From a355b05b2a81539d7da2e7c7c173ee296651feaf Mon Sep 17 00:00:00 2001
From: Andreas Schildbach <andreas.schildbach@bloq.com>
Date: Tue, 22 Aug 2017 10:22:52 +0200
Subject: [PATCH] Peer: Drop Bitcoin Cash peers early, based on service bit 5.

They will fail the difficulty check anyway.
---
 core/src/main/java/org/bitcoinj/core/Peer.java           | 7 +++++++
 core/src/main/java/org/bitcoinj/core/VersionMessage.java | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/core/src/main/java/org/bitcoinj/core/Peer.java b/core/src/main/java/org/bitcoinj/core/Peer.java
index 00064ed0..9f873348 100644
--- a/core/src/main/java/org/bitcoinj/core/Peer.java
+++ b/core/src/main/java/org/bitcoinj/core/Peer.java
@@ -564,6 +564,13 @@ public class Peer extends PeerSocketHandler {
             close();
             return;
         }
+        if ((vPeerVersionMessage.localServices
+                & VersionMessage.NODE_BITCOIN_CASH) == VersionMessage.NODE_BITCOIN_CASH) {
+            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);
diff --git a/core/src/main/java/org/bitcoinj/core/VersionMessage.java b/core/src/main/java/org/bitcoinj/core/VersionMessage.java
index eac0f54b..7421fd5d 100644
--- a/core/src/main/java/org/bitcoinj/core/VersionMessage.java
+++ b/core/src/main/java/org/bitcoinj/core/VersionMessage.java
@@ -41,6 +41,8 @@ public class VersionMessage extends Message {
     public static final int NODE_NETWORK = 1 << 0;
     /** A service bit 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;
 
     /**
      * The version number of the protocol spoken.