From 152b7fb25fc1e5255ab038a8a3f6a3ce1c540892 Mon Sep 17 00:00:00 2001
From: James O'Beirne <james.obeirne@gmail.com>
Date: Tue, 13 Feb 2018 22:37:36 -0500
Subject: [PATCH 1/2] [tests] Add a (failing) test for waitforblockheight

Demonstrates the presence of a bug in in `validation.cpp:InvalidateBlock`
which will update `rpc/blockchain.cpp:latestblock` erroneously.
---
 test/functional/rpc_blockchain.py | 57 +++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/test/functional/rpc_blockchain.py b/test/functional/rpc_blockchain.py
index 7cf2abe6f0e..7b04e4465f9 100755
--- a/test/functional/rpc_blockchain.py
+++ b/test/functional/rpc_blockchain.py
@@ -32,6 +32,18 @@ from test_framework.util import (
     assert_is_hex_string,
     assert_is_hash_string,
 )
+from test_framework.blocktools import (
+    create_block,
+    create_coinbase,
+)
+from test_framework.messages import (
+    msg_block,
+)
+from test_framework.mininode import (
+    P2PInterface,
+    network_thread_start,
+)
+
 
 class BlockchainTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -46,6 +58,7 @@ class BlockchainTest(BitcoinTestFramework):
         self._test_getdifficulty()
         self._test_getnetworkhashps()
         self._test_stopatheight()
+        self._test_waitforblockheight()
         assert self.nodes[0].verifychain(4, 0)
 
     def _test_getblockchaininfo(self):
@@ -227,6 +240,50 @@ class BlockchainTest(BitcoinTestFramework):
         self.start_node(0)
         assert_equal(self.nodes[0].getblockcount(), 207)
 
+    def _test_waitforblockheight(self):
+        self.log.info("Test waitforblockheight")
+
+        node = self.nodes[0]
+
+        # Start a P2P connection since we'll need to create some blocks.
+        node.add_p2p_connection(P2PInterface())
+        network_thread_start()
+        node.p2p.wait_for_verack()
+
+        current_height = node.getblock(node.getbestblockhash())['height']
+
+        # Create a fork somewhere below our current height, invalidate the tip
+        # of that fork, and then ensure that waitforblockheight still
+        # works as expected.
+        #
+        # (Previously this was broken based on setting
+        # `rpc/blockchain.cpp:latestblock` incorrectly.)
+        #
+        b20hash = node.getblockhash(20)
+        b20 = node.getblock(b20hash)
+
+        def solve_and_send_block(prevhash, height, time):
+            b = create_block(prevhash, create_coinbase(height), time)
+            b.solve()
+            node.p2p.send_message(msg_block(b))
+            node.p2p.sync_with_ping()
+            return b
+
+        b21f = solve_and_send_block(int(b20hash, 16), 21, b20['time'] + 1)
+        b22f = solve_and_send_block(b21f.sha256, 22, b21f.nTime + 1)
+
+        node.invalidateblock(b22f.hash)
+
+        def assert_waitforheight(height, timeout=2):
+            assert_equal(
+                node.waitforblockheight(height, timeout)['height'],
+                current_height)
+
+        assert_waitforheight(0)
+        assert_waitforheight(current_height - 1)
+        assert_waitforheight(current_height)
+        assert_waitforheight(current_height + 1)
+
 
 if __name__ == '__main__':
     BlockchainTest().main()

From f98b543522687a4ff93ad7d53fa3cc67b5c6d752 Mon Sep 17 00:00:00 2001
From: James O'Beirne <james.obeirne@gmail.com>
Date: Tue, 13 Feb 2018 22:39:04 -0500
Subject: [PATCH 2/2] Only call NotifyBlockTip when the active chain changes

Previously, if `invalidateblock` was called on a block in a branch,
NotifyBlockTip would be called on that block's predecessor, creating an
incorrect `rpc/blockchain.cpp:latestblock` value.

Only call NotifyBlockTip if the chain being modified is activeChain.
---
 src/validation.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index d9e877f2ebe..6b96344d369 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2731,7 +2731,11 @@ bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& c
     }
 
     InvalidChainFound(pindex);
-    uiInterface.NotifyBlockTip(IsInitialBlockDownload(), pindex->pprev);
+
+    // Only notify about a new block tip if the active chain was modified.
+    if (pindex_was_in_chain) {
+        uiInterface.NotifyBlockTip(IsInitialBlockDownload(), pindex->pprev);
+    }
     return true;
 }
 bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex) {