Use pong(+nonce) messages.

* Adds a Pong class
* Uses nonces in pings (when applicable)
* Responds to pings with pongs (when applicable)
* Changes protocol version to 60001

core/src/main/java/com/google/bitcoin/core/BitcoinSerializer.java

@@ -64,6 +64,7 @@ public class BitcoinSerializer {
         names.put(Transaction.class, "tx");
         names.put(AddressMessage.class, "addr");
         names.put(Ping.class, "ping");
+        names.put(Pong.class, "pong");
         names.put(VersionAck.class, "verack");
         names.put(GetBlocksMessage.class, "getblocks");
         names.put(GetHeadersMessage.class, "getheaders");
@@ -264,7 +265,9 @@ public class BitcoinSerializer {
         } else if (command.equals("addr")) {
             message = new AddressMessage(params, payloadBytes, parseLazy, parseRetain, length);
         } else if (command.equals("ping")) {
-            return new Ping();
+            message = new Ping(params, payloadBytes);
+        } else if (command.equals("pong")) {
+            message = new Pong(params, payloadBytes);
         } else if (command.equals("verack")) {
             return new VersionAck(params, payloadBytes);
         } else if (command.equals("headers")) {

core/src/main/java/com/google/bitcoin/core/NetworkParameters.java

@@ -36,9 +36,9 @@ public class NetworkParameters implements Serializable {
     private static final long serialVersionUID = 3L;
 
     /**
-     * The protocol version this library implements. A value of 31800 means 0.3.18.00.
+     * The protocol version this library implements.
      */
-    public static final int PROTOCOL_VERSION = 31800;
+    public static final int PROTOCOL_VERSION = 60001;
 
     /**
      * The alert signing key originally owned by Satoshi, and now passed on to Gavin along with a few others.

core/src/main/java/com/google/bitcoin/core/Peer.java

@@ -237,6 +237,11 @@ public class Peer {
                     throw new ProtocolException("got more than one version ack");
                 }
                 isAcked = true;
+            } else if (m instanceof Ping) {
+                if (((Ping) m).hasNonce())
+                    sendMessage(new Pong(((Ping) m).getNonce()));
+            } else if (m instanceof Pong) {
+                // We don't do anything with pongs right now, leave that to eventListeners
             } else {
                 // TODO: Handle the other messages we can receive.
                 log.warn("Received unhandled message: {}", m);

core/src/main/java/com/google/bitcoin/core/Ping.java

@@ -16,6 +16,60 @@
 
 package com.google.bitcoin.core;
 
-public class Ping extends EmptyMessage {
+import java.io.IOException;
+import java.io.OutputStream;
 
+public class Ping extends Message {
+    private long nonce;
+    private boolean hasNonce;
+    
+    public Ping(NetworkParameters params, byte[] payloadBytes) throws ProtocolException {
+        super(params, payloadBytes, 0);
+    }
+    
+    /**
+     * Create a Ping with a nonce value.
+     * Only use this if the remote node has a protocol version > 60000
+     */
+    public Ping(long nonce) {
+        this.nonce = nonce;
+        this.hasNonce = true;
+    }
+    
+    /**
+     * Create a Ping without a nonce value.
+     * Only use this if the remote node has a protocol version <= 60000
+     */
+    public Ping() {
+        this.hasNonce = false;
+    }
+    
+    public void bitcoinSerializeToStream(OutputStream stream) throws IOException {
+        if (hasNonce)
+            Utils.int64ToByteStreamLE(nonce, stream);
+    }
+
+    @Override
+    void parse() throws ProtocolException {
+        try {
+            nonce = readInt64();
+            hasNonce = true;
+        } catch(ArrayIndexOutOfBoundsException e) {
+            hasNonce = false;
+        }
+        length = hasNonce ? 8 : 0;
+    }
+    
+    @Override
+    protected void parseLite() {
+        
+    }
+    
+    boolean hasNonce() {
+        return hasNonce;
+    }
+    
+    long getNonce() {
+        return nonce;
+    }
 }

core/src/main/java/com/google/bitcoin/core/Pong.java

@@ -0,0 +1,55 @@
+/**
+ * Copyright 2012 Matt Corallo
+ *
+ * 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 java.io.IOException;
+import java.io.OutputStream;
+
+public class Pong extends Message {
+    private long nonce;
+    
+    public Pong(NetworkParameters params, byte[] payloadBytes) throws ProtocolException {
+        super(params, payloadBytes, 0);
+    }
+    
+    /**
+     * Create a Pong with a nonce value.
+     * Only use this if the remote node has a protocol version > 60000
+     */
+    public Pong(long nonce) {
+        this.nonce = nonce;
+    }
+    
+    @Override
+    void parse() throws ProtocolException {
+        nonce = readInt64();
+        length = 8;
+    }
+    
+    public void bitcoinSerializeToStream(OutputStream stream) throws IOException {
+        Utils.int64ToByteStreamLE(nonce, stream);
+    }
+    
+    @Override
+    protected void parseLite() {
+        
+    }
+    
+    long getNonce() {
+        return nonce;
+    }
+}

core/src/main/java/com/google/bitcoin/core/TCPNetworkConnection.java

@@ -31,6 +31,7 @@ import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
 import java.util.Date;
+import java.util.Random;
 
 import static org.jboss.netty.channel.Channels.write;
 
@@ -114,7 +115,11 @@ public class TCPNetworkConnection {
     }
 
     public void ping() throws IOException {
-        write(channel, new Ping());
+        // pong/nonce messages were added to any protocol version greater than 60000
+        if (versionMessage.clientVersion > 60000)
+            write(channel, new Ping(new Random().nextLong()));
+        else
+            write(channel, new Ping());
     }
 
     @Override

core/src/main/java/com/google/bitcoin/core/Utils.java

@@ -115,6 +115,17 @@ public class Utils {
         stream.write((int) (0xFF & (val >> 16)));
         stream.write((int) (0xFF & (val >> 24)));
     }
+    
+    public static void int64ToByteStreamLE(long val, OutputStream stream) throws IOException {
+        stream.write((int) (0xFF & (val >> 0)));
+        stream.write((int) (0xFF & (val >> 8)));
+        stream.write((int) (0xFF & (val >> 16)));
+        stream.write((int) (0xFF & (val >> 24)));
+        stream.write((int) (0xFF & (val >> 32)));
+        stream.write((int) (0xFF & (val >> 40)));
+        stream.write((int) (0xFF & (val >> 48)));
+        stream.write((int) (0xFF & (val >> 56)));
+    }
 
     public static void uint64ToByteStreamLE(BigInteger val, OutputStream stream) throws IOException {
         byte[] bytes = val.toByteArray();