From ed9aa2b62a9c65d152f7560368d407794caa6d72 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Wed, 21 Feb 2018 21:02:09 +0000
Subject: [PATCH] Add branch IDs for current and next block to
 getblockchaininfo

Closes #2974.
---
 qa/rpc-tests/wallet_overwintertx.py | 8 ++++++++
 src/rpcblockchain.cpp               | 9 +++++++++
 2 files changed, 17 insertions(+)

diff --git a/qa/rpc-tests/wallet_overwintertx.py b/qa/rpc-tests/wallet_overwintertx.py
index 84215eb6b..91bdb7764 100755
--- a/qa/rpc-tests/wallet_overwintertx.py
+++ b/qa/rpc-tests/wallet_overwintertx.py
@@ -38,6 +38,9 @@ class WalletOverwinterTxTest (BitcoinTestFramework):
         #
         # Currently at block 198. The next block to be mined 199 is a Sprout block
         #
+        assert_equal(self.nodes[0].getblockchaininfo()['consensus']['chaintip'], '00000000')
+        assert_equal(self.nodes[0].getblockchaininfo()['consensus']['nextblock'], '00000000')
+
         taddr0 = self.nodes[0].getnewaddress()
         taddr2 = self.nodes[2].getnewaddress()
         zaddr2 = self.nodes[2].z_getnewaddress()
@@ -76,6 +79,8 @@ class WalletOverwinterTxTest (BitcoinTestFramework):
         #
         # Currently at block 199. The next block to be mined 200 is an Overwinter block
         #
+        assert_equal(self.nodes[0].getblockchaininfo()['consensus']['chaintip'], '00000000')
+        assert_equal(self.nodes[0].getblockchaininfo()['consensus']['nextblock'], '5ba81b19')
 
         # Send taddr to taddr
         tsendamount = Decimal('4.56')
@@ -88,9 +93,12 @@ class WalletOverwinterTxTest (BitcoinTestFramework):
         myopid = self.nodes[0].z_sendmany(taddr0, recipients)
         txid_shielded = wait_and_assert_operationid_status(self.nodes[0], myopid)
 
+        # Mine the first Overwinter block
         self.sync_all()
         self.nodes[0].generate(1)
         self.sync_all()
+        assert_equal(self.nodes[0].getblockchaininfo()['consensus']['chaintip'], '5ba81b19')
+        assert_equal(self.nodes[0].getblockchaininfo()['consensus']['nextblock'], '5ba81b19')
 
         # Verify balance
         assert_equal(self.nodes[3].getbalance(), tsendamount)
diff --git a/src/rpcblockchain.cpp b/src/rpcblockchain.cpp
index ebd4a733a..32f3f0fee 100644
--- a/src/rpcblockchain.cpp
+++ b/src/rpcblockchain.cpp
@@ -726,6 +726,10 @@ UniValue getblockchaininfo(const UniValue& params, bool fHelp)
             "        \"status\": \"xxxx\",       (string) status of upgrade\n"
             "        \"info\": \"xxxx\",         (string) additional information about upgrade\n"
             "     }, ...\n"
+            "  },\n"
+            "  \"consensus\": {               (object) branch IDs of the current and upcoming consensus rules\n"
+            "     \"chaintip\": \"xxxxxxxx\",   (string) branch ID used to validate the current chain tip\n"
+            "     \"nextblock\": \"xxxxxxxx\"   (string) branch ID that the next block will be validated under\n"
             "  }\n"
             "}\n"
             "\nExamples:\n"
@@ -767,6 +771,11 @@ UniValue getblockchaininfo(const UniValue& params, bool fHelp)
     }
     obj.push_back(Pair("upgrades", upgrades));
 
+    UniValue consensus(UniValue::VOBJ);
+    consensus.push_back(Pair("chaintip", HexInt(CurrentEpochBranchId(tip->nHeight, consensusParams))));
+    consensus.push_back(Pair("nextblock", HexInt(CurrentEpochBranchId(tip->nHeight + 1, consensusParams))));
+    obj.push_back(Pair("consensus", consensus));
+
     if (fPruneMode)
     {
         CBlockIndex *block = chainActive.Tip();