Merge 618c5f08f8 into a50af6e4c4

src/CMakeLists.txt

@@ -234,6 +234,7 @@ add_library(bitcoin_node STATIC EXCLUDE_FROM_ALL
   index/blockfilterindex.cpp
   index/coinstatsindex.cpp
   index/txindex.cpp
+  index/txospenderindex.cpp
   init.cpp
   kernel/chain.cpp
   kernel/checks.cpp

src/index/txospenderindex.cpp

@@ -0,0 +1,187 @@
+// Copyright (c) 2022 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 <common/args.h>
+#include <crypto/siphash.h>
+#include <index/disktxpos.h>
+#include <index/txospenderindex.h>
+#include <logging.h>
+#include <node/blockstorage.h>
+#include <random.h>
+#include <uint256.h>
+#include <validation.h>
+
+// LeveLDB key prefix. We only have one key for now but it will make it easier to add others if needed.
+constexpr uint8_t DB_TXOSPENDERINDEX{'s'};
+
+std::unique_ptr<TxoSpenderIndex> g_txospenderindex;
+
+TxoSpenderIndex::TxoSpenderIndex(std::unique_ptr<interfaces::Chain> chain, size_t n_cache_size, bool f_memory, bool f_wipe)
+    : BaseIndex(std::move(chain), "txospenderindex")
+{
+    fs::path path{gArgs.GetDataDirNet() / "indexes" / "txospenderindex"};
+    fs::create_directories(path);
+
+    m_db = std::make_unique<TxoSpenderIndex::DB>(path / "db", n_cache_size, f_memory, f_wipe);
+    if (!m_db->Read("siphash_key", m_siphash_key)) {
+        FastRandomContext rng(false);
+        m_siphash_key = {rng.rand64(), rng.rand64()};
+        assert(m_db->Write("siphash_key", m_siphash_key));
+    }
+}
+
+TxoSpenderIndex::~TxoSpenderIndex() = default;
+
+uint64_t TxoSpenderIndex::CreateKey(const COutPoint& vout) const
+{
+    return SipHashUint256Extra(m_siphash_key.first, m_siphash_key.second, vout.hash.ToUint256(), vout.n);
+}
+
+bool TxoSpenderIndex::WriteSpenderInfos(const std::vector<std::pair<COutPoint, CDiskTxPos>>& items)
+{
+    CDBBatch batch(*m_db);
+    for (const auto& [outpoint, pos] : items) {
+        std::vector<CDiskTxPos> positions;
+        std::pair<uint8_t, uint64_t> key{DB_TXOSPENDERINDEX, CreateKey(outpoint)};
+        if (m_db->Exists(key)) {
+            if (!m_db->Read(key, positions)) {
+                LogError("Cannot read current state; tx spender index may be corrupted\n");
+            }
+        }
+        if (std::find(positions.begin(), positions.end(), pos) == positions.end()) {
+            positions.push_back(pos);
+            batch.Write(key, positions);
+        }
+    }
+    return m_db->WriteBatch(batch);
+}
+
+
+bool TxoSpenderIndex::EraseSpenderInfos(const std::vector<COutPoint>& items)
+{
+    CDBBatch batch(*m_db);
+    for (const auto& outpoint : items) {
+        std::vector<CDiskTxPos> positions;
+        std::pair<uint8_t, uint64_t> key{DB_TXOSPENDERINDEX, CreateKey(outpoint)};
+        if (!m_db->Read(key, positions)) {
+            LogWarning("Could not read expected entry");
+            continue;
+        }
+        if (positions.size() > 1) {
+            // there are collisions: find the position of the tx that spends the outpoint we want to erase
+            // this is expensive but extremely uncommon
+            size_t index = std::numeric_limits<size_t>::max();
+            for (size_t i = 0; i < positions.size(); i++) {
+                CTransactionRef tx;
+                if (!ReadTransaction(positions[i], tx)) continue;
+                for (const auto& input : tx->vin) {
+                    if (input.prevout == outpoint) {
+                        index = i;
+                        break;
+                    }
+                }
+            }
+            if (index != std::numeric_limits<size_t>::max()) {
+                // remove it from the list
+                positions.erase(positions.begin() + index);
+                batch.Write(key, positions);
+            }
+        } else {
+            batch.Erase(key);
+        }
+    }
+    return m_db->WriteBatch(batch);
+}
+
+bool TxoSpenderIndex::CustomAppend(const interfaces::BlockInfo& block)
+{
+    std::vector<std::pair<COutPoint, CDiskTxPos>> items;
+    items.reserve(block.data->vtx.size());
+
+    CDiskTxPos pos({block.file_number, block.data_pos}, GetSizeOfCompactSize(block.data->vtx.size()));
+    for (const auto& tx : block.data->vtx) {
+        if (!tx->IsCoinBase()) {
+            for (const auto& input : tx->vin) {
+                items.emplace_back(input.prevout, pos);
+            }
+        }
+        pos.nTxOffset += ::GetSerializeSize(TX_WITH_WITNESS(*tx));
+    }
+
+    return WriteSpenderInfos(items);
+}
+
+bool TxoSpenderIndex::CustomRewind(const interfaces::BlockRef& current_tip, const interfaces::BlockRef& new_tip)
+{
+    LOCK(cs_main);
+    const CBlockIndex* iter_tip{m_chainstate->m_blockman.LookupBlockIndex(current_tip.hash)};
+    const CBlockIndex* new_tip_index{m_chainstate->m_blockman.LookupBlockIndex(new_tip.hash)};
+
+    do {
+        CBlock block;
+        if (!m_chainstate->m_blockman.ReadBlock(block, *iter_tip)) {
+            LogError("Failed to read block %s from disk\n", iter_tip->GetBlockHash().ToString());
+            return false;
+        }
+        std::vector<COutPoint> items;
+        items.reserve(block.vtx.size());
+        for (const auto& tx : block.vtx) {
+            if (tx->IsCoinBase()) {
+                continue;
+            }
+            for (const auto& input : tx->vin) {
+                items.emplace_back(input.prevout);
+            }
+        }
+        if (!EraseSpenderInfos(items)) {
+            LogError("Failed to erase indexed data for disconnected block %s from disk\n", iter_tip->GetBlockHash().ToString());
+            return false;
+        }
+
+        iter_tip = iter_tip->GetAncestor(iter_tip->nHeight - 1);
+    } while (new_tip_index != iter_tip);
+
+    return true;
+}
+
+bool TxoSpenderIndex::ReadTransaction(const CDiskTxPos& tx_pos, CTransactionRef& tx) const
+{
+    AutoFile file{m_chainstate->m_blockman.OpenBlockFile(tx_pos, true)};
+    if (file.IsNull()) {
+        return false;
+    }
+    CBlockHeader header;
+    try {
+        file >> header;
+        file.seek(tx_pos.nTxOffset, SEEK_CUR);
+        file >> TX_WITH_WITNESS(tx);
+        return true;
+    } catch (const std::exception& e) {
+        LogError("Deserialize or I/O error - %s\n", e.what());
+        return false;
+    }
+}
+
+CTransactionRef TxoSpenderIndex::FindSpender(const COutPoint& txo) const
+{
+    std::vector<CDiskTxPos> positions;
+    // read all tx position candidates from the db. there may be index collisions, in which case the db will return more than one tx position
+    if (!m_db->Read(std::pair{DB_TXOSPENDERINDEX, CreateKey(txo)}, positions)) {
+        return nullptr;
+    }
+    // loop until we find a tx that spends our outpoint
+    for (const auto& postx : positions) {
+        CTransactionRef tx;
+        if (ReadTransaction(postx, tx)) {
+            for (const auto& input : tx->vin) {
+                if (input.prevout == txo) {
+                    return tx;
+                }
+            }
+        }
+    }
+    return nullptr;
+}
+
+BaseIndex::DB& TxoSpenderIndex::GetDB() const { return *m_db; }

src/index/txospenderindex.h

@@ -0,0 +1,49 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_INDEX_TXOSPENDERINDEX_H
+#define BITCOIN_INDEX_TXOSPENDERINDEX_H
+
+#include <index/base.h>
+#include <index/disktxpos.h>
+
+static constexpr bool DEFAULT_TXOSPENDERINDEX{false};
+
+/**
+ * TxoSpenderIndex is used to look up which transaction spent a given output.
+ * The index is written to a LevelDB database and, for each input of each transaction in a block,
+ * records the outpoint that is spent and the hash of the spending transaction.
+ */
+class TxoSpenderIndex final : public BaseIndex
+{
+private:
+    std::unique_ptr<BaseIndex::DB> m_db;
+    std::pair<uint64_t, uint64_t> m_siphash_key;
+    uint64_t CreateKey(const COutPoint& vout) const;
+    bool AllowPrune() const override { return true; }
+    bool WriteSpenderInfos(const std::vector<std::pair<COutPoint, CDiskTxPos>>& items);
+    bool EraseSpenderInfos(const std::vector<COutPoint>& items);
+    bool ReadTransaction(const CDiskTxPos& pos, CTransactionRef& tx) const;
+
+protected:
+    bool CustomAppend(const interfaces::BlockInfo& block) override;
+
+    bool CustomRewind(const interfaces::BlockRef& current_tip, const interfaces::BlockRef& new_tip) override;
+
+    BaseIndex::DB& GetDB() const override;
+
+public:
+    explicit TxoSpenderIndex(std::unique_ptr<interfaces::Chain> chain, size_t n_cache_size, bool f_memory = false, bool f_wipe = false);
+
+    // Destroys unique_ptr to an incomplete type.
+    virtual ~TxoSpenderIndex() override;
+
+    CTransactionRef FindSpender(const COutPoint& txo) const;
+};
+
+/// The global txo spender index. May be null.
+extern std::unique_ptr<TxoSpenderIndex> g_txospenderindex;
+
+
+#endif // BITCOIN_INDEX_TXOSPENDERINDEX_H

src/init.cpp

@@ -27,6 +27,7 @@
 #include <index/blockfilterindex.h>
 #include <index/coinstatsindex.h>
 #include <index/txindex.h>
+#include <index/txospenderindex.h>
 #include <init/common.h>
 #include <interfaces/chain.h>
 #include <interfaces/init.h>
@@ -354,6 +355,7 @@ void Shutdown(NodeContext& node)
     // Stop and delete all indexes only after flushing background callbacks.
     for (auto* index : node.indexes) index->Stop();
     if (g_txindex) g_txindex.reset();
+    if (g_txospenderindex) g_txospenderindex.reset();
     if (g_coin_stats_index) g_coin_stats_index.reset();
     DestroyAllBlockFilterIndexes();
     node.indexes.clear(); // all instances are nullptr now
@@ -516,6 +518,7 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
     argsman.AddArg("-shutdownnotify=<cmd>", "Execute command immediately before beginning shutdown. The need for shutdown may be urgent, so be careful not to delay it long (if the command doesn't require interaction with the server, consider having it fork into the background).", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
 #endif
     argsman.AddArg("-txindex", strprintf("Maintain a full transaction index, used by the getrawtransaction rpc call (default: %u)", DEFAULT_TXINDEX), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-txospenderindex", strprintf("Maintain a transaction output spender index, used by the gettxospender rpc call (default: %u)", DEFAULT_TXOSPENDERINDEX), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-blockfilterindex=<type>",
                  strprintf("Maintain an index of compact filters by block (default: %s, values: %s).", DEFAULT_BLOCKFILTERINDEX, ListBlockFilterTypes()) +
                  " If <type> is not supplied or if <type> = 1, indexes for all known types are enabled.",
@@ -1672,6 +1675,9 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     if (args.GetBoolArg("-txindex", DEFAULT_TXINDEX)) {
         LogInfo("* Using %.1f MiB for transaction index database", index_cache_sizes.tx_index * (1.0 / 1024 / 1024));
     }
+    if (args.GetBoolArg("-txospenderindex", DEFAULT_TXOSPENDERINDEX)) {
+        LogInfo("* Using %.1f MiB for transaction output spender index database", index_cache_sizes.txospender_index * (1.0 / 1024 / 1024));
+    }
     for (BlockFilterType filter_type : g_enabled_filter_types) {
         LogInfo("* Using %.1f MiB for %s block filter index database",
                   index_cache_sizes.filter_index * (1.0 / 1024 / 1024), BlockFilterTypeName(filter_type));
@@ -1738,6 +1744,11 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         node.indexes.emplace_back(g_txindex.get());
     }
 
+    if (args.GetBoolArg("-txospenderindex", DEFAULT_TXOSPENDERINDEX)) {
+        g_txospenderindex = std::make_unique<TxoSpenderIndex>(interfaces::MakeChain(node), index_cache_sizes.txospender_index, false, do_reindex);
+        node.indexes.emplace_back(g_txospenderindex.get());
+    }
+
     for (const auto& filter_type : g_enabled_filter_types) {
         InitBlockFilterIndex([&]{ return interfaces::MakeChain(node); }, filter_type, index_cache_sizes.filter_index, false, do_reindex);
         node.indexes.emplace_back(GetBlockFilterIndex(filter_type));

src/node/caches.cpp

@@ -6,6 +6,7 @@
 
 #include <common/args.h>
 #include <index/txindex.h>
+#include <index/txospenderindex.h>
 #include <kernel/caches.h>
 #include <logging.h>
 #include <util/byte_units.h>
@@ -19,6 +20,8 @@
 static constexpr size_t MAX_TX_INDEX_CACHE{1024_MiB};
 //! Max memory allocated to all block filter index caches combined in bytes.
 static constexpr size_t MAX_FILTER_INDEX_CACHE{1024_MiB};
+//! Max memory allocated to tx spenderindex DB specific cache in bytes.
+static constexpr size_t MAX_TXOSPENDER_INDEX_CACHE{1024_MiB};
 
 namespace node {
 CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
@@ -34,6 +37,8 @@ CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
     IndexCacheSizes index_sizes;
     index_sizes.tx_index = std::min(total_cache / 8, args.GetBoolArg("-txindex", DEFAULT_TXINDEX) ? MAX_TX_INDEX_CACHE : 0);
     total_cache -= index_sizes.tx_index;
+    index_sizes.txospender_index = std::min(total_cache / 8, args.GetBoolArg("-txospenderindex", DEFAULT_TXOSPENDERINDEX) ? MAX_TXOSPENDER_INDEX_CACHE : 0);
+    total_cache -= index_sizes.txospender_index;
     if (n_indexes > 0) {
         size_t max_cache = std::min(total_cache / 8, MAX_FILTER_INDEX_CACHE);
         index_sizes.filter_index = max_cache / n_indexes;

src/node/caches.h

@@ -21,6 +21,7 @@ namespace node {
 struct IndexCacheSizes {
     size_t tx_index{0};
     size_t filter_index{0};
+    size_t txospender_index{0};
 };
 struct CacheSizes {
     IndexCacheSizes index;

src/rpc/client.cpp

@@ -270,6 +270,9 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "getmempoolancestors", 1, "verbose" },
     { "getmempooldescendants", 1, "verbose" },
     { "gettxspendingprevout", 0, "outputs" },
+    { "gettxspendingprevout", 1, "options" },
+    { "gettxspendingprevout", 1, "mempool_only" },
+    { "gettxspendingprevout", 1, "return_spending_tx" },
     { "bumpfee", 1, "options" },
     { "bumpfee", 1, "conf_target"},
     { "bumpfee", 1, "fee_rate"},

src/rpc/mempool.cpp

@@ -10,6 +10,7 @@
 #include <chainparams.h>
 #include <consensus/validation.h>
 #include <core_io.h>
+#include <index/txospenderindex.h>
 #include <kernel/mempool_entry.h>
 #include <net_processing.h>
 #include <node/mempool_persist_args.h>
@@ -602,6 +603,12 @@ static RPCHelpMan gettxspendingprevout()
                     },
                 },
             },
+            {"options", RPCArg::Type::OBJ_NAMED_PARAMS, RPCArg::Optional::OMITTED, "",
+                {
+                    {"mempool_only", RPCArg::Type::BOOL, RPCArg::DefaultHint{"true if txospenderindex unavailable, otherwise false"}, "If false and empool lacks a relevant spend, use txospenderindex (throws an exception if not available)."},
+                    {"return_spending_tx", RPCArg::Type::BOOL, RPCArg::DefaultHint{"false"}, "If true, return the full spending tx."},
+                },
+            },
         },
         RPCResult{
             RPCResult::Type::ARR, "", "",
@@ -611,6 +618,11 @@ static RPCHelpMan gettxspendingprevout()
                     {RPCResult::Type::STR_HEX, "txid", "the transaction id of the checked output"},
                     {RPCResult::Type::NUM, "vout", "the vout value of the checked output"},
                     {RPCResult::Type::STR_HEX, "spendingtxid", /*optional=*/true, "the transaction id of the mempool transaction spending this output (omitted if unspent)"},
+                    {RPCResult::Type::STR_HEX, "spendingtx", /*optional=*/true, "the transaction spending this output (only if return_spending_tx is set, omitted if unspent)"},
+                    {RPCResult::Type::ARR, "warnings", /* optional */ true, "If spendingtxid isn't found in the mempool, and the mempool_only option isn't set explicitly, this will advise of issues using the txospenderindex.",
+                    {
+                        {RPCResult::Type::STR, "", ""},
+                    }},
                 }},
             }
         },
@@ -625,6 +637,24 @@ static RPCHelpMan gettxspendingprevout()
                 throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, outputs are missing");
             }
 
+            std::optional<bool> mempool_only;
+            std::optional<bool> return_spending_tx;
+            if (!request.params[1].isNull()) {
+                const UniValue& options = request.params[1];
+                RPCTypeCheckObj(options,
+                    {
+                        {"mempool_only", UniValueType(UniValue::VBOOL)},
+                        {"return_spending_tx", UniValueType(UniValue::VBOOL)},
+                    },
+                    /*fAllowNull=*/true, /*fStrict=*/true);
+                if (options.exists("mempool_only")) {
+                    mempool_only = options["mempool_only"].get_bool();
+                }
+                if (options.exists("return_spending_tx")) {
+                    return_spending_tx = options["return_spending_tx"].get_bool();
+                }
+            }
+
             std::vector<COutPoint> prevouts;
             prevouts.reserve(output_params.size());
 
@@ -646,6 +676,8 @@ static RPCHelpMan gettxspendingprevout()
                 prevouts.emplace_back(txid, nOutput);
             }
 
+            const bool f_txospenderindex_ready = !mempool_only.value_or(false) && g_txospenderindex && g_txospenderindex->BlockUntilSyncedToCurrentChain();
+
             const CTxMemPool& mempool = EnsureAnyMemPool(request.context);
             LOCK(mempool.cs);
 
@@ -659,6 +691,41 @@ static RPCHelpMan gettxspendingprevout()
                 const CTransaction* spendingTx = mempool.GetConflictTx(prevout);
                 if (spendingTx != nullptr) {
                     o.pushKV("spendingtxid", spendingTx->GetHash().ToString());
+                    if (return_spending_tx) {
+                        o.pushKV("spendingtx", EncodeHexTx(*spendingTx));
+                    }
+                } else if (mempool_only.value_or(false)) {
+                    // do nothing, caller has selected to only query the mempool
+                } else if (g_txospenderindex) {
+                    // no spending tx in mempool, query txospender index
+                    if (auto spending_tx{g_txospenderindex->FindSpender(prevout)}) {
+                        o.pushKV("spendingtxid", spending_tx->GetHash().GetHex());
+                        if (return_spending_tx) {
+                            o.pushKV("spendingtx", EncodeHexTx(*spending_tx));
+                        }
+                        if (!f_txospenderindex_ready) {
+                            // warn if index is not ready as the spending tx that we found may be stale (it may be reorged out)
+                            UniValue warnings(UniValue::VARR);
+                            warnings.push_back("txospenderindex is still being synced.");
+                            o.pushKV("warnings", warnings);
+                        }
+                    } else if (!f_txospenderindex_ready) {
+                        if (mempool_only.has_value()) {  // NOTE: caller explicitly set value to false
+                            throw JSONRPCError(RPC_MISC_ERROR, strprintf("No spending tx for the outpoint %s:%d found, and txospenderindex is still being synced.", prevout.hash.GetHex(), prevout.n));
+                        } else {
+                            UniValue warnings(UniValue::VARR);
+                            warnings.push_back("txospenderindex is still being synced.");
+                            o.pushKV("warnings", warnings);
+                        }
+                    }
+                } else {
+                    if (mempool_only.has_value()) {  // NOTE: caller explicitly set value to false
+                        throw JSONRPCError(RPC_MISC_ERROR, strprintf("No spending tx for the outpoint %s:%d in mempool, and txospenderindex is unavailable.", prevout.hash.GetHex(), prevout.n));
+                    } else {
+                        UniValue warnings(UniValue::VARR);
+                        warnings.push_back("txospenderindex is unavailable.");
+                        o.pushKV("warnings", warnings);
+                    }
                 }
 
                 result.push_back(std::move(o));

src/rpc/node.cpp

@@ -10,6 +10,7 @@
 #include <index/blockfilterindex.h>
 #include <index/coinstatsindex.h>
 #include <index/txindex.h>
+#include <index/txospenderindex.h>
 #include <interfaces/chain.h>
 #include <interfaces/echo.h>
 #include <interfaces/init.h>
@@ -391,6 +392,10 @@ static RPCHelpMan getindexinfo()
         result.pushKVs(SummaryToJSON(g_coin_stats_index->GetSummary(), index_name));
     }
 
+    if (g_txospenderindex) {
+        result.pushKVs(SummaryToJSON(g_txospenderindex->GetSummary(), index_name));
+    }
+
     ForEachBlockFilterIndex([&result, &index_name](const BlockFilterIndex& index) {
         result.pushKVs(SummaryToJSON(index.GetSummary(), index_name));
     });

src/test/CMakeLists.txt

@@ -106,6 +106,7 @@ add_executable(test_bitcoin
   translation_tests.cpp
   txdownload_tests.cpp
   txindex_tests.cpp
+  txospenderindex_tests.cpp
   txpackage_tests.cpp
   txreconciliation_tests.cpp
   txrequest_tests.cpp

src/test/txospenderindex_tests.cpp

@@ -0,0 +1,81 @@
+// Copyright (c) 2017-2022 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 <chainparams.h>
+#include <index/txospenderindex.h>
+#include <test/util/setup_common.h>
+#include <util/time.h>
+#include <validation.h>
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_AUTO_TEST_SUITE(txospenderindex_tests)
+
+BOOST_FIXTURE_TEST_CASE(txospenderindex_initial_sync, TestChain100Setup)
+{
+    TxoSpenderIndex txospenderindex(interfaces::MakeChain(m_node), 1 << 20, true);
+    BOOST_REQUIRE(txospenderindex.Init());
+
+    // Mine blocks for coinbase maturity, so we can spend some coinbase outputs in the test.
+     for (int i = 0; i < 50; i++) {
+         std::vector<CMutableTransaction> no_txns;
+         CreateAndProcessBlock(no_txns, this->m_coinbase_txns[i]->vout[0].scriptPubKey);
+     }
+    std::vector<COutPoint> spent(10);
+    std::vector<CMutableTransaction> spender(spent.size());
+
+    for (size_t i = 0; i < spent.size(); i++) {
+        spent[i] = COutPoint(this->m_coinbase_txns[i]->GetHash(), 0);
+        spender[i].version = 1;
+        spender[i].vin.resize(1);
+        spender[i].vin[0].prevout.hash = spent[i].hash;
+        spender[i].vin[0].prevout.n = spent[i].n;
+        spender[i].vout.resize(1);
+        spender[i].vout[0].nValue = this->m_coinbase_txns[i]->GetValueOut();
+        spender[i].vout[0].scriptPubKey = this->m_coinbase_txns[i]->vout[0].scriptPubKey;
+
+        // Sign:
+        std::vector<unsigned char> vchSig;
+        const uint256 hash = SignatureHash(this->m_coinbase_txns[i]->vout[0].scriptPubKey, spender[i], 0, SIGHASH_ALL, 0, SigVersion::BASE);
+        coinbaseKey.Sign(hash, vchSig);
+        vchSig.push_back((unsigned char)SIGHASH_ALL);
+        spender[i].vin[0].scriptSig << vchSig;
+    }
+
+    CreateAndProcessBlock(spender, this->m_coinbase_txns[0]->vout[0].scriptPubKey);
+
+    // Transaction should not be found in the index before it is started.
+    for (const auto& outpoint : spent) {
+        BOOST_CHECK(!txospenderindex.FindSpender(outpoint));
+    }
+
+    // BlockUntilSyncedToCurrentChain should return false before txospenderindex is started.
+    BOOST_CHECK(!txospenderindex.BlockUntilSyncedToCurrentChain());
+
+    BOOST_REQUIRE(txospenderindex.StartBackgroundSync());
+
+    // Allow tx index to catch up with the block index.
+    constexpr auto timeout{10s};
+    const auto time_start{SteadyClock::now()};
+    while (!txospenderindex.BlockUntilSyncedToCurrentChain()) {
+        BOOST_REQUIRE(time_start + timeout > SteadyClock::now());
+        UninterruptibleSleep(std::chrono::milliseconds{100});
+    }
+    for (size_t i = 0; i < spent.size(); i++) {
+        BOOST_CHECK_EQUAL(txospenderindex.FindSpender(spent[i])->GetHash(), spender[i].GetHash());
+    }
+
+    // It is not safe to stop and destroy the index until it finishes handling
+    // the last BlockConnected notification. The BlockUntilSyncedToCurrentChain()
+    // call above is sufficient to ensure this, but the
+    // SyncWithValidationInterfaceQueue() call below is also needed to ensure
+    // TSAN always sees the test thread waiting for the notification thread, and
+    // avoid potential false positive reports.
+    m_node.validation_signals->SyncWithValidationInterfaceQueue();
+
+    // shutdown sequence (c.f. Shutdown() in init.cpp)
+    txospenderindex.Stop();
+}
+
+BOOST_AUTO_TEST_SUITE_END()

test/functional/rpc_mempool_info.py

@@ -14,7 +14,12 @@ from test_framework.wallet import MiniWallet
 
 class RPCMempoolInfoTest(BitcoinTestFramework):
     def set_test_params(self):
-        self.num_nodes = 1
+        self.num_nodes = 3
+        self.extra_args = [
+            ["-txospenderindex", "-whitelist=noban@127.0.0.1"],
+            ["-txospenderindex", "-whitelist=noban@127.0.0.1"],
+            ["-whitelist=noban@127.0.0.1"],
+        ]
 
     def run_test(self):
         self.wallet = MiniWallet(self.nodes[0])
@@ -59,8 +64,11 @@ class RPCMempoolInfoTest(BitcoinTestFramework):
             assert_equal(txid in mempool, True)
 
         self.log.info("Find transactions spending outputs")
+        # wait until spending transactions are found in the mempool of node 0, 1 and 2
         result = self.nodes[0].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0}, {'txid' : txidA, 'vout' : 1} ])
         assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : txidA}, {'txid' : txidA, 'vout' : 1, 'spendingtxid' : txidC} ])
+        self.wait_until(lambda: self.nodes[1].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0}, {'txid' : txidA, 'vout' : 1} ]) == result)
+        self.wait_until(lambda: self.nodes[2].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0}, {'txid' : txidA, 'vout' : 1} ]) == result)
 
         self.log.info("Find transaction spending multiple outputs")
         result = self.nodes[0].gettxspendingprevout([ {'txid' : txidE, 'vout' : 0}, {'txid' : txidF, 'vout' : 0} ])
@@ -71,6 +79,11 @@ class RPCMempoolInfoTest(BitcoinTestFramework):
         assert_equal(result, [ {'txid' : txidH, 'vout' : 0} ])
         result = self.nodes[0].gettxspendingprevout([ {'txid' : txidA, 'vout' : 5} ])
         assert_equal(result, [ {'txid' : txidA, 'vout' : 5} ])
+        result = self.nodes[1].gettxspendingprevout([ {'txid' : txidA, 'vout' : 5} ])
+        assert_equal(result, [ {'txid' : txidA, 'vout' : 5} ])
+        # on node 2 you also get a warning as txospenderindex is not activated
+        result = self.nodes[2].gettxspendingprevout([ {'txid' : txidA, 'vout' : 5} ])
+        assert_equal(result, [ {'txid' : txidA, 'vout' : 5, 'warnings': ['txospenderindex is unavailable.']} ])
 
         self.log.info("Mixed spent and unspent outputs")
         result = self.nodes[0].gettxspendingprevout([ {'txid' : txidB, 'vout' : 0}, {'txid' : txidG, 'vout' : 3} ])
@@ -94,6 +107,77 @@ class RPCMempoolInfoTest(BitcoinTestFramework):
         self.log.info("Missing txid")
         assert_raises_rpc_error(-3, "Missing txid", self.nodes[0].gettxspendingprevout, [{'vout' : 3}])
 
+        self.generate(self.wallet, 1)
+        # spending transactions are found in the index of nodes 0 and 1 but not node 2
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0}, {'txid' : txidA, 'vout' : 1} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : txidA, 'spendingtx' : txA['hex']}, {'txid' : txidA, 'vout' : 1, 'spendingtxid' : txidC, 'spendingtx' : txC['hex']} ])
+        result = self.nodes[1].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0}, {'txid' : txidA, 'vout' : 1} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : txidA, 'spendingtx' : txA['hex']}, {'txid' : txidA, 'vout' : 1, 'spendingtxid' : txidC, 'spendingtx' : txC['hex']} ])
+        result = self.nodes[2].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0}, {'txid' : txidA, 'vout' : 1} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'warnings': ['txospenderindex is unavailable.']}, {'txid' : txidA, 'vout' : 1, 'warnings': ['txospenderindex is unavailable.']} ])
+
+
+        self.log.info("Check that our txospenderindex is updated when a reorg replaces a spending transaction")
+        confirmed_utxo = self.wallet.get_utxo(mark_as_spent = False)
+        tx1 = create_tx(utxos_to_spend=[confirmed_utxo], num_outputs=1)
+        self.generate(self.wallet, 1)
+        # tx1 is confirmed, and indexed in txospenderindex as spending our utxo
+        assert not tx1["txid"] in self.nodes[0].getrawmempool()
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : tx1["txid"], 'spendingtx' : tx1['hex']} ])
+        # replace tx1 with tx2
+        self.nodes[0].invalidateblock(self.nodes[0].getbestblockhash())
+        self.nodes[1].invalidateblock(self.nodes[1].getbestblockhash())
+        self.nodes[2].invalidateblock(self.nodes[2].getbestblockhash())
+        assert tx1["txid"] in self.nodes[0].getrawmempool()
+        assert tx1["txid"] in self.nodes[1].getrawmempool()
+        tx2 = create_tx(utxos_to_spend=[confirmed_utxo], num_outputs=2)
+        assert tx2["txid"] in self.nodes[0].getrawmempool()
+
+        # check that when we find tx2 when we look in the mempool for a tx spending our output
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : tx2["txid"], 'spendingtx' : tx2['hex']} ])
+
+        # check that our txospenderindex has been updated
+        self.generate(self.wallet, 1)
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : tx2["txid"], 'spendingtx' : tx2['hex']} ])
+
+        self.log.info("Check that our txospenderindex is updated when a reorg cancels a spending transaction")
+        confirmed_utxo = self.wallet.get_utxo(mark_as_spent = False)
+        tx1 = create_tx(utxos_to_spend=[confirmed_utxo], num_outputs=1)
+        tx2 = create_tx(utxos_to_spend=[tx1["new_utxos"][0]], num_outputs=1)
+        # tx1 spends our utxo, tx2 spends tx1
+        self.generate(self.wallet, 1)
+        # tx1 and tx2 are confirmed, and indexed in txospenderindex
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : tx1["txid"], 'spendingtx' : tx1['hex']} ])
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : tx1['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : tx1['txid'], 'vout' : 0, 'spendingtxid' : tx2["txid"], 'spendingtx' : tx2['hex']} ])
+        # replace tx1 with tx3
+        blockhash= self.nodes[0].getbestblockhash()
+        self.nodes[0].invalidateblock(blockhash)
+        self.nodes[1].invalidateblock(blockhash)
+        self.nodes[2].invalidateblock(blockhash)
+        tx3 = create_tx(utxos_to_spend=[confirmed_utxo], num_outputs=2, fee_per_output=2000)
+        assert tx3["txid"] in self.nodes[0].getrawmempool()
+        assert not tx1["txid"] in self.nodes[0].getrawmempool()
+        assert not tx2["txid"] in self.nodes[0].getrawmempool()
+        # tx2 is not in the mempool anymore, but still in txospender index which has not been rewound yet
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : tx1['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : tx1['txid'], 'vout' : 0, 'spendingtxid' : tx2["txid"], 'spendingtx' : tx2['hex']} ])
+        txinfo = self.nodes[0].getrawtransaction(tx2["txid"], verbose = True, blockhash = blockhash)
+        assert_equal(txinfo["confirmations"], 0)
+        assert_equal(txinfo["in_active_chain"], False)
+
+        self.generate(self.wallet, 1)
+        # we check that the spending tx for tx1 is now tx3
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : confirmed_utxo['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : confirmed_utxo['txid'], 'vout' : 0, 'spendingtxid' : tx3["txid"], 'spendingtx' : tx3['hex']} ])
+        # we check that there is no more spending tx for tx1
+        result = self.nodes[0].gettxspendingprevout([ {'txid' : tx1['txid'], 'vout' : 0} ], return_spending_tx=True)
+        assert_equal(result, [ {'txid' : tx1['txid'], 'vout' : 0} ])
+
 
 if __name__ == '__main__':
     RPCMempoolInfoTest(__file__).main()