Content Refresh Operation improvement

- Added the improvement for content refresh operation from the paper, we keep the last time a content was republished, and on content update operations, we only republish if the last republish was before (current time - republishing time interval)

src/kademlia/Kademlia.java

@@ -268,6 +268,7 @@ public class Kademlia
      * @return DHTContent The content
      *
      * @throws java.io.IOException
+     * @throws kademlia.exceptions.ContentNotFoundException
      */
     public StorageEntry get(GetParameter param) throws NoSuchElementException, IOException, ContentNotFoundException
     {

src/kademlia/dht/DHT.java

@@ -86,6 +86,10 @@ public class DHT
         if (this.entriesManager.contains(content.getContentMetadata()))
         {
             StorageEntryMetadata current = this.entriesManager.get(content.getContentMetadata());
+
+            /* update the last republished time */
+            current.updateLastRepublished();
+
             if (current.getLastUpdatedTimestamp() >= content.getContentMetadata().getLastUpdatedTimestamp())
             {
                 /* We have the current content, no need to update it! just leave this method now */

src/kademlia/dht/StorageEntryMetadata.java

@@ -19,6 +19,9 @@ public class StorageEntryMetadata
     private final int contentHash;
     private final long updatedTs;
 
+    /* This value is the last time this content was last updated from the network */
+    private long lastRepublished;
+
     public StorageEntryMetadata(KadContent content)
     {
         this.key = content.getKey();
@@ -26,6 +29,8 @@ public class StorageEntryMetadata
         this.type = content.getType();
         this.contentHash = content.hashCode();
         this.updatedTs = content.getLastUpdatedTimestamp();
+
+        this.lastRepublished = System.currentTimeMillis() / 1000L;
     }
 
     public NodeId getKey()
@@ -84,6 +89,19 @@ public class StorageEntryMetadata
         return true;
     }
 
+    public long lastRepublished()
+    {
+        return this.lastRepublished;
+    }
+
+    /**
+     * Whenever we republish a content or get this content from the network, we update the last republished time
+     */
+    public void updateLastRepublished()
+    {
+        this.lastRepublished = System.currentTimeMillis() / 1000L;
+    }
+
     @Override
     public boolean equals(Object o)
     {

src/kademlia/operation/ContentRefreshOperation.java

@@ -47,14 +47,21 @@ public class ContentRefreshOperation implements Operation
         /* Get a list of all storage entries for content */
         List<StorageEntryMetadata> entries = this.dht.getStorageEntries();
 
+        /* If a content was last republished before this time, then we need to republish it */
+        final long minRepublishTime = (System.currentTimeMillis() / 1000L) - this.config.restoreInterval();
+
         /* For each storage entry, distribute it */
         for (StorageEntryMetadata e : entries)
         {
-            /**
-             * @todo - Paper improvement 1 -
-             * Check last update time of this entry and
-             * only distribute it if it has been last updated > 1 hour ago
-             */
+            /* Check last update time of this entry and only distribute it if it has been last updated > 1 hour ago */
+            if (e.lastRepublished() > minRepublishTime)
+            {
+                continue;
+            }
+
+            /* Set that this content is now republished */
+            e.updateLastRepublished();
+
             /* Get the K closest nodes to this entries */
             List<Node> closestNodes = this.localNode.getRoutingTable().findClosest(e.getKey(), this.config.k());