Allow blockChain to be skipped when creating PeerGroups/Peers.

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

@@ -67,8 +67,8 @@ public class Peer {
     private MemoryPool memoryPool;
     // A time before which we only download block headers, after that point we download block bodies.
     private long fastCatchupTimeSecs;
-    // Whether we are currently downloading headers only or block bodies. Defaults to true, if the fast catchup time
+    // Whether we are currently downloading headers only or block bodies. Starts at true. If the fast catchup time is
-    // is set AND our best block is before that date, switch to false until block headers beyond that point have been
+    // set AND our best block is before that date, switch to false until block headers beyond that point have been
     // received at which point it gets set to true again. This isn't relevant unless downloadData is true.
     private boolean downloadBlockBodies = true;
     // Keeps track of things we requested internally with getdata but didn't receive yet, so we can avoid re-requests.
@@ -87,10 +87,10 @@ public class Peer {
     /**
      * Construct a peer that reads/writes from the given block chain.
      */
-    public Peer(NetworkParameters params, AbstractBlockChain chain2, VersionMessage ver) {
+    public Peer(NetworkParameters params, AbstractBlockChain chain, VersionMessage ver) {
-        this.params = params;
+        this.params = Preconditions.checkNotNull(params);
-        this.blockChain = chain2;
+        this.versionMessage = Preconditions.checkNotNull(ver);
-        this.versionMessage = ver;
+        this.blockChain = chain;  // Allowed to be null.
         this.pendingGetBlockFutures = new ArrayList<GetDataFuture<Block>>();
         this.eventListeners = new CopyOnWriteArrayList<PeerEventListener>();
         this.lifecycleListeners = new CopyOnWriteArrayList<PeerLifecycleListener>();
@@ -104,8 +104,7 @@ public class Peer {
      * given software name/version strings, which should be something like "MySimpleTool", "1.0"
      */
     public Peer(NetworkParameters params, AbstractBlockChain blockChain, String thisSoftwareName, String thisSoftwareVersion) {
-        this(params, blockChain, null);
+        this(params, blockChain, new VersionMessage(params, blockChain.getBestChainHeight()));
-        this.versionMessage = new VersionMessage(params, blockChain.getBestChainHeight());
         this.versionMessage.appendToSubVer(thisSoftwareName, thisSoftwareVersion, null);
     }
 
@@ -457,7 +456,7 @@ public class Peer {
             }
         }
 
-        if (blocks.size() > 0 && downloadData) {
+        if (blocks.size() > 0 && downloadData && blockChain != null) {
             // Ideally, we'd only ask for the data here if we actually needed it. However that can imply a lot of
             // disk IO to figure out what we've got. Normally peers will not send us inv for things we already have
             // so we just re-request it here, and if we get duplicates the block chain / wallet will filter them out.
@@ -532,6 +531,7 @@ public class Peer {
      * @param secondsSinceEpoch Time in seconds since the epoch or 0 to reset to always downloading block bodies.
      */
     public void setFastCatchupTime(long secondsSinceEpoch) {
+        Preconditions.checkNotNull(blockChain);
         if (secondsSinceEpoch == 0) {
             fastCatchupTimeSecs = params.genesisBlock.getTimeSeconds();
             downloadBlockBodies = true;

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

@@ -122,14 +122,23 @@ public class PeerGroup {
     Peer.PeerLifecycleListener startupListener = new PeerStartupListener();
 
     /**
-     * Creates a PeerGroup with the given parameters and a default 5 second connection timeout. If you don't care
+     * Creates a PeerGroup with the given parameters and a default 5 second connection timeout.
-     * about blocks or pending transactions, you can just provide a MemoryBlockStore and a newly created Wallet.
      *
      * @param params Network parameters
-     * @param chain2 a BlockChain object that will receive and handle block messages.
+     * @param chain a BlockChain object that will receive and handle block messages.
      */
-    public PeerGroup(NetworkParameters params, AbstractBlockChain chain2) {
+    public PeerGroup(NetworkParameters params, AbstractBlockChain chain) {
-        this(params, chain2, DEFAULT_CONNECTION_DELAY_MILLIS);
+        this(params, chain, DEFAULT_CONNECTION_DELAY_MILLIS);
+    }
+
+    /**
+     * Creates a PeerGroup with the given parameters and a default 5 second connection timeout. No chain is
+     * provided so this node will report its chain height as zero to other peers.
+     *
+     * @param params Network parameters
+     */
+    public PeerGroup(NetworkParameters params) {
+        this(params, null, DEFAULT_CONNECTION_DELAY_MILLIS);
     }
 
     /**
@@ -152,7 +161,7 @@ public class PeerGroup {
     PeerGroup(final NetworkParameters params, final AbstractBlockChain chain,
               int connectionDelayMillis, ClientBootstrap bootstrap) {
         this.params = params;
-        this.chain = chain;
+        this.chain = chain;  // Can be null.
         this.connectionDelayMillis = connectionDelayMillis;
         this.fastCatchupTimeSecs = params.genesisBlock.getTimeSeconds();
         this.wallets = new ArrayList<Wallet>(1);
@@ -162,9 +171,8 @@ public class PeerGroup {
         //   - using connectTo() will increment it by one
         this.maxConnections = 0;
 
-        // Set up a default template version message that doesn't tell the other side what kind of bitcoinj user
+        int height = chain == null ? 0 : chain.getBestChainHeight();
-        // this is.
+        this.versionMessage = new VersionMessage(params, height);
-        this.versionMessage = new VersionMessage(params, chain.getBestChainHeight());
 
         memoryPool = new MemoryPool();
         this.bootstrap = bootstrap;
@@ -194,7 +202,7 @@ public class PeerGroup {
         return new ChannelPipelineFactory() {
             public ChannelPipeline getPipeline() throws Exception {
                 VersionMessage ver = getVersionMessage().duplicate();
-                ver.bestHeight = chain.getBestChainHeight();
+                ver.bestHeight = chain == null ? 0 : chain.getBestChainHeight();
                 ver.time = Utils.now().getTime() / 1000;
 
                 ChannelPipeline p = Channels.pipeline();
@@ -685,6 +693,7 @@ public class PeerGroup {
         if (downloadPeer != null) {
             log.info("Setting download peer: {}", downloadPeer);
             downloadPeer.setDownloadData(true);
+            if (chain != null)
                 downloadPeer.setFastCatchupTime(fastCatchupTimeSecs);
         }
     }