don't follow incompatible chain

core/src/main/java/org/bitcoinj/core/Peer.java

@@ -564,6 +564,15 @@ public class Peer extends PeerSocketHandler {
             close();
             return;
         }
+        if (((vPeerVersionMessage.localServices
+                & VersionMessage.NODE_BITCOIN_CASH) == VersionMessage.NODE_BITCOIN_CASH) ||
+                ((vPeerVersionMessage.localServices
+                & VersionMessage.NODE_SEGWIT2X) == VersionMessage.NODE_SEGWIT2X)) {
+              log.info("{}: Peer follows an incompatible block chain.", this);
+              // Shut down the channel gracefully.
+              close();
+              return;
+        }
         if (vPeerVersionMessage.bestHeight < 0)
             // In this case, it's a protocol violation.
             throw new ProtocolException("Peer reports invalid best height: " + vPeerVersionMessage.bestHeight);

core/src/main/java/org/bitcoinj/core/VersionMessage.java

@@ -29,13 +29,13 @@ import java.util.Locale;
 
 /**
  * <p>A VersionMessage holds information exchanged during connection setup with another peer. Most of the fields are not
- * particularly interesting. The subVer field, since BIP 14, acts as a User-Agent string would. You can and should 
+ * particularly interesting. The subVer field, since BIP 14, acts as a User-Agent string would. You can and should
  * append to or change the subVer for your own software so other implementations can identify it, and you can look at
  * the subVer field received from other nodes to see what they are running.</p>
  *
  * <p>After creating yourself a VersionMessage, you can pass it to {@link PeerGroup#setVersionMessage(VersionMessage)}
  * to ensure it will be used for each new connection.</p>
- * 
+ *
  * <p>Instances of this class are not safe for use by multiple threads.</p>
  */
 public class VersionMessage extends Message {
@@ -49,6 +49,10 @@ public class VersionMessage extends Message {
     public static final int NODE_NETWORK = 1 << 0;
     /** A flag that denotes whether the peer supports the getutxos message or not. */
     public static final int NODE_GETUTXOS = 1 << 1;
+    /** A service bit used by Bitcoin-ABC to announce Bitcoin Cash nodes. */
+    public static final int NODE_BITCOIN_CASH = 1 << 5;
+    /** A service bit used by BTC1 to announce Segwit2x nodes. */
+    public static final int NODE_SEGWIT2X = 1 << 7;
     /** Indicates that a node can be asked for blocks and transactions including witness data. */
     public static final int NODE_WITNESS = 1 << 3;
 
@@ -94,7 +98,7 @@ public class VersionMessage extends Message {
     // It doesn't really make sense to ever lazily parse a version message or to retain the backing bytes.
     // If you're receiving this on the wire you need to check the protocol version and it will never need to be sent
     // back down the wire.
-    
+
     public VersionMessage(NetworkParameters params, int newBestHeight) {
         super(params);
         clientVersion = params.getProtocolVersionNum(NetworkParameters.ProtocolVersion.CURRENT);
@@ -167,7 +171,7 @@ public class VersionMessage extends Message {
             throw new RuntimeException(e);  // Can't happen.
         }
         // Next up is the "local host nonce", this is to detect the case of connecting
-        // back to yourself. We don't care about this as we won't be accepting inbound 
+        // back to yourself. We don't care about this as we won't be accepting inbound
         // connections.
         Utils.uint32ToByteStreamLE(0, buf);
         Utils.uint32ToByteStreamLE(0, buf);