PeerGroup connect/disconnect callback

src/com/google/bitcoin/core/AbstractPeerEventListener.java

@@ -30,4 +30,10 @@ public class AbstractPeerEventListener extends Object implements PeerEventListen
 
     public void onChainDownloadStarted(Peer peer, int blocksLeft) {
     }
+    
+    public void onPeerConnected(Peer peer, int peerCount) {
+    }
+    
+    public void onPeerDisconnected(Peer peer, int peerCount) {
+    }
 }

src/com/google/bitcoin/core/PeerEventListener.java

@@ -45,4 +45,20 @@ public interface PeerEventListener {
      * @param blocksLeft the number of blocks left to download
      */
     public void onChainDownloadStarted(Peer peer, int blocksLeft);
+    
+    /**
+     * Called when a peer is connected
+     * 
+     * @param peer 
+     * @param peerCount the total number of connected peers
+     */
+    public void onPeerConnected(Peer peer, int peerCount);
+    
+    /**
+     * Called when a peer is disconnected
+     * 
+     * @param peer 
+     * @param peerCount the total number of connected peers
+     */
+    public void onPeerDisconnected(Peer peer, int peerCount);
 }

src/com/google/bitcoin/core/PeerGroup.java

@@ -78,6 +78,9 @@ public class PeerGroup {
     // Callback for events related to chain download
     private PeerEventListener downloadListener;
     
+    // Callbacks for events related to peer connection/disconnection
+    private Set<PeerEventListener> peerEventListeners;
+    
     private NetworkParameters params;
     private BlockStore blockStore;
     private BlockChain chain;
@@ -93,12 +96,27 @@ public class PeerGroup {
         inactives = new LinkedBlockingQueue<PeerAddress>();
         
         peers = Collections.synchronizedSet(new HashSet<Peer>());
+
+        peerEventListeners = Collections.synchronizedSet(new HashSet<PeerEventListener>());
+
         peerPool = new ThreadPoolExecutor(CORE_THREADS, DEFAULT_CONNECTIONS,
                 THREAD_KEEP_ALIVE_SECONDS, TimeUnit.SECONDS,
                 new LinkedBlockingQueue<Runnable>(1),
                 new PeerGroupThreadFactory());
     }
 
+    /**
+     * Callbacks to the listener are performed in the connection thread.  The callback
+     * should not perform time consuming tasks.
+     */
+    public void addEventListener(PeerEventListener listener) {
+        peerEventListeners.add(listener);
+    }
+    
+    public boolean removeEventListener(PeerEventListener listener) {
+        return peerEventListeners.remove(listener);
+    }
+    
     /**
      * Depending on the environment, this should normally be between 1 and 10, default is 4.
      * 
@@ -305,6 +323,13 @@ public class PeerGroup {
     protected synchronized void handleNewPeer(Peer peer) {
         if (downloadListener != null && downloadPeer == null)
             startBlockChainDownloadFromPeer(peer);
+        synchronized (peerEventListeners) {
+            for (PeerEventListener listener : peerEventListeners) {
+                synchronized (listener) {
+                    listener.onPeerConnected(peer, peers.size());
+                }
+            }
+        }
     }
     
     protected synchronized void handlePeerDeath(Peer peer) {
@@ -316,6 +341,14 @@ public class PeerGroup {
                 }
             }
         }
+
+        synchronized (peerEventListeners) {
+            for (PeerEventListener listener : peerEventListeners) {
+                synchronized (listener) {
+                    listener.onPeerDisconnected(peer, peers.size());
+                }
+            }
+        }
     }
 
     private synchronized void startBlockChainDownloadFromPeer(Peer peer) {