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) {

tests/com/google/bitcoin/core/PeerGroupTest.java

@@ -0,0 +1,49 @@
+/**
+ * Copyright 2011 Google Inc.
+ *
+ * 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 com.google.bitcoin.core;
+
+import static org.junit.Assert.assertTrue;
+
+import com.google.bitcoin.store.BlockStore;
+import com.google.bitcoin.store.MemoryBlockStore;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class PeerGroupTest {
+    static final NetworkParameters params = NetworkParameters.unitTests();
+
+    private Wallet wallet;
+    private BlockStore blockStore;
+    private PeerGroup peerGroup;
+
+    @Before
+    public void setUp() throws Exception {
+        wallet = new Wallet(params);
+        blockStore = new MemoryBlockStore(params);
+        BlockChain chain = new BlockChain(params, wallet, blockStore);
+        peerGroup = new PeerGroup(blockStore, params, chain);
+    }
+
+    @Test
+    public void listener() throws Exception {
+        AbstractPeerEventListener listener = new AbstractPeerEventListener() {
+        };
+        peerGroup.addEventListener(listener);
+        assertTrue(peerGroup.removeEventListener(listener));
+    }
+}