to wrap.
+         */
+        public CacheObject(Object object) {
+            this.object = object;
+        }
+
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (!(o instanceof CacheObject)) {
+                return false;
+            }
+
+            final CacheObject cacheObject = (CacheObject) o;
+
+            if (!object.equals(cacheObject.object)) {
+                return false;
+            }
+
+            return true;
+        }
+
+        public int hashCode() {
+            return object.hashCode();
+        }
+    }
+
+    /**
+     * Simple LinkedList implementation. The main feature is that list nodes
+     * are public, which allows very fast delete operations when one has a
+     * reference to the node that is to be deleted.<p>
+     */
+    private static class LinkedList {
+
+        /**
+         * The root of the list keeps a reference to both the first and last
+         * elements of the list.
+         */
+        private LinkedListNode head = new LinkedListNode("head", null, null);
+
+        /**
+         * Creates a new linked list.
+         */
+        public LinkedList() {
+            head.next = head.previous = head;
+        }
+
+        /**
+         * Returns the first linked list node in the list.
+         *
+         * @return the first element of the list.
+         */
+        public LinkedListNode getFirst() {
+            LinkedListNode node = head.next;
+            if (node == head) {
+                return null;
+            }
+            return node;
+        }
+
+        /**
+         * Returns the last linked list node in the list.
+         *
+         * @return the last element of the list.
+         */
+        public LinkedListNode getLast() {
+            LinkedListNode node = head.previous;
+            if (node == head) {
+                return null;
+            }
+            return node;
+        }
+
+        /**
+         * Adds a node to the beginning of the list.
+         *
+         * @param node the node to add to the beginning of the list.
+         */
+        public LinkedListNode addFirst(LinkedListNode node) {
+            node.next = head.next;
+            node.previous = head;
+            node.previous.next = node;
+            node.next.previous = node;
+            return node;
+        }
+
+        /**
+         * Adds an object to the beginning of the list by automatically creating a
+         * a new node and adding it to the beginning of the list.
+         *
+         * @param object the object to add to the beginning of the list.
+         * @return the node created to wrap the object.
+         */
+        public LinkedListNode addFirst(Object object) {
+            LinkedListNode node = new LinkedListNode(object, head.next, head);
+            node.previous.next = node;
+            node.next.previous = node;
+            return node;
+        }
+
+        /**
+         * Adds an object to the end of the list by automatically creating a
+         * a new node and adding it to the end of the list.
+         *
+         * @param object the object to add to the end of the list.
+         * @return the node created to wrap the object.
+         */
+        public LinkedListNode addLast(Object object) {
+            LinkedListNode node = new LinkedListNode(object, head, head.previous);
+            node.previous.next = node;
+            node.next.previous = node;
+            return node;
+        }
+
+        /**
+         * Erases all elements in the list and re-initializes it.
+         */
+        public void clear() {
+            //Remove all references in the list.
+            LinkedListNode node = getLast();
+            while (node != null) {
+                node.remove();
+                node = getLast();
+            }
+
+            //Re-initialize.
+            head.next = head.previous = head;
+        }
+
+        /**
+         * Returns a String representation of the linked list with a comma
+         * delimited list of all the elements in the list.
+         *
+         * @return a String representation of the LinkedList.
+         */
+        public String toString() {
+            LinkedListNode node = head.next;
+            StringBuffer buf = new StringBuffer();
+            while (node != head) {
+                buf.append(node.toString()).append(", ");
+                node = node.next;
+            }
+            return buf.toString();
+        }
+    }
+
+    /**
+     * Doubly linked node in a LinkedList. Most LinkedList implementations keep the
+     * equivalent of this class private. We make it public so that references
+     * to each node in the list can be maintained externally.
+     *
+     * Exposing this class lets us make remove operations very fast. Remove is
+     * built into this class and only requires two reference reassignments. If
+     * remove existed in the main LinkedList class, a linear scan would have to
+     * be performed to find the correct node to delete.
+     *
+     * The linked list implementation was specifically written for the Jive
+     * cache system. While it can be used as a general purpose linked list, for
+     * most applications, it is more suitable to use the linked list that is part
+     * of the Java Collections package.
+     */
+    private static class LinkedListNode {
+
+        public LinkedListNode previous;
+        public LinkedListNode next;
+        public Object object;
+
+        /**
+         * This class is further customized for the Jive cache system. It
+         * maintains a timestamp of when a Cacheable object was first added to
+         * cache. Timestamps are stored as long values and represent the number
+         * of milliseconds passed since January 1, 1970 00:00:00.000 GMT.<p>
+         *
+         * The creation timestamp is used in the case that the cache has a
+         * maximum lifetime set. In that case, when
+         * [current time] - [creation time] > [max lifetime], the object will be
+         * deleted from cache.
+         */
+        public long timestamp;
+
+        /**
+         * Constructs a new linked list node.
+         *
+         * @param object the Object that the node represents.
+         * @param next a reference to the next LinkedListNode in the list.
+         * @param previous a reference to the previous LinkedListNode in the list.
+         */
+        public LinkedListNode(Object object, LinkedListNode next,
+                LinkedListNode previous)
+        {
+            this.object = object;
+            this.next = next;
+            this.previous = previous;
+        }
+
+        /**
+         * Removes this node from the linked list that it is a part of.
+         */
+        public void remove() {
+            previous.next = next;
+            next.previous = previous;
+        }
+
+        /**
+         * Returns a String representation of the linked list node by calling the
+         * toString method of the node's object.
+         *
+         * @return a String representation of the LinkedListNode.
+         */
+        public String toString() {
+            return object.toString();
+        }
+    }
+}
\ No newline at end of file
diff --git a/source/org/jivesoftware/smack/util/DNSUtil.java b/source/org/jivesoftware/smack/util/DNSUtil.java
new file mode 100644
index 000000000..a483be66d
--- /dev/null
+++ b/source/org/jivesoftware/smack/util/DNSUtil.java
@@ -0,0 +1,219 @@
+/**
+ * $Revision: 1456 $
+ * $Date: 2005-06-01 22:04:54 -0700 (Wed, 01 Jun 2005) $
+ *
+ * Copyright 2003-2005 Jive Software.
+ *
+ * All rights reserved. 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 org.jivesoftware.smack.util;
+
+import javax.naming.directory.DirContext;
+import javax.naming.directory.InitialDirContext;
+import javax.naming.directory.Attributes;
+import java.util.Hashtable;
+import java.util.Map;
+
+/**
+ * Utilty class to perform DNS lookups for XMPP services.
+ *
+ * @author Matt Tucker
+ */
+public class DNSUtil {
+
+    /**
+     * Create a cache to hold the 100 most recently accessed DNS lookups for a period of
+     * 10 minutes.
+     */
+    private static Map cache = new Cache(100, 1000*60*10);
+
+    private static DirContext context;
+
+    static {
+        try {
+            Hashtable env = new Hashtable();
+            env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
+            context = new InitialDirContext(env);
+        }
+        catch (Exception e) {
+            // Ignore.
+        }
+    }
+
+    /**
+     * Returns the host name and port that the specified XMPP server can be
+     * reached at for client-to-server communication. A DNS lookup for a SRV
+     * record in the form "_xmpp-client._tcp.example.com" is attempted, according
+     * to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
+     * of "_jabber._tcp.example.com" is attempted since servers that implement an
+     * older version of the protocol may be listed using that notation. If that
+     * lookup fails as well, it's assumed that the XMPP server lives at the
+     * host resolved by a DNS lookup at the specified domain on the default port
+     * of 5222.<p>
+     *
+     * As an example, a lookup for "example.com" may return "im.example.com:5269".
+     *
+     * @param domain the domain.
+     * @return a HostAddress, which encompasses the hostname and port that the XMPP
+     *      server can be reached at for the specified domain.
+     */
+    public static HostAddress resolveXMPPDomain(String domain) {
+        if (context == null) {
+            return new HostAddress(domain, 5222);
+        }
+        String key = "c" + domain;
+        // Return item from cache if it exists.
+        if (cache.containsKey(key)) {
+            HostAddress address = (HostAddress)cache.get(key);
+            if (address != null) {
+                return address;
+            }
+        }
+        String host = domain;
+        int port = 5222;
+        try {
+            Attributes dnsLookup = context.getAttributes("_xmpp-client._tcp." + domain);
+            String srvRecord = (String)dnsLookup.get("SRV").get();
+            String [] srvRecordEntries = srvRecord.split(" ");
+            port = Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
+            host = srvRecordEntries[srvRecordEntries.length-1];
+        }
+        catch (Exception e) {
+            // Ignore.
+        }
+        // Host entries in DNS should end with a ".".
+        if (host.endsWith(".")) {
+            host = host.substring(0, host.length()-1);
+        }
+        HostAddress address = new HostAddress(host, port);
+        // Add item to cache.
+        cache.put(key, address);
+        return address;
+    }
+
+    /**
+     * Returns the host name and port that the specified XMPP server can be
+     * reached at for server-to-server communication. A DNS lookup for a SRV
+     * record in the form "_xmpp-server._tcp.example.com" is attempted, according
+     * to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
+     * of "_jabber._tcp.example.com" is attempted since servers that implement an
+     * older version of the protocol may be listed using that notation. If that
+     * lookup fails as well, it's assumed that the XMPP server lives at the
+     * host resolved by a DNS lookup at the specified domain on the default port
+     * of 5269.<p>
+     *
+     * As an example, a lookup for "example.com" may return "im.example.com:5269".
+     *
+     * @param domain the domain.
+     * @return a HostAddress, which encompasses the hostname and port that the XMPP
+     *      server can be reached at for the specified domain.
+     */
+    public static HostAddress resolveXMPPServerDomain(String domain) {
+        if (context == null) {
+            return new HostAddress(domain, 5269);
+        }
+        String key = "s" + domain;
+        // Return item from cache if it exists.
+        if (cache.containsKey(key)) {
+            HostAddress address = (HostAddress)cache.get(key);
+            if (address != null) {
+                return address;
+            }
+        }
+        String host = domain;
+        int port = 5269;
+        try {
+            Attributes dnsLookup = context.getAttributes("_xmpp-server._tcp." + domain);
+            String srvRecord = (String)dnsLookup.get("SRV").get();
+            String [] srvRecordEntries = srvRecord.split(" ");
+            port = Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
+            host = srvRecordEntries[srvRecordEntries.length-1];
+        }
+        catch (Exception e) {
+            // Attempt lookup with older "jabber" name.
+            try {
+                Attributes dnsLookup = context.getAttributes("_jabber._tcp." + domain);
+                String srvRecord = (String)dnsLookup.get("SRV").get();
+                String [] srvRecordEntries = srvRecord.split(" ");
+                port = Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
+                host = srvRecordEntries[srvRecordEntries.length-1];
+            }
+            catch (Exception e2) { }
+        }
+        // Host entries in DNS should end with a ".".
+        if (host.endsWith(".")) {
+            host = host.substring(0, host.length()-1);
+        }
+        HostAddress address = new HostAddress(host, port);
+        // Add item to cache.
+        cache.put(key, address);
+        return address;
+    }
+
+    /**
+     * Encapsulates a hostname and port.
+     */
+    public static class HostAddress {
+
+        private String host;
+        private int port;
+
+        private HostAddress(String host, int port) {
+            this.host = host;
+            this.port = port;
+        }
+
+        /**
+         * Returns the hostname.
+         *
+         * @return the hostname.
+         */
+        public String getHost() {
+            return host;
+        }
+
+        /**
+         * Returns the port.
+         *
+         * @return the port.
+         */
+        public int getPort() {
+            return port;
+        }
+
+        public String toString() {
+            return host + ":" + port;
+        }
+
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (!(o instanceof HostAddress)) {
+                return false;
+            }
+
+            final HostAddress address = (HostAddress) o;
+
+            if (!host.equals(address.host)) {
+                return false;
+            }
+            if (port != address.port) {
+                return false;
+            }
+
+            return true;
+        }
+    }
+}
\ No newline at end of file
diff --git a/test/org/jivesoftware/smack/util/CacheTest.java b/test/org/jivesoftware/smack/util/CacheTest.java
new file mode 100644
index 000000000..34ce3251a
--- /dev/null
+++ b/test/org/jivesoftware/smack/util/CacheTest.java
@@ -0,0 +1,77 @@
+/**
+ * $RCSfile$
+ * $Revision: 2485 $
+ * $Date: 2005-04-14 17:56:37 -0700 (Thu, 14 Apr 2005) $
+ *
+ * Copyright (C) 2002-2003 Jive Software. All rights reserved.
+ * ====================================================================
+ * The Jive Software License (based on Apache Software License, Version 1.1)
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. The end-user documentation included with the redistribution,
+ *    if any, must include the following acknowledgment:
+ *       "This product includes software developed by
+ *        Jive Software (http://www.jivesoftware.com)."
+ *    Alternately, this acknowledgment may appear in the software itself,
+ *    if and wherever such third-party acknowledgments normally appear.
+ *
+ * 4. The names "Smack" and "Jive Software" must not be used to
+ *    endorse or promote products derived from this software without
+ *    prior written permission. For written permission, please
+ *    contact webmaster@jivesoftware.com.
+ *
+ * 5. Products derived from this software may not be called "Smack",
+ *    nor may "Smack" appear in their name, without prior written
+ *    permission of Jive Software.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL JIVE SOFTWARE OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * ====================================================================
+ */
+
+package org.jivesoftware.smack.util;
+
+import junit.framework.TestCase;
+
+/**
+ * A test case for the Cache class.
+ */
+public class CacheTest extends TestCase {
+
+    public void testMaxSize() {
+        Cache cache = new Cache(100, -1);
+        for (int i=0; i<1000; i++) {
+            cache.put(new Integer(i), "value");
+            assertTrue("Cache size must never be larger than 100.", cache.size() <= 100);
+        }
+    }
+
+    public void testLRU() {
+        Cache cache = new Cache(100, -1);
+        for (int i=0; i<1000; i++) {
+            cache.put(new Integer(i), "value");
+            assertTrue("LRU algorithm for cache key of '0' failed.", cache.get(new Integer(0)) != null);
+        }
+    }
+}