Keep mempool consistent during block-reorgs

This fixes a subtle bug involving block re-orgs and non-standard transactions.

Start with a block containing a non-standard transaction, and
one or more transactions spending it in the memory pool.

Then re-org away from that block to another chain that does
not contain the non-standard transaction.

Result before this fix: the dependent transactions get stuck
in the mempool without their parent, putting the mempool
in an inconsistent state.

Tested with a new unit test (adapted for 0.10).

Rebased-From: ad9e86dca11dce023d827d342e966f3806c39d27
Github-Pull: #5945

3 files changed, 115 insertions, 0 deletions

diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index 0a9a335e7a..9cc479c305 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -51,6 +51,7 @@ BITCOIN_TESTS =\
   test/hash_tests.cpp \
   test/key_tests.cpp \
   test/main_tests.cpp \
+  test/mempool_tests.cpp \
   test/miner_tests.cpp \
   test/mruset_tests.cpp \
   test/multisig_tests.cpp \
diff --git a/src/test/mempool_tests.cpp b/src/test/mempool_tests.cpp
new file mode 100644
index 0000000000..b85f768ed5
--- /dev/null
+++ b/src/test/mempool_tests.cpp
@@ -0,0 +1,102 @@
+// Copyright (c) 2011-2014 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "main.h"
+#include "txmempool.h"
+#include "util.h"
+
+#include <boost/test/unit_test.hpp>
+#include <list>
+
+BOOST_AUTO_TEST_SUITE(mempool_tests)
+
+BOOST_AUTO_TEST_CASE(MempoolRemoveTest)
+{
+    // Test CTxMemPool::remove functionality
+
+    // Parent transaction with three children,
+    // and three grand-children:
+    CMutableTransaction txParent;
+    txParent.vin.resize(1);
+    txParent.vin[0].scriptSig = CScript() << OP_11;
+    txParent.vout.resize(3);
+    for (int i = 0; i < 3; i++)
+    {
+        txParent.vout[i].scriptPubKey = CScript() << OP_11 << OP_EQUAL;
+        txParent.vout[i].nValue = 33000LL;
+    }
+    CMutableTransaction txChild[3];
+    for (int i = 0; i < 3; i++)
+    {
+        txChild[i].vin.resize(1);
+        txChild[i].vin[0].scriptSig = CScript() << OP_11;
+        txChild[i].vin[0].prevout.hash = txParent.GetHash();
+        txChild[i].vin[0].prevout.n = i;
+        txChild[i].vout.resize(1);
+        txChild[i].vout[0].scriptPubKey = CScript() << OP_11 << OP_EQUAL;
+        txChild[i].vout[0].nValue = 11000LL;
+    }
+    CMutableTransaction txGrandChild[3];
+    for (int i = 0; i < 3; i++)
+    {
+        txGrandChild[i].vin.resize(1);
+        txGrandChild[i].vin[0].scriptSig = CScript() << OP_11;
+        txGrandChild[i].vin[0].prevout.hash = txChild[i].GetHash();
+        txGrandChild[i].vin[0].prevout.n = 0;
+        txGrandChild[i].vout.resize(1);
+        txGrandChild[i].vout[0].scriptPubKey = CScript() << OP_11 << OP_EQUAL;
+        txGrandChild[i].vout[0].nValue = 11000LL;
+    }
+
+
+    CTxMemPool testPool(CFeeRate(0));
+    std::list<CTransaction> removed;
+
+    // Nothing in pool, remove should do nothing:
+    testPool.remove(txParent, removed, true);
+    BOOST_CHECK_EQUAL(removed.size(), 0);
+
+    // Just the parent:
+    testPool.addUnchecked(txParent.GetHash(), CTxMemPoolEntry(txParent, 0, 0, 0.0, 1));
+    testPool.remove(txParent, removed, true);
+    BOOST_CHECK_EQUAL(removed.size(), 1);
+    removed.clear();
+    
+    // Parent, children, grandchildren:
+    testPool.addUnchecked(txParent.GetHash(), CTxMemPoolEntry(txParent, 0, 0, 0.0, 1));
+    for (int i = 0; i < 3; i++)
+    {
+        testPool.addUnchecked(txChild[i].GetHash(), CTxMemPoolEntry(txChild[i], 0, 0, 0.0, 1));
+        testPool.addUnchecked(txGrandChild[i].GetHash(), CTxMemPoolEntry(txGrandChild[i], 0, 0, 0.0, 1));
+    }
+    // Remove Child[0], GrandChild[0] should be removed:
+    testPool.remove(txChild[0], removed, true);
+    BOOST_CHECK_EQUAL(removed.size(), 2);
+    removed.clear();
+    // ... make sure grandchild and child are gone:
+    testPool.remove(txGrandChild[0], removed, true);
+    BOOST_CHECK_EQUAL(removed.size(), 0);
+    testPool.remove(txChild[0], removed, true);
+    BOOST_CHECK_EQUAL(removed.size(), 0);
+    // Remove parent, all children/grandchildren should go:
+    testPool.remove(txParent, removed, true);
+    BOOST_CHECK_EQUAL(removed.size(), 5);
+    BOOST_CHECK_EQUAL(testPool.size(), 0);
+    removed.clear();
+
+    // Add children and grandchildren, but NOT the parent (simulate the parent being in a block)
+    for (int i = 0; i < 3; i++)
+    {
+        testPool.addUnchecked(txChild[i].GetHash(), CTxMemPoolEntry(txChild[i], 0, 0, 0.0, 1));
+        testPool.addUnchecked(txGrandChild[i].GetHash(), CTxMemPoolEntry(txGrandChild[i], 0, 0, 0.0, 1));
+    }
+    // Now remove the parent, as might happen if a block-re-org occurs but the parent cannot be
+    // put into the mempool (maybe because it is non-standard):
+    testPool.remove(txParent, removed, true);
+    BOOST_CHECK_EQUAL(removed.size(), 6);
+    BOOST_CHECK_EQUAL(testPool.size(), 0);
+    removed.clear();
+}
+
+BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index dcdf5653fe..db598a1dfa 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -444,6 +444,18 @@ void CTxMemPool::remove(const CTransaction &origTx, std::list<CTransaction>& rem
         LOCK(cs);
         std::deque<uint256> txToRemove;
         txToRemove.push_back(origTx.GetHash());
+        if (fRecursive && !mapTx.count(origTx.GetHash())) {
+            // If recursively removing but origTx isn't in the mempool
+            // be sure to remove any children that are in the pool. This can
+            // happen during chain re-orgs if origTx isn't re-accepted into
+            // the mempool for any reason.
+            for (unsigned int i = 0; i < origTx.vout.size(); i++) {
+                std::map<COutPoint, CInPoint>::iterator it = mapNextTx.find(COutPoint(origTx.GetHash(), i));
+                if (it == mapNextTx.end())
+                    continue;
+                txToRemove.push_back(it->second.ptx->GetHash());
+            }
+        }
         while (!txToRemove.empty())
         {
             uint256 hash = txToRemove.front();