xref: /dports/net-p2p/namecoin-daemon/namecoin-core-nc0.21.0.1/src/validation.cpp

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2020 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 <validation.h>

#include <arith_uint256.h>
#include <auxpow.h>
#include <chain.h>
#include <chainparams.h>
#include <checkqueue.h>
#include <consensus/consensus.h>
#include <consensus/merkle.h>
#include <consensus/tx_check.h>
#include <consensus/tx_verify.h>
#include <consensus/validation.h>
#include <cuckoocache.h>
#include <flatfile.h>
#include <hash.h>
#include <index/txindex.h>
#include <logging.h>
#include <logging/timer.h>
#include <names/main.h>
#include <names/mempool.h>
#include <node/ui_interface.h>
#include <optional.h>
#include <policy/fees.h>
#include <policy/policy.h>
#include <policy/settings.h>
#include <pow.h>
#include <primitives/block.h>
#include <primitives/transaction.h>
#include <random.h>
#include <reverse_iterator.h>
#include <script/script.h>
#include <script/sigcache.h>
#include <shutdown.h>
#include <signet.h>
#include <timedata.h>
#include <tinyformat.h>
#include <txdb.h>
#include <txmempool.h>
#include <uint256.h>
#include <undo.h>
#include <util/check.h> // For NDEBUG compile time check
#include <util/moneystr.h>
#include <util/rbf.h>
#include <util/strencodings.h>
#include <util/system.h>
#include <util/translation.h>
#include <validationinterface.h>
#include <warnings.h>

#include <string>

#include <boost/algorithm/string/replace.hpp>

#define MICRO 0.000001
#define MILLI 0.001

/**
 * An extra transaction can be added to a package, as long as it only has one
 * ancestor and is no larger than this. Not really any reason to make this
 * configurable as it doesn't materially change DoS parameters.
 */
static const unsigned int EXTRA_DESCENDANT_TX_SIZE_LIMIT = 10000;
/** Maximum kilobytes for transactions to store for processing during reorg */
static const unsigned int MAX_DISCONNECTED_TX_POOL_SIZE = 20000;
/** The pre-allocation chunk size for blk?????.dat files (since 0.8) */
static const unsigned int BLOCKFILE_CHUNK_SIZE = 0x1000000; // 16 MiB
/** The pre-allocation chunk size for rev?????.dat files (since 0.8) */
static const unsigned int UNDOFILE_CHUNK_SIZE = 0x100000; // 1 MiB
/** Time to wait between writing blocks/block index to disk. */
static constexpr std::chrono::hours DATABASE_WRITE_INTERVAL{1};
/** Time to wait between flushing chainstate to disk. */
static constexpr std::chrono::hours DATABASE_FLUSH_INTERVAL{24};
/** Maximum age of our tip for us to be considered current for fee estimation */
static constexpr std::chrono::hours MAX_FEE_ESTIMATION_TIP_AGE{3};
const std::vector<std::string> CHECKLEVEL_DOC {
    "level 0 reads the blocks from disk",
    "level 1 verifies block validity",
    "level 2 verifies undo data",
    "level 3 checks disconnection of tip blocks",
    "level 4 tries to reconnect the blocks",
    "each level includes the checks of the previous levels",
};

bool CBlockIndexWorkComparator::operator()(const CBlockIndex *pa, const CBlockIndex *pb) const {
    // First sort by most total work, ...
    if (pa->nChainWork > pb->nChainWork) return false;
    if (pa->nChainWork < pb->nChainWork) return true;

    // ... then by earliest time received, ...
    if (pa->nSequenceId < pb->nSequenceId) return false;
    if (pa->nSequenceId > pb->nSequenceId) return true;

    // Use pointer address as tie breaker (should only happen with blocks
    // loaded from disk, as those all have id 0).
    if (pa < pb) return false;
    if (pa > pb) return true;

    // Identical blocks.
    return false;
}

ChainstateManager g_chainman;

CChainState& ChainstateActive()
{
    LOCK(::cs_main);
    assert(g_chainman.m_active_chainstate);
    return *g_chainman.m_active_chainstate;
}

CChain& ChainActive()
{
    LOCK(::cs_main);
    return ::ChainstateActive().m_chain;
}

/**
 * Mutex to guard access to validation specific variables, such as reading
 * or changing the chainstate.
 *
 * This may also need to be locked when updating the transaction pool, e.g. on
 * AcceptToMemoryPool. See CTxMemPool::cs comment for details.
 *
 * The transaction pool has a separate lock to allow reading from it and the
 * chainstate at the same time.
 */
RecursiveMutex cs_main;

CBlockIndex *pindexBestHeader = nullptr;
Mutex g_best_block_mutex;
std::condition_variable g_best_block_cv;
uint256 g_best_block;
bool g_parallel_script_checks{false};
std::atomic_bool fImporting(false);
std::atomic_bool fReindex(false);
bool fHavePruned = false;
bool fPruneMode = false;
bool fRequireStandard = true;
bool fCheckBlockIndex = false;
bool fCheckpointsEnabled = DEFAULT_CHECKPOINTS_ENABLED;
uint64_t nPruneTarget = 0;
int64_t nMaxTipAge = DEFAULT_MAX_TIP_AGE;

uint256 hashAssumeValid;
arith_uint256 nMinimumChainWork;

CFeeRate minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);

CBlockPolicyEstimator feeEstimator;

// Internal stuff
namespace {
    CBlockIndex* pindexBestInvalid = nullptr;

    RecursiveMutex cs_LastBlockFile;
    std::vector<CBlockFileInfo> vinfoBlockFile;
    int nLastBlockFile = 0;
    /** Global flag to indicate we should check to see if there are
     *  block/undo files that should be deleted.  Set on startup
     *  or if we allocate more file space when we're in prune mode
     */
    bool fCheckForPruning = false;

    /** Dirty block index entries. */
    std::set<CBlockIndex*> setDirtyBlockIndex;

    /** Dirty block file entries. */
    std::set<int> setDirtyFileInfo;
} // anon namespace

CBlockIndex* LookupBlockIndex(const uint256& hash)
{
    AssertLockHeld(cs_main);
    BlockMap::const_iterator it = g_chainman.BlockIndex().find(hash);
    return it == g_chainman.BlockIndex().end() ? nullptr : it->second;
}

CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator)
{
    AssertLockHeld(cs_main);

    // Find the latest block common to locator and chain - we expect that
    // locator.vHave is sorted descending by height.
    for (const uint256& hash : locator.vHave) {
        CBlockIndex* pindex = LookupBlockIndex(hash);
        if (pindex) {
            if (chain.Contains(pindex))
                return pindex;
            if (pindex->GetAncestor(chain.Height()) == chain.Tip()) {
                return chain.Tip();
            }
        }
    }
    return chain.Genesis();
}

std::unique_ptr<CBlockTreeDB> pblocktree;

bool CheckInputScripts(const CTransaction& tx, TxValidationState &state, const CCoinsViewCache &inputs, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks = nullptr);
static FILE* OpenUndoFile(const FlatFilePos &pos, bool fReadOnly = false);
static FlatFileSeq BlockFileSeq();
static FlatFileSeq UndoFileSeq();

bool CheckFinalTx(const CTransaction &tx, int flags)
{
    AssertLockHeld(cs_main);

    // By convention a negative value for flags indicates that the
    // current network-enforced consensus rules should be used. In
    // a future soft-fork scenario that would mean checking which
    // rules would be enforced for the next block and setting the
    // appropriate flags. At the present time no soft-forks are
    // scheduled, so no flags are set.
    flags = std::max(flags, 0);

    // CheckFinalTx() uses ::ChainActive().Height()+1 to evaluate
    // nLockTime because when IsFinalTx() is called within
    // CBlock::AcceptBlock(), the height of the block *being*
    // evaluated is what is used. Thus if we want to know if a
    // transaction can be part of the *next* block, we need to call
    // IsFinalTx() with one more than ::ChainActive().Height().
    const int nBlockHeight = ::ChainActive().Height() + 1;

    // BIP113 requires that time-locked transactions have nLockTime set to
    // less than the median time of the previous block they're contained in.
    // When the next block is created its previous block will be the current
    // chain tip, so we use that to calculate the median time passed to
    // IsFinalTx() if LOCKTIME_MEDIAN_TIME_PAST is set.
    const int64_t nBlockTime = (flags & LOCKTIME_MEDIAN_TIME_PAST)
                             ? ::ChainActive().Tip()->GetMedianTimePast()
                             : GetAdjustedTime();

    return IsFinalTx(tx, nBlockHeight, nBlockTime);
}

bool TestLockPointValidity(const LockPoints* lp)
{
    AssertLockHeld(cs_main);
    assert(lp);
    // If there are relative lock times then the maxInputBlock will be set
    // If there are no relative lock times, the LockPoints don't depend on the chain
    if (lp->maxInputBlock) {
        // Check whether ::ChainActive() is an extension of the block at which the LockPoints
        // calculation was valid.  If not LockPoints are no longer valid
        if (!::ChainActive().Contains(lp->maxInputBlock)) {
            return false;
        }
    }

    // LockPoints still valid
    return true;
}

bool CheckSequenceLocks(const CTxMemPool& pool, const CTransaction& tx, int flags, LockPoints* lp, bool useExistingLockPoints)
{
    AssertLockHeld(cs_main);
    AssertLockHeld(pool.cs);

    CBlockIndex* tip = ::ChainActive().Tip();
    assert(tip != nullptr);

    CBlockIndex index;
    index.pprev = tip;
    // CheckSequenceLocks() uses ::ChainActive().Height()+1 to evaluate
    // height based locks because when SequenceLocks() is called within
    // ConnectBlock(), the height of the block *being*
    // evaluated is what is used.
    // Thus if we want to know if a transaction can be part of the
    // *next* block, we need to use one more than ::ChainActive().Height()
    index.nHeight = tip->nHeight + 1;

    std::pair<int, int64_t> lockPair;
    if (useExistingLockPoints) {
        assert(lp);
        lockPair.first = lp->height;
        lockPair.second = lp->time;
    }
    else {
        // CoinsTip() contains the UTXO set for ::ChainActive().Tip()
        CCoinsViewMemPool viewMemPool(&::ChainstateActive().CoinsTip(), pool);
        std::vector<int> prevheights;
        prevheights.resize(tx.vin.size());
        for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
            const CTxIn& txin = tx.vin[txinIndex];
            Coin coin;
            if (!viewMemPool.GetCoin(txin.prevout, coin)) {
                return error("%s: Missing input", __func__);
            }
            if (coin.nHeight == MEMPOOL_HEIGHT) {
                // Assume all mempool transaction confirm in the next block
                prevheights[txinIndex] = tip->nHeight + 1;
            } else {
                prevheights[txinIndex] = coin.nHeight;
            }
        }
        lockPair = CalculateSequenceLocks(tx, flags, prevheights, index);
        if (lp) {
            lp->height = lockPair.first;
            lp->time = lockPair.second;
            // Also store the hash of the block with the highest height of
            // all the blocks which have sequence locked prevouts.
            // This hash needs to still be on the chain
            // for these LockPoint calculations to be valid
            // Note: It is impossible to correctly calculate a maxInputBlock
            // if any of the sequence locked inputs depend on unconfirmed txs,
            // except in the special case where the relative lock time/height
            // is 0, which is equivalent to no sequence lock. Since we assume
            // input height of tip+1 for mempool txs and test the resulting
            // lockPair from CalculateSequenceLocks against tip+1.  We know
            // EvaluateSequenceLocks will fail if there was a non-zero sequence
            // lock on a mempool input, so we can use the return value of
            // CheckSequenceLocks to indicate the LockPoints validity
            int maxInputHeight = 0;
            for (const int height : prevheights) {
                // Can ignore mempool inputs since we'll fail if they had non-zero locks
                if (height != tip->nHeight+1) {
                    maxInputHeight = std::max(maxInputHeight, height);
                }
            }
            lp->maxInputBlock = tip->GetAncestor(maxInputHeight);
        }
    }
    return EvaluateSequenceLocks(index, lockPair);
}

// Returns the script flags which should be checked for a given block
static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consensus::Params& chainparams);

static void LimitMempoolSize(CTxMemPool& pool, size_t limit, std::chrono::seconds age)
    EXCLUSIVE_LOCKS_REQUIRED(pool.cs, ::cs_main)
{
    int expired = pool.Expire(GetTime<std::chrono::seconds>() - age);
    if (expired != 0) {
        LogPrint(BCLog::MEMPOOL, "Expired %i transactions from the memory pool\n", expired);
    }

    std::vector<COutPoint> vNoSpendsRemaining;
    pool.TrimToSize(limit, &vNoSpendsRemaining);
    for (const COutPoint& removed : vNoSpendsRemaining)
        ::ChainstateActive().CoinsTip().Uncache(removed);
}

static bool IsCurrentForFeeEstimation() EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    AssertLockHeld(cs_main);
    if (::ChainstateActive().IsInitialBlockDownload())
        return false;
    if (::ChainActive().Tip()->GetBlockTime() < count_seconds(GetTime<std::chrono::seconds>() - MAX_FEE_ESTIMATION_TIP_AGE))
        return false;
    if (::ChainActive().Height() < pindexBestHeader->nHeight - 1)
        return false;
    return true;
}

/* Make mempool consistent after a reorg, by re-adding or recursively erasing
 * disconnected block transactions from the mempool, and also removing any
 * other transactions from the mempool that are no longer valid given the new
 * tip/height.
 *
 * Note: we assume that disconnectpool only contains transactions that are NOT
 * confirmed in the current chain nor already in the mempool (otherwise,
 * in-mempool descendants of such transactions would be removed).
 *
 * Passing fAddToMempool=false will skip trying to add the transactions back,
 * and instead just erase from the mempool as needed.
 */

static void UpdateMempoolForReorg(CTxMemPool& mempool, DisconnectedBlockTransactions& disconnectpool, bool fAddToMempool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, mempool.cs)
{
    AssertLockHeld(cs_main);
    AssertLockHeld(mempool.cs);
    std::vector<uint256> vHashUpdate;
    // disconnectpool's insertion_order index sorts the entries from
    // oldest to newest, but the oldest entry will be the last tx from the
    // latest mined block that was disconnected.
    // Iterate disconnectpool in reverse, so that we add transactions
    // back to the mempool starting with the earliest transaction that had
    // been previously seen in a block.
    auto it = disconnectpool.queuedTx.get<insertion_order>().rbegin();
    while (it != disconnectpool.queuedTx.get<insertion_order>().rend()) {
        // ignore validation errors in resurrected transactions
        TxValidationState stateDummy;
        if (!fAddToMempool || (*it)->IsCoinBase() ||
            !AcceptToMemoryPool(mempool, stateDummy, *it,
                                nullptr /* plTxnReplaced */, true /* bypass_limits */)) {
            // If the transaction doesn't make it in to the mempool, remove any
            // transactions that depend on it (which would now be orphans).
            mempool.removeRecursive(**it, MemPoolRemovalReason::REORG);
        } else if (mempool.exists((*it)->GetHash())) {
            vHashUpdate.push_back((*it)->GetHash());
        }
        ++it;
    }
    disconnectpool.queuedTx.clear();
    // AcceptToMemoryPool/addUnchecked all assume that new mempool entries have
    // no in-mempool children, which is generally not true when adding
    // previously-confirmed transactions back to the mempool.
    // UpdateTransactionsFromBlock finds descendants of any transactions in
    // the disconnectpool that were added back and cleans up the mempool state.
    mempool.UpdateTransactionsFromBlock(vHashUpdate);

    // We also need to remove any now-immature transactions
    mempool.removeForReorg(&::ChainstateActive().CoinsTip(), ::ChainActive().Tip()->nHeight + 1, STANDARD_LOCKTIME_VERIFY_FLAGS);
    // Re-limit mempool size, in case we added any transactions
    LimitMempoolSize(mempool, gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000, std::chrono::hours{gArgs.GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY)});
}

// Used to avoid mempool polluting consensus critical paths if CCoinsViewMempool
// were somehow broken and returning the wrong scriptPubKeys
static bool CheckInputsFromMempoolAndCache(const CTransaction& tx, TxValidationState& state, const CCoinsViewCache& view, const CTxMemPool& pool,
                 unsigned int flags, PrecomputedTransactionData& txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
    AssertLockHeld(cs_main);

    // pool.cs should be locked already, but go ahead and re-take the lock here
    // to enforce that mempool doesn't change between when we check the view
    // and when we actually call through to CheckInputScripts
    LOCK(pool.cs);

    assert(!tx.IsCoinBase());
    for (const CTxIn& txin : tx.vin) {
        const Coin& coin = view.AccessCoin(txin.prevout);

        // AcceptToMemoryPoolWorker has already checked that the coins are
        // available, so this shouldn't fail. If the inputs are not available
        // here then return false.
        if (coin.IsSpent()) return false;

        // Check equivalence for available inputs.
        const CTransactionRef& txFrom = pool.get(txin.prevout.hash);
        if (txFrom) {
            assert(txFrom->GetHash() == txin.prevout.hash);
            assert(txFrom->vout.size() > txin.prevout.n);
            assert(txFrom->vout[txin.prevout.n] == coin.out);
        } else {
            const Coin& coinFromDisk = ::ChainstateActive().CoinsTip().AccessCoin(txin.prevout);
            assert(!coinFromDisk.IsSpent());
            assert(coinFromDisk.out == coin.out);
        }
    }

    // Call CheckInputScripts() to cache signature and script validity against current tip consensus rules.
    return CheckInputScripts(tx, state, view, flags, /* cacheSigStore = */ true, /* cacheFullSciptStore = */ true, txdata);
}

namespace {

class MemPoolAccept
{
public:
    MemPoolAccept(CTxMemPool& mempool) : m_pool(mempool), m_view(&m_dummy), m_viewmempool(&::ChainstateActive().CoinsTip(), m_pool),
        m_limit_ancestors(gArgs.GetArg("-limitancestorcount", DEFAULT_ANCESTOR_LIMIT)),
        m_limit_ancestor_size(gArgs.GetArg("-limitancestorsize", DEFAULT_ANCESTOR_SIZE_LIMIT)*1000),
        m_limit_descendants(gArgs.GetArg("-limitdescendantcount", DEFAULT_DESCENDANT_LIMIT)),
        m_limit_descendant_size(gArgs.GetArg("-limitdescendantsize", DEFAULT_DESCENDANT_SIZE_LIMIT)*1000) {}

    // We put the arguments we're handed into a struct, so we can pass them
    // around easier.
    struct ATMPArgs {
        const CChainParams& m_chainparams;
        TxValidationState &m_state;
        const int64_t m_accept_time;
        std::list<CTransactionRef>* m_replaced_transactions;
        const bool m_bypass_limits;
        /*
         * Return any outpoints which were not previously present in the coins
         * cache, but were added as a result of validating the tx for mempool
         * acceptance. This allows the caller to optionally remove the cache
         * additions if the associated transaction ends up being rejected by
         * the mempool.
         */
        std::vector<COutPoint>& m_coins_to_uncache;
        const bool m_test_accept;
        CAmount* m_fee_out;
    };

    // Single transaction acceptance
    bool AcceptSingleTransaction(const CTransactionRef& ptx, ATMPArgs& args) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

private:
    // All the intermediate state that gets passed between the various levels
    // of checking a given transaction.
    struct Workspace {
        Workspace(const CTransactionRef& ptx) : m_ptx(ptx), m_hash(ptx->GetHash()) {}
        std::set<uint256> m_conflicts;
        CTxMemPool::setEntries m_all_conflicting;
        CTxMemPool::setEntries m_ancestors;
        std::unique_ptr<CTxMemPoolEntry> m_entry;

        bool m_replacement_transaction;
        CAmount m_modified_fees;
        CAmount m_conflicting_fees;
        size_t m_conflicting_size;

        const CTransactionRef& m_ptx;
        const uint256& m_hash;
    };

    // Run the policy checks on a given transaction, excluding any script checks.
    // Looks up inputs, calculates feerate, considers replacement, evaluates
    // package limits, etc. As this function can be invoked for "free" by a peer,
    // only tests that are fast should be done here (to avoid CPU DoS).
    bool PreChecks(ATMPArgs& args, Workspace& ws) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);

    // Run the script checks using our policy flags. As this can be slow, we should
    // only invoke this on transactions that have otherwise passed policy checks.
    bool PolicyScriptChecks(ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    // Re-run the script checks, using consensus flags, and try to cache the
    // result in the scriptcache. This should be done after
    // PolicyScriptChecks(). This requires that all inputs either be in our
    // utxo set or in the mempool.
    bool ConsensusScriptChecks(ATMPArgs& args, Workspace& ws, PrecomputedTransactionData &txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    // Try to add the transaction to the mempool, removing any conflicts first.
    // Returns true if the transaction is in the mempool after any size
    // limiting is performed, false otherwise.
    bool Finalize(ATMPArgs& args, Workspace& ws) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);

    // Compare a package's feerate against minimum allowed.
    bool CheckFeeRate(size_t package_size, CAmount package_fee, TxValidationState& state)
    {
        CAmount mempoolRejectFee = m_pool.GetMinFee(gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000).GetFee(package_size);
        if (mempoolRejectFee > 0 && package_fee < mempoolRejectFee) {
            return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "mempool min fee not met", strprintf("%d < %d", package_fee, mempoolRejectFee));
        }

        if (package_fee < ::minRelayTxFee.GetFee(package_size)) {
            return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "min relay fee not met", strprintf("%d < %d", package_fee, ::minRelayTxFee.GetFee(package_size)));
        }
        return true;
    }

private:
    CTxMemPool& m_pool;
    CCoinsViewCache m_view;
    CCoinsViewMemPool m_viewmempool;
    CCoinsView m_dummy;

    // The package limits in effect at the time of invocation.
    const size_t m_limit_ancestors;
    const size_t m_limit_ancestor_size;
    // These may be modified while evaluating a transaction (eg to account for
    // in-mempool conflicts; see below).
    size_t m_limit_descendants;
    size_t m_limit_descendant_size;
};

bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
{
    const CTransactionRef& ptx = ws.m_ptx;
    const CTransaction& tx = *ws.m_ptx;
    const uint256& hash = ws.m_hash;

    // Copy/alias what we need out of args
    TxValidationState &state = args.m_state;
    const int64_t nAcceptTime = args.m_accept_time;
    const bool bypass_limits = args.m_bypass_limits;
    std::vector<COutPoint>& coins_to_uncache = args.m_coins_to_uncache;

    // Alias what we need out of ws
    std::set<uint256>& setConflicts = ws.m_conflicts;
    CTxMemPool::setEntries& allConflicting = ws.m_all_conflicting;
    CTxMemPool::setEntries& setAncestors = ws.m_ancestors;
    std::unique_ptr<CTxMemPoolEntry>& entry = ws.m_entry;
    bool& fReplacementTransaction = ws.m_replacement_transaction;
    CAmount& nModifiedFees = ws.m_modified_fees;
    CAmount& nConflictingFees = ws.m_conflicting_fees;
    size_t& nConflictingSize = ws.m_conflicting_size;

    if (!CheckTransaction(tx, state)) {
        return false; // state filled in by CheckTransaction
    }

    // Coinbase is only valid in a block, not as a loose transaction
    if (tx.IsCoinBase())
        return state.Invalid(TxValidationResult::TX_CONSENSUS, "coinbase");

    // Rather not work on nonstandard transactions (unless -testnet/-regtest)
    std::string reason;
    if (fRequireStandard && !IsStandardTx(tx, reason))
        return state.Invalid(TxValidationResult::TX_NOT_STANDARD, reason);

    // Do not work on transactions that are too small.
    // A transaction with 1 segwit input and 1 P2WPHK output has non-witness size of 82 bytes.
    // Transactions smaller than this are not relayed to mitigate CVE-2017-12842 by not relaying
    // 64-byte transactions.
    if (::GetSerializeSize(tx, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) < MIN_STANDARD_TX_NONWITNESS_SIZE)
        return state.Invalid(TxValidationResult::TX_NOT_STANDARD, "tx-size-small");

    // Only accept nLockTime-using transactions that can be mined in the next
    // block; we don't want our mempool filled up with transactions that can't
    // be mined yet.
    if (!CheckFinalTx(tx, STANDARD_LOCKTIME_VERIFY_FLAGS))
        return state.Invalid(TxValidationResult::TX_PREMATURE_SPEND, "non-final");

    // is it already in the memory pool?
    if (m_pool.exists(hash)) {
        return state.Invalid(TxValidationResult::TX_CONFLICT, "txn-already-in-mempool");
    }

    // Check for conflicts with in-memory transactions
    for (const CTxIn &txin : tx.vin)
    {
        const CTransaction* ptxConflicting = m_pool.GetConflictTx(txin.prevout);
        if (ptxConflicting) {
            if (!setConflicts.count(ptxConflicting->GetHash()))
            {
                // Allow opt-out of transaction replacement by setting
                // nSequence > MAX_BIP125_RBF_SEQUENCE (SEQUENCE_FINAL-2) on all inputs.
                //
                // SEQUENCE_FINAL-1 is picked to still allow use of nLockTime by
                // non-replaceable transactions. All inputs rather than just one
                // is for the sake of multi-party protocols, where we don't
                // want a single party to be able to disable replacement.
                //
                // The opt-out ignores descendants as anyone relying on
                // first-seen mempool behavior should be checking all
                // unconfirmed ancestors anyway; doing otherwise is hopelessly
                // insecure.
                bool fReplacementOptOut = true;
                for (const CTxIn &_txin : ptxConflicting->vin)
                {
                    if (_txin.nSequence <= MAX_BIP125_RBF_SEQUENCE)
                    {
                        fReplacementOptOut = false;
                        break;
                    }
                }
                if (fReplacementOptOut) {
                    return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "txn-mempool-conflict");
                }

                setConflicts.insert(ptxConflicting->GetHash());
            }
        }
    }

    if (!m_pool.checkNameOps(tx))
        return state.Invalid(TxValidationResult::TX_CONFLICT,
                             "txn-mempool-name-error");

    LockPoints lp;
    m_view.SetBackend(m_viewmempool);

    CCoinsViewCache& coins_cache = ::ChainstateActive().CoinsTip();
    // do all inputs exist?
    for (const CTxIn& txin : tx.vin) {
        if (!coins_cache.HaveCoinInCache(txin.prevout)) {
            coins_to_uncache.push_back(txin.prevout);
        }

        // Note: this call may add txin.prevout to the coins cache
        // (coins_cache.cacheCoins) by way of FetchCoin(). It should be removed
        // later (via coins_to_uncache) if this tx turns out to be invalid.
        if (!m_view.HaveCoin(txin.prevout)) {
            // Are inputs missing because we already have the tx?
            for (size_t out = 0; out < tx.vout.size(); out++) {
                // See if we have any output in the UTXO set.
                if (coins_cache.HaveCoin(COutPoint(hash, out))) {
                    return state.Invalid(TxValidationResult::TX_CONFLICT, "txn-already-known");
                }
            }
            // Otherwise assume this might be an orphan tx for which we just haven't seen parents yet
            return state.Invalid(TxValidationResult::TX_MISSING_INPUTS, "bad-txns-inputs-missingorspent");
        }
    }

    // Bring the best block into scope
    m_view.GetBestBlock();

    /* If this is a name update (or firstupdate), make sure that the
       existing name entry (if any) is in the dummy cache.  Otherwise
       tx validation done below (in CheckInputs) will not be correct.  */
    for (const auto& txout : tx.vout)
    {
        const CNameScript nameOp(txout.scriptPubKey);
        if (nameOp.isNameOp() && nameOp.isAnyUpdate())
        {
            const valtype& name = nameOp.getOpName();
            CNameData data;
            if (m_view.GetName(name, data))
                m_view.SetName(name, data, false);
        }
    }

    // we have all inputs cached now, so switch back to dummy (to protect
    // against bugs where we pull more inputs from disk that miss being added
    // to coins_to_uncache)
    m_view.SetBackend(m_dummy);

    // Only accept BIP68 sequence locked transactions that can be mined in the next
    // block; we don't want our mempool filled up with transactions that can't
    // be mined yet.
    // Must keep pool.cs for this unless we change CheckSequenceLocks to take a
    // CoinsViewCache instead of create its own
    if (!CheckSequenceLocks(m_pool, tx, STANDARD_LOCKTIME_VERIFY_FLAGS, &lp))
        return state.Invalid(TxValidationResult::TX_PREMATURE_SPEND, "non-BIP68-final");

    CAmount nFees = 0;
    if (!Consensus::CheckTxInputs(tx, state, m_view, GetSpendHeight(m_view), SCRIPT_VERIFY_NAMES_MEMPOOL, nFees)) {
        return false; // state filled in by CheckTxInputs
    }

    // If fee_out is passed, return the fee to the caller
    if (args.m_fee_out) {
        *args.m_fee_out = nFees;
    }

    // Check for non-standard pay-to-script-hash in inputs
    const auto& params = args.m_chainparams.GetConsensus();
    auto taproot_state = VersionBitsState(::ChainActive().Tip(), params, Consensus::DEPLOYMENT_TAPROOT, versionbitscache);
    if (fRequireStandard && !AreInputsStandard(tx, m_view, taproot_state == ThresholdState::ACTIVE)) {
        return state.Invalid(TxValidationResult::TX_INPUTS_NOT_STANDARD, "bad-txns-nonstandard-inputs");
    }

    // Check for non-standard witness in P2WSH
    if (tx.HasWitness() && fRequireStandard && !IsWitnessStandard(tx, m_view))
        return state.Invalid(TxValidationResult::TX_WITNESS_MUTATED, "bad-witness-nonstandard");

    int64_t nSigOpsCost = GetTransactionSigOpCost(tx, m_view, STANDARD_SCRIPT_VERIFY_FLAGS);

    // nModifiedFees includes any fee deltas from PrioritiseTransaction
    nModifiedFees = nFees;
    m_pool.ApplyDelta(hash, nModifiedFees);

    // Keep track of transactions that spend a coinbase, which we re-scan
    // during reorgs to ensure COINBASE_MATURITY is still met.
    bool fSpendsCoinbase = false;
    for (const CTxIn &txin : tx.vin) {
        const Coin &coin = m_view.AccessCoin(txin.prevout);
        if (coin.IsCoinBase()) {
            fSpendsCoinbase = true;
            break;
        }
    }

    entry.reset(new CTxMemPoolEntry(ptx, nFees, nAcceptTime, ::ChainActive().Height(),
            fSpendsCoinbase, nSigOpsCost, lp));
    unsigned int nSize = entry->GetTxSize();

    if (nSigOpsCost > MAX_STANDARD_TX_SIGOPS_COST)
        return state.Invalid(TxValidationResult::TX_NOT_STANDARD, "bad-txns-too-many-sigops",
                strprintf("%d", nSigOpsCost));

    // No transactions are allowed below minRelayTxFee except from disconnected
    // blocks
    if (!bypass_limits && !CheckFeeRate(nSize, nModifiedFees, state)) return false;

    const CTxMemPool::setEntries setIterConflicting = m_pool.GetIterSet(setConflicts);
    // Calculate in-mempool ancestors, up to a limit.
    if (setConflicts.size() == 1) {
        // In general, when we receive an RBF transaction with mempool conflicts, we want to know whether we
        // would meet the chain limits after the conflicts have been removed. However, there isn't a practical
        // way to do this short of calculating the ancestor and descendant sets with an overlay cache of
        // changed mempool entries. Due to both implementation and runtime complexity concerns, this isn't
        // very realistic, thus we only ensure a limited set of transactions are RBF'able despite mempool
        // conflicts here. Importantly, we need to ensure that some transactions which were accepted using
        // the below carve-out are able to be RBF'ed, without impacting the security the carve-out provides
        // for off-chain contract systems (see link in the comment below).
        //
        // Specifically, the subset of RBF transactions which we allow despite chain limits are those which
        // conflict directly with exactly one other transaction (but may evict children of said transaction),
        // and which are not adding any new mempool dependencies. Note that the "no new mempool dependencies"
        // check is accomplished later, so we don't bother doing anything about it here, but if BIP 125 is
        // amended, we may need to move that check to here instead of removing it wholesale.
        //
        // Such transactions are clearly not merging any existing packages, so we are only concerned with
        // ensuring that (a) no package is growing past the package size (not count) limits and (b) we are
        // not allowing something to effectively use the (below) carve-out spot when it shouldn't be allowed
        // to.
        //
        // To check these we first check if we meet the RBF criteria, above, and increment the descendant
        // limits by the direct conflict and its descendants (as these are recalculated in
        // CalculateMempoolAncestors by assuming the new transaction being added is a new descendant, with no
        // removals, of each parent's existing dependent set). The ancestor count limits are unmodified (as
        // the ancestor limits should be the same for both our new transaction and any conflicts).
        // We don't bother incrementing m_limit_descendants by the full removal count as that limit never comes
        // into force here (as we're only adding a single transaction).
        assert(setIterConflicting.size() == 1);
        CTxMemPool::txiter conflict = *setIterConflicting.begin();

        m_limit_descendants += 1;
        m_limit_descendant_size += conflict->GetSizeWithDescendants();
    }

    std::string errString;
    if (!m_pool.CalculateMemPoolAncestors(*entry, setAncestors, m_limit_ancestors, m_limit_ancestor_size, m_limit_descendants, m_limit_descendant_size, errString)) {
        setAncestors.clear();
        // If CalculateMemPoolAncestors fails second time, we want the original error string.
        std::string dummy_err_string;
        // Contracting/payment channels CPFP carve-out:
        // If the new transaction is relatively small (up to 40k weight)
        // and has at most one ancestor (ie ancestor limit of 2, including
        // the new transaction), allow it if its parent has exactly the
        // descendant limit descendants.
        //
        // This allows protocols which rely on distrusting counterparties
        // being able to broadcast descendants of an unconfirmed transaction
        // to be secure by simply only having two immediately-spendable
        // outputs - one for each counterparty. For more info on the uses for
        // this, see https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-November/016518.html
        if (nSize >  EXTRA_DESCENDANT_TX_SIZE_LIMIT ||
                !m_pool.CalculateMemPoolAncestors(*entry, setAncestors, 2, m_limit_ancestor_size, m_limit_descendants + 1, m_limit_descendant_size + EXTRA_DESCENDANT_TX_SIZE_LIMIT, dummy_err_string)) {
            return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "too-long-mempool-chain", errString);
        }
    }

    // A transaction that spends outputs that would be replaced by it is invalid. Now
    // that we have the set of all ancestors we can detect this
    // pathological case by making sure setConflicts and setAncestors don't
    // intersect.
    for (CTxMemPool::txiter ancestorIt : setAncestors)
    {
        const uint256 &hashAncestor = ancestorIt->GetTx().GetHash();
        if (setConflicts.count(hashAncestor))
        {
            return state.Invalid(TxValidationResult::TX_CONSENSUS, "bad-txns-spends-conflicting-tx",
                    strprintf("%s spends conflicting transaction %s",
                        hash.ToString(),
                        hashAncestor.ToString()));
        }
    }

    // Check if it's economically rational to mine this transaction rather
    // than the ones it replaces.
    nConflictingFees = 0;
    nConflictingSize = 0;
    uint64_t nConflictingCount = 0;

    // If we don't hold the lock allConflicting might be incomplete; the
    // subsequent RemoveStaged() and addUnchecked() calls don't guarantee
    // mempool consistency for us.
    fReplacementTransaction = setConflicts.size();
    if (fReplacementTransaction)
    {
        CFeeRate newFeeRate(nModifiedFees, nSize);
        std::set<uint256> setConflictsParents;
        const int maxDescendantsToVisit = 100;
        for (const auto& mi : setIterConflicting) {
            // Don't allow the replacement to reduce the feerate of the
            // mempool.
            //
            // We usually don't want to accept replacements with lower
            // feerates than what they replaced as that would lower the
            // feerate of the next block. Requiring that the feerate always
            // be increased is also an easy-to-reason about way to prevent
            // DoS attacks via replacements.
            //
            // We only consider the feerates of transactions being directly
            // replaced, not their indirect descendants. While that does
            // mean high feerate children are ignored when deciding whether
            // or not to replace, we do require the replacement to pay more
            // overall fees too, mitigating most cases.
            CFeeRate oldFeeRate(mi->GetModifiedFee(), mi->GetTxSize());
            if (newFeeRate <= oldFeeRate)
            {
                return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "insufficient fee",
                        strprintf("rejecting replacement %s; new feerate %s <= old feerate %s",
                            hash.ToString(),
                            newFeeRate.ToString(),
                            oldFeeRate.ToString()));
            }

            for (const CTxIn &txin : mi->GetTx().vin)
            {
                setConflictsParents.insert(txin.prevout.hash);
            }

            nConflictingCount += mi->GetCountWithDescendants();
        }
        // This potentially overestimates the number of actual descendants
        // but we just want to be conservative to avoid doing too much
        // work.
        if (nConflictingCount <= maxDescendantsToVisit) {
            // If not too many to replace, then calculate the set of
            // transactions that would have to be evicted
            for (CTxMemPool::txiter it : setIterConflicting) {
                m_pool.CalculateDescendants(it, allConflicting);
            }
            for (CTxMemPool::txiter it : allConflicting) {
                nConflictingFees += it->GetModifiedFee();
                nConflictingSize += it->GetTxSize();
            }
        } else {
            return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "too many potential replacements",
                    strprintf("rejecting replacement %s; too many potential replacements (%d > %d)\n",
                        hash.ToString(),
                        nConflictingCount,
                        maxDescendantsToVisit));
        }

        for (unsigned int j = 0; j < tx.vin.size(); j++)
        {
            // We don't want to accept replacements that require low
            // feerate junk to be mined first. Ideally we'd keep track of
            // the ancestor feerates and make the decision based on that,
            // but for now requiring all new inputs to be confirmed works.
            //
            // Note that if you relax this to make RBF a little more useful,
            // this may break the CalculateMempoolAncestors RBF relaxation,
            // above. See the comment above the first CalculateMempoolAncestors
            // call for more info.
            if (!setConflictsParents.count(tx.vin[j].prevout.hash))
            {
                // Rather than check the UTXO set - potentially expensive -
                // it's cheaper to just check if the new input refers to a
                // tx that's in the mempool.
                if (m_pool.exists(tx.vin[j].prevout.hash)) {
                    return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "replacement-adds-unconfirmed",
                            strprintf("replacement %s adds unconfirmed input, idx %d",
                                hash.ToString(), j));
                }
            }
        }

        // The replacement must pay greater fees than the transactions it
        // replaces - if we did the bandwidth used by those conflicting
        // transactions would not be paid for.
        if (nModifiedFees < nConflictingFees)
        {
            return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "insufficient fee",
                    strprintf("rejecting replacement %s, less fees than conflicting txs; %s < %s",
                        hash.ToString(), FormatMoney(nModifiedFees), FormatMoney(nConflictingFees)));
        }

        // Finally in addition to paying more fees than the conflicts the
        // new transaction must pay for its own bandwidth.
        CAmount nDeltaFees = nModifiedFees - nConflictingFees;
        if (nDeltaFees < ::incrementalRelayFee.GetFee(nSize))
        {
            return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "insufficient fee",
                    strprintf("rejecting replacement %s, not enough additional fees to relay; %s < %s",
                        hash.ToString(),
                        FormatMoney(nDeltaFees),
                        FormatMoney(::incrementalRelayFee.GetFee(nSize))));
        }
    }
    return true;
}

bool MemPoolAccept::PolicyScriptChecks(ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata)
{
    const CTransaction& tx = *ws.m_ptx;

    TxValidationState &state = args.m_state;

    constexpr unsigned int scriptVerifyFlags = STANDARD_SCRIPT_VERIFY_FLAGS | SCRIPT_VERIFY_NAMES_MEMPOOL;

    // Check input scripts and signatures.
    // This is done last to help prevent CPU exhaustion denial-of-service attacks.
    if (!CheckInputScripts(tx, state, m_view, scriptVerifyFlags, true, false, txdata)) {
        // SCRIPT_VERIFY_CLEANSTACK requires SCRIPT_VERIFY_WITNESS, so we
        // need to turn both off, and compare against just turning off CLEANSTACK
        // to see if the failure is specifically due to witness validation.
        TxValidationState state_dummy; // Want reported failures to be from first CheckInputScripts
        if (!tx.HasWitness() && CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, false, txdata) &&
                !CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, false, txdata)) {
            // Only the witness is missing, so the transaction itself may be fine.
            state.Invalid(TxValidationResult::TX_WITNESS_STRIPPED,
                    state.GetRejectReason(), state.GetDebugMessage());
        }
        return false; // state filled in by CheckInputScripts
    }

    return true;
}

bool MemPoolAccept::ConsensusScriptChecks(ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata)
{
    const CTransaction& tx = *ws.m_ptx;
    const uint256& hash = ws.m_hash;

    TxValidationState &state = args.m_state;
    const CChainParams& chainparams = args.m_chainparams;

    // Check again against the current block tip's script verification
    // flags to cache our script execution flags. This is, of course,
    // useless if the next block has different script flags from the
    // previous one, but because the cache tracks script flags for us it
    // will auto-invalidate and we'll just have a few blocks of extra
    // misses on soft-fork activation.
    //
    // This is also useful in case of bugs in the standard flags that cause
    // transactions to pass as valid when they're actually invalid. For
    // instance the STRICTENC flag was incorrectly allowing certain
    // CHECKSIG NOT scripts to pass, even though they were invalid.
    //
    // There is a similar check in CreateNewBlock() to prevent creating
    // invalid blocks (using TestBlockValidity), however allowing such
    // transactions into the mempool can be exploited as a DoS attack.
    //
    // Namecoin actually allows some scripts into the mempool that would
    // not (yet) be valid in a block, namely premature NAME_FIRSTUPDATE's.
    // Thus add the mempool-flag here.
    unsigned int currentBlockScriptVerifyFlags = GetBlockScriptFlags(::ChainActive().Tip(), chainparams.GetConsensus());
    currentBlockScriptVerifyFlags |= SCRIPT_VERIFY_NAMES_MEMPOOL;
    if (!CheckInputsFromMempoolAndCache(tx, state, m_view, m_pool, currentBlockScriptVerifyFlags, txdata)) {
        return error("%s: BUG! PLEASE REPORT THIS! CheckInputScripts failed against latest-block but not STANDARD flags %s, %s",
                __func__, hash.ToString(), state.ToString());
    }

    return true;
}

bool MemPoolAccept::Finalize(ATMPArgs& args, Workspace& ws)
{
    const CTransaction& tx = *ws.m_ptx;
    const uint256& hash = ws.m_hash;
    TxValidationState &state = args.m_state;
    const bool bypass_limits = args.m_bypass_limits;

    CTxMemPool::setEntries& allConflicting = ws.m_all_conflicting;
    CTxMemPool::setEntries& setAncestors = ws.m_ancestors;
    const CAmount& nModifiedFees = ws.m_modified_fees;
    const CAmount& nConflictingFees = ws.m_conflicting_fees;
    const size_t& nConflictingSize = ws.m_conflicting_size;
    const bool fReplacementTransaction = ws.m_replacement_transaction;
    std::unique_ptr<CTxMemPoolEntry>& entry = ws.m_entry;

    // Remove conflicting transactions from the mempool
    for (CTxMemPool::txiter it : allConflicting)
    {
        LogPrint(BCLog::MEMPOOL, "replacing tx %s with %s for %s additional fees, %d delta bytes\n",
                it->GetTx().GetHash().ToString(),
                hash.ToString(),
                FormatMoney(nModifiedFees - nConflictingFees),
                (int)entry->GetTxSize() - (int)nConflictingSize);
        if (args.m_replaced_transactions)
            args.m_replaced_transactions->push_back(it->GetSharedTx());
    }
    m_pool.RemoveStaged(allConflicting, false, MemPoolRemovalReason::REPLACED);

    // This transaction should only count for fee estimation if:
    // - it isn't a BIP 125 replacement transaction (may not be widely supported)
    // - it's not being re-added during a reorg which bypasses typical mempool fee limits
    // - the node is not behind
    // - the transaction is not dependent on any other transactions in the mempool
    bool validForFeeEstimation = !fReplacementTransaction && !bypass_limits && IsCurrentForFeeEstimation() && m_pool.HasNoInputsOf(tx);

    // Store transaction in memory
    m_pool.addUnchecked(*entry, setAncestors, validForFeeEstimation);

    // trim mempool and check if tx was trimmed
    if (!bypass_limits) {
        LimitMempoolSize(m_pool, gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000, std::chrono::hours{gArgs.GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY)});
        if (!m_pool.exists(hash))
            return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "mempool full");
    }
    return true;
}

bool MemPoolAccept::AcceptSingleTransaction(const CTransactionRef& ptx, ATMPArgs& args)
{
    AssertLockHeld(cs_main);
    LOCK(m_pool.cs); // mempool "read lock" (held through GetMainSignals().TransactionAddedToMempool())

    Workspace workspace(ptx);

    if (!PreChecks(args, workspace)) return false;

    // Only compute the precomputed transaction data if we need to verify
    // scripts (ie, other policy checks pass). We perform the inexpensive
    // checks first and avoid hashing and signature verification unless those
    // checks pass, to mitigate CPU exhaustion denial-of-service attacks.
    PrecomputedTransactionData txdata;

    if (!PolicyScriptChecks(args, workspace, txdata)) return false;

    if (!ConsensusScriptChecks(args, workspace, txdata)) return false;

    // Tx was accepted, but not added
    if (args.m_test_accept) return true;

    if (!Finalize(args, workspace)) return false;

    GetMainSignals().TransactionAddedToMempool(ptx, m_pool.GetAndIncrementSequence());

    return true;
}

} // anon namespace

/** (try to) add transaction to memory pool with a specified acceptance time **/
static bool AcceptToMemoryPoolWithTime(const CChainParams& chainparams, CTxMemPool& pool, TxValidationState &state, const CTransactionRef &tx,
                        int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
                        bool bypass_limits, bool test_accept, CAmount* fee_out=nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    std::vector<COutPoint> coins_to_uncache;
    MemPoolAccept::ATMPArgs args { chainparams, state, nAcceptTime, plTxnReplaced, bypass_limits, coins_to_uncache, test_accept, fee_out };
    bool res = MemPoolAccept(pool).AcceptSingleTransaction(tx, args);
    if (!res) {
        // Remove coins that were not present in the coins cache before calling ATMPW;
        // this is to prevent memory DoS in case we receive a large number of
        // invalid transactions that attempt to overrun the in-memory coins cache
        // (`CCoinsViewCache::cacheCoins`).

        for (const COutPoint& hashTx : coins_to_uncache)
            ::ChainstateActive().CoinsTip().Uncache(hashTx);
    }
    // After we've (potentially) uncached entries, ensure our coins cache is still within its size limits
    BlockValidationState state_dummy;
    ::ChainstateActive().FlushStateToDisk(chainparams, state_dummy, FlushStateMode::PERIODIC);
    return res;
}

bool AcceptToMemoryPool(CTxMemPool& pool, TxValidationState &state, const CTransactionRef &tx,
                        std::list<CTransactionRef>* plTxnReplaced,
                        bool bypass_limits, bool test_accept, CAmount* fee_out)
{
    const CChainParams& chainparams = Params();
    return AcceptToMemoryPoolWithTime(chainparams, pool, state, tx, GetTime(), plTxnReplaced, bypass_limits, test_accept, fee_out);
}

CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMemPool* const mempool, const uint256& hash, const Consensus::Params& consensusParams, uint256& hashBlock)
{
    LOCK(cs_main);

    if (block_index) {
        CBlock block;
        if (ReadBlockFromDisk(block, block_index, consensusParams)) {
            for (const auto& tx : block.vtx) {
                if (tx->GetHash() == hash) {
                    hashBlock = block_index->GetBlockHash();
                    return tx;
                }
            }
        }
        return nullptr;
    }
    if (mempool) {
        CTransactionRef ptx = mempool->get(hash);
        if (ptx) return ptx;
    }
    if (g_txindex) {
        CTransactionRef tx;
        if (g_txindex->FindTx(hash, hashBlock, tx)) return tx;
    }
    return nullptr;
}

//////////////////////////////////////////////////////////////////////////////
//
// CBlock and CBlockIndex
//

bool CheckProofOfWork(const CBlockHeader& block, const Consensus::Params& params)
{
    /* Except for legacy blocks with full version 1, ensure that
       the chain ID is correct.  Legacy blocks are not allowed since
       the merge-mining start, which is checked in AcceptBlockHeader
       where the height is known.  */
    if (!block.IsLegacy() && params.fStrictChainId
        && block.GetChainId() != params.nAuxpowChainId)
        return error("%s : block does not have our chain ID"
                     " (got %d, expected %d, full nVersion %d)",
                     __func__, block.GetChainId(),
                     params.nAuxpowChainId, block.nVersion);

    /* If there is no auxpow, just check the block hash.  */
    if (!block.auxpow)
    {
        if (block.IsAuxpow())
            return error("%s : no auxpow on block with auxpow version",
                         __func__);

        if (!CheckProofOfWork(block.GetHash(), block.nBits, params))
            return error("%s : non-AUX proof of work failed", __func__);

        return true;
    }

    /* We have auxpow.  Check it.  */

    if (!block.IsAuxpow())
        return error("%s : auxpow on block with non-auxpow version", __func__);

    /* Temporary check:  Disallow parent blocks with auxpow version.  This is
       for compatibility with the old client.  */
    /* FIXME: Remove this check with a hardfork later on.  */
    if (block.auxpow->getParentBlock().IsAuxpow())
        return error("%s : auxpow parent block has auxpow version", __func__);

    if (!CheckProofOfWork(block.auxpow->getParentBlockHash(), block.nBits, params))
        return error("%s : AUX proof of work failed", __func__);
    if (!block.auxpow->check(block.GetHash(), block.GetChainId(), params))
        return error("%s : AUX POW is not valid", __func__);

    return true;
}

static bool WriteBlockToDisk(const CBlock& block, FlatFilePos& pos, const CMessageHeader::MessageStartChars& messageStart)
{
    // Open history file to append
    CAutoFile fileout(OpenBlockFile(pos), SER_DISK, CLIENT_VERSION);
    if (fileout.IsNull())
        return error("WriteBlockToDisk: OpenBlockFile failed");

    // Write index header
    unsigned int nSize = GetSerializeSize(block, fileout.GetVersion());
    fileout << messageStart << nSize;

    // Write block
    long fileOutPos = ftell(fileout.Get());
    if (fileOutPos < 0)
        return error("WriteBlockToDisk: ftell failed");
    pos.nPos = (unsigned int)fileOutPos;
    fileout << block;

    return true;
}

/* Generic implementation of block reading that can handle
   both a block and its header.  */

template<typename T>
static bool ReadBlockOrHeader(T& block, const FlatFilePos& pos, const Consensus::Params& consensusParams)
{
    block.SetNull();

    // Open history file to read
    CAutoFile filein(OpenBlockFile(pos, true), SER_DISK, CLIENT_VERSION);
    if (filein.IsNull())
        return error("ReadBlockFromDisk: OpenBlockFile failed for %s", pos.ToString());

    // Read block
    try {
        filein >> block;
    }
    catch (const std::exception& e) {
        return error("%s: Deserialize or I/O error - %s at %s", __func__, e.what(), pos.ToString());
    }

    // Check the header
    if (!CheckProofOfWork(block, consensusParams))
        return error("ReadBlockFromDisk: Errors in block header at %s", pos.ToString());

    // Signet only: check block solution
    if (consensusParams.signet_blocks && !CheckSignetBlockSolution(block, consensusParams)) {
        return error("ReadBlockFromDisk: Errors in block solution at %s", pos.ToString());
    }

    return true;
}

template<typename T>
static bool ReadBlockOrHeader(T& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
{
    FlatFilePos blockPos;
    {
        LOCK(cs_main);
        blockPos = pindex->GetBlockPos();
    }

    if (!ReadBlockOrHeader(block, blockPos, consensusParams))
        return false;
    if (block.GetHash() != pindex->GetBlockHash())
        return error("ReadBlockFromDisk(CBlock&, CBlockIndex*): GetHash() doesn't match index for %s at %s",
                pindex->ToString(), pindex->GetBlockPos().ToString());
    return true;
}

bool ReadBlockFromDisk(CBlock& block, const FlatFilePos& pos, const Consensus::Params& consensusParams)
{
    return ReadBlockOrHeader(block, pos, consensusParams);
}

bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
{
    return ReadBlockOrHeader(block, pindex, consensusParams);
}

bool ReadBlockHeaderFromDisk(CBlockHeader& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
{
    return ReadBlockOrHeader(block, pindex, consensusParams);
}

bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, const CMessageHeader::MessageStartChars& message_start)
{
    FlatFilePos hpos = pos;
    hpos.nPos -= 8; // Seek back 8 bytes for meta header
    CAutoFile filein(OpenBlockFile(hpos, true), SER_DISK, CLIENT_VERSION);
    if (filein.IsNull()) {
        return error("%s: OpenBlockFile failed for %s", __func__, pos.ToString());
    }

    try {
        CMessageHeader::MessageStartChars blk_start;
        unsigned int blk_size;

        filein >> blk_start >> blk_size;

        if (memcmp(blk_start, message_start, CMessageHeader::MESSAGE_START_SIZE)) {
            return error("%s: Block magic mismatch for %s: %s versus expected %s", __func__, pos.ToString(),
                    HexStr(blk_start),
                    HexStr(message_start));
        }

        if (blk_size > MAX_SIZE) {
            return error("%s: Block data is larger than maximum deserialization size for %s: %s versus %s", __func__, pos.ToString(),
                    blk_size, MAX_SIZE);
        }

        block.resize(blk_size); // Zeroing of memory is intentional here
        filein.read((char*)block.data(), blk_size);
    } catch(const std::exception& e) {
        return error("%s: Read from block file failed: %s for %s", __func__, e.what(), pos.ToString());
    }

    return true;
}

bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const CBlockIndex* pindex, const CMessageHeader::MessageStartChars& message_start)
{
    FlatFilePos block_pos;
    {
        LOCK(cs_main);
        block_pos = pindex->GetBlockPos();
    }

    return ReadRawBlockFromDisk(block, block_pos, message_start);
}

CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
{
    int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
    // Force block reward to zero when right shift is undefined.
    if (halvings >= 64)
        return 0;

    CAmount nSubsidy = 50 * COIN;
    // Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
    nSubsidy >>= halvings;
    return nSubsidy;
}

CoinsViews::CoinsViews(
    std::string ldb_name,
    size_t cache_size_bytes,
    bool in_memory,
    bool should_wipe) : m_dbview(
                            GetDataDir() / ldb_name, cache_size_bytes, in_memory, should_wipe),
                        m_catcherview(&m_dbview) {}

void CoinsViews::InitCache()
{
    m_cacheview = MakeUnique<CCoinsViewCache>(&m_catcherview);
}

CChainState::CChainState(CTxMemPool& mempool, BlockManager& blockman, uint256 from_snapshot_blockhash)
    : m_blockman(blockman),
      m_mempool(mempool),
      m_from_snapshot_blockhash(from_snapshot_blockhash) {}

void CChainState::InitCoinsDB(
    size_t cache_size_bytes,
    bool in_memory,
    bool should_wipe,
    std::string leveldb_name)
{
    if (!m_from_snapshot_blockhash.IsNull()) {
        leveldb_name += "_" + m_from_snapshot_blockhash.ToString();
    }

    m_coins_views = MakeUnique<CoinsViews>(
        leveldb_name, cache_size_bytes, in_memory, should_wipe);
}

void CChainState::InitCoinsCache(size_t cache_size_bytes)
{
    assert(m_coins_views != nullptr);
    m_coinstip_cache_size_bytes = cache_size_bytes;
    m_coins_views->InitCache();
}

// Note that though this is marked const, we may end up modifying `m_cached_finished_ibd`, which
// is a performance-related implementation detail. This function must be marked
// `const` so that `CValidationInterface` clients (which are given a `const CChainState*`)
// can call it.
//
bool CChainState::IsInitialBlockDownload() const
{
    // Optimization: pre-test latch before taking the lock.
    if (m_cached_finished_ibd.load(std::memory_order_relaxed))
        return false;

    LOCK(cs_main);
    if (m_cached_finished_ibd.load(std::memory_order_relaxed))
        return false;
    if (fImporting || fReindex)
        return true;
    if (m_chain.Tip() == nullptr)
        return true;
    if (m_chain.Tip()->nChainWork < nMinimumChainWork)
        return true;
    if (m_chain.Tip()->GetBlockTime() < (GetTime() - nMaxTipAge))
        return true;
    LogPrintf("Leaving InitialBlockDownload (latching to false)\n");
    m_cached_finished_ibd.store(true, std::memory_order_relaxed);
    return false;
}

static CBlockIndex *pindexBestForkTip = nullptr, *pindexBestForkBase = nullptr;

static void AlertNotify(const std::string& strMessage)
{
    uiInterface.NotifyAlertChanged();
#if HAVE_SYSTEM
    std::string strCmd = gArgs.GetArg("-alertnotify", "");
    if (strCmd.empty()) return;

    // Alert text should be plain ascii coming from a trusted source, but to
    // be safe we first strip anything not in safeChars, then add single quotes around
    // the whole string before passing it to the shell:
    std::string singleQuote("'");
    std::string safeStatus = SanitizeString(strMessage);
    safeStatus = singleQuote+safeStatus+singleQuote;
    boost::replace_all(strCmd, "%s", safeStatus);

    std::thread t(runCommand, strCmd);
    t.detach(); // thread runs free
#endif
}

static void CheckForkWarningConditions() EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    AssertLockHeld(cs_main);
    // Before we get past initial download, we cannot reliably alert about forks
    // (we assume we don't get stuck on a fork before finishing our initial sync)
    if (::ChainstateActive().IsInitialBlockDownload())
        return;

    // If our best fork is no longer within 72 blocks (+/- 12 hours if no one mines it)
    // of our head, drop it
    if (pindexBestForkTip && ::ChainActive().Height() - pindexBestForkTip->nHeight >= 72)
        pindexBestForkTip = nullptr;

    if (pindexBestForkTip || (pindexBestInvalid && pindexBestInvalid->nChainWork > ::ChainActive().Tip()->nChainWork + (GetBlockProof(*::ChainActive().Tip()) * 6)))
    {
        if (!GetfLargeWorkForkFound() && pindexBestForkBase)
        {
            std::string warning = std::string("'Warning: Large-work fork detected, forking after block ") +
                pindexBestForkBase->phashBlock->ToString() + std::string("'");
            AlertNotify(warning);
        }
        if (pindexBestForkTip && pindexBestForkBase)
        {
            LogPrintf("%s: Warning: Large valid fork found\n  forking the chain at height %d (%s)\n  lasting to height %d (%s).\nChain state database corruption likely.\n", __func__,
                   pindexBestForkBase->nHeight, pindexBestForkBase->phashBlock->ToString(),
                   pindexBestForkTip->nHeight, pindexBestForkTip->phashBlock->ToString());
            SetfLargeWorkForkFound(true);
        }
        else
        {
            LogPrintf("%s: Warning: Found invalid chain at least ~6 blocks longer than our best chain.\nChain state database corruption likely.\n", __func__);
            SetfLargeWorkInvalidChainFound(true);
        }
    }
    else
    {
        SetfLargeWorkForkFound(false);
        SetfLargeWorkInvalidChainFound(false);
    }
}

static void CheckForkWarningConditionsOnNewFork(CBlockIndex* pindexNewForkTip) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    AssertLockHeld(cs_main);
    // If we are on a fork that is sufficiently large, set a warning flag
    CBlockIndex* pfork = pindexNewForkTip;
    CBlockIndex* plonger = ::ChainActive().Tip();
    while (pfork && pfork != plonger)
    {
        while (plonger && plonger->nHeight > pfork->nHeight)
            plonger = plonger->pprev;
        if (pfork == plonger)
            break;
        pfork = pfork->pprev;
    }

    // We define a condition where we should warn the user about as a fork of at least 7 blocks
    // with a tip within 72 blocks (+/- 12 hours if no one mines it) of ours
    // We use 7 blocks rather arbitrarily as it represents just under 10% of sustained network
    // hash rate operating on the fork.
    // or a chain that is entirely longer than ours and invalid (note that this should be detected by both)
    // We define it this way because it allows us to only store the highest fork tip (+ base) which meets
    // the 7-block condition and from this always have the most-likely-to-cause-warning fork
    if (pfork && (!pindexBestForkTip || pindexNewForkTip->nHeight > pindexBestForkTip->nHeight) &&
            pindexNewForkTip->nChainWork - pfork->nChainWork > (GetBlockProof(*pfork) * 7) &&
            ::ChainActive().Height() - pindexNewForkTip->nHeight < 72)
    {
        pindexBestForkTip = pindexNewForkTip;
        pindexBestForkBase = pfork;
    }

    CheckForkWarningConditions();
}

// Called both upon regular invalid block discovery *and* InvalidateBlock
void static InvalidChainFound(CBlockIndex* pindexNew) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    if (!pindexBestInvalid || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
        pindexBestInvalid = pindexNew;
    if (pindexBestHeader != nullptr && pindexBestHeader->GetAncestor(pindexNew->nHeight) == pindexNew) {
        pindexBestHeader = ::ChainActive().Tip();
    }

    LogPrintf("%s: invalid block=%s  height=%d  log2_work=%f  date=%s\n", __func__,
      pindexNew->GetBlockHash().ToString(), pindexNew->nHeight,
      log(pindexNew->nChainWork.getdouble())/log(2.0), FormatISO8601DateTime(pindexNew->GetBlockTime()));
    CBlockIndex *tip = ::ChainActive().Tip();
    assert (tip);
    LogPrintf("%s:  current best=%s  height=%d  log2_work=%f  date=%s\n", __func__,
      tip->GetBlockHash().ToString(), ::ChainActive().Height(), log(tip->nChainWork.getdouble())/log(2.0),
      FormatISO8601DateTime(tip->GetBlockTime()));
    CheckForkWarningConditions();
}

// Same as InvalidChainFound, above, except not called directly from InvalidateBlock,
// which does its own setBlockIndexCandidates manageent.
void CChainState::InvalidBlockFound(CBlockIndex *pindex, const BlockValidationState &state) {
    if (state.GetResult() != BlockValidationResult::BLOCK_MUTATED) {
        pindex->nStatus |= BLOCK_FAILED_VALID;
        m_blockman.m_failed_blocks.insert(pindex);
        setDirtyBlockIndex.insert(pindex);
        setBlockIndexCandidates.erase(pindex);
        InvalidChainFound(pindex);
    }
}

void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, CTxUndo &txundo, int nHeight)
{
    // mark inputs spent
    if (!tx.IsCoinBase()) {
        txundo.vprevout.reserve(tx.vin.size());
        for (const CTxIn &txin : tx.vin) {
            txundo.vprevout.emplace_back();
            bool is_spent = inputs.SpendCoin(txin.prevout, &txundo.vprevout.back());
            assert(is_spent);
        }
    }
    // add outputs
    AddCoins(inputs, tx, nHeight);
}

void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, int nHeight)
{
    CTxUndo txundo;
    UpdateCoins(tx, inputs, txundo, nHeight);
}

bool CScriptCheck::operator()() {
    const CScript &scriptSig = ptxTo->vin[nIn].scriptSig;
    const CScriptWitness *witness = &ptxTo->vin[nIn].scriptWitness;
    return VerifyScript(scriptSig, m_tx_out.scriptPubKey, witness, nFlags, CachingTransactionSignatureChecker(ptxTo, nIn, m_tx_out.nValue, cacheStore, *txdata), &error);
}

int GetSpendHeight(const CCoinsViewCache& inputs)
{
    LOCK(cs_main);
    CBlockIndex* pindexPrev = LookupBlockIndex(inputs.GetBestBlock());
    return pindexPrev->nHeight + 1;
}


static CuckooCache::cache<uint256, SignatureCacheHasher> g_scriptExecutionCache;
static CSHA256 g_scriptExecutionCacheHasher;

void InitScriptExecutionCache() {
    // Setup the salted hasher
    uint256 nonce = GetRandHash();
    // We want the nonce to be 64 bytes long to force the hasher to process
    // this chunk, which makes later hash computations more efficient. We
    // just write our 32-byte entropy twice to fill the 64 bytes.
    g_scriptExecutionCacheHasher.Write(nonce.begin(), 32);
    g_scriptExecutionCacheHasher.Write(nonce.begin(), 32);
    // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
    // setup_bytes creates the minimum possible cache (2 elements).
    size_t nMaxCacheSize = std::min(std::max((int64_t)0, gArgs.GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
    size_t nElems = g_scriptExecutionCache.setup_bytes(nMaxCacheSize);
    LogPrintf("Using %zu MiB out of %zu/2 requested for script execution cache, able to store %zu elements\n",
            (nElems*sizeof(uint256)) >>20, (nMaxCacheSize*2)>>20, nElems);
}

/**
 * Check whether all of this transaction's input scripts succeed.
 *
 * This involves ECDSA signature checks so can be computationally intensive. This function should
 * only be called after the cheap sanity checks in CheckTxInputs passed.
 *
 * If pvChecks is not nullptr, script checks are pushed onto it instead of being performed inline. Any
 * script checks which are not necessary (eg due to script execution cache hits) are, obviously,
 * not pushed onto pvChecks/run.
 *
 * Setting cacheSigStore/cacheFullScriptStore to false will remove elements from the corresponding cache
 * which are matched. This is useful for checking blocks where we will likely never need the cache
 * entry again.
 *
 * Note that we may set state.reason to NOT_STANDARD for extra soft-fork flags in flags, block-checking
 * callers should probably reset it to CONSENSUS in such cases.
 *
 * Non-static (and re-declared) in src/test/txvalidationcache_tests.cpp
 */
bool CheckInputScripts(const CTransaction& tx, TxValidationState &state, const CCoinsViewCache &inputs, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    if (tx.IsCoinBase()) return true;

    if (pvChecks) {
        pvChecks->reserve(tx.vin.size());
    }

    // First check if script executions have been cached with the same
    // flags. Note that this assumes that the inputs provided are
    // correct (ie that the transaction hash which is in tx's prevouts
    // properly commits to the scriptPubKey in the inputs view of that
    // transaction).
    uint256 hashCacheEntry;
    CSHA256 hasher = g_scriptExecutionCacheHasher;
    hasher.Write(tx.GetWitnessHash().begin(), 32).Write((unsigned char*)&flags, sizeof(flags)).Finalize(hashCacheEntry.begin());
    AssertLockHeld(cs_main); //TODO: Remove this requirement by making CuckooCache not require external locks
    if (g_scriptExecutionCache.contains(hashCacheEntry, !cacheFullScriptStore)) {
        return true;
    }

    if (!txdata.m_spent_outputs_ready) {
        std::vector<CTxOut> spent_outputs;
        spent_outputs.reserve(tx.vin.size());

        for (const auto& txin : tx.vin) {
            const COutPoint& prevout = txin.prevout;
            const Coin& coin = inputs.AccessCoin(prevout);
            assert(!coin.IsSpent());
            spent_outputs.emplace_back(coin.out);
        }
        txdata.Init(tx, std::move(spent_outputs));
    }
    assert(txdata.m_spent_outputs.size() == tx.vin.size());

    for (unsigned int i = 0; i < tx.vin.size(); i++) {

        // We very carefully only pass in things to CScriptCheck which
        // are clearly committed to by tx' witness hash. This provides
        // a sanity check that our caching is not introducing consensus
        // failures through additional data in, eg, the coins being
        // spent being checked as a part of CScriptCheck.

        // Verify signature
        CScriptCheck check(txdata.m_spent_outputs[i], tx, i, flags, cacheSigStore, &txdata);
        if (pvChecks) {
            pvChecks->push_back(CScriptCheck());
            check.swap(pvChecks->back());
        } else if (!check()) {
            if (flags & STANDARD_NOT_MANDATORY_VERIFY_FLAGS) {
                // Check whether the failure was caused by a
                // non-mandatory script verification check, such as
                // non-standard DER encodings or non-null dummy
                // arguments; if so, ensure we return NOT_STANDARD
                // instead of CONSENSUS to avoid downstream users
                // splitting the network between upgraded and
                // non-upgraded nodes by banning CONSENSUS-failing
                // data providers.
                CScriptCheck check2(txdata.m_spent_outputs[i], tx, i,
                        flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheSigStore, &txdata);
                if (check2())
                    return state.Invalid(TxValidationResult::TX_NOT_STANDARD, strprintf("non-mandatory-script-verify-flag (%s)", ScriptErrorString(check.GetScriptError())));
            }
            // MANDATORY flag failures correspond to
            // TxValidationResult::TX_CONSENSUS. Because CONSENSUS
            // failures are the most serious case of validation
            // failures, we may need to consider using
            // RECENT_CONSENSUS_CHANGE for any script failure that
            // could be due to non-upgraded nodes which we may want to
            // support, to avoid splitting the network (but this
            // depends on the details of how net_processing handles
            // such errors).
            return state.Invalid(TxValidationResult::TX_CONSENSUS, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(check.GetScriptError())));
        }
    }

    if (cacheFullScriptStore && !pvChecks) {
        // We executed all of the provided scripts, and were told to
        // cache the result. Do so now.
        g_scriptExecutionCache.insert(hashCacheEntry);
    }

    return true;
}

static bool UndoWriteToDisk(const CBlockUndo& blockundo, FlatFilePos& pos, const uint256& hashBlock, const CMessageHeader::MessageStartChars& messageStart)
{
    // Open history file to append
    CAutoFile fileout(OpenUndoFile(pos), SER_DISK, CLIENT_VERSION);
    if (fileout.IsNull())
        return error("%s: OpenUndoFile failed", __func__);

    // Write index header
    unsigned int nSize = GetSerializeSize(blockundo, fileout.GetVersion());
    fileout << messageStart << nSize;

    // Write undo data
    long fileOutPos = ftell(fileout.Get());
    if (fileOutPos < 0)
        return error("%s: ftell failed", __func__);
    pos.nPos = (unsigned int)fileOutPos;
    fileout << blockundo;

    // calculate & write checksum
    CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
    hasher << hashBlock;
    hasher << blockundo;
    fileout << hasher.GetHash();

    return true;
}

bool UndoReadFromDisk(CBlockUndo& blockundo, const CBlockIndex* pindex)
{
    FlatFilePos pos = pindex->GetUndoPos();
    if (pos.IsNull()) {
        return error("%s: no undo data available", __func__);
    }

    // Open history file to read
    CAutoFile filein(OpenUndoFile(pos, true), SER_DISK, CLIENT_VERSION);
    if (filein.IsNull())
        return error("%s: OpenUndoFile failed", __func__);

    // Read block
    uint256 hashChecksum;
    CHashVerifier<CAutoFile> verifier(&filein); // We need a CHashVerifier as reserializing may lose data
    try {
        verifier << pindex->pprev->GetBlockHash();
        verifier >> blockundo;
        filein >> hashChecksum;
    }
    catch (const std::exception& e) {
        return error("%s: Deserialize or I/O error - %s", __func__, e.what());
    }

    // Verify checksum
    if (hashChecksum != verifier.GetHash())
        return error("%s: Checksum mismatch", __func__);

    return true;
}

/** Abort with a message */
static bool AbortNode(const std::string& strMessage, bilingual_str user_message = bilingual_str())
{
    SetMiscWarning(Untranslated(strMessage));
    LogPrintf("*** %s\n", strMessage);
    if (user_message.empty()) {
        user_message = _("A fatal internal error occurred, see debug.log for details");
    }
    AbortError(user_message);
    StartShutdown();
    return false;
}

static bool AbortNode(BlockValidationState& state, const std::string& strMessage, const bilingual_str& userMessage = bilingual_str())
{
    AbortNode(strMessage, userMessage);
    return state.Error(strMessage);
}

/**
 * Restore the UTXO in a Coin at a given COutPoint
 * @param undo The Coin to be restored.
 * @param view The coins view to which to apply the changes.
 * @param out The out point that corresponds to the tx input.
 * @return A DisconnectResult as an int
 */
int ApplyTxInUndo(Coin&& undo, CCoinsViewCache& view, const COutPoint& out)
{
    bool fClean = true;

    if (view.HaveCoin(out)) fClean = false; // overwriting transaction output

    if (undo.nHeight == 0) {
        // Missing undo metadata (height and coinbase). Older versions included this
        // information only in undo records for the last spend of a transactions'
        // outputs. This implies that it must be present for some other output of the same tx.
        const Coin& alternate = AccessByTxid(view, out.hash);
        if (!alternate.IsSpent()) {
            undo.nHeight = alternate.nHeight;
            undo.fCoinBase = alternate.fCoinBase;
        } else {
            return DISCONNECT_FAILED; // adding output for transaction without known metadata
        }
    }
    // If the coin already exists as an unspent coin in the cache, then the
    // possible_overwrite parameter to AddCoin must be set to true. We have
    // already checked whether an unspent coin exists above using HaveCoin, so
    // we don't need to guess. When fClean is false, an unspent coin already
    // existed and it is an overwrite.
    view.AddCoin(out, std::move(undo), !fClean);

    return fClean ? DISCONNECT_OK : DISCONNECT_UNCLEAN;
}

/** Undo the effects of this block (with given index) on the UTXO set represented by coins.
 *  When FAILED is returned, view is left in an indeterminate state. */
DisconnectResult CChainState::DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view, std::set<valtype>& unexpiredNames)
{
    bool fClean = true;

    CBlockUndo blockUndo;
    if (!UndoReadFromDisk(blockUndo, pindex)) {
        error("DisconnectBlock(): failure reading undo data");
        return DISCONNECT_FAILED;
    }

    if (blockUndo.vtxundo.size() + 1 != block.vtx.size()) {
        error("DisconnectBlock(): block and undo data inconsistent");
        return DISCONNECT_FAILED;
    }

    /* Undo name expirations.  We use nHeight+1 here in sync with
       the call to ExpireNames, because that's the height at which a
       possible name_update could be (thus it counts for spendability
       of the name).  This is done first to match the order
       in which names are expired when connecting blocks.  */
    if (!UnexpireNames (pindex->nHeight + 1, blockUndo, view, unexpiredNames))
      fClean = false;

    // undo transactions in reverse order
    for (int i = block.vtx.size() - 1; i >= 0; i--) {
        const CTransaction &tx = *(block.vtx[i]);
        uint256 hash = tx.GetHash();
        bool is_coinbase = tx.IsCoinBase();

        // Check that all outputs are available and match the outputs in the block itself
        // exactly.
        for (size_t o = 0; o < tx.vout.size(); o++) {
            if (!tx.vout[o].scriptPubKey.IsUnspendable()) {
                COutPoint out(hash, o);
                Coin coin;
                bool is_spent = view.SpendCoin(out, &coin);
                if (!is_spent || tx.vout[o] != coin.out || pindex->nHeight != coin.nHeight || is_coinbase != coin.fCoinBase) {
                    /* This may be due to a historic bug.  For them, some names
                       are marked immediately as unspendable.  They fail this check
                       when undoing, thus ignore them here.  */
                    CChainParams::BugType type;
                    if (!Params ().IsHistoricBug (tx.GetHash (), pindex->nHeight, type) || type != CChainParams::BUG_FULLY_IGNORE) {
                        fClean = false; // transaction output mismatch
                    }
                }
            }
        }

        // restore inputs
        if (i > 0) { // not coinbases
            CTxUndo &txundo = blockUndo.vtxundo[i-1];
            if (txundo.vprevout.size() != tx.vin.size()) {
                error("DisconnectBlock(): transaction and undo data inconsistent");
                return DISCONNECT_FAILED;
            }
            for (unsigned int j = tx.vin.size(); j-- > 0;) {
                const COutPoint &out = tx.vin[j].prevout;
                int res = ApplyTxInUndo(std::move(txundo.vprevout[j]), view, out);
                if (res == DISCONNECT_FAILED) return DISCONNECT_FAILED;
                fClean = fClean && res != DISCONNECT_UNCLEAN;
            }
            // At this point, all of txundo.vprevout should have been moved out.
        }
    }

    // undo name operations in reverse order
    std::vector<CNameTxUndo>::const_reverse_iterator nameUndoIter;
    for (nameUndoIter = blockUndo.vnameundo.rbegin ();
         nameUndoIter != blockUndo.vnameundo.rend (); ++nameUndoIter)
      nameUndoIter->apply (view);

    // move best block pointer to prevout block
    view.SetBestBlock(pindex->pprev->GetBlockHash());

    return fClean ? DISCONNECT_OK : DISCONNECT_UNCLEAN;
}

static void FlushUndoFile(int block_file, bool finalize = false)
{
    FlatFilePos undo_pos_old(block_file, vinfoBlockFile[block_file].nUndoSize);
    if (!UndoFileSeq().Flush(undo_pos_old, finalize)) {
        AbortNode("Flushing undo file to disk failed. This is likely the result of an I/O error.");
    }
}

static void FlushBlockFile(bool fFinalize = false, bool finalize_undo = false)
{
    LOCK(cs_LastBlockFile);
    FlatFilePos block_pos_old(nLastBlockFile, vinfoBlockFile[nLastBlockFile].nSize);
    if (!BlockFileSeq().Flush(block_pos_old, fFinalize)) {
        AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");
    }
    // we do not always flush the undo file, as the chain tip may be lagging behind the incoming blocks,
    // e.g. during IBD or a sync after a node going offline
    if (!fFinalize || finalize_undo) FlushUndoFile(nLastBlockFile, finalize_undo);
}

static bool FindUndoPos(BlockValidationState &state, int nFile, FlatFilePos &pos, unsigned int nAddSize);

static bool WriteUndoDataForBlock(const CBlockUndo& blockundo, BlockValidationState& state, CBlockIndex* pindex, const CChainParams& chainparams)
{
    // Write undo information to disk
    if (pindex->GetUndoPos().IsNull()) {
        FlatFilePos _pos;
        if (!FindUndoPos(state, pindex->nFile, _pos, ::GetSerializeSize(blockundo, CLIENT_VERSION) + 40))
            return error("ConnectBlock(): FindUndoPos failed");
        if (!UndoWriteToDisk(blockundo, _pos, pindex->pprev->GetBlockHash(), chainparams.MessageStart()))
            return AbortNode(state, "Failed to write undo data");
        // rev files are written in block height order, whereas blk files are written as blocks come in (often out of order)
        // we want to flush the rev (undo) file once we've written the last block, which is indicated by the last height
        // in the block file info as below; note that this does not catch the case where the undo writes are keeping up
        // with the block writes (usually when a synced up node is getting newly mined blocks) -- this case is caught in
        // the FindBlockPos function
        if (_pos.nFile < nLastBlockFile && static_cast<uint32_t>(pindex->nHeight) == vinfoBlockFile[_pos.nFile].nHeightLast) {
            FlushUndoFile(_pos.nFile, true);
        }

        // update nUndoPos in block index
        pindex->nUndoPos = _pos.nPos;
        pindex->nStatus |= BLOCK_HAVE_UNDO;
        setDirtyBlockIndex.insert(pindex);
    }

    return true;
}

static CCheckQueue<CScriptCheck> scriptcheckqueue(128);

void ThreadScriptCheck(int worker_num) {
    util::ThreadRename(strprintf("scriptch.%i", worker_num));
    scriptcheckqueue.Thread();
}

VersionBitsCache versionbitscache GUARDED_BY(cs_main);

int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params)
{
    LOCK(cs_main);
    int32_t nVersion = VERSIONBITS_TOP_BITS;

    for (int i = 0; i < (int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; i++) {
        ThresholdState state = VersionBitsState(pindexPrev, params, static_cast<Consensus::DeploymentPos>(i), versionbitscache);
        if (state == ThresholdState::LOCKED_IN || state == ThresholdState::STARTED) {
            nVersion |= VersionBitsMask(params, static_cast<Consensus::DeploymentPos>(i));
        }
    }

    return nVersion;
}

/**
 * Threshold condition checker that triggers when unknown versionbits are seen on the network.
 */
class WarningBitsConditionChecker : public AbstractThresholdConditionChecker
{
private:
    int bit;

public:
    explicit WarningBitsConditionChecker(int bitIn) : bit(bitIn) {}

    int64_t BeginTime(const Consensus::Params& params) const override { return 0; }
    int64_t EndTime(const Consensus::Params& params) const override { return std::numeric_limits<int64_t>::max(); }
    int Period(const Consensus::Params& params) const override { return params.nMinerConfirmationWindow; }
    int Threshold(const Consensus::Params& params) const override { return params.nRuleChangeActivationThreshold; }

    bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const override
    {
        return pindex->nHeight >= params.MinBIP9WarningHeight &&
               ((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) &&
               ((pindex->nVersion >> bit) & 1) != 0 &&
               ((ComputeBlockVersion(pindex->pprev, params) >> bit) & 1) == 0;
    }
};

static ThresholdConditionCache warningcache[VERSIONBITS_NUM_BITS] GUARDED_BY(cs_main);

static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consensus::Params& consensusparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
    AssertLockHeld(cs_main);

    unsigned int flags = SCRIPT_VERIFY_NONE;

    if (pindex->nHeight >= consensusparams.BIP16Height) {
        flags |= SCRIPT_VERIFY_P2SH;
    }

    // Start enforcing the DERSIG (BIP66) rule
    if (pindex->nHeight >= consensusparams.BIP66Height) {
        flags |= SCRIPT_VERIFY_DERSIG;
    }

    // Start enforcing CHECKLOCKTIMEVERIFY (BIP65) rule
    if (pindex->nHeight >= consensusparams.BIP65Height) {
        flags |= SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY;
    }

    // Start enforcing BIP112 (CHECKSEQUENCEVERIFY)
    if (pindex->nHeight >= consensusparams.CSVHeight) {
        flags |= SCRIPT_VERIFY_CHECKSEQUENCEVERIFY;
    }

    // Start enforcing Taproot using versionbits logic.
    if (VersionBitsState(pindex->pprev, consensusparams, Consensus::DEPLOYMENT_TAPROOT, versionbitscache) == ThresholdState::ACTIVE) {
        flags |= SCRIPT_VERIFY_TAPROOT;
    }

    // Start enforcing BIP147 NULLDUMMY (activated simultaneously with segwit)
    if (IsWitnessEnabled(pindex->pprev, consensusparams)) {
        flags |= SCRIPT_VERIFY_NULLDUMMY;
        flags |= SCRIPT_VERIFY_WITNESS;
    }

    return flags;
}



static int64_t nTimeCheck = 0;
static int64_t nTimeForks = 0;
static int64_t nTimeVerify = 0;
static int64_t nTimeConnect = 0;
static int64_t nTimeIndex = 0;
static int64_t nTimeCallbacks = 0;
static int64_t nTimeTotal = 0;
static int64_t nBlocksTotal = 0;

/** Apply the effects of this block (with given index) on the UTXO set represented by coins.
 *  Validity checks that depend on the UTXO set are also done; ConnectBlock()
 *  can fail if those validity checks fail (among other reasons). */
bool CChainState::ConnectBlock(const CBlock& block, BlockValidationState& state, CBlockIndex* pindex,
                  CCoinsViewCache& view,
                  std::set<valtype>& expiredNames,
                  const CChainParams& chainparams, bool fJustCheck)
{
    AssertLockHeld(cs_main);
    assert(pindex);
    assert(*pindex->phashBlock == block.GetHash());
    int64_t nTimeStart = GetTimeMicros();

    // Check it again in case a previous version let a bad block in
    // NOTE: We don't currently (re-)invoke ContextualCheckBlock() or
    // ContextualCheckBlockHeader() here. This means that if we add a new
    // consensus rule that is enforced in one of those two functions, then we
    // may have let in a block that violates the rule prior to updating the
    // software, and we would NOT be enforcing the rule here. Fully solving
    // upgrade from one software version to the next after a consensus rule
    // change is potentially tricky and issue-specific (see RewindBlockIndex()
    // for one general approach that was used for BIP 141 deployment).
    // Also, currently the rule against blocks more than 2 hours in the future
    // is enforced in ContextualCheckBlockHeader(); we wouldn't want to
    // re-enforce that rule here (at least until we make it impossible for
    // GetAdjustedTime() to go backward).
    if (!CheckBlock(block, state, chainparams.GetConsensus(), !fJustCheck, !fJustCheck)) {
        if (state.GetResult() == BlockValidationResult::BLOCK_MUTATED) {
            // We don't write down blocks to disk if they may have been
            // corrupted, so this should be impossible unless we're having hardware
            // problems.
            return AbortNode(state, "Corrupt block found indicating potential hardware failure; shutting down");
        }
        return error("%s: Consensus::CheckBlock: %s", __func__, state.ToString());
    }

    // verify that the view's current state corresponds to the previous block
    uint256 hashPrevBlock = pindex->pprev == nullptr ? uint256() : pindex->pprev->GetBlockHash();
    assert(hashPrevBlock == view.GetBestBlock());

    nBlocksTotal++;

    // Special case for the genesis block, skipping connection of its transactions
    // (its coinbase is unspendable)
    if (block.GetHash() == chainparams.GetConsensus().hashGenesisBlock) {
        if (!fJustCheck)
            view.SetBestBlock(pindex->GetBlockHash());
        return true;
    }

    bool fScriptChecks = true;
    if (!hashAssumeValid.IsNull()) {
        // We've been configured with the hash of a block which has been externally verified to have a valid history.
        // A suitable default value is included with the software and updated from time to time.  Because validity
        //  relative to a piece of software is an objective fact these defaults can be easily reviewed.
        // This setting doesn't force the selection of any particular chain but makes validating some faster by
        //  effectively caching the result of part of the verification.
        BlockMap::const_iterator  it = m_blockman.m_block_index.find(hashAssumeValid);
        if (it != m_blockman.m_block_index.end()) {
            if (it->second->GetAncestor(pindex->nHeight) == pindex &&
                pindexBestHeader->GetAncestor(pindex->nHeight) == pindex &&
                pindexBestHeader->nChainWork >= nMinimumChainWork) {
                // This block is a member of the assumed verified chain and an ancestor of the best header.
                // Script verification is skipped when connecting blocks under the
                // assumevalid block. Assuming the assumevalid block is valid this
                // is safe because block merkle hashes are still computed and checked,
                // Of course, if an assumed valid block is invalid due to false scriptSigs
                // this optimization would allow an invalid chain to be accepted.
                // The equivalent time check discourages hash power from extorting the network via DOS attack
                //  into accepting an invalid block through telling users they must manually set assumevalid.
                //  Requiring a software change or burying the invalid block, regardless of the setting, makes
                //  it hard to hide the implication of the demand.  This also avoids having release candidates
                //  that are hardly doing any signature verification at all in testing without having to
                //  artificially set the default assumed verified block further back.
                // The test against nMinimumChainWork prevents the skipping when denied access to any chain at
                //  least as good as the expected chain.
                fScriptChecks = (GetBlockProofEquivalentTime(*pindexBestHeader, *pindex, *pindexBestHeader, chainparams.GetConsensus()) <= 60 * 60 * 24 * 7 * 2);
            }
        }
    }

    int64_t nTime1 = GetTimeMicros(); nTimeCheck += nTime1 - nTimeStart;
    LogPrint(BCLog::BENCH, "    - Sanity checks: %.2fms [%.2fs (%.2fms/blk)]\n", MILLI * (nTime1 - nTimeStart), nTimeCheck * MICRO, nTimeCheck * MILLI / nBlocksTotal);

    // Do not allow blocks that contain transactions which 'overwrite' older transactions,
    // unless those are already completely spent.
    // If such overwrites are allowed, coinbases and transactions depending upon those
    // can be duplicated to remove the ability to spend the first instance -- even after
    // being sent to another address.
    // See BIP30, CVE-2012-1909, and http://r6.ca/blog/20120206T005236Z.html for more information.
    // This logic is not necessary for memory pool transactions, as AcceptToMemoryPool
    // already refuses previously-known transaction ids entirely.
    // FIXME: Enable strict check after appropriate fork.
    bool fEnforceBIP30 = (!pindex->phashBlock) || // Enforce on CreateNewBlock invocations which don't have a hash.
                          !(true);
    assert(pindex->pprev);

    if (fEnforceBIP30) {
        for (const auto& tx : block.vtx) {
            for (size_t o = 0; o < tx->vout.size(); o++) {
                if (view.HaveCoin(COutPoint(tx->GetHash(), o))) {
                    LogPrintf("ERROR: ConnectBlock(): tried to overwrite transaction\n");
                    return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-txns-BIP30");
                }
            }
        }
    }

    // Start enforcing BIP68 (sequence locks)
    int nLockTimeFlags = 0;
    if (pindex->nHeight >= chainparams.GetConsensus().CSVHeight) {
        nLockTimeFlags |= LOCKTIME_VERIFY_SEQUENCE;
    }

    // Get the script flags for this block
    unsigned int flags = GetBlockScriptFlags(pindex, chainparams.GetConsensus());

    int64_t nTime2 = GetTimeMicros(); nTimeForks += nTime2 - nTime1;
    LogPrint(BCLog::BENCH, "    - Fork checks: %.2fms [%.2fs (%.2fms/blk)]\n", MILLI * (nTime2 - nTime1), nTimeForks * MICRO, nTimeForks * MILLI / nBlocksTotal);

    CBlockUndo blockundo;

    // Precomputed transaction data pointers must not be invalidated
    // until after `control` has run the script checks (potentially
    // in multiple threads). Preallocate the vector size so a new allocation
    // doesn't invalidate pointers into the vector, and keep txsdata in scope
    // for as long as `control`.
    CCheckQueueControl<CScriptCheck> control(fScriptChecks && g_parallel_script_checks ? &scriptcheckqueue : nullptr);
    std::vector<PrecomputedTransactionData> txsdata(block.vtx.size());

    std::vector<int> prevheights;
    CAmount nFees = 0;
    int nInputs = 0;
    int64_t nSigOpsCost = 0;
    blockundo.vtxundo.reserve(block.vtx.size() - 1);
    for (unsigned int i = 0; i < block.vtx.size(); i++)
    {
        const CTransaction &tx = *(block.vtx[i]);

        nInputs += tx.vin.size();

        if (!tx.IsCoinBase())
        {
            CAmount txfee = 0;
            TxValidationState tx_state;
            if (!Consensus::CheckTxInputs(tx, tx_state, view, pindex->nHeight, flags, txfee)) {
                // Any transaction validation failure in ConnectBlock is a block consensus failure
                state.Invalid(BlockValidationResult::BLOCK_CONSENSUS,
                            tx_state.GetRejectReason(), tx_state.GetDebugMessage());
                return error("%s: Consensus::CheckTxInputs: %s, %s", __func__, tx.GetHash().ToString(), state.ToString());
            }
            nFees += txfee;
            if (!MoneyRange(nFees)) {
                LogPrintf("ERROR: %s: accumulated fee in the block out of range.\n", __func__);
                return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-txns-accumulated-fee-outofrange");
            }

            // Check that transaction is BIP68 final
            // BIP68 lock checks (as opposed to nLockTime checks) must
            // be in ConnectBlock because they require the UTXO set
            prevheights.resize(tx.vin.size());
            for (size_t j = 0; j < tx.vin.size(); j++) {
                prevheights[j] = view.AccessCoin(tx.vin[j].prevout).nHeight;
            }

            if (!SequenceLocks(tx, nLockTimeFlags, prevheights, *pindex)) {
                LogPrintf("ERROR: %s: contains a non-BIP68-final transaction\n", __func__);
                return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-txns-nonfinal");
            }
        }

        // GetTransactionSigOpCost counts 3 types of sigops:
        // * legacy (always)
        // * p2sh (when P2SH enabled in flags and excludes coinbase)
        // * witness (when witness enabled in flags and excludes coinbase)
        nSigOpsCost += GetTransactionSigOpCost(tx, view, flags);
        if (nSigOpsCost > MAX_BLOCK_SIGOPS_COST) {
            LogPrintf("ERROR: ConnectBlock(): too many sigops\n");
            return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-blk-sigops");
        }

        if (!tx.IsCoinBase())
        {
            std::vector<CScriptCheck> vChecks;
            bool fCacheResults = fJustCheck; /* Don't cache results if we're actually connecting blocks (still consult the cache, though) */
            TxValidationState tx_state;
            if (fScriptChecks && !CheckInputScripts(tx, tx_state, view, flags, fCacheResults, fCacheResults, txsdata[i], g_parallel_script_checks ? &vChecks : nullptr)) {
                // Any transaction validation failure in ConnectBlock is a block consensus failure
                state.Invalid(BlockValidationResult::BLOCK_CONSENSUS,
                              tx_state.GetRejectReason(), tx_state.GetDebugMessage());
                return error("ConnectBlock(): CheckInputScripts on %s failed with %s",
                    tx.GetHash().ToString(), state.ToString());
            }
            control.Add(vChecks);
        }

        CTxUndo undoDummy;
        if (i > 0) {
            blockundo.vtxundo.push_back(CTxUndo());
        }
        UpdateCoins(tx, view, i == 0 ? undoDummy : blockundo.vtxundo.back(), pindex->nHeight);
        ApplyNameTransaction(tx, pindex->nHeight, view, blockundo);
    }
    int64_t nTime3 = GetTimeMicros(); nTimeConnect += nTime3 - nTime2;
    LogPrint(BCLog::BENCH, "      - Connect %u transactions: %.2fms (%.3fms/tx, %.3fms/txin) [%.2fs (%.2fms/blk)]\n", (unsigned)block.vtx.size(), MILLI * (nTime3 - nTime2), MILLI * (nTime3 - nTime2) / block.vtx.size(), nInputs <= 1 ? 0 : MILLI * (nTime3 - nTime2) / (nInputs-1), nTimeConnect * MICRO, nTimeConnect * MILLI / nBlocksTotal);

    CAmount blockReward = nFees + GetBlockSubsidy(pindex->nHeight, chainparams.GetConsensus());
    if (block.vtx[0]->GetValueOut() > blockReward) {
        LogPrintf("ERROR: ConnectBlock(): coinbase pays too much (actual=%d vs limit=%d)\n", block.vtx[0]->GetValueOut(), blockReward);
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-cb-amount");
    }

    if (!control.Wait()) {
        LogPrintf("ERROR: %s: CheckQueue failed\n", __func__);
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "block-validation-failed");
    }
    int64_t nTime4 = GetTimeMicros(); nTimeVerify += nTime4 - nTime2;
    LogPrint(BCLog::BENCH, "    - Verify %u txins: %.2fms (%.3fms/txin) [%.2fs (%.2fms/blk)]\n", nInputs - 1, MILLI * (nTime4 - nTime2), nInputs <= 1 ? 0 : MILLI * (nTime4 - nTime2) / (nInputs-1), nTimeVerify * MICRO, nTimeVerify * MILLI / nBlocksTotal);

    if (fJustCheck)
        return true;

    /* Remove expired names from the UTXO set.  They become permanently
       unspendable.  Note that we use nHeight+1 here because a possible
       spending transaction would be at least at that height.  This has
       to be done after checking the transactions themselves, because
       spending a name would still be valid in the current block.  */
    if (!ExpireNames(pindex->nHeight + 1, view, blockundo, expiredNames))
        return error("%s : ExpireNames failed", __func__);

    if (!WriteUndoDataForBlock(blockundo, state, pindex, chainparams))
        return false;

    if (!pindex->IsValid(BLOCK_VALID_SCRIPTS)) {
        pindex->RaiseValidity(BLOCK_VALID_SCRIPTS);
        setDirtyBlockIndex.insert(pindex);
    }

    assert(pindex->phashBlock);
    // add this block to the view's block chain
    view.SetBestBlock(pindex->GetBlockHash());

    int64_t nTime5 = GetTimeMicros(); nTimeIndex += nTime5 - nTime4;
    LogPrint(BCLog::BENCH, "    - Index writing: %.2fms [%.2fs (%.2fms/blk)]\n", MILLI * (nTime5 - nTime4), nTimeIndex * MICRO, nTimeIndex * MILLI / nBlocksTotal);

    int64_t nTime6 = GetTimeMicros(); nTimeCallbacks += nTime6 - nTime5;
    LogPrint(BCLog::BENCH, "    - Callbacks: %.2fms [%.2fs (%.2fms/blk)]\n", MILLI * (nTime6 - nTime5), nTimeCallbacks * MICRO, nTimeCallbacks * MILLI / nBlocksTotal);

    return true;
}

CoinsCacheSizeState CChainState::GetCoinsCacheSizeState(const CTxMemPool* tx_pool)
{
    return this->GetCoinsCacheSizeState(
        tx_pool,
        m_coinstip_cache_size_bytes,
        gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000);
}

CoinsCacheSizeState CChainState::GetCoinsCacheSizeState(
    const CTxMemPool* tx_pool,
    size_t max_coins_cache_size_bytes,
    size_t max_mempool_size_bytes)
{
    const int64_t nMempoolUsage = tx_pool ? tx_pool->DynamicMemoryUsage() : 0;
    int64_t cacheSize = CoinsTip().DynamicMemoryUsage();
    int64_t nTotalSpace =
        max_coins_cache_size_bytes + std::max<int64_t>(max_mempool_size_bytes - nMempoolUsage, 0);

    //! No need to periodic flush if at least this much space still available.
    static constexpr int64_t MAX_BLOCK_COINSDB_USAGE_BYTES = 10 * 1024 * 1024;  // 10MB
    int64_t large_threshold =
        std::max((9 * nTotalSpace) / 10, nTotalSpace - MAX_BLOCK_COINSDB_USAGE_BYTES);

    if (cacheSize > nTotalSpace) {
        LogPrintf("Cache size (%s) exceeds total space (%s)\n", cacheSize, nTotalSpace);
        return CoinsCacheSizeState::CRITICAL;
    } else if (cacheSize > large_threshold) {
        return CoinsCacheSizeState::LARGE;
    }
    return CoinsCacheSizeState::OK;
}

bool CChainState::FlushStateToDisk(
    const CChainParams& chainparams,
    BlockValidationState &state,
    FlushStateMode mode,
    int nManualPruneHeight)
{
    LOCK(cs_main);
    assert(this->CanFlushToDisk());
    static std::chrono::microseconds nLastWrite{0};
    static std::chrono::microseconds nLastFlush{0};
    std::set<int> setFilesToPrune;
    bool full_flush_completed = false;

    const size_t coins_count = CoinsTip().GetCacheSize();
    const size_t coins_mem_usage = CoinsTip().DynamicMemoryUsage();

    try {
    {
        bool fFlushForPrune = false;
        bool fDoFullFlush = false;
        CoinsCacheSizeState cache_state = GetCoinsCacheSizeState(&m_mempool);
        LOCK(cs_LastBlockFile);
        if (fPruneMode && (fCheckForPruning || nManualPruneHeight > 0) && !fReindex) {
            if (nManualPruneHeight > 0) {
                LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune (manual)", BCLog::BENCH);

                m_blockman.FindFilesToPruneManual(setFilesToPrune, nManualPruneHeight, m_chain.Height());
            } else {
                LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune", BCLog::BENCH);

                m_blockman.FindFilesToPrune(setFilesToPrune, chainparams.PruneAfterHeight(), m_chain.Height(), IsInitialBlockDownload());
                fCheckForPruning = false;
            }
            if (!setFilesToPrune.empty()) {
                fFlushForPrune = true;
                if (!fHavePruned) {
                    pblocktree->WriteFlag("prunedblockfiles", true);
                    fHavePruned = true;
                }
            }
        }
        const auto nNow = GetTime<std::chrono::microseconds>();
        // Avoid writing/flushing immediately after startup.
        if (nLastWrite.count() == 0) {
            nLastWrite = nNow;
        }
        if (nLastFlush.count() == 0) {
            nLastFlush = nNow;
        }
        // The cache is large and we're within 10% and 10 MiB of the limit, but we have time now (not in the middle of a block processing).
        bool fCacheLarge = mode == FlushStateMode::PERIODIC && cache_state >= CoinsCacheSizeState::LARGE;
        // The cache is over the limit, we have to write now.
        bool fCacheCritical = mode == FlushStateMode::IF_NEEDED && cache_state >= CoinsCacheSizeState::CRITICAL;
        // It's been a while since we wrote the block index to disk. Do this frequently, so we don't need to redownload after a crash.
        bool fPeriodicWrite = mode == FlushStateMode::PERIODIC && nNow > nLastWrite + DATABASE_WRITE_INTERVAL;
        // It's been very long since we flushed the cache. Do this infrequently, to optimize cache usage.
        bool fPeriodicFlush = mode == FlushStateMode::PERIODIC && nNow > nLastFlush + DATABASE_FLUSH_INTERVAL;
        // Combine all conditions that result in a full cache flush.
        fDoFullFlush = (mode == FlushStateMode::ALWAYS) || fCacheLarge || fCacheCritical || fPeriodicFlush || fFlushForPrune;
        // Write blocks and block index to disk.
        if (fDoFullFlush || fPeriodicWrite) {
            // Depend on nMinDiskSpace to ensure we can write block index
            if (!CheckDiskSpace(GetBlocksDir())) {
                return AbortNode(state, "Disk space is too low!", _("Disk space is too low!"));
            }
            {
                LOG_TIME_MILLIS_WITH_CATEGORY("write block and undo data to disk", BCLog::BENCH);

                // First make sure all block and undo data is flushed to disk.
                FlushBlockFile();
            }

            // Then update all block file information (which may refer to block and undo files).
            {
                LOG_TIME_MILLIS_WITH_CATEGORY("write block index to disk", BCLog::BENCH);

                std::vector<std::pair<int, const CBlockFileInfo*> > vFiles;
                vFiles.reserve(setDirtyFileInfo.size());
                for (std::set<int>::iterator it = setDirtyFileInfo.begin(); it != setDirtyFileInfo.end(); ) {
                    vFiles.push_back(std::make_pair(*it, &vinfoBlockFile[*it]));
                    setDirtyFileInfo.erase(it++);
                }
                std::vector<const CBlockIndex*> vBlocks;
                vBlocks.reserve(setDirtyBlockIndex.size());
                for (std::set<CBlockIndex*>::iterator it = setDirtyBlockIndex.begin(); it != setDirtyBlockIndex.end(); ) {
                    vBlocks.push_back(*it);
                    setDirtyBlockIndex.erase(it++);
                }
                if (!pblocktree->WriteBatchSync(vFiles, nLastBlockFile, vBlocks)) {
                    return AbortNode(state, "Failed to write to block index database");
                }
            }
            // Finally remove any pruned files
            if (fFlushForPrune) {
                LOG_TIME_MILLIS_WITH_CATEGORY("unlink pruned files", BCLog::BENCH);

                UnlinkPrunedFiles(setFilesToPrune);
            }
            nLastWrite = nNow;
        }
        // Flush best chain related state. This can only be done if the blocks / block index write was also done.
        if (fDoFullFlush && !CoinsTip().GetBestBlock().IsNull()) {
            LOG_TIME_SECONDS(strprintf("write coins cache to disk (%d coins, %.2fkB)",
                coins_count, coins_mem_usage / 1000));

            // Typical Coin structures on disk are around 48 bytes in size.
            // Pushing a new one to the database can cause it to be written
            // twice (once in the log, and once in the tables). This is already
            // an overestimation, as most will delete an existing entry or
            // overwrite one. Still, use a conservative safety factor of 2.
            if (!CheckDiskSpace(GetDataDir(), 48 * 2 * 2 * CoinsTip().GetCacheSize())) {
                return AbortNode(state, "Disk space is too low!", _("Disk space is too low!"));
            }
            // Flush the chainstate (which may refer to block index entries).
            if (!CoinsTip().Flush())
                return AbortNode(state, "Failed to write to coin database");
            nLastFlush = nNow;
            full_flush_completed = true;
        }
    }
    if (full_flush_completed) {
        // Update best block in wallet (so we can detect restored wallets).
        GetMainSignals().ChainStateFlushed(m_chain.GetLocator());
    }
    } catch (const std::runtime_error& e) {
        return AbortNode(state, std::string("System error while flushing: ") + e.what());
    }
    return true;
}

void CChainState::ForceFlushStateToDisk() {
    BlockValidationState state;
    const CChainParams& chainparams = Params();
    if (!this->FlushStateToDisk(chainparams, state, FlushStateMode::ALWAYS)) {
        LogPrintf("%s: failed to flush state (%s)\n", __func__, state.ToString());
    }
}

void CChainState::PruneAndFlush() {
    BlockValidationState state;
    fCheckForPruning = true;
    const CChainParams& chainparams = Params();

    if (!this->FlushStateToDisk(chainparams, state, FlushStateMode::NONE)) {
        LogPrintf("%s: failed to flush state (%s)\n", __func__, state.ToString());
    }
}

static void DoWarning(const bilingual_str& warning)
{
    static bool fWarned = false;
    SetMiscWarning(warning);
    if (!fWarned) {
        AlertNotify(warning.original);
        fWarned = true;
    }
}

/** Private helper function that concatenates warning messages. */
static void AppendWarning(bilingual_str& res, const bilingual_str& warn)
{
    if (!res.empty()) res += Untranslated(", ");
    res += warn;
}

/** Check warning conditions and do some notifications on new chain tip set. */
static void UpdateTip(CTxMemPool& mempool, const CBlockIndex* pindexNew, const CChainParams& chainParams)
    EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
{
    // New best block
    mempool.AddTransactionsUpdated(1);

    {
        LOCK(g_best_block_mutex);
        g_best_block = pindexNew->GetBlockHash();
        g_best_block_cv.notify_all();
    }

    bilingual_str warning_messages;
    int num_unexpected_version = 0;
    if (!::ChainstateActive().IsInitialBlockDownload())
    {
        const CBlockIndex* pindex = pindexNew;
        for (int bit = 0; bit < VERSIONBITS_NUM_BITS; bit++) {
            WarningBitsConditionChecker checker(bit);
            ThresholdState state = checker.GetStateFor(pindex, chainParams.GetConsensus(), warningcache[bit]);
            if (state == ThresholdState::ACTIVE || state == ThresholdState::LOCKED_IN) {
                const bilingual_str warning = strprintf(_("Warning: unknown new rules activated (versionbit %i)"), bit);
                if (state == ThresholdState::ACTIVE) {
                    DoWarning(warning);
                } else {
                    AppendWarning(warning_messages, warning);
                }
            }
        }
        // Check the version of the last 100 blocks to see if we need to upgrade:
        for (int i = 0; i < 100 && pindex != nullptr; i++)
        {
            int32_t nExpectedVersion = ComputeBlockVersion(pindex->pprev, chainParams.GetConsensus());
            if (pindex->GetBaseVersion() > VERSIONBITS_LAST_OLD_BLOCK_VERSION && (pindex->GetBaseVersion() & ~nExpectedVersion) != 0)
                ++num_unexpected_version;
            pindex = pindex->pprev;
        }
    }
    LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%f tx=%lu date='%s' progress=%f cache=%.1fMiB(%utxo)%s\n", __func__,
      pindexNew->GetBlockHash().ToString(), pindexNew->nHeight, pindexNew->nVersion,
      log(pindexNew->nChainWork.getdouble())/log(2.0), (unsigned long)pindexNew->nChainTx,
      FormatISO8601DateTime(pindexNew->GetBlockTime()),
      GuessVerificationProgress(chainParams.TxData(), pindexNew), ::ChainstateActive().CoinsTip().DynamicMemoryUsage() * (1.0 / (1<<20)), ::ChainstateActive().CoinsTip().GetCacheSize(),
      !warning_messages.empty() ? strprintf(" warning='%s'", warning_messages.original) : "");

    if (num_unexpected_version > 0) {
        LogPrint(BCLog::VALIDATION, "%d of last 100 blocks have unexpected version\n", num_unexpected_version);
    }
}

/** Disconnect m_chain's tip.
  * After calling, the mempool will be in an inconsistent state, with
  * transactions from disconnected blocks being added to disconnectpool.  You
  * should make the mempool consistent again by calling UpdateMempoolForReorg.
  * with cs_main held.
  *
  * If disconnectpool is nullptr, then no disconnected transactions are added to
  * disconnectpool (note that the caller is responsible for mempool consistency
  * in any case).
  */
bool CChainState::DisconnectTip(BlockValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions* disconnectpool)
{
    AssertLockHeld(cs_main);
    AssertLockHeld(m_mempool.cs);

    CBlockIndex *pindexDelete = m_chain.Tip();
    assert(pindexDelete);
    CheckNameDB (g_chainman, true);
    // Read block from disk.
    std::shared_ptr<CBlock> pblock = std::make_shared<CBlock>();
    CBlock& block = *pblock;
    if (!ReadBlockFromDisk(block, pindexDelete, chainparams.GetConsensus()))
        return error("DisconnectTip(): Failed to read block");
    // Apply the block atomically to the chain state.
    std::set<valtype> unexpiredNames;
    int64_t nStart = GetTimeMicros();
    {
        CCoinsViewCache view(&CoinsTip());
        assert(view.GetBestBlock() == pindexDelete->GetBlockHash());
        if (DisconnectBlock(block, pindexDelete, view, unexpiredNames) != DISCONNECT_OK)
            return error("DisconnectTip(): DisconnectBlock %s failed", pindexDelete->GetBlockHash().ToString());
        bool flushed = view.Flush();
        assert(flushed);
    }
    LogPrint(BCLog::BENCH, "- Disconnect block: %.2fms\n", (GetTimeMicros() - nStart) * MILLI);
    // Write the chain state to disk, if necessary.
    if (!FlushStateToDisk(chainparams, state, FlushStateMode::IF_NEEDED))
        return false;

    AssertLockHeld(cs_main);

    // Fix the memool for conflicts due to unexpired names.
    m_mempool.removeUnexpireConflicts(unexpiredNames);

    if (disconnectpool) {
        // Save transactions to re-add to mempool at end of reorg
        for (auto it = block.vtx.rbegin(); it != block.vtx.rend(); ++it) {
            disconnectpool->addTransaction(*it);
        }
        while (disconnectpool->DynamicMemoryUsage() > MAX_DISCONNECTED_TX_POOL_SIZE * 1000) {
            // Drop the earliest entry, and remove its children from the mempool.
            auto it = disconnectpool->queuedTx.get<insertion_order>().begin();
            m_mempool.removeRecursive(**it, MemPoolRemovalReason::REORG);
            disconnectpool->removeEntry(it);
        }
    }

    m_chain.SetTip(pindexDelete->pprev);

    UpdateTip(m_mempool, pindexDelete->pprev, chainparams);
    CheckNameDB (g_chainman, true);
    // Let wallets know transactions went from 1-confirmed to
    // 0-confirmed or conflicted:
    GetMainSignals().BlockDisconnected(pblock, pindexDelete);
    return true;
}

static int64_t nTimeReadFromDisk = 0;
static int64_t nTimeConnectTotal = 0;
static int64_t nTimeFlush = 0;
static int64_t nTimeChainState = 0;
static int64_t nTimePostConnect = 0;

struct PerBlockConnectTrace {
    CBlockIndex* pindex = nullptr;
    std::shared_ptr<const CBlock> pblock;
    PerBlockConnectTrace() {}
};
/**
 * Used to track blocks whose transactions were applied to the UTXO state as a
 * part of a single ActivateBestChainStep call.
 *
 * This class is single-use, once you call GetBlocksConnected() you have to throw
 * it away and make a new one.
 */
class ConnectTrace {
private:
    std::vector<PerBlockConnectTrace> blocksConnected;

public:
    explicit ConnectTrace() : blocksConnected(1) {}

    void BlockConnected(CBlockIndex* pindex, std::shared_ptr<const CBlock> pblock) {
        assert(!blocksConnected.back().pindex);
        assert(pindex);
        assert(pblock);
        blocksConnected.back().pindex = pindex;
        blocksConnected.back().pblock = std::move(pblock);
        blocksConnected.emplace_back();
    }

    std::vector<PerBlockConnectTrace>& GetBlocksConnected() {
        // We always keep one extra block at the end of our list because
        // blocks are added after all the conflicted transactions have
        // been filled in. Thus, the last entry should always be an empty
        // one waiting for the transactions from the next block. We pop
        // the last entry here to make sure the list we return is sane.
        assert(!blocksConnected.back().pindex);
        blocksConnected.pop_back();
        return blocksConnected;
    }
};

/**
 * Connect a new block to m_chain. pblock is either nullptr or a pointer to a CBlock
 * corresponding to pindexNew, to bypass loading it again from disk.
 *
 * The block is added to connectTrace if connection succeeds.
 */
bool CChainState::ConnectTip(BlockValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions &disconnectpool)
{
    AssertLockHeld(cs_main);
    AssertLockHeld(m_mempool.cs);

    assert(pindexNew->pprev == m_chain.Tip());
    CheckNameDB (g_chainman, true);
    // Read block from disk.
    int64_t nTime1 = GetTimeMicros();
    std::shared_ptr<const CBlock> pthisBlock;
    if (!pblock) {
        std::shared_ptr<CBlock> pblockNew = std::make_shared<CBlock>();
        if (!ReadBlockFromDisk(*pblockNew, pindexNew, chainparams.GetConsensus()))
            return AbortNode(state, "Failed to read block");
        pthisBlock = pblockNew;
    } else {
        pthisBlock = pblock;
    }
    const CBlock& blockConnecting = *pthisBlock;
    // Apply the block atomically to the chain state.
    std::set<valtype> expiredNames;
    int64_t nTime2 = GetTimeMicros(); nTimeReadFromDisk += nTime2 - nTime1;
    int64_t nTime3;
    LogPrint(BCLog::BENCH, "  - Load block from disk: %.2fms [%.2fs]\n", (nTime2 - nTime1) * MILLI, nTimeReadFromDisk * MICRO);
    {
        CCoinsViewCache view(&CoinsTip());
        bool rv = ConnectBlock(blockConnecting, state, pindexNew, view, expiredNames, chainparams);
        GetMainSignals().BlockChecked(blockConnecting, state);
        if (!rv) {
            if (state.IsInvalid())
                InvalidBlockFound(pindexNew, state);
            return error("%s: ConnectBlock %s failed, %s", __func__, pindexNew->GetBlockHash().ToString(), state.ToString());
        }
        nTime3 = GetTimeMicros(); nTimeConnectTotal += nTime3 - nTime2;
        assert(nBlocksTotal > 0);
        LogPrint(BCLog::BENCH, "  - Connect total: %.2fms [%.2fs (%.2fms/blk)]\n", (nTime3 - nTime2) * MILLI, nTimeConnectTotal * MICRO, nTimeConnectTotal * MILLI / nBlocksTotal);
        bool flushed = view.Flush();
        assert(flushed);
    }
    int64_t nTime4 = GetTimeMicros(); nTimeFlush += nTime4 - nTime3;
    LogPrint(BCLog::BENCH, "  - Flush: %.2fms [%.2fs (%.2fms/blk)]\n", (nTime4 - nTime3) * MILLI, nTimeFlush * MICRO, nTimeFlush * MILLI / nBlocksTotal);
    // Write the chain state to disk, if necessary.
    if (!FlushStateToDisk(chainparams, state, FlushStateMode::IF_NEEDED))
        return false;
    int64_t nTime5 = GetTimeMicros(); nTimeChainState += nTime5 - nTime4;
    LogPrint(BCLog::BENCH, "  - Writing chainstate: %.2fms [%.2fs (%.2fms/blk)]\n", (nTime5 - nTime4) * MILLI, nTimeChainState * MICRO, nTimeChainState * MILLI / nBlocksTotal);
    // Remove conflicting transactions from the mempool.;
    m_mempool.removeForBlock(blockConnecting.vtx, pindexNew->nHeight);
    m_mempool.removeExpireConflicts(expiredNames);
    disconnectpool.removeForBlock(blockConnecting.vtx);
    // Update m_chain & related variables.
    m_chain.SetTip(pindexNew);
    UpdateTip(m_mempool, pindexNew, chainparams);
    CheckNameDB (g_chainman, false);

    int64_t nTime6 = GetTimeMicros(); nTimePostConnect += nTime6 - nTime5; nTimeTotal += nTime6 - nTime1;
    LogPrint(BCLog::BENCH, "  - Connect postprocess: %.2fms [%.2fs (%.2fms/blk)]\n", (nTime6 - nTime5) * MILLI, nTimePostConnect * MICRO, nTimePostConnect * MILLI / nBlocksTotal);
    LogPrint(BCLog::BENCH, "- Connect block: %.2fms [%.2fs (%.2fms/blk)]\n", (nTime6 - nTime1) * MILLI, nTimeTotal * MICRO, nTimeTotal * MILLI / nBlocksTotal);

    connectTrace.BlockConnected(pindexNew, std::move(pthisBlock));
    return true;
}

/**
 * Return the tip of the chain with the most work in it, that isn't
 * known to be invalid (it's however far from certain to be valid).
 */
CBlockIndex* CChainState::FindMostWorkChain() {
    do {
        CBlockIndex *pindexNew = nullptr;

        // Find the best candidate header.
        {
            std::set<CBlockIndex*, CBlockIndexWorkComparator>::reverse_iterator it = setBlockIndexCandidates.rbegin();
            if (it == setBlockIndexCandidates.rend())
                return nullptr;
            pindexNew = *it;
        }

        // Check whether all blocks on the path between the currently active chain and the candidate are valid.
        // Just going until the active chain is an optimization, as we know all blocks in it are valid already.
        CBlockIndex *pindexTest = pindexNew;
        bool fInvalidAncestor = false;
        while (pindexTest && !m_chain.Contains(pindexTest)) {
            assert(pindexTest->HaveTxsDownloaded() || pindexTest->nHeight == 0);

            // Pruned nodes may have entries in setBlockIndexCandidates for
            // which block files have been deleted.  Remove those as candidates
            // for the most work chain if we come across them; we can't switch
            // to a chain unless we have all the non-active-chain parent blocks.
            bool fFailedChain = pindexTest->nStatus & BLOCK_FAILED_MASK;
            bool fMissingData = !(pindexTest->nStatus & BLOCK_HAVE_DATA);
            if (fFailedChain || fMissingData) {
                // Candidate chain is not usable (either invalid or missing data)
                if (fFailedChain && (pindexBestInvalid == nullptr || pindexNew->nChainWork > pindexBestInvalid->nChainWork))
                    pindexBestInvalid = pindexNew;
                CBlockIndex *pindexFailed = pindexNew;
                // Remove the entire chain from the set.
                while (pindexTest != pindexFailed) {
                    if (fFailedChain) {
                        pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
                    } else if (fMissingData) {
                        // If we're missing data, then add back to m_blocks_unlinked,
                        // so that if the block arrives in the future we can try adding
                        // to setBlockIndexCandidates again.
                        m_blockman.m_blocks_unlinked.insert(
                            std::make_pair(pindexFailed->pprev, pindexFailed));
                    }
                    setBlockIndexCandidates.erase(pindexFailed);
                    pindexFailed = pindexFailed->pprev;
                }
                setBlockIndexCandidates.erase(pindexTest);
                fInvalidAncestor = true;
                break;
            }
            pindexTest = pindexTest->pprev;
        }
        if (!fInvalidAncestor)
            return pindexNew;
    } while(true);
}

/** Delete all entries in setBlockIndexCandidates that are worse than the current tip. */
void CChainState::PruneBlockIndexCandidates() {
    // Note that we can't delete the current block itself, as we may need to return to it later in case a
    // reorganization to a better block fails.
    std::set<CBlockIndex*, CBlockIndexWorkComparator>::iterator it = setBlockIndexCandidates.begin();
    while (it != setBlockIndexCandidates.end() && setBlockIndexCandidates.value_comp()(*it, m_chain.Tip())) {
        setBlockIndexCandidates.erase(it++);
    }
    // Either the current tip or a successor of it we're working towards is left in setBlockIndexCandidates.
    assert(!setBlockIndexCandidates.empty());
}

/**
 * Try to make some progress towards making pindexMostWork the active block.
 * pblock is either nullptr or a pointer to a CBlock corresponding to pindexMostWork.
 *
 * @returns true unless a system error occurred
 */
bool CChainState::ActivateBestChainStep(BlockValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace)
{
    AssertLockHeld(cs_main);
    AssertLockHeld(m_mempool.cs);

    const CBlockIndex *pindexOldTip = m_chain.Tip();
    const CBlockIndex *pindexFork = m_chain.FindFork(pindexMostWork);

    // Disconnect active blocks which are no longer in the best chain.
    bool fBlocksDisconnected = false;
    DisconnectedBlockTransactions disconnectpool;
    while (m_chain.Tip() && m_chain.Tip() != pindexFork) {
        if (!DisconnectTip(state, chainparams, &disconnectpool)) {
            // This is likely a fatal error, but keep the mempool consistent,
            // just in case. Only remove from the mempool in this case.
            UpdateMempoolForReorg(m_mempool, disconnectpool, false);

            // If we're unable to disconnect a block during normal operation,
            // then that is a failure of our local system -- we should abort
            // rather than stay on a less work chain.
            AbortNode(state, "Failed to disconnect block; see debug.log for details");
            return false;
        }
        fBlocksDisconnected = true;
    }

    // Build list of new blocks to connect.
    std::vector<CBlockIndex*> vpindexToConnect;
    bool fContinue = true;
    int nHeight = pindexFork ? pindexFork->nHeight : -1;
    while (fContinue && nHeight != pindexMostWork->nHeight) {
        // Don't iterate the entire list of potential improvements toward the best tip, as we likely only need
        // a few blocks along the way.
        int nTargetHeight = std::min(nHeight + 32, pindexMostWork->nHeight);
        vpindexToConnect.clear();
        vpindexToConnect.reserve(nTargetHeight - nHeight);
        CBlockIndex *pindexIter = pindexMostWork->GetAncestor(nTargetHeight);
        while (pindexIter && pindexIter->nHeight != nHeight) {
            vpindexToConnect.push_back(pindexIter);
            pindexIter = pindexIter->pprev;
        }
        nHeight = nTargetHeight;

        // Connect new blocks.
        for (CBlockIndex *pindexConnect : reverse_iterate(vpindexToConnect)) {
            if (!ConnectTip(state, chainparams, pindexConnect, pindexConnect == pindexMostWork ? pblock : std::shared_ptr<const CBlock>(), connectTrace, disconnectpool)) {
                if (state.IsInvalid()) {
                    // The block violates a consensus rule.
                    if (state.GetResult() != BlockValidationResult::BLOCK_MUTATED) {
                        InvalidChainFound(vpindexToConnect.front());
                    }
                    state = BlockValidationState();
                    fInvalidFound = true;
                    fContinue = false;
                    break;
                } else {
                    // A system error occurred (disk space, database error, ...).
                    // Make the mempool consistent with the current tip, just in case
                    // any observers try to use it before shutdown.
                    UpdateMempoolForReorg(m_mempool, disconnectpool, false);
                    return false;
                }
            } else {
                PruneBlockIndexCandidates();
                if (!pindexOldTip || m_chain.Tip()->nChainWork > pindexOldTip->nChainWork) {
                    // We're in a better position than we were. Return temporarily to release the lock.
                    fContinue = false;
                    break;
                }
            }
        }
    }

    if (fBlocksDisconnected) {
        // If any blocks were disconnected, disconnectpool may be non empty.  Add
        // any disconnected transactions back to the mempool.
        UpdateMempoolForReorg(m_mempool, disconnectpool, true);
    }
    m_mempool.check(g_chainman, &CoinsTip());

    // Callbacks/notifications for a new best chain.
    if (fInvalidFound)
        CheckForkWarningConditionsOnNewFork(vpindexToConnect.back());
    else
        CheckForkWarningConditions();

    return true;
}

static SynchronizationState GetSynchronizationState(bool init)
{
    if (!init) return SynchronizationState::POST_INIT;
    if (::fReindex) return SynchronizationState::INIT_REINDEX;
    return SynchronizationState::INIT_DOWNLOAD;
}

static bool NotifyHeaderTip() LOCKS_EXCLUDED(cs_main) {
    bool fNotify = false;
    bool fInitialBlockDownload = false;
    static CBlockIndex* pindexHeaderOld = nullptr;
    CBlockIndex* pindexHeader = nullptr;
    {
        LOCK(cs_main);
        pindexHeader = pindexBestHeader;

        if (pindexHeader != pindexHeaderOld) {
            fNotify = true;
            fInitialBlockDownload = ::ChainstateActive().IsInitialBlockDownload();
            pindexHeaderOld = pindexHeader;
        }
    }
    // Send block tip changed notifications without cs_main
    if (fNotify) {
        uiInterface.NotifyHeaderTip(GetSynchronizationState(fInitialBlockDownload), pindexHeader);
    }
    return fNotify;
}

static void LimitValidationInterfaceQueue() LOCKS_EXCLUDED(cs_main) {
    AssertLockNotHeld(cs_main);

    if (GetMainSignals().CallbacksPending() > 10) {
        SyncWithValidationInterfaceQueue();
    }
}

bool CChainState::ActivateBestChain(BlockValidationState &state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock) {
    // Note that while we're often called here from ProcessNewBlock, this is
    // far from a guarantee. Things in the P2P/RPC will often end up calling
    // us in the middle of ProcessNewBlock - do not assume pblock is set
    // sanely for performance or correctness!
    AssertLockNotHeld(cs_main);

    // ABC maintains a fair degree of expensive-to-calculate internal state
    // because this function periodically releases cs_main so that it does not lock up other threads for too long
    // during large connects - and to allow for e.g. the callback queue to drain
    // we use m_cs_chainstate to enforce mutual exclusion so that only one caller may execute this function at a time
    LOCK(m_cs_chainstate);

    CBlockIndex *pindexMostWork = nullptr;
    CBlockIndex *pindexNewTip = nullptr;
    int nStopAtHeight = gArgs.GetArg("-stopatheight", DEFAULT_STOPATHEIGHT);
    do {
        // Block until the validation queue drains. This should largely
        // never happen in normal operation, however may happen during
        // reindex, causing memory blowup if we run too far ahead.
        // Note that if a validationinterface callback ends up calling
        // ActivateBestChain this may lead to a deadlock! We should
        // probably have a DEBUG_LOCKORDER test for this in the future.
        LimitValidationInterfaceQueue();

        {
            LOCK(cs_main);
            LOCK(m_mempool.cs); // Lock transaction pool for at least as long as it takes for connectTrace to be consumed
            CBlockIndex* starting_tip = m_chain.Tip();
            bool blocks_connected = false;
            do {
                // We absolutely may not unlock cs_main until we've made forward progress
                // (with the exception of shutdown due to hardware issues, low disk space, etc).
                ConnectTrace connectTrace; // Destructed before cs_main is unlocked

                if (pindexMostWork == nullptr) {
                    pindexMostWork = FindMostWorkChain();
                }

                // Whether we have anything to do at all.
                if (pindexMostWork == nullptr || pindexMostWork == m_chain.Tip()) {
                    break;
                }

                bool fInvalidFound = false;
                std::shared_ptr<const CBlock> nullBlockPtr;
                if (!ActivateBestChainStep(state, chainparams, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : nullBlockPtr, fInvalidFound, connectTrace)) {
                    // A system error occurred
                    return false;
                }
                blocks_connected = true;

                if (fInvalidFound) {
                    // Wipe cache, we may need another branch now.
                    pindexMostWork = nullptr;
                }
                pindexNewTip = m_chain.Tip();

                for (const PerBlockConnectTrace& trace : connectTrace.GetBlocksConnected()) {
                    assert(trace.pblock && trace.pindex);
                    GetMainSignals().BlockConnected(trace.pblock, trace.pindex);
                }
            } while (!m_chain.Tip() || (starting_tip && CBlockIndexWorkComparator()(m_chain.Tip(), starting_tip)));
            if (!blocks_connected) return true;

            const CBlockIndex* pindexFork = m_chain.FindFork(starting_tip);
            bool fInitialDownload = IsInitialBlockDownload();

            // Notify external listeners about the new tip.
            // Enqueue while holding cs_main to ensure that UpdatedBlockTip is called in the order in which blocks are connected
            if (pindexFork != pindexNewTip) {
                // Notify ValidationInterface subscribers
                GetMainSignals().UpdatedBlockTip(pindexNewTip, pindexFork, fInitialDownload);

                // Always notify the UI if a new block tip was connected
                uiInterface.NotifyBlockTip(GetSynchronizationState(fInitialDownload), pindexNewTip);
            }
        }
        // When we reach this point, we switched to a new tip (stored in pindexNewTip).

        if (nStopAtHeight && pindexNewTip && pindexNewTip->nHeight >= nStopAtHeight) StartShutdown();

        // We check shutdown only after giving ActivateBestChainStep a chance to run once so that we
        // never shutdown before connecting the genesis block during LoadChainTip(). Previously this
        // caused an assert() failure during shutdown in such cases as the UTXO DB flushing checks
        // that the best block hash is non-null.
        if (ShutdownRequested()) break;
    } while (pindexNewTip != pindexMostWork);
    CheckBlockIndex(chainparams.GetConsensus());

    // Write changes periodically to disk, after relay.
    if (!FlushStateToDisk(chainparams, state, FlushStateMode::PERIODIC)) {
        return false;
    }

    return true;
}

bool ActivateBestChain(BlockValidationState &state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock) {
    return ::ChainstateActive().ActivateBestChain(state, chainparams, std::move(pblock));
}

bool CChainState::PreciousBlock(BlockValidationState& state, const CChainParams& params, CBlockIndex *pindex)
{
    {
        LOCK(cs_main);
        if (pindex->nChainWork < m_chain.Tip()->nChainWork) {
            // Nothing to do, this block is not at the tip.
            return true;
        }
        if (m_chain.Tip()->nChainWork > nLastPreciousChainwork) {
            // The chain has been extended since the last call, reset the counter.
            nBlockReverseSequenceId = -1;
        }
        nLastPreciousChainwork = m_chain.Tip()->nChainWork;
        setBlockIndexCandidates.erase(pindex);
        pindex->nSequenceId = nBlockReverseSequenceId;
        if (nBlockReverseSequenceId > std::numeric_limits<int32_t>::min()) {
            // We can't keep reducing the counter if somebody really wants to
            // call preciousblock 2**31-1 times on the same set of tips...
            nBlockReverseSequenceId--;
        }
        if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) && pindex->HaveTxsDownloaded()) {
            setBlockIndexCandidates.insert(pindex);
            PruneBlockIndexCandidates();
        }
    }

    return ActivateBestChain(state, params, std::shared_ptr<const CBlock>());
}
bool PreciousBlock(BlockValidationState& state, const CChainParams& params, CBlockIndex *pindex) {
    return ::ChainstateActive().PreciousBlock(state, params, pindex);
}

bool CChainState::InvalidateBlock(BlockValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex)
{
    CBlockIndex* to_mark_failed = pindex;
    bool pindex_was_in_chain = false;
    int disconnected = 0;

    // We do not allow ActivateBestChain() to run while InvalidateBlock() is
    // running, as that could cause the tip to change while we disconnect
    // blocks.
    LOCK(m_cs_chainstate);

    // We'll be acquiring and releasing cs_main below, to allow the validation
    // callbacks to run. However, we should keep the block index in a
    // consistent state as we disconnect blocks -- in particular we need to
    // add equal-work blocks to setBlockIndexCandidates as we disconnect.
    // To avoid walking the block index repeatedly in search of candidates,
    // build a map once so that we can look up candidate blocks by chain
    // work as we go.
    std::multimap<const arith_uint256, CBlockIndex *> candidate_blocks_by_work;

    {
        LOCK(cs_main);
        for (const auto& entry : m_blockman.m_block_index) {
            CBlockIndex *candidate = entry.second;
            // We don't need to put anything in our active chain into the
            // multimap, because those candidates will be found and considered
            // as we disconnect.
            // Instead, consider only non-active-chain blocks that have at
            // least as much work as where we expect the new tip to end up.
            if (!m_chain.Contains(candidate) &&
                    !CBlockIndexWorkComparator()(candidate, pindex->pprev) &&
                    candidate->IsValid(BLOCK_VALID_TRANSACTIONS) &&
                    candidate->HaveTxsDownloaded()) {
                candidate_blocks_by_work.insert(std::make_pair(candidate->nChainWork, candidate));
            }
        }
    }

    // Disconnect (descendants of) pindex, and mark them invalid.
    while (true) {
        if (ShutdownRequested()) break;

        // Make sure the queue of validation callbacks doesn't grow unboundedly.
        LimitValidationInterfaceQueue();

        LOCK(cs_main);
        LOCK(m_mempool.cs); // Lock for as long as disconnectpool is in scope to make sure UpdateMempoolForReorg is called after DisconnectTip without unlocking in between
        if (!m_chain.Contains(pindex)) break;
        pindex_was_in_chain = true;
        CBlockIndex *invalid_walk_tip = m_chain.Tip();

        // ActivateBestChain considers blocks already in m_chain
        // unconditionally valid already, so force disconnect away from it.
        DisconnectedBlockTransactions disconnectpool;
        bool ret = DisconnectTip(state, chainparams, &disconnectpool);
        // DisconnectTip will add transactions to disconnectpool.
        // Adjust the mempool to be consistent with the new tip, adding
        // transactions back to the mempool if disconnecting was successful,
        // and we're not doing a very deep invalidation (in which case
        // keeping the mempool up to date is probably futile anyway).
        UpdateMempoolForReorg(m_mempool, disconnectpool, /* fAddToMempool = */ (++disconnected <= 10) && ret);
        if (!ret) return false;
        assert(invalid_walk_tip->pprev == m_chain.Tip());

        // We immediately mark the disconnected blocks as invalid.
        // This prevents a case where pruned nodes may fail to invalidateblock
        // and be left unable to start as they have no tip candidates (as there
        // are no blocks that meet the "have data and are not invalid per
        // nStatus" criteria for inclusion in setBlockIndexCandidates).
        invalid_walk_tip->nStatus |= BLOCK_FAILED_VALID;
        setDirtyBlockIndex.insert(invalid_walk_tip);
        setBlockIndexCandidates.erase(invalid_walk_tip);
        setBlockIndexCandidates.insert(invalid_walk_tip->pprev);
        if (invalid_walk_tip->pprev == to_mark_failed && (to_mark_failed->nStatus & BLOCK_FAILED_VALID)) {
            // We only want to mark the last disconnected block as BLOCK_FAILED_VALID; its children
            // need to be BLOCK_FAILED_CHILD instead.
            to_mark_failed->nStatus = (to_mark_failed->nStatus ^ BLOCK_FAILED_VALID) | BLOCK_FAILED_CHILD;
            setDirtyBlockIndex.insert(to_mark_failed);
        }

        // Add any equal or more work headers to setBlockIndexCandidates
        auto candidate_it = candidate_blocks_by_work.lower_bound(invalid_walk_tip->pprev->nChainWork);
        while (candidate_it != candidate_blocks_by_work.end()) {
            if (!CBlockIndexWorkComparator()(candidate_it->second, invalid_walk_tip->pprev)) {
                setBlockIndexCandidates.insert(candidate_it->second);
                candidate_it = candidate_blocks_by_work.erase(candidate_it);
            } else {
                ++candidate_it;
            }
        }

        // Track the last disconnected block, so we can correct its BLOCK_FAILED_CHILD status in future
        // iterations, or, if it's the last one, call InvalidChainFound on it.
        to_mark_failed = invalid_walk_tip;
    }

    CheckBlockIndex(chainparams.GetConsensus());

    {
        LOCK(cs_main);
        if (m_chain.Contains(to_mark_failed)) {
            // If the to-be-marked invalid block is in the active chain, something is interfering and we can't proceed.
            return false;
        }

        // Mark pindex (or the last disconnected block) as invalid, even when it never was in the main chain
        to_mark_failed->nStatus |= BLOCK_FAILED_VALID;
        setDirtyBlockIndex.insert(to_mark_failed);
        setBlockIndexCandidates.erase(to_mark_failed);
        m_blockman.m_failed_blocks.insert(to_mark_failed);

        // If any new blocks somehow arrived while we were disconnecting
        // (above), then the pre-calculation of what should go into
        // setBlockIndexCandidates may have missed entries. This would
        // technically be an inconsistency in the block index, but if we clean
        // it up here, this should be an essentially unobservable error.
        // Loop back over all block index entries and add any missing entries
        // to setBlockIndexCandidates.
        BlockMap::iterator it = m_blockman.m_block_index.begin();
        while (it != m_blockman.m_block_index.end()) {
            if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && !setBlockIndexCandidates.value_comp()(it->second, m_chain.Tip())) {
                setBlockIndexCandidates.insert(it->second);
            }
            it++;
        }

        InvalidChainFound(to_mark_failed);
    }

    // Only notify about a new block tip if the active chain was modified.
    if (pindex_was_in_chain) {
        uiInterface.NotifyBlockTip(GetSynchronizationState(IsInitialBlockDownload()), to_mark_failed->pprev);
    }
    return true;
}

bool InvalidateBlock(BlockValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex) {
    return ::ChainstateActive().InvalidateBlock(state, chainparams, pindex);
}

void CChainState::ResetBlockFailureFlags(CBlockIndex *pindex) {
    AssertLockHeld(cs_main);

    int nHeight = pindex->nHeight;

    // Remove the invalidity flag from this block and all its descendants.
    BlockMap::iterator it = m_blockman.m_block_index.begin();
    while (it != m_blockman.m_block_index.end()) {
        if (!it->second->IsValid() && it->second->GetAncestor(nHeight) == pindex) {
            it->second->nStatus &= ~BLOCK_FAILED_MASK;
            setDirtyBlockIndex.insert(it->second);
            if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && setBlockIndexCandidates.value_comp()(m_chain.Tip(), it->second)) {
                setBlockIndexCandidates.insert(it->second);
            }
            if (it->second == pindexBestInvalid) {
                // Reset invalid block marker if it was pointing to one of those.
                pindexBestInvalid = nullptr;
            }
            m_blockman.m_failed_blocks.erase(it->second);
        }
        it++;
    }

    // Remove the invalidity flag from all ancestors too.
    while (pindex != nullptr) {
        if (pindex->nStatus & BLOCK_FAILED_MASK) {
            pindex->nStatus &= ~BLOCK_FAILED_MASK;
            setDirtyBlockIndex.insert(pindex);
            m_blockman.m_failed_blocks.erase(pindex);
        }
        pindex = pindex->pprev;
    }
}

void ResetBlockFailureFlags(CBlockIndex *pindex) {
    return ::ChainstateActive().ResetBlockFailureFlags(pindex);
}

CBlockIndex* BlockManager::AddToBlockIndex(const CBlockHeader& block)
{
    AssertLockHeld(cs_main);

    // Check for duplicate
    uint256 hash = block.GetHash();
    BlockMap::iterator it = m_block_index.find(hash);
    if (it != m_block_index.end())
        return it->second;

    // Construct new block index object
    CBlockIndex* pindexNew = new CBlockIndex(block);
    // We assign the sequence id to blocks only when the full data is available,
    // to avoid miners withholding blocks but broadcasting headers, to get a
    // competitive advantage.
    pindexNew->nSequenceId = 0;
    BlockMap::iterator mi = m_block_index.insert(std::make_pair(hash, pindexNew)).first;
    pindexNew->phashBlock = &((*mi).first);
    BlockMap::iterator miPrev = m_block_index.find(block.hashPrevBlock);
    if (miPrev != m_block_index.end())
    {
        pindexNew->pprev = (*miPrev).second;
        pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
        pindexNew->BuildSkip();
    }
    pindexNew->nTimeMax = (pindexNew->pprev ? std::max(pindexNew->pprev->nTimeMax, pindexNew->nTime) : pindexNew->nTime);
    pindexNew->nChainWork = (pindexNew->pprev ? pindexNew->pprev->nChainWork : 0) + GetBlockProof(*pindexNew);
    pindexNew->RaiseValidity(BLOCK_VALID_TREE);
    if (pindexBestHeader == nullptr || pindexBestHeader->nChainWork < pindexNew->nChainWork)
        pindexBestHeader = pindexNew;

    setDirtyBlockIndex.insert(pindexNew);

    return pindexNew;
}

/** Mark a block as having its data received and checked (up to BLOCK_VALID_TRANSACTIONS). */
void CChainState::ReceivedBlockTransactions(const CBlock& block, CBlockIndex* pindexNew, const FlatFilePos& pos, const Consensus::Params& consensusParams)
{
    pindexNew->nTx = block.vtx.size();
    pindexNew->nChainTx = 0;
    pindexNew->nFile = pos.nFile;
    pindexNew->nDataPos = pos.nPos;
    pindexNew->nUndoPos = 0;
    pindexNew->nStatus |= BLOCK_HAVE_DATA;
    if (IsWitnessEnabled(pindexNew->pprev, consensusParams)) {
        pindexNew->nStatus |= BLOCK_OPT_WITNESS;
    }
    pindexNew->RaiseValidity(BLOCK_VALID_TRANSACTIONS);
    setDirtyBlockIndex.insert(pindexNew);

    if (pindexNew->pprev == nullptr || pindexNew->pprev->HaveTxsDownloaded()) {
        // If pindexNew is the genesis block or all parents are BLOCK_VALID_TRANSACTIONS.
        std::deque<CBlockIndex*> queue;
        queue.push_back(pindexNew);

        // Recursively process any descendant blocks that now may be eligible to be connected.
        while (!queue.empty()) {
            CBlockIndex *pindex = queue.front();
            queue.pop_front();
            pindex->nChainTx = (pindex->pprev ? pindex->pprev->nChainTx : 0) + pindex->nTx;
            {
                LOCK(cs_nBlockSequenceId);
                pindex->nSequenceId = nBlockSequenceId++;
            }
            if (m_chain.Tip() == nullptr || !setBlockIndexCandidates.value_comp()(pindex, m_chain.Tip())) {
                setBlockIndexCandidates.insert(pindex);
            }
            std::pair<std::multimap<CBlockIndex*, CBlockIndex*>::iterator, std::multimap<CBlockIndex*, CBlockIndex*>::iterator> range = m_blockman.m_blocks_unlinked.equal_range(pindex);
            while (range.first != range.second) {
                std::multimap<CBlockIndex*, CBlockIndex*>::iterator it = range.first;
                queue.push_back(it->second);
                range.first++;
                m_blockman.m_blocks_unlinked.erase(it);
            }
        }
    } else {
        if (pindexNew->pprev && pindexNew->pprev->IsValid(BLOCK_VALID_TREE)) {
            m_blockman.m_blocks_unlinked.insert(std::make_pair(pindexNew->pprev, pindexNew));
        }
    }
}

static bool FindBlockPos(FlatFilePos &pos, unsigned int nAddSize, unsigned int nHeight, uint64_t nTime, bool fKnown = false)
{
    LOCK(cs_LastBlockFile);

    unsigned int nFile = fKnown ? pos.nFile : nLastBlockFile;
    if (vinfoBlockFile.size() <= nFile) {
        vinfoBlockFile.resize(nFile + 1);
    }

    bool finalize_undo = false;
    if (!fKnown) {
        while (vinfoBlockFile[nFile].nSize + nAddSize >= MAX_BLOCKFILE_SIZE) {
            // when the undo file is keeping up with the block file, we want to flush it explicitly
            // when it is lagging behind (more blocks arrive than are being connected), we let the
            // undo block write case handle it
            finalize_undo = (vinfoBlockFile[nFile].nHeightLast == (unsigned int)ChainActive().Tip()->nHeight);
            nFile++;
            if (vinfoBlockFile.size() <= nFile) {
                vinfoBlockFile.resize(nFile + 1);
            }
        }
        pos.nFile = nFile;
        pos.nPos = vinfoBlockFile[nFile].nSize;
    }

    if ((int)nFile != nLastBlockFile) {
        if (!fKnown) {
            LogPrintf("Leaving block file %i: %s\n", nLastBlockFile, vinfoBlockFile[nLastBlockFile].ToString());
        }
        FlushBlockFile(!fKnown, finalize_undo);
        nLastBlockFile = nFile;
    }

    vinfoBlockFile[nFile].AddBlock(nHeight, nTime);
    if (fKnown)
        vinfoBlockFile[nFile].nSize = std::max(pos.nPos + nAddSize, vinfoBlockFile[nFile].nSize);
    else
        vinfoBlockFile[nFile].nSize += nAddSize;

    if (!fKnown) {
        bool out_of_space;
        size_t bytes_allocated = BlockFileSeq().Allocate(pos, nAddSize, out_of_space);
        if (out_of_space) {
            return AbortNode("Disk space is too low!", _("Disk space is too low!"));
        }
        if (bytes_allocated != 0 && fPruneMode) {
            fCheckForPruning = true;
        }
    }

    setDirtyFileInfo.insert(nFile);
    return true;
}

static bool FindUndoPos(BlockValidationState &state, int nFile, FlatFilePos &pos, unsigned int nAddSize)
{
    pos.nFile = nFile;

    LOCK(cs_LastBlockFile);

    pos.nPos = vinfoBlockFile[nFile].nUndoSize;
    vinfoBlockFile[nFile].nUndoSize += nAddSize;
    setDirtyFileInfo.insert(nFile);

    bool out_of_space;
    size_t bytes_allocated = UndoFileSeq().Allocate(pos, nAddSize, out_of_space);
    if (out_of_space) {
        return AbortNode(state, "Disk space is too low!", _("Disk space is too low!"));
    }
    if (bytes_allocated != 0 && fPruneMode) {
        fCheckForPruning = true;
    }

    return true;
}

/* Temporary check that blocks are compatible with BDB's 10,000 lock limit.
   This is based on Bitcoin's commit 8c222dca4f961ad13ec64d690134a40d09b20813.
   Each "object" touched in the DB may cause two locks (one read and one
   write lock).  Objects are transaction IDs and names.  Thus, count the
   total number of transaction IDs (tx themselves plus all distinct inputs).
   In addition, each Namecoin transaction could touch at most one name,
   so add them as well.  */
bool CheckDbLockLimit(const std::vector<CTransactionRef>& vtx)
{
    std::set<uint256> setTxIds;
    unsigned nNames = 0;
    for (const auto& tx : vtx)
    {
        setTxIds.insert(tx->GetHash());
        if (tx->IsNamecoin())
            ++nNames;

        for (const auto& txIn : tx->vin)
            setTxIds.insert(txIn.prevout.hash);
    }

    const unsigned nTotalIds = setTxIds.size() + nNames;
    if (nTotalIds > 4500)
        return error("%s : %u locks estimated, that is too much for BDB",
                     __func__, nTotalIds);

    //LogPrintf ("%s : need %u locks\n", __func__, nTotalIds);
    return true;
}

static bool CheckBlockHeader(const CBlockHeader& block, BlockValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW = true)
{
    // Check proof of work matches claimed amount
    if (fCheckPOW && !CheckProofOfWork(block, consensusParams))
        return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "high-hash", "proof of work failed");

    return true;
}

bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW, bool fCheckMerkleRoot)
{
    // These are checks that are independent of context.

    if (block.fChecked)
        return true;

    // Check that the header is valid (particularly PoW).  This is mostly
    // redundant with the call in AcceptBlockHeader.
    if (!CheckBlockHeader(block, state, consensusParams, fCheckPOW))
        return false;

    // Signet only: check block solution
    if (consensusParams.signet_blocks && fCheckPOW && !CheckSignetBlockSolution(block, consensusParams)) {
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-signet-blksig", "signet block signature validation failure");
    }

    // Check the merkle root.
    if (fCheckMerkleRoot) {
        bool mutated;
        uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated);
        if (block.hashMerkleRoot != hashMerkleRoot2)
            return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txnmrklroot", "hashMerkleRoot mismatch");

        // Check for merkle tree malleability (CVE-2012-2459): repeating sequences
        // of transactions in a block without affecting the merkle root of a block,
        // while still invalidating it.
        if (mutated)
            return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txns-duplicate", "duplicate transaction");
    }

    // All potential-corruption validation must be done before we do any
    // transaction validation, as otherwise we may mark the header as invalid
    // because we receive the wrong transactions for it.
    // Note that witness malleability is checked in ContextualCheckBlock, so no
    // checks that use witness data may be performed here.

    // Size limits
    if (block.vtx.empty() || block.vtx.size() * WITNESS_SCALE_FACTOR > MAX_BLOCK_WEIGHT || ::GetSerializeSize(block, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) * WITNESS_SCALE_FACTOR > MAX_BLOCK_WEIGHT)
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-blk-length", "size limits failed");

    // Enforce the temporary DB lock limit.
    // TODO: Remove with a hardfork in the future.
    if (!CheckDbLockLimit(block.vtx))
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS,
                             "bad-db-locks",
                             "DB lock limit exceeded");

    // First transaction must be coinbase, the rest must not be
    if (block.vtx.empty() || !block.vtx[0]->IsCoinBase())
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-cb-missing", "first tx is not coinbase");
    for (unsigned int i = 1; i < block.vtx.size(); i++)
        if (block.vtx[i]->IsCoinBase())
            return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-cb-multiple", "more than one coinbase");

    // Check transactions
    // Must check for duplicate inputs (see CVE-2018-17144)
    for (const auto& tx : block.vtx) {
        TxValidationState tx_state;
        if (!CheckTransaction(*tx, tx_state)) {
            // CheckBlock() does context-free validation checks. The only
            // possible failures are consensus failures.
            assert(tx_state.GetResult() == TxValidationResult::TX_CONSENSUS);
            return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, tx_state.GetRejectReason(),
                                 strprintf("Transaction check failed (tx hash %s) %s", tx->GetHash().ToString(), tx_state.GetDebugMessage()));
        }
    }
    unsigned int nSigOps = 0;
    for (const auto& tx : block.vtx)
    {
        nSigOps += GetLegacySigOpCount(*tx);
    }
    if (nSigOps * WITNESS_SCALE_FACTOR > MAX_BLOCK_SIGOPS_COST)
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-blk-sigops", "out-of-bounds SigOpCount");

    if (fCheckPOW && fCheckMerkleRoot)
        block.fChecked = true;

    return true;
}

bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params)
{
    int height = pindexPrev == nullptr ? 0 : pindexPrev->nHeight + 1;
    return (height >= params.SegwitHeight);
}

void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams)
{
    int commitpos = GetWitnessCommitmentIndex(block);
    static const std::vector<unsigned char> nonce(32, 0x00);
    if (commitpos != NO_WITNESS_COMMITMENT && IsWitnessEnabled(pindexPrev, consensusParams) && !block.vtx[0]->HasWitness()) {
        CMutableTransaction tx(*block.vtx[0]);
        tx.vin[0].scriptWitness.stack.resize(1);
        tx.vin[0].scriptWitness.stack[0] = nonce;
        block.vtx[0] = MakeTransactionRef(std::move(tx));
    }
}

std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams)
{
    std::vector<unsigned char> commitment;
    int commitpos = GetWitnessCommitmentIndex(block);
    std::vector<unsigned char> ret(32, 0x00);
    if (consensusParams.SegwitHeight != std::numeric_limits<int>::max()) {
        if (commitpos == NO_WITNESS_COMMITMENT) {
            uint256 witnessroot = BlockWitnessMerkleRoot(block, nullptr);
            CHash256().Write(witnessroot).Write(ret).Finalize(witnessroot);
            CTxOut out;
            out.nValue = 0;
            out.scriptPubKey.resize(MINIMUM_WITNESS_COMMITMENT);
            out.scriptPubKey[0] = OP_RETURN;
            out.scriptPubKey[1] = 0x24;
            out.scriptPubKey[2] = 0xaa;
            out.scriptPubKey[3] = 0x21;
            out.scriptPubKey[4] = 0xa9;
            out.scriptPubKey[5] = 0xed;
            memcpy(&out.scriptPubKey[6], witnessroot.begin(), 32);
            commitment = std::vector<unsigned char>(out.scriptPubKey.begin(), out.scriptPubKey.end());
            CMutableTransaction tx(*block.vtx[0]);
            tx.vout.push_back(out);
            block.vtx[0] = MakeTransactionRef(std::move(tx));
        }
    }
    UpdateUncommittedBlockStructures(block, pindexPrev, consensusParams);
    return commitment;
}

//! Returns last CBlockIndex* that is a checkpoint
static CBlockIndex* GetLastCheckpoint(const CCheckpointData& data) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    const MapCheckpoints& checkpoints = data.mapCheckpoints;

    for (const MapCheckpoints::value_type& i : reverse_iterate(checkpoints))
    {
        const uint256& hash = i.second;
        CBlockIndex* pindex = LookupBlockIndex(hash);
        if (pindex) {
            return pindex;
        }
    }
    return nullptr;
}

/** Context-dependent validity checks.
 *  By "context", we mean only the previous block headers, but not the UTXO
 *  set; UTXO-related validity checks are done in ConnectBlock().
 *  NOTE: This function is not currently invoked by ConnectBlock(), so we
 *  should consider upgrade issues if we change which consensus rules are
 *  enforced in this function (eg by adding a new consensus rule). See comment
 *  in ConnectBlock().
 *  Note that -reindex-chainstate skips the validation that happens here!
 */
static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidationState& state, const CChainParams& params, const CBlockIndex* pindexPrev, int64_t nAdjustedTime) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    assert(pindexPrev != nullptr);
    const int nHeight = pindexPrev->nHeight + 1;

    // Disallow legacy blocks after merge-mining start.
    const Consensus::Params& consensusParams = params.GetConsensus();
    if (!consensusParams.AllowLegacyBlocks(nHeight) && block.IsLegacy())
        return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER,
                             "late-legacy-block",
                             "legacy block after auxpow start");

    // Check proof of work
    if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))
        return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "bad-diffbits", "incorrect proof of work");

    // Check against checkpoints
    if (fCheckpointsEnabled) {
        // Don't accept any forks from the main chain prior to last checkpoint.
        // GetLastCheckpoint finds the last checkpoint in MapCheckpoints that's in our
        // BlockIndex().
        CBlockIndex* pcheckpoint = GetLastCheckpoint(params.Checkpoints());
        if (pcheckpoint && nHeight < pcheckpoint->nHeight) {
            LogPrintf("ERROR: %s: forked chain older than last checkpoint (height %d)\n", __func__, nHeight);
            return state.Invalid(BlockValidationResult::BLOCK_CHECKPOINT, "bad-fork-prior-to-checkpoint");
        }
    }

    // Check timestamp against prev
    if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
        return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "time-too-old", "block's timestamp is too early");

    // Check timestamp
    if (block.GetBlockTime() > nAdjustedTime + MAX_FUTURE_BLOCK_TIME)
        return state.Invalid(BlockValidationResult::BLOCK_TIME_FUTURE, "time-too-new", "block timestamp too far in the future");

    // Reject outdated version blocks when 95% (75% on testnet) of the network has upgraded:
    // check for version 2, 3 and 4 upgrades
    if((block.GetBaseVersion() < 2 && nHeight >= consensusParams.BIP34Height) ||
       (block.GetBaseVersion() < 3 && nHeight >= consensusParams.BIP66Height) ||
       (block.GetBaseVersion() < 4 && nHeight >= consensusParams.BIP65Height))
            return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, strprintf("bad-version(0x%08x)", block.nVersion),
                                 strprintf("rejected nVersion=0x%08x block", block.nVersion));

    return true;
}

/** NOTE: This function is not currently invoked by ConnectBlock(), so we
 *  should consider upgrade issues if we change which consensus rules are
 *  enforced in this function (eg by adding a new consensus rule). See comment
 *  in ConnectBlock().
 *  Note that -reindex-chainstate skips the validation that happens here!
 */
static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& state, const Consensus::Params& consensusParams, const CBlockIndex* pindexPrev)
{
    const int nHeight = pindexPrev == nullptr ? 0 : pindexPrev->nHeight + 1;

    // Start enforcing BIP113 (Median Time Past).
    int nLockTimeFlags = 0;
    if (nHeight >= consensusParams.CSVHeight) {
        assert(pindexPrev != nullptr);
        nLockTimeFlags |= LOCKTIME_MEDIAN_TIME_PAST;
    }

    int64_t nLockTimeCutoff = (nLockTimeFlags & LOCKTIME_MEDIAN_TIME_PAST)
                              ? pindexPrev->GetMedianTimePast()
                              : block.GetBlockTime();

    // Check that all transactions are finalized
    for (const auto& tx : block.vtx) {
        if (!IsFinalTx(*tx, nHeight, nLockTimeCutoff)) {
            return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-txns-nonfinal", "non-final transaction");
        }
    }

    // Enforce rule that the coinbase starts with serialized block height
    if (nHeight >= consensusParams.BIP34Height)
    {
        CScript expect = CScript() << nHeight;
        if (block.vtx[0]->vin[0].scriptSig.size() < expect.size() ||
            !std::equal(expect.begin(), expect.end(), block.vtx[0]->vin[0].scriptSig.begin())) {
            return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-cb-height", "block height mismatch in coinbase");
        }
    }

    // Validation for witness commitments.
    // * We compute the witness hash (which is the hash including witnesses) of all the block's transactions, except the
    //   coinbase (where 0x0000....0000 is used instead).
    // * The coinbase scriptWitness is a stack of a single 32-byte vector, containing a witness reserved value (unconstrained).
    // * We build a merkle tree with all those witness hashes as leaves (similar to the hashMerkleRoot in the block header).
    // * There must be at least one output whose scriptPubKey is a single 36-byte push, the first 4 bytes of which are
    //   {0xaa, 0x21, 0xa9, 0xed}, and the following 32 bytes are SHA256^2(witness root, witness reserved value). In case there are
    //   multiple, the last one is used.
    bool fHaveWitness = false;
    if (nHeight >= consensusParams.SegwitHeight) {
        int commitpos = GetWitnessCommitmentIndex(block);
        if (commitpos != NO_WITNESS_COMMITMENT) {
            bool malleated = false;
            uint256 hashWitness = BlockWitnessMerkleRoot(block, &malleated);
            // The malleation check is ignored; as the transaction tree itself
            // already does not permit it, it is impossible to trigger in the
            // witness tree.
            if (block.vtx[0]->vin[0].scriptWitness.stack.size() != 1 || block.vtx[0]->vin[0].scriptWitness.stack[0].size() != 32) {
                return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-nonce-size", strprintf("%s : invalid witness reserved value size", __func__));
            }
            CHash256().Write(hashWitness).Write(block.vtx[0]->vin[0].scriptWitness.stack[0]).Finalize(hashWitness);
            if (memcmp(hashWitness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) {
                return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-merkle-match", strprintf("%s : witness merkle commitment mismatch", __func__));
            }
            fHaveWitness = true;
        }
    }

    // No witness data is allowed in blocks that don't commit to witness data, as this would otherwise leave room for spam
    if (!fHaveWitness) {
      for (const auto& tx : block.vtx) {
            if (tx->HasWitness()) {
                return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "unexpected-witness", strprintf("%s : unexpected witness data found", __func__));
            }
        }
    }

    // After the coinbase witness reserved value and commitment are verified,
    // we can check if the block weight passes (before we've checked the
    // coinbase witness, it would be possible for the weight to be too
    // large by filling up the coinbase witness, which doesn't change
    // the block hash, so we couldn't mark the block as permanently
    // failed).
    if (GetBlockWeight(block) > MAX_BLOCK_WEIGHT) {
        return state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-blk-weight", strprintf("%s : weight limit failed", __func__));
    }

    return true;
}

bool BlockManager::AcceptBlockHeader(const CBlockHeader& block, BlockValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex)
{
    AssertLockHeld(cs_main);
    // Check for duplicate
    uint256 hash = block.GetHash();
    BlockMap::iterator miSelf = m_block_index.find(hash);
    CBlockIndex *pindex = nullptr;
    if (hash != chainparams.GetConsensus().hashGenesisBlock) {
        if (miSelf != m_block_index.end()) {
            // Block header is already known.
            pindex = miSelf->second;
            if (ppindex)
                *ppindex = pindex;
            if (pindex->nStatus & BLOCK_FAILED_MASK) {
                LogPrintf("ERROR: %s: block %s is marked invalid\n", __func__, hash.ToString());
                return state.Invalid(BlockValidationResult::BLOCK_CACHED_INVALID, "duplicate");
            }
            return true;
        }

        if (!CheckBlockHeader(block, state, chainparams.GetConsensus())) {
            LogPrint(BCLog::VALIDATION, "%s: Consensus::CheckBlockHeader: %s, %s\n", __func__, hash.ToString(), state.ToString());
            return false;
        }

        // Get prev block index
        CBlockIndex* pindexPrev = nullptr;
        BlockMap::iterator mi = m_block_index.find(block.hashPrevBlock);
        if (mi == m_block_index.end()) {
            LogPrintf("ERROR: %s: prev block not found\n", __func__);
            return state.Invalid(BlockValidationResult::BLOCK_MISSING_PREV, "prev-blk-not-found");
        }
        pindexPrev = (*mi).second;
        if (pindexPrev->nStatus & BLOCK_FAILED_MASK) {
            LogPrintf("ERROR: %s: prev block invalid\n", __func__);
            return state.Invalid(BlockValidationResult::BLOCK_INVALID_PREV, "bad-prevblk");
        }
        if (!ContextualCheckBlockHeader(block, state, chainparams, pindexPrev, GetAdjustedTime()))
            return error("%s: Consensus::ContextualCheckBlockHeader: %s, %s", __func__, hash.ToString(), state.ToString());

        /* Determine if this block descends from any block which has been found
         * invalid (m_failed_blocks), then mark pindexPrev and any blocks between
         * them as failed. For example:
         *
         *                D3
         *              /
         *      B2 - C2
         *    /         \
         *  A             D2 - E2 - F2
         *    \
         *      B1 - C1 - D1 - E1
         *
         * In the case that we attempted to reorg from E1 to F2, only to find
         * C2 to be invalid, we would mark D2, E2, and F2 as BLOCK_FAILED_CHILD
         * but NOT D3 (it was not in any of our candidate sets at the time).
         *
         * In any case D3 will also be marked as BLOCK_FAILED_CHILD at restart
         * in LoadBlockIndex.
         */
        if (!pindexPrev->IsValid(BLOCK_VALID_SCRIPTS)) {
            // The above does not mean "invalid": it checks if the previous block
            // hasn't been validated up to BLOCK_VALID_SCRIPTS. This is a performance
            // optimization, in the common case of adding a new block to the tip,
            // we don't need to iterate over the failed blocks list.
            for (const CBlockIndex* failedit : m_failed_blocks) {
                if (pindexPrev->GetAncestor(failedit->nHeight) == failedit) {
                    assert(failedit->nStatus & BLOCK_FAILED_VALID);
                    CBlockIndex* invalid_walk = pindexPrev;
                    while (invalid_walk != failedit) {
                        invalid_walk->nStatus |= BLOCK_FAILED_CHILD;
                        setDirtyBlockIndex.insert(invalid_walk);
                        invalid_walk = invalid_walk->pprev;
                    }
                    LogPrintf("ERROR: %s: prev block invalid\n", __func__);
                    return state.Invalid(BlockValidationResult::BLOCK_INVALID_PREV, "bad-prevblk");
                }
            }
        }
    }
    if (pindex == nullptr)
        pindex = AddToBlockIndex(block);

    if (ppindex)
        *ppindex = pindex;

    return true;
}

// Exposed wrapper for AcceptBlockHeader
bool ChainstateManager::ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, BlockValidationState& state, const CChainParams& chainparams, const CBlockIndex** ppindex)
{
    AssertLockNotHeld(cs_main);
    {
        LOCK(cs_main);
        for (const CBlockHeader& header : headers) {
            CBlockIndex *pindex = nullptr; // Use a temp pindex instead of ppindex to avoid a const_cast
            bool accepted = m_blockman.AcceptBlockHeader(
                header, state, chainparams, &pindex);
            ::ChainstateActive().CheckBlockIndex(chainparams.GetConsensus());

            if (!accepted) {
                return false;
            }
            if (ppindex) {
                *ppindex = pindex;
            }
        }
    }
    if (NotifyHeaderTip()) {
        if (::ChainstateActive().IsInitialBlockDownload() && ppindex && *ppindex) {
            LogPrintf("Synchronizing blockheaders, height: %d (~%.2f%%)\n", (*ppindex)->nHeight, 100.0/((*ppindex)->nHeight+(GetAdjustedTime() - (*ppindex)->GetBlockTime()) / Params().GetConsensus().nPowTargetSpacing) * (*ppindex)->nHeight);
        }
    }
    return true;
}

/** Store block on disk. If dbp is non-nullptr, the file is known to already reside on disk */
static FlatFilePos SaveBlockToDisk(const CBlock& block, int nHeight, const CChainParams& chainparams, const FlatFilePos* dbp) {
    unsigned int nBlockSize = ::GetSerializeSize(block, CLIENT_VERSION);
    FlatFilePos blockPos;
    if (dbp != nullptr)
        blockPos = *dbp;
    if (!FindBlockPos(blockPos, nBlockSize+8, nHeight, block.GetBlockTime(), dbp != nullptr)) {
        error("%s: FindBlockPos failed", __func__);
        return FlatFilePos();
    }
    if (dbp == nullptr) {
        if (!WriteBlockToDisk(block, blockPos, chainparams.MessageStart())) {
            AbortNode("Failed to write block");
            return FlatFilePos();
        }
    }
    return blockPos;
}

/** Store block on disk. If dbp is non-nullptr, the file is known to already reside on disk */
bool CChainState::AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock)
{
    const CBlock& block = *pblock;

    if (fNewBlock) *fNewBlock = false;
    AssertLockHeld(cs_main);

    CBlockIndex *pindexDummy = nullptr;
    CBlockIndex *&pindex = ppindex ? *ppindex : pindexDummy;

    bool accepted_header = m_blockman.AcceptBlockHeader(block, state, chainparams, &pindex);
    CheckBlockIndex(chainparams.GetConsensus());

    if (!accepted_header)
        return false;

    // Try to process all requested blocks that we don't have, but only
    // process an unrequested block if it's new and has enough work to
    // advance our tip, and isn't too many blocks ahead.
    bool fAlreadyHave = pindex->nStatus & BLOCK_HAVE_DATA;
    bool fHasMoreOrSameWork = (m_chain.Tip() ? pindex->nChainWork >= m_chain.Tip()->nChainWork : true);
    // Blocks that are too out-of-order needlessly limit the effectiveness of
    // pruning, because pruning will not delete block files that contain any
    // blocks which are too close in height to the tip.  Apply this test
    // regardless of whether pruning is enabled; it should generally be safe to
    // not process unrequested blocks.
    bool fTooFarAhead = (pindex->nHeight > int(m_chain.Height() + MIN_BLOCKS_TO_KEEP));

    // TODO: Decouple this function from the block download logic by removing fRequested
    // This requires some new chain data structure to efficiently look up if a
    // block is in a chain leading to a candidate for best tip, despite not
    // being such a candidate itself.

    // TODO: deal better with return value and error conditions for duplicate
    // and unrequested blocks.
    if (fAlreadyHave) return true;
    if (!fRequested) {  // If we didn't ask for it:
        if (pindex->nTx != 0) return true;    // This is a previously-processed block that was pruned
        if (!fHasMoreOrSameWork) return true; // Don't process less-work chains
        if (fTooFarAhead) return true;        // Block height is too high

        // Protect against DoS attacks from low-work chains.
        // If our tip is behind, a peer could try to send us
        // low-work blocks on a fake chain that we would never
        // request; don't process these.
        if (pindex->nChainWork < nMinimumChainWork) return true;
    }

    if (!CheckBlock(block, state, chainparams.GetConsensus()) ||
        !ContextualCheckBlock(block, state, chainparams.GetConsensus(), pindex->pprev)) {
        if (state.IsInvalid() && state.GetResult() != BlockValidationResult::BLOCK_MUTATED) {
            pindex->nStatus |= BLOCK_FAILED_VALID;
            setDirtyBlockIndex.insert(pindex);
        }
        return error("%s: %s", __func__, state.ToString());
    }

    // Header is valid/has work, merkle tree and segwit merkle tree are good...RELAY NOW
    // (but if it does not build on our best tip, let the SendMessages loop relay it)
    if (!IsInitialBlockDownload() && m_chain.Tip() == pindex->pprev)
        GetMainSignals().NewPoWValidBlock(pindex, pblock);

    // Write block to history file
    if (fNewBlock) *fNewBlock = true;
    try {
        FlatFilePos blockPos = SaveBlockToDisk(block, pindex->nHeight, chainparams, dbp);
        if (blockPos.IsNull()) {
            state.Error(strprintf("%s: Failed to find position to write new block to disk", __func__));
            return false;
        }
        ReceivedBlockTransactions(block, pindex, blockPos, chainparams.GetConsensus());
    } catch (const std::runtime_error& e) {
        return AbortNode(state, std::string("System error: ") + e.what());
    }

    FlushStateToDisk(chainparams, state, FlushStateMode::NONE);

    CheckBlockIndex(chainparams.GetConsensus());

    return true;
}

bool ChainstateManager::ProcessNewBlock(const CChainParams& chainparams, const std::shared_ptr<const CBlock> pblock, bool fForceProcessing, bool* fNewBlock)
{
    AssertLockNotHeld(cs_main);

    {
        CBlockIndex *pindex = nullptr;
        if (fNewBlock) *fNewBlock = false;
        BlockValidationState state;

        // CheckBlock() does not support multi-threaded block validation because CBlock::fChecked can cause data race.
        // Therefore, the following critical section must include the CheckBlock() call as well.
        LOCK(cs_main);

        // Ensure that CheckBlock() passes before calling AcceptBlock, as
        // belt-and-suspenders.
        bool ret = CheckBlock(*pblock, state, chainparams.GetConsensus());
        if (ret) {
            // Store to disk
            ret = ::ChainstateActive().AcceptBlock(pblock, state, chainparams, &pindex, fForceProcessing, nullptr, fNewBlock);
        }
        if (!ret) {
            GetMainSignals().BlockChecked(*pblock, state);
            return error("%s: AcceptBlock FAILED (%s)", __func__, state.ToString());
        }
    }

    NotifyHeaderTip();

    BlockValidationState state; // Only used to report errors, not invalidity - ignore it
    if (!::ChainstateActive().ActivateBestChain(state, chainparams, pblock))
        return error("%s: ActivateBestChain failed (%s)", __func__, state.ToString());

    return true;
}

bool TestBlockValidity(BlockValidationState& state, const CChainParams& chainparams, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW, bool fCheckMerkleRoot)
{
    AssertLockHeld(cs_main);
    assert(pindexPrev && pindexPrev == ::ChainActive().Tip());
    std::set<valtype> namesDummy;
    CCoinsViewCache viewNew(&::ChainstateActive().CoinsTip());
    uint256 block_hash(block.GetHash());
    CBlockIndex indexDummy(block);
    indexDummy.pprev = pindexPrev;
    indexDummy.nHeight = pindexPrev->nHeight + 1;
    indexDummy.phashBlock = &block_hash;

    // NOTE: CheckBlockHeader is called by CheckBlock
    if (!ContextualCheckBlockHeader(block, state, chainparams, pindexPrev, GetAdjustedTime()))
        return error("%s: Consensus::ContextualCheckBlockHeader: %s", __func__, state.ToString());
    if (!CheckBlock(block, state, chainparams.GetConsensus(), fCheckPOW, fCheckMerkleRoot))
        return error("%s: Consensus::CheckBlock: %s", __func__, state.ToString());
    if (!ContextualCheckBlock(block, state, chainparams.GetConsensus(), pindexPrev))
        return error("%s: Consensus::ContextualCheckBlock: %s", __func__, state.ToString());
    if (!::ChainstateActive().ConnectBlock(block, state, &indexDummy, viewNew, namesDummy, chainparams, true))
        return false;
    assert(state.IsValid());

    return true;
}

/**
 * BLOCK PRUNING CODE
 */

/* Calculate the amount of disk space the block & undo files currently use */
uint64_t CalculateCurrentUsage()
{
    LOCK(cs_LastBlockFile);

    uint64_t retval = 0;
    for (const CBlockFileInfo &file : vinfoBlockFile) {
        retval += file.nSize + file.nUndoSize;
    }
    return retval;
}

void BlockManager::PruneOneBlockFile(const int fileNumber)
{
    AssertLockHeld(cs_main);
    LOCK(cs_LastBlockFile);

    for (const auto& entry : m_block_index) {
        CBlockIndex* pindex = entry.second;
        if (pindex->nFile == fileNumber) {
            pindex->nStatus &= ~BLOCK_HAVE_DATA;
            pindex->nStatus &= ~BLOCK_HAVE_UNDO;
            pindex->nFile = 0;
            pindex->nDataPos = 0;
            pindex->nUndoPos = 0;
            setDirtyBlockIndex.insert(pindex);

            // Prune from m_blocks_unlinked -- any block we prune would have
            // to be downloaded again in order to consider its chain, at which
            // point it would be considered as a candidate for
            // m_blocks_unlinked or setBlockIndexCandidates.
            auto range = m_blocks_unlinked.equal_range(pindex->pprev);
            while (range.first != range.second) {
                std::multimap<CBlockIndex *, CBlockIndex *>::iterator _it = range.first;
                range.first++;
                if (_it->second == pindex) {
                    m_blocks_unlinked.erase(_it);
                }
            }
        }
    }

    vinfoBlockFile[fileNumber].SetNull();
    setDirtyFileInfo.insert(fileNumber);
}


void UnlinkPrunedFiles(const std::set<int>& setFilesToPrune)
{
    for (std::set<int>::iterator it = setFilesToPrune.begin(); it != setFilesToPrune.end(); ++it) {
        FlatFilePos pos(*it, 0);
        fs::remove(BlockFileSeq().FileName(pos));
        fs::remove(UndoFileSeq().FileName(pos));
        LogPrintf("Prune: %s deleted blk/rev (%05u)\n", __func__, *it);
    }
}

void BlockManager::FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight, int chain_tip_height)
{
    assert(fPruneMode && nManualPruneHeight > 0);

    LOCK2(cs_main, cs_LastBlockFile);
    if (chain_tip_height < 0) {
        return;
    }

    // last block to prune is the lesser of (user-specified height, MIN_BLOCKS_TO_KEEP from the tip)
    unsigned int nLastBlockWeCanPrune = std::min((unsigned)nManualPruneHeight, chain_tip_height - MIN_BLOCKS_TO_KEEP);
    int count = 0;
    for (int fileNumber = 0; fileNumber < nLastBlockFile; fileNumber++) {
        if (vinfoBlockFile[fileNumber].nSize == 0 || vinfoBlockFile[fileNumber].nHeightLast > nLastBlockWeCanPrune) {
            continue;
        }
        PruneOneBlockFile(fileNumber);
        setFilesToPrune.insert(fileNumber);
        count++;
    }
    LogPrintf("Prune (Manual): prune_height=%d removed %d blk/rev pairs\n", nLastBlockWeCanPrune, count);
}

/* This function is called from the RPC code for pruneblockchain */
void PruneBlockFilesManual(int nManualPruneHeight)
{
    BlockValidationState state;
    const CChainParams& chainparams = Params();
    if (!::ChainstateActive().FlushStateToDisk(
            chainparams, state, FlushStateMode::NONE, nManualPruneHeight)) {
        LogPrintf("%s: failed to flush state (%s)\n", __func__, state.ToString());
    }
}

void BlockManager::FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, bool is_ibd)
{
    LOCK2(cs_main, cs_LastBlockFile);
    if (chain_tip_height < 0 || nPruneTarget == 0) {
        return;
    }
    if ((uint64_t)chain_tip_height <= nPruneAfterHeight) {
        return;
    }

    unsigned int nLastBlockWeCanPrune = chain_tip_height - MIN_BLOCKS_TO_KEEP;
    uint64_t nCurrentUsage = CalculateCurrentUsage();
    // We don't check to prune until after we've allocated new space for files
    // So we should leave a buffer under our target to account for another allocation
    // before the next pruning.
    uint64_t nBuffer = BLOCKFILE_CHUNK_SIZE + UNDOFILE_CHUNK_SIZE;
    uint64_t nBytesToPrune;
    int count = 0;

    if (nCurrentUsage + nBuffer >= nPruneTarget) {
        // On a prune event, the chainstate DB is flushed.
        // To avoid excessive prune events negating the benefit of high dbcache
        // values, we should not prune too rapidly.
        // So when pruning in IBD, increase the buffer a bit to avoid a re-prune too soon.
        if (is_ibd) {
            // Since this is only relevant during IBD, we use a fixed 10%
            nBuffer += nPruneTarget / 10;
        }

        for (int fileNumber = 0; fileNumber < nLastBlockFile; fileNumber++) {
            nBytesToPrune = vinfoBlockFile[fileNumber].nSize + vinfoBlockFile[fileNumber].nUndoSize;

            if (vinfoBlockFile[fileNumber].nSize == 0) {
                continue;
            }

            if (nCurrentUsage + nBuffer < nPruneTarget) { // are we below our target?
                break;
            }

            // don't prune files that could have a block within MIN_BLOCKS_TO_KEEP of the main chain's tip but keep scanning
            if (vinfoBlockFile[fileNumber].nHeightLast > nLastBlockWeCanPrune) {
                continue;
            }

            PruneOneBlockFile(fileNumber);
            // Queue up the files for removal
            setFilesToPrune.insert(fileNumber);
            nCurrentUsage -= nBytesToPrune;
            count++;
        }
    }

    LogPrint(BCLog::PRUNE, "Prune: target=%dMiB actual=%dMiB diff=%dMiB max_prune_height=%d removed %d blk/rev pairs\n",
           nPruneTarget/1024/1024, nCurrentUsage/1024/1024,
           ((int64_t)nPruneTarget - (int64_t)nCurrentUsage)/1024/1024,
           nLastBlockWeCanPrune, count);
}

static FlatFileSeq BlockFileSeq()
{
    return FlatFileSeq(GetBlocksDir(), "blk", BLOCKFILE_CHUNK_SIZE);
}

static FlatFileSeq UndoFileSeq()
{
    return FlatFileSeq(GetBlocksDir(), "rev", UNDOFILE_CHUNK_SIZE);
}

FILE* OpenBlockFile(const FlatFilePos &pos, bool fReadOnly) {
    return BlockFileSeq().Open(pos, fReadOnly);
}

/** Open an undo file (rev?????.dat) */
static FILE* OpenUndoFile(const FlatFilePos &pos, bool fReadOnly) {
    return UndoFileSeq().Open(pos, fReadOnly);
}

fs::path GetBlockPosFilename(const FlatFilePos &pos)
{
    return BlockFileSeq().FileName(pos);
}

CBlockIndex * BlockManager::InsertBlockIndex(const uint256& hash)
{
    AssertLockHeld(cs_main);

    if (hash.IsNull())
        return nullptr;

    // Return existing
    BlockMap::iterator mi = m_block_index.find(hash);
    if (mi != m_block_index.end())
        return (*mi).second;

    // Create new
    CBlockIndex* pindexNew = new CBlockIndex();
    mi = m_block_index.insert(std::make_pair(hash, pindexNew)).first;
    pindexNew->phashBlock = &((*mi).first);

    return pindexNew;
}

bool BlockManager::LoadBlockIndex(
    const Consensus::Params& consensus_params,
    CBlockTreeDB& blocktree,
    std::set<CBlockIndex*, CBlockIndexWorkComparator>& block_index_candidates)
{
    if (!blocktree.LoadBlockIndexGuts(consensus_params, [this](const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main) { return this->InsertBlockIndex(hash); }))
        return false;

    // Calculate nChainWork
    std::vector<std::pair<int, CBlockIndex*> > vSortedByHeight;
    vSortedByHeight.reserve(m_block_index.size());
    for (const std::pair<const uint256, CBlockIndex*>& item : m_block_index)
    {
        CBlockIndex* pindex = item.second;
        vSortedByHeight.push_back(std::make_pair(pindex->nHeight, pindex));
    }
    sort(vSortedByHeight.begin(), vSortedByHeight.end());
    for (const std::pair<int, CBlockIndex*>& item : vSortedByHeight)
    {
        if (ShutdownRequested()) return false;
        CBlockIndex* pindex = item.second;
        pindex->nChainWork = (pindex->pprev ? pindex->pprev->nChainWork : 0) + GetBlockProof(*pindex);
        pindex->nTimeMax = (pindex->pprev ? std::max(pindex->pprev->nTimeMax, pindex->nTime) : pindex->nTime);
        // We can link the chain of blocks for which we've received transactions at some point.
        // Pruned nodes may have deleted the block.
        if (pindex->nTx > 0) {
            if (pindex->pprev) {
                if (pindex->pprev->HaveTxsDownloaded()) {
                    pindex->nChainTx = pindex->pprev->nChainTx + pindex->nTx;
                } else {
                    pindex->nChainTx = 0;
                    m_blocks_unlinked.insert(std::make_pair(pindex->pprev, pindex));
                }
            } else {
                pindex->nChainTx = pindex->nTx;
            }
        }
        if (!(pindex->nStatus & BLOCK_FAILED_MASK) && pindex->pprev && (pindex->pprev->nStatus & BLOCK_FAILED_MASK)) {
            pindex->nStatus |= BLOCK_FAILED_CHILD;
            setDirtyBlockIndex.insert(pindex);
        }
        if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) && (pindex->HaveTxsDownloaded() || pindex->pprev == nullptr)) {
            block_index_candidates.insert(pindex);
        }
        if (pindex->nStatus & BLOCK_FAILED_MASK && (!pindexBestInvalid || pindex->nChainWork > pindexBestInvalid->nChainWork))
            pindexBestInvalid = pindex;
        if (pindex->pprev)
            pindex->BuildSkip();
        if (pindex->IsValid(BLOCK_VALID_TREE) && (pindexBestHeader == nullptr || CBlockIndexWorkComparator()(pindexBestHeader, pindex)))
            pindexBestHeader = pindex;
    }

    return true;
}

void BlockManager::Unload() {
    m_failed_blocks.clear();
    m_blocks_unlinked.clear();

    for (const BlockMap::value_type& entry : m_block_index) {
        delete entry.second;
    }

    m_block_index.clear();
}

bool static LoadBlockIndexDB(ChainstateManager& chainman, const CChainParams& chainparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    if (!chainman.m_blockman.LoadBlockIndex(
            chainparams.GetConsensus(), *pblocktree,
            ::ChainstateActive().setBlockIndexCandidates)) {
        return false;
    }

    // Load block file info
    pblocktree->ReadLastBlockFile(nLastBlockFile);
    vinfoBlockFile.resize(nLastBlockFile + 1);
    LogPrintf("%s: last block file = %i\n", __func__, nLastBlockFile);
    for (int nFile = 0; nFile <= nLastBlockFile; nFile++) {
        pblocktree->ReadBlockFileInfo(nFile, vinfoBlockFile[nFile]);
    }
    LogPrintf("%s: last block file info: %s\n", __func__, vinfoBlockFile[nLastBlockFile].ToString());
    for (int nFile = nLastBlockFile + 1; true; nFile++) {
        CBlockFileInfo info;
        if (pblocktree->ReadBlockFileInfo(nFile, info)) {
            vinfoBlockFile.push_back(info);
        } else {
            break;
        }
    }

    // Check presence of blk files
    LogPrintf("Checking all blk files are present...\n");
    std::set<int> setBlkDataFiles;
    for (const std::pair<const uint256, CBlockIndex*>& item : chainman.BlockIndex()) {
        CBlockIndex* pindex = item.second;
        if (pindex->nStatus & BLOCK_HAVE_DATA) {
            setBlkDataFiles.insert(pindex->nFile);
        }
    }
    for (std::set<int>::iterator it = setBlkDataFiles.begin(); it != setBlkDataFiles.end(); it++)
    {
        FlatFilePos pos(*it, 0);
        if (CAutoFile(OpenBlockFile(pos, true), SER_DISK, CLIENT_VERSION).IsNull()) {
            return false;
        }
    }

    // Check whether we have ever pruned block & undo files
    pblocktree->ReadFlag("prunedblockfiles", fHavePruned);
    if (fHavePruned)
        LogPrintf("LoadBlockIndexDB(): Block files have previously been pruned\n");

    // Check whether we need to continue reindexing
    bool fReindexing = false;
    pblocktree->ReadReindexing(fReindexing);
    if(fReindexing) fReindex = true;

    // Check whether we have the name history
    pblocktree->ReadFlag("namehistory", fNameHistory);
    LogPrintf("LoadBlockIndexDB(): name history %s\n", fNameHistory ? "enabled" : "disabled");

    return true;
}

void CChainState::LoadMempool(const ArgsManager& args)
{
    if (args.GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
        ::LoadMempool(m_mempool);
    }
    m_mempool.SetIsLoaded(!ShutdownRequested());
}

bool CChainState::LoadChainTip(const CChainParams& chainparams)
{
    AssertLockHeld(cs_main);
    const CCoinsViewCache& coins_cache = CoinsTip();
    assert(!coins_cache.GetBestBlock().IsNull()); // Never called when the coins view is empty
    const CBlockIndex* tip = m_chain.Tip();

    if (tip && tip->GetBlockHash() == coins_cache.GetBestBlock()) {
        return true;
    }

    // Load pointer to end of best chain
    CBlockIndex* pindex = LookupBlockIndex(coins_cache.GetBestBlock());
    if (!pindex) {
        return false;
    }
    m_chain.SetTip(pindex);
    PruneBlockIndexCandidates();

    tip = m_chain.Tip();
    LogPrintf("Loaded best chain: hashBestChain=%s height=%d date=%s progress=%f\n",
        tip->GetBlockHash().ToString(),
        m_chain.Height(),
        FormatISO8601DateTime(tip->GetBlockTime()),
        GuessVerificationProgress(chainparams.TxData(), tip));
    return true;
}

CVerifyDB::CVerifyDB()
{
    uiInterface.ShowProgress(_("Verifying blocks...").translated, 0, false);
}

CVerifyDB::~CVerifyDB()
{
    uiInterface.ShowProgress("", 100, false);
}

bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview, int nCheckLevel, int nCheckDepth)
{
    LOCK(cs_main);
    if (::ChainActive().Tip() == nullptr || ::ChainActive().Tip()->pprev == nullptr)
        return true;

    // Verify blocks in the best chain
    if (nCheckDepth <= 0 || nCheckDepth > ::ChainActive().Height())
        nCheckDepth = ::ChainActive().Height();
    nCheckLevel = std::max(0, std::min(4, nCheckLevel));
    LogPrintf("Verifying last %i blocks at level %i\n", nCheckDepth, nCheckLevel);
    CCoinsViewCache coins(coinsview);
    std::set<valtype> dummyNames;
    CBlockIndex* pindex;
    CBlockIndex* pindexFailure = nullptr;
    int nGoodTransactions = 0;
    BlockValidationState state;
    int reportDone = 0;
    LogPrintf("[0%%]..."); /* Continued */
    for (pindex = ::ChainActive().Tip(); pindex && pindex->pprev; pindex = pindex->pprev) {
        const int percentageDone = std::max(1, std::min(99, (int)(((double)(::ChainActive().Height() - pindex->nHeight)) / (double)nCheckDepth * (nCheckLevel >= 4 ? 50 : 100))));
        if (reportDone < percentageDone/10) {
            // report every 10% step
            LogPrintf("[%d%%]...", percentageDone); /* Continued */
            reportDone = percentageDone/10;
        }
        uiInterface.ShowProgress(_("Verifying blocks...").translated, percentageDone, false);
        if (pindex->nHeight <= ::ChainActive().Height()-nCheckDepth)
            break;
        if (fPruneMode && !(pindex->nStatus & BLOCK_HAVE_DATA)) {
            // If pruning, only go back as far as we have data.
            LogPrintf("VerifyDB(): block verification stopping at height %d (pruning, no data)\n", pindex->nHeight);
            break;
        }
        CBlock block;
        // check level 0: read from disk
        if (!ReadBlockFromDisk(block, pindex, chainparams.GetConsensus()))
            return error("VerifyDB(): *** ReadBlockFromDisk failed at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
        // check level 1: verify block validity
        if (nCheckLevel >= 1 && !CheckBlock(block, state, chainparams.GetConsensus()))
            return error("%s: *** found bad block at %d, hash=%s (%s)\n", __func__,
                         pindex->nHeight, pindex->GetBlockHash().ToString(), state.ToString());
        // check level 2: verify undo validity
        if (nCheckLevel >= 2 && pindex) {
            CBlockUndo undo;
            if (!pindex->GetUndoPos().IsNull()) {
                if (!UndoReadFromDisk(undo, pindex)) {
                    return error("VerifyDB(): *** found bad undo data at %d, hash=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
                }
            }
        }
        // check level 3: check for inconsistencies during memory-only disconnect of tip blocks
        if (nCheckLevel >= 3 && (coins.DynamicMemoryUsage() + ::ChainstateActive().CoinsTip().DynamicMemoryUsage()) <= ::ChainstateActive().m_coinstip_cache_size_bytes) {
            assert(coins.GetBestBlock() == pindex->GetBlockHash());
            DisconnectResult res = ::ChainstateActive().DisconnectBlock(block, pindex, coins, dummyNames);
            if (res == DISCONNECT_FAILED) {
                return error("VerifyDB(): *** irrecoverable inconsistency in block data at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
            }
            if (res == DISCONNECT_UNCLEAN) {
                nGoodTransactions = 0;
                pindexFailure = pindex;
            } else {
                nGoodTransactions += block.vtx.size();
            }
        }
        if (ShutdownRequested()) return true;
    }
    if (pindexFailure)
        return error("VerifyDB(): *** coin database inconsistencies found (last %i blocks, %i good transactions before that)\n", ::ChainActive().Height() - pindexFailure->nHeight + 1, nGoodTransactions);

    // store block count as we move pindex at check level >= 4
    int block_count = ::ChainActive().Height() - pindex->nHeight;

    // check level 4: try reconnecting blocks
    if (nCheckLevel >= 4) {
        while (pindex != ::ChainActive().Tip()) {
            const int percentageDone = std::max(1, std::min(99, 100 - (int)(((double)(::ChainActive().Height() - pindex->nHeight)) / (double)nCheckDepth * 50)));
            if (reportDone < percentageDone/10) {
                // report every 10% step
                LogPrintf("[%d%%]...", percentageDone); /* Continued */
                reportDone = percentageDone/10;
            }
            uiInterface.ShowProgress(_("Verifying blocks...").translated, percentageDone, false);
            pindex = ::ChainActive().Next(pindex);
            CBlock block;
            if (!ReadBlockFromDisk(block, pindex, chainparams.GetConsensus()))
                return error("VerifyDB(): *** ReadBlockFromDisk failed at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
            if (!::ChainstateActive().ConnectBlock(block, state, pindex, coins, dummyNames, chainparams))
                return error("VerifyDB(): *** found unconnectable block at %d, hash=%s (%s)", pindex->nHeight, pindex->GetBlockHash().ToString(), state.ToString());
            if (ShutdownRequested()) return true;
        }
    }

    LogPrintf("[DONE].\n");
    LogPrintf("No coin database inconsistencies in last %i blocks (%i transactions)\n", block_count, nGoodTransactions);

    return true;
}

/** Apply the effects of a block on the utxo cache, ignoring that it may already have been applied. */
bool CChainState::RollforwardBlock(const CBlockIndex* pindex, CCoinsViewCache& inputs, const CChainParams& params)
{
    // TODO: merge with ConnectBlock
    CBlock block;
    if (!ReadBlockFromDisk(block, pindex, params.GetConsensus())) {
        return error("ReplayBlock(): ReadBlockFromDisk failed at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
    }

    for (const CTransactionRef& tx : block.vtx) {
        if (!tx->IsCoinBase()) {
            for (const CTxIn &txin : tx->vin) {
                inputs.SpendCoin(txin.prevout);
            }
        }
        // Pass check = true as every addition may be an overwrite.
        AddCoins(inputs, *tx, pindex->nHeight, true);
    }
    return true;
}

bool CChainState::ReplayBlocks(const CChainParams& params)
{
    LOCK(cs_main);

    CCoinsView& db = this->CoinsDB();
    CCoinsViewCache cache(&db);

    std::vector<uint256> hashHeads = db.GetHeadBlocks();
    if (hashHeads.empty()) return true; // We're already in a consistent state.
    if (hashHeads.size() != 2) return error("ReplayBlocks(): unknown inconsistent state");

    uiInterface.ShowProgress(_("Replaying blocks...").translated, 0, false);
    LogPrintf("Replaying blocks\n");

    const CBlockIndex* pindexOld = nullptr;  // Old tip during the interrupted flush.
    const CBlockIndex* pindexNew;            // New tip during the interrupted flush.
    const CBlockIndex* pindexFork = nullptr; // Latest block common to both the old and the new tip.

    if (m_blockman.m_block_index.count(hashHeads[0]) == 0) {
        return error("ReplayBlocks(): reorganization to unknown block requested");
    }
    pindexNew = m_blockman.m_block_index[hashHeads[0]];

    if (!hashHeads[1].IsNull()) { // The old tip is allowed to be 0, indicating it's the first flush.
        if (m_blockman.m_block_index.count(hashHeads[1]) == 0) {
            return error("ReplayBlocks(): reorganization from unknown block requested");
        }
        pindexOld = m_blockman.m_block_index[hashHeads[1]];
        pindexFork = LastCommonAncestor(pindexOld, pindexNew);
        assert(pindexFork != nullptr);
    }

    // Rollback along the old branch.
    while (pindexOld != pindexFork) {
        if (pindexOld->nHeight > 0) { // Never disconnect the genesis block.
            CBlock block;
            if (!ReadBlockFromDisk(block, pindexOld, params.GetConsensus())) {
                return error("RollbackBlock(): ReadBlockFromDisk() failed at %d, hash=%s", pindexOld->nHeight, pindexOld->GetBlockHash().ToString());
            }
            LogPrintf("Rolling back %s (%i)\n", pindexOld->GetBlockHash().ToString(), pindexOld->nHeight);
            std::set<valtype> dummyNames;
            DisconnectResult res = DisconnectBlock(block, pindexOld, cache, dummyNames);
            if (res == DISCONNECT_FAILED) {
                return error("RollbackBlock(): DisconnectBlock failed at %d, hash=%s", pindexOld->nHeight, pindexOld->GetBlockHash().ToString());
            }
            // If DISCONNECT_UNCLEAN is returned, it means a non-existing UTXO was deleted, or an existing UTXO was
            // overwritten. It corresponds to cases where the block-to-be-disconnect never had all its operations
            // applied to the UTXO set. However, as both writing a UTXO and deleting a UTXO are idempotent operations,
            // the result is still a version of the UTXO set with the effects of that block undone.
        }
        pindexOld = pindexOld->pprev;
    }

    // Roll forward from the forking point to the new tip.
    int nForkHeight = pindexFork ? pindexFork->nHeight : 0;
    for (int nHeight = nForkHeight + 1; nHeight <= pindexNew->nHeight; ++nHeight) {
        const CBlockIndex* pindex = pindexNew->GetAncestor(nHeight);
        LogPrintf("Rolling forward %s (%i)\n", pindex->GetBlockHash().ToString(), nHeight);
        uiInterface.ShowProgress(_("Replaying blocks...").translated, (int) ((nHeight - nForkHeight) * 100.0 / (pindexNew->nHeight - nForkHeight)) , false);
        if (!RollforwardBlock(pindex, cache, params)) return false;
    }

    cache.SetBestBlock(pindexNew->GetBlockHash());
    cache.Flush();
    uiInterface.ShowProgress("", 100, false);
    return true;
}

//! Helper for CChainState::RewindBlockIndex
void CChainState::EraseBlockData(CBlockIndex* index)
{
    AssertLockHeld(cs_main);
    assert(!m_chain.Contains(index)); // Make sure this block isn't active

    // Reduce validity
    index->nStatus = std::min<unsigned int>(index->nStatus & BLOCK_VALID_MASK, BLOCK_VALID_TREE) | (index->nStatus & ~BLOCK_VALID_MASK);
    // Remove have-data flags.
    index->nStatus &= ~(BLOCK_HAVE_DATA | BLOCK_HAVE_UNDO);
    // Remove storage location.
    index->nFile = 0;
    index->nDataPos = 0;
    index->nUndoPos = 0;
    // Remove various other things
    index->nTx = 0;
    index->nChainTx = 0;
    index->nSequenceId = 0;
    // Make sure it gets written.
    setDirtyBlockIndex.insert(index);
    // Update indexes
    setBlockIndexCandidates.erase(index);
    auto ret = m_blockman.m_blocks_unlinked.equal_range(index->pprev);
    while (ret.first != ret.second) {
        if (ret.first->second == index) {
            m_blockman.m_blocks_unlinked.erase(ret.first++);
        } else {
            ++ret.first;
        }
    }
    // Mark parent as eligible for main chain again
    if (index->pprev && index->pprev->IsValid(BLOCK_VALID_TRANSACTIONS) && index->pprev->HaveTxsDownloaded()) {
        setBlockIndexCandidates.insert(index->pprev);
    }
}

bool CChainState::RewindBlockIndex(const CChainParams& params)
{
    // Note that during -reindex-chainstate we are called with an empty m_chain!

    // First erase all post-segwit blocks without witness not in the main chain,
    // as this can we done without costly DisconnectTip calls. Active
    // blocks will be dealt with below (releasing cs_main in between).
    {
        LOCK(cs_main);
        for (const auto& entry : m_blockman.m_block_index) {
            if (IsWitnessEnabled(entry.second->pprev, params.GetConsensus()) && !(entry.second->nStatus & BLOCK_OPT_WITNESS) && !m_chain.Contains(entry.second)) {
                EraseBlockData(entry.second);
            }
        }
    }

    // Find what height we need to reorganize to.
    CBlockIndex *tip;
    int nHeight = 1;
    {
        LOCK(cs_main);
        while (nHeight <= m_chain.Height()) {
            // Although SCRIPT_VERIFY_WITNESS is now generally enforced on all
            // blocks in ConnectBlock, we don't need to go back and
            // re-download/re-verify blocks from before segwit actually activated.
            if (IsWitnessEnabled(m_chain[nHeight - 1], params.GetConsensus()) && !(m_chain[nHeight]->nStatus & BLOCK_OPT_WITNESS)) {
                break;
            }
            nHeight++;
        }

        tip = m_chain.Tip();
    }
    // nHeight is now the height of the first insufficiently-validated block, or tipheight + 1

    BlockValidationState state;
    // Loop until the tip is below nHeight, or we reach a pruned block.
    while (!ShutdownRequested()) {
        {
            LOCK(cs_main);
            LOCK(m_mempool.cs);
            // Make sure nothing changed from under us (this won't happen because RewindBlockIndex runs before importing/network are active)
            assert(tip == m_chain.Tip());
            if (tip == nullptr || tip->nHeight < nHeight) break;
            if (fPruneMode && !(tip->nStatus & BLOCK_HAVE_DATA)) {
                // If pruning, don't try rewinding past the HAVE_DATA point;
                // since older blocks can't be served anyway, there's
                // no need to walk further, and trying to DisconnectTip()
                // will fail (and require a needless reindex/redownload
                // of the blockchain).
                break;
            }

            // Disconnect block
            if (!DisconnectTip(state, params, nullptr)) {
                return error("RewindBlockIndex: unable to disconnect block at height %i (%s)", tip->nHeight, state.ToString());
            }

            // Reduce validity flag and have-data flags.
            // We do this after actual disconnecting, otherwise we'll end up writing the lack of data
            // to disk before writing the chainstate, resulting in a failure to continue if interrupted.
            // Note: If we encounter an insufficiently validated block that
            // is on m_chain, it must be because we are a pruning node, and
            // this block or some successor doesn't HAVE_DATA, so we were unable to
            // rewind all the way.  Blocks remaining on m_chain at this point
            // must not have their validity reduced.
            EraseBlockData(tip);

            tip = tip->pprev;
        }
        // Make sure the queue of validation callbacks doesn't grow unboundedly.
        LimitValidationInterfaceQueue();

        // Occasionally flush state to disk.
        if (!FlushStateToDisk(params, state, FlushStateMode::PERIODIC)) {
            LogPrintf("RewindBlockIndex: unable to flush state to disk (%s)\n", state.ToString());
            return false;
        }
    }

    {
        LOCK(cs_main);
        if (m_chain.Tip() != nullptr) {
            // We can't prune block index candidates based on our tip if we have
            // no tip due to m_chain being empty!
            PruneBlockIndexCandidates();

            CheckBlockIndex(params.GetConsensus());

            // FlushStateToDisk can possibly read ::ChainActive(). Be conservative
            // and skip it here, we're about to -reindex-chainstate anyway, so
            // it'll get called a bunch real soon.
            BlockValidationState state;
            if (!FlushStateToDisk(params, state, FlushStateMode::ALWAYS)) {
                LogPrintf("RewindBlockIndex: unable to flush state to disk (%s)\n", state.ToString());
                return false;
            }
        }
    }

    return true;
}

void CChainState::UnloadBlockIndex() {
    nBlockSequenceId = 1;
    setBlockIndexCandidates.clear();
}

// May NOT be used after any connections are up as much
// of the peer-processing logic assumes a consistent
// block index state
void UnloadBlockIndex(CTxMemPool* mempool, ChainstateManager& chainman)
{
    LOCK(cs_main);
    chainman.Unload();
    pindexBestInvalid = nullptr;
    pindexBestHeader = nullptr;
    if (mempool) mempool->clear();
    vinfoBlockFile.clear();
    nLastBlockFile = 0;
    setDirtyBlockIndex.clear();
    setDirtyFileInfo.clear();
    versionbitscache.Clear();
    for (int b = 0; b < VERSIONBITS_NUM_BITS; b++) {
        warningcache[b].clear();
    }
    fHavePruned = false;
}

bool ChainstateManager::LoadBlockIndex(const CChainParams& chainparams)
{
    AssertLockHeld(cs_main);
    // Load block index from databases
    bool needs_init = fReindex;
    if (!fReindex) {
        bool ret = LoadBlockIndexDB(*this, chainparams);
        if (!ret) return false;
        needs_init = m_blockman.m_block_index.empty();
    }

    if (needs_init) {
        // Everything here is for *new* reindex/DBs. Thus, though
        // LoadBlockIndexDB may have set fReindex if we shut down
        // mid-reindex previously, we don't check fReindex and
        // instead only check it prior to LoadBlockIndexDB to set
        // needs_init.

        LogPrintf("Initializing databases...\n");
        fNameHistory = gArgs.GetBoolArg("-namehistory", false);
        pblocktree->WriteFlag("namehistory", fNameHistory);
    }
    return true;
}

bool CChainState::LoadGenesisBlock(const CChainParams& chainparams)
{
    LOCK(cs_main);

    // Check whether we're already initialized by checking for genesis in
    // m_blockman.m_block_index. Note that we can't use m_chain here, since it is
    // set based on the coins db, not the block index db, which is the only
    // thing loaded at this point.
    if (m_blockman.m_block_index.count(chainparams.GenesisBlock().GetHash()))
        return true;

    try {
        const CBlock& block = chainparams.GenesisBlock();
        FlatFilePos blockPos = SaveBlockToDisk(block, 0, chainparams, nullptr);
        if (blockPos.IsNull())
            return error("%s: writing genesis block to disk failed", __func__);
        CBlockIndex *pindex = m_blockman.AddToBlockIndex(block);
        ReceivedBlockTransactions(block, pindex, blockPos, chainparams.GetConsensus());
    } catch (const std::runtime_error& e) {
        return error("%s: failed to write genesis block: %s", __func__, e.what());
    }

    return true;
}

bool LoadGenesisBlock(const CChainParams& chainparams)
{
    return ::ChainstateActive().LoadGenesisBlock(chainparams);
}

void LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, FlatFilePos* dbp)
{
    // Map of disk positions for blocks with unknown parent (only used for reindex)
    static std::multimap<uint256, FlatFilePos> mapBlocksUnknownParent;
    int64_t nStart = GetTimeMillis();

    int nLoaded = 0;
    try {
        // This takes over fileIn and calls fclose() on it in the CBufferedFile destructor
        CBufferedFile blkdat(fileIn, 2*MAX_BLOCK_SERIALIZED_SIZE, MAX_BLOCK_SERIALIZED_SIZE+8, SER_DISK, CLIENT_VERSION);
        uint64_t nRewind = blkdat.GetPos();
        while (!blkdat.eof()) {
            if (ShutdownRequested()) return;

            blkdat.SetPos(nRewind);
            nRewind++; // start one byte further next time, in case of failure
            blkdat.SetLimit(); // remove former limit
            unsigned int nSize = 0;
            try {
                // locate a header
                unsigned char buf[CMessageHeader::MESSAGE_START_SIZE];
                blkdat.FindByte(chainparams.MessageStart()[0]);
                nRewind = blkdat.GetPos()+1;
                blkdat >> buf;
                if (memcmp(buf, chainparams.MessageStart(), CMessageHeader::MESSAGE_START_SIZE))
                    continue;
                // read size
                blkdat >> nSize;
                if (nSize < 80 || nSize > MAX_BLOCK_SERIALIZED_SIZE)
                    continue;
            } catch (const std::exception&) {
                // no valid block header found; don't complain
                break;
            }
            try {
                // read block
                uint64_t nBlockPos = blkdat.GetPos();
                if (dbp)
                    dbp->nPos = nBlockPos;
                blkdat.SetLimit(nBlockPos + nSize);
                std::shared_ptr<CBlock> pblock = std::make_shared<CBlock>();
                CBlock& block = *pblock;
                blkdat >> block;
                nRewind = blkdat.GetPos();

                uint256 hash = block.GetHash();
                {
                    LOCK(cs_main);
                    // detect out of order blocks, and store them for later
                    if (hash != chainparams.GetConsensus().hashGenesisBlock && !LookupBlockIndex(block.hashPrevBlock)) {
                        LogPrint(BCLog::REINDEX, "%s: Out of order block %s, parent %s not known\n", __func__, hash.ToString(),
                                block.hashPrevBlock.ToString());
                        if (dbp)
                            mapBlocksUnknownParent.insert(std::make_pair(block.hashPrevBlock, *dbp));
                        continue;
                    }

                    // process in case the block isn't known yet
                    CBlockIndex* pindex = LookupBlockIndex(hash);
                    if (!pindex || (pindex->nStatus & BLOCK_HAVE_DATA) == 0) {
                      BlockValidationState state;
                      if (::ChainstateActive().AcceptBlock(pblock, state, chainparams, nullptr, true, dbp, nullptr)) {
                          nLoaded++;
                      }
                      if (state.IsError()) {
                          break;
                      }
                    } else if (hash != chainparams.GetConsensus().hashGenesisBlock && pindex->nHeight % 1000 == 0) {
                      LogPrint(BCLog::REINDEX, "Block Import: already had block %s at height %d\n", hash.ToString(), pindex->nHeight);
                    }
                }

                // Activate the genesis block so normal node progress can continue
                if (hash == chainparams.GetConsensus().hashGenesisBlock) {
                    BlockValidationState state;
                    if (!ActivateBestChain(state, chainparams, nullptr)) {
                        break;
                    }
                }

                NotifyHeaderTip();

                // Recursively process earlier encountered successors of this block
                std::deque<uint256> queue;
                queue.push_back(hash);
                while (!queue.empty()) {
                    uint256 head = queue.front();
                    queue.pop_front();
                    std::pair<std::multimap<uint256, FlatFilePos>::iterator, std::multimap<uint256, FlatFilePos>::iterator> range = mapBlocksUnknownParent.equal_range(head);
                    while (range.first != range.second) {
                        std::multimap<uint256, FlatFilePos>::iterator it = range.first;
                        std::shared_ptr<CBlock> pblockrecursive = std::make_shared<CBlock>();
                        if (ReadBlockFromDisk(*pblockrecursive, it->second, chainparams.GetConsensus()))
                        {
                            LogPrint(BCLog::REINDEX, "%s: Processing out of order child %s of %s\n", __func__, pblockrecursive->GetHash().ToString(),
                                    head.ToString());
                            LOCK(cs_main);
                            BlockValidationState dummy;
                            if (::ChainstateActive().AcceptBlock(pblockrecursive, dummy, chainparams, nullptr, true, &it->second, nullptr))
                            {
                                nLoaded++;
                                queue.push_back(pblockrecursive->GetHash());
                            }
                        }
                        range.first++;
                        mapBlocksUnknownParent.erase(it);
                        NotifyHeaderTip();
                    }
                }
            } catch (const std::exception& e) {
                LogPrintf("%s: Deserialize or I/O error - %s\n", __func__, e.what());
            }
        }
    } catch (const std::runtime_error& e) {
        AbortNode(std::string("System error: ") + e.what());
    }
    LogPrintf("Loaded %i blocks from external file in %dms\n", nLoaded, GetTimeMillis() - nStart);
}

void CChainState::CheckBlockIndex(const Consensus::Params& consensusParams)
{
    if (!fCheckBlockIndex) {
        return;
    }

    LOCK(cs_main);

    // During a reindex, we read the genesis block and call CheckBlockIndex before ActivateBestChain,
    // so we have the genesis block in m_blockman.m_block_index but no active chain. (A few of the
    // tests when iterating the block tree require that m_chain has been initialized.)
    if (m_chain.Height() < 0) {
        assert(m_blockman.m_block_index.size() <= 1);
        return;
    }

    // Build forward-pointing map of the entire block tree.
    std::multimap<CBlockIndex*,CBlockIndex*> forward;
    for (const std::pair<const uint256, CBlockIndex*>& entry : m_blockman.m_block_index) {
        forward.insert(std::make_pair(entry.second->pprev, entry.second));
    }

    assert(forward.size() == m_blockman.m_block_index.size());

    std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> rangeGenesis = forward.equal_range(nullptr);
    CBlockIndex *pindex = rangeGenesis.first->second;
    rangeGenesis.first++;
    assert(rangeGenesis.first == rangeGenesis.second); // There is only one index entry with parent nullptr.

    // Iterate over the entire block tree, using depth-first search.
    // Along the way, remember whether there are blocks on the path from genesis
    // block being explored which are the first to have certain properties.
    size_t nNodes = 0;
    int nHeight = 0;
    CBlockIndex* pindexFirstInvalid = nullptr; // Oldest ancestor of pindex which is invalid.
    CBlockIndex* pindexFirstMissing = nullptr; // Oldest ancestor of pindex which does not have BLOCK_HAVE_DATA.
    CBlockIndex* pindexFirstNeverProcessed = nullptr; // Oldest ancestor of pindex for which nTx == 0.
    CBlockIndex* pindexFirstNotTreeValid = nullptr; // Oldest ancestor of pindex which does not have BLOCK_VALID_TREE (regardless of being valid or not).
    CBlockIndex* pindexFirstNotTransactionsValid = nullptr; // Oldest ancestor of pindex which does not have BLOCK_VALID_TRANSACTIONS (regardless of being valid or not).
    CBlockIndex* pindexFirstNotChainValid = nullptr; // Oldest ancestor of pindex which does not have BLOCK_VALID_CHAIN (regardless of being valid or not).
    CBlockIndex* pindexFirstNotScriptsValid = nullptr; // Oldest ancestor of pindex which does not have BLOCK_VALID_SCRIPTS (regardless of being valid or not).
    while (pindex != nullptr) {
        nNodes++;
        if (pindexFirstInvalid == nullptr && pindex->nStatus & BLOCK_FAILED_VALID) pindexFirstInvalid = pindex;
        if (pindexFirstMissing == nullptr && !(pindex->nStatus & BLOCK_HAVE_DATA)) pindexFirstMissing = pindex;
        if (pindexFirstNeverProcessed == nullptr && pindex->nTx == 0) pindexFirstNeverProcessed = pindex;
        if (pindex->pprev != nullptr && pindexFirstNotTreeValid == nullptr && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_TREE) pindexFirstNotTreeValid = pindex;
        if (pindex->pprev != nullptr && pindexFirstNotTransactionsValid == nullptr && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_TRANSACTIONS) pindexFirstNotTransactionsValid = pindex;
        if (pindex->pprev != nullptr && pindexFirstNotChainValid == nullptr && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_CHAIN) pindexFirstNotChainValid = pindex;
        if (pindex->pprev != nullptr && pindexFirstNotScriptsValid == nullptr && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_SCRIPTS) pindexFirstNotScriptsValid = pindex;

        // Begin: actual consistency checks.
        if (pindex->pprev == nullptr) {
            // Genesis block checks.
            assert(pindex->GetBlockHash() == consensusParams.hashGenesisBlock); // Genesis block's hash must match.
            assert(pindex == m_chain.Genesis()); // The current active chain's genesis block must be this block.
        }
        if (!pindex->HaveTxsDownloaded()) assert(pindex->nSequenceId <= 0); // nSequenceId can't be set positive for blocks that aren't linked (negative is used for preciousblock)
        // VALID_TRANSACTIONS is equivalent to nTx > 0 for all nodes (whether or not pruning has occurred).
        // HAVE_DATA is only equivalent to nTx > 0 (or VALID_TRANSACTIONS) if no pruning has occurred.
        if (!fHavePruned) {
            // If we've never pruned, then HAVE_DATA should be equivalent to nTx > 0
            assert(!(pindex->nStatus & BLOCK_HAVE_DATA) == (pindex->nTx == 0));
            assert(pindexFirstMissing == pindexFirstNeverProcessed);
        } else {
            // If we have pruned, then we can only say that HAVE_DATA implies nTx > 0
            if (pindex->nStatus & BLOCK_HAVE_DATA) assert(pindex->nTx > 0);
        }
        if (pindex->nStatus & BLOCK_HAVE_UNDO) assert(pindex->nStatus & BLOCK_HAVE_DATA);
        assert(((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_TRANSACTIONS) == (pindex->nTx > 0)); // This is pruning-independent.
        // All parents having had data (at some point) is equivalent to all parents being VALID_TRANSACTIONS, which is equivalent to HaveTxsDownloaded().
        assert((pindexFirstNeverProcessed == nullptr) == pindex->HaveTxsDownloaded());
        assert((pindexFirstNotTransactionsValid == nullptr) == pindex->HaveTxsDownloaded());
        assert(pindex->nHeight == nHeight); // nHeight must be consistent.
        assert(pindex->pprev == nullptr || pindex->nChainWork >= pindex->pprev->nChainWork); // For every block except the genesis block, the chainwork must be larger than the parent's.
        assert(nHeight < 2 || (pindex->pskip && (pindex->pskip->nHeight < nHeight))); // The pskip pointer must point back for all but the first 2 blocks.
        assert(pindexFirstNotTreeValid == nullptr); // All m_blockman.m_block_index entries must at least be TREE valid
        if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_TREE) assert(pindexFirstNotTreeValid == nullptr); // TREE valid implies all parents are TREE valid
        if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_CHAIN) assert(pindexFirstNotChainValid == nullptr); // CHAIN valid implies all parents are CHAIN valid
        if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_SCRIPTS) assert(pindexFirstNotScriptsValid == nullptr); // SCRIPTS valid implies all parents are SCRIPTS valid
        if (pindexFirstInvalid == nullptr) {
            // Checks for not-invalid blocks.
            assert((pindex->nStatus & BLOCK_FAILED_MASK) == 0); // The failed mask cannot be set for blocks without invalid parents.
        }
        if (!CBlockIndexWorkComparator()(pindex, m_chain.Tip()) && pindexFirstNeverProcessed == nullptr) {
            if (pindexFirstInvalid == nullptr) {
                // If this block sorts at least as good as the current tip and
                // is valid and we have all data for its parents, it must be in
                // setBlockIndexCandidates.  m_chain.Tip() must also be there
                // even if some data has been pruned.
                if (pindexFirstMissing == nullptr || pindex == m_chain.Tip()) {
                    assert(setBlockIndexCandidates.count(pindex));
                }
                // If some parent is missing, then it could be that this block was in
                // setBlockIndexCandidates but had to be removed because of the missing data.
                // In this case it must be in m_blocks_unlinked -- see test below.
            }
        } else { // If this block sorts worse than the current tip or some ancestor's block has never been seen, it cannot be in setBlockIndexCandidates.
            assert(setBlockIndexCandidates.count(pindex) == 0);
        }
        // Check whether this block is in m_blocks_unlinked.
        std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> rangeUnlinked = m_blockman.m_blocks_unlinked.equal_range(pindex->pprev);
        bool foundInUnlinked = false;
        while (rangeUnlinked.first != rangeUnlinked.second) {
            assert(rangeUnlinked.first->first == pindex->pprev);
            if (rangeUnlinked.first->second == pindex) {
                foundInUnlinked = true;
                break;
            }
            rangeUnlinked.first++;
        }
        if (pindex->pprev && (pindex->nStatus & BLOCK_HAVE_DATA) && pindexFirstNeverProcessed != nullptr && pindexFirstInvalid == nullptr) {
            // If this block has block data available, some parent was never received, and has no invalid parents, it must be in m_blocks_unlinked.
            assert(foundInUnlinked);
        }
        if (!(pindex->nStatus & BLOCK_HAVE_DATA)) assert(!foundInUnlinked); // Can't be in m_blocks_unlinked if we don't HAVE_DATA
        if (pindexFirstMissing == nullptr) assert(!foundInUnlinked); // We aren't missing data for any parent -- cannot be in m_blocks_unlinked.
        if (pindex->pprev && (pindex->nStatus & BLOCK_HAVE_DATA) && pindexFirstNeverProcessed == nullptr && pindexFirstMissing != nullptr) {
            // We HAVE_DATA for this block, have received data for all parents at some point, but we're currently missing data for some parent.
            assert(fHavePruned); // We must have pruned.
            // This block may have entered m_blocks_unlinked if:
            //  - it has a descendant that at some point had more work than the
            //    tip, and
            //  - we tried switching to that descendant but were missing
            //    data for some intermediate block between m_chain and the
            //    tip.
            // So if this block is itself better than m_chain.Tip() and it wasn't in
            // setBlockIndexCandidates, then it must be in m_blocks_unlinked.
            if (!CBlockIndexWorkComparator()(pindex, m_chain.Tip()) && setBlockIndexCandidates.count(pindex) == 0) {
                if (pindexFirstInvalid == nullptr) {
                    assert(foundInUnlinked);
                }
            }
        }
        // assert(pindex->GetBlockHash() == pindex->GetBlockHeader().GetHash()); // Perhaps too slow
        // End: actual consistency checks.

        // Try descending into the first subnode.
        std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> range = forward.equal_range(pindex);
        if (range.first != range.second) {
            // A subnode was found.
            pindex = range.first->second;
            nHeight++;
            continue;
        }
        // This is a leaf node.
        // Move upwards until we reach a node of which we have not yet visited the last child.
        while (pindex) {
            // We are going to either move to a parent or a sibling of pindex.
            // If pindex was the first with a certain property, unset the corresponding variable.
            if (pindex == pindexFirstInvalid) pindexFirstInvalid = nullptr;
            if (pindex == pindexFirstMissing) pindexFirstMissing = nullptr;
            if (pindex == pindexFirstNeverProcessed) pindexFirstNeverProcessed = nullptr;
            if (pindex == pindexFirstNotTreeValid) pindexFirstNotTreeValid = nullptr;
            if (pindex == pindexFirstNotTransactionsValid) pindexFirstNotTransactionsValid = nullptr;
            if (pindex == pindexFirstNotChainValid) pindexFirstNotChainValid = nullptr;
            if (pindex == pindexFirstNotScriptsValid) pindexFirstNotScriptsValid = nullptr;
            // Find our parent.
            CBlockIndex* pindexPar = pindex->pprev;
            // Find which child we just visited.
            std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> rangePar = forward.equal_range(pindexPar);
            while (rangePar.first->second != pindex) {
                assert(rangePar.first != rangePar.second); // Our parent must have at least the node we're coming from as child.
                rangePar.first++;
            }
            // Proceed to the next one.
            rangePar.first++;
            if (rangePar.first != rangePar.second) {
                // Move to the sibling.
                pindex = rangePar.first->second;
                break;
            } else {
                // Move up further.
                pindex = pindexPar;
                nHeight--;
                continue;
            }
        }
    }

    // Check that we actually traversed the entire map.
    assert(nNodes == forward.size());
}

std::string CChainState::ToString()
{
    CBlockIndex* tip = m_chain.Tip();
    return strprintf("Chainstate [%s] @ height %d (%s)",
        m_from_snapshot_blockhash.IsNull() ? "ibd" : "snapshot",
        tip ? tip->nHeight : -1, tip ? tip->GetBlockHash().ToString() : "null");
}

bool CChainState::ResizeCoinsCaches(size_t coinstip_size, size_t coinsdb_size)
{
    if (coinstip_size == m_coinstip_cache_size_bytes &&
            coinsdb_size == m_coinsdb_cache_size_bytes) {
        // Cache sizes are unchanged, no need to continue.
        return true;
    }
    size_t old_coinstip_size = m_coinstip_cache_size_bytes;
    m_coinstip_cache_size_bytes = coinstip_size;
    m_coinsdb_cache_size_bytes = coinsdb_size;
    CoinsDB().ResizeCache(coinsdb_size);

    LogPrintf("[%s] resized coinsdb cache to %.1f MiB\n",
        this->ToString(), coinsdb_size * (1.0 / 1024 / 1024));
    LogPrintf("[%s] resized coinstip cache to %.1f MiB\n",
        this->ToString(), coinstip_size * (1.0 / 1024 / 1024));

    BlockValidationState state;
    const CChainParams& chainparams = Params();

    bool ret;

    if (coinstip_size > old_coinstip_size) {
        // Likely no need to flush if cache sizes have grown.
        ret = FlushStateToDisk(chainparams, state, FlushStateMode::IF_NEEDED);
    } else {
        // Otherwise, flush state to disk and deallocate the in-memory coins map.
        ret = FlushStateToDisk(chainparams, state, FlushStateMode::ALWAYS);
        CoinsTip().ReallocateCache();
    }
    return ret;
}

std::string CBlockFileInfo::ToString() const
{
    return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, FormatISO8601Date(nTimeFirst), FormatISO8601Date(nTimeLast));
}

CBlockFileInfo* GetBlockFileInfo(size_t n)
{
    LOCK(cs_LastBlockFile);

    return &vinfoBlockFile.at(n);
}

ThresholdState VersionBitsTipState(const Consensus::Params& params, Consensus::DeploymentPos pos)
{
    LOCK(cs_main);
    return VersionBitsState(::ChainActive().Tip(), params, pos, versionbitscache);
}

BIP9Stats VersionBitsTipStatistics(const Consensus::Params& params, Consensus::DeploymentPos pos)
{
    LOCK(cs_main);
    return VersionBitsStatistics(::ChainActive().Tip(), params, pos);
}

int VersionBitsTipStateSinceHeight(const Consensus::Params& params, Consensus::DeploymentPos pos)
{
    LOCK(cs_main);
    return VersionBitsStateSinceHeight(::ChainActive().Tip(), params, pos, versionbitscache);
}

static const uint64_t MEMPOOL_DUMP_VERSION = 1;

bool LoadMempool(CTxMemPool& pool)
{
    const CChainParams& chainparams = Params();
    int64_t nExpiryTimeout = gArgs.GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY) * 60 * 60;
    FILE* filestr = fsbridge::fopen(GetDataDir() / "mempool.dat", "rb");
    CAutoFile file(filestr, SER_DISK, CLIENT_VERSION);
    if (file.IsNull()) {
        LogPrintf("Failed to open mempool file from disk. Continuing anyway.\n");
        return false;
    }

    int64_t count = 0;
    int64_t expired = 0;
    int64_t failed = 0;
    int64_t already_there = 0;
    int64_t unbroadcast = 0;
    int64_t nNow = GetTime();

    try {
        uint64_t version;
        file >> version;
        if (version != MEMPOOL_DUMP_VERSION) {
            return false;
        }
        uint64_t num;
        file >> num;
        while (num--) {
            CTransactionRef tx;
            int64_t nTime;
            int64_t nFeeDelta;
            file >> tx;
            file >> nTime;
            file >> nFeeDelta;

            CAmount amountdelta = nFeeDelta;
            if (amountdelta) {
                pool.PrioritiseTransaction(tx->GetHash(), amountdelta);
            }
            TxValidationState state;
            if (nTime > nNow - nExpiryTimeout) {
                LOCK(cs_main);
                AcceptToMemoryPoolWithTime(chainparams, pool, state, tx, nTime,
                                           nullptr /* plTxnReplaced */, false /* bypass_limits */,
                                           false /* test_accept */);
                if (state.IsValid()) {
                    ++count;
                } else {
                    // mempool may contain the transaction already, e.g. from
                    // wallet(s) having loaded it while we were processing
                    // mempool transactions; consider these as valid, instead of
                    // failed, but mark them as 'already there'
                    if (pool.exists(tx->GetHash())) {
                        ++already_there;
                    } else {
                        ++failed;
                    }
                }
            } else {
                ++expired;
            }
            if (ShutdownRequested())
                return false;
        }
        std::map<uint256, CAmount> mapDeltas;
        file >> mapDeltas;

        for (const auto& i : mapDeltas) {
            pool.PrioritiseTransaction(i.first, i.second);
        }

        // TODO: remove this try except in v0.22
        std::set<uint256> unbroadcast_txids;
        try {
          file >> unbroadcast_txids;
          unbroadcast = unbroadcast_txids.size();
        } catch (const std::exception&) {
          // mempool.dat files created prior to v0.21 will not have an
          // unbroadcast set. No need to log a failure if parsing fails here.
        }
        for (const auto& txid : unbroadcast_txids) {
            // Ensure transactions were accepted to mempool then add to
            // unbroadcast set.
            if (pool.get(txid) != nullptr) pool.AddUnbroadcastTx(txid);
        }
    } catch (const std::exception& e) {
        LogPrintf("Failed to deserialize mempool data on disk: %s. Continuing anyway.\n", e.what());
        return false;
    }

    LogPrintf("Imported mempool transactions from disk: %i succeeded, %i failed, %i expired, %i already there, %i waiting for initial broadcast\n", count, failed, expired, already_there, unbroadcast);
    return true;
}

bool DumpMempool(const CTxMemPool& pool)
{
    int64_t start = GetTimeMicros();

    std::map<uint256, CAmount> mapDeltas;
    std::vector<TxMempoolInfo> vinfo;
    std::set<uint256> unbroadcast_txids;

    static Mutex dump_mutex;
    LOCK(dump_mutex);

    {
        LOCK(pool.cs);
        for (const auto &i : pool.mapDeltas) {
            mapDeltas[i.first] = i.second;
        }
        vinfo = pool.infoAll();
        unbroadcast_txids = pool.GetUnbroadcastTxs();
    }

    int64_t mid = GetTimeMicros();

    try {
        FILE* filestr = fsbridge::fopen(GetDataDir() / "mempool.dat.new", "wb");
        if (!filestr) {
            return false;
        }

        CAutoFile file(filestr, SER_DISK, CLIENT_VERSION);

        uint64_t version = MEMPOOL_DUMP_VERSION;
        file << version;

        file << (uint64_t)vinfo.size();
        for (const auto& i : vinfo) {
            file << *(i.tx);
            file << int64_t{count_seconds(i.m_time)};
            file << int64_t{i.nFeeDelta};
            mapDeltas.erase(i.tx->GetHash());
        }

        file << mapDeltas;

        LogPrintf("Writing %d unbroadcast transactions to disk.\n", unbroadcast_txids.size());
        file << unbroadcast_txids;

        if (!FileCommit(file.Get()))
            throw std::runtime_error("FileCommit failed");
        file.fclose();
        RenameOver(GetDataDir() / "mempool.dat.new", GetDataDir() / "mempool.dat");
        int64_t last = GetTimeMicros();
        LogPrintf("Dumped mempool: %gs to copy, %gs to dump\n", (mid-start)*MICRO, (last-mid)*MICRO);
    } catch (const std::exception& e) {
        LogPrintf("Failed to dump mempool: %s. Continuing anyway.\n", e.what());
        return false;
    }
    return true;
}

//! Guess how far we are in the verification process at the given block index
//! require cs_main if pindex has not been validated yet (because nChainTx might be unset)
double GuessVerificationProgress(const ChainTxData& data, const CBlockIndex *pindex) {
    if (pindex == nullptr)
        return 0.0;

    int64_t nNow = time(nullptr);

    double fTxTotal;

    if (pindex->nChainTx <= data.nTxCount) {
        fTxTotal = data.nTxCount + (nNow - data.nTime) * data.dTxRate;
    } else {
        fTxTotal = pindex->nChainTx + (nNow - pindex->GetBlockTime()) * data.dTxRate;
    }

    return std::min<double>(pindex->nChainTx / fTxTotal, 1.0);
}

Optional<uint256> ChainstateManager::SnapshotBlockhash() const {
    if (m_active_chainstate != nullptr) {
        // If a snapshot chainstate exists, it will always be our active.
        return m_active_chainstate->m_from_snapshot_blockhash;
    }
    return {};
}

std::vector<CChainState*> ChainstateManager::GetAll()
{
    std::vector<CChainState*> out;

    if (!IsSnapshotValidated() && m_ibd_chainstate) {
        out.push_back(m_ibd_chainstate.get());
    }

    if (m_snapshot_chainstate) {
        out.push_back(m_snapshot_chainstate.get());
    }

    return out;
}

CChainState& ChainstateManager::InitializeChainstate(CTxMemPool& mempool, const uint256& snapshot_blockhash)
{
    bool is_snapshot = !snapshot_blockhash.IsNull();
    std::unique_ptr<CChainState>& to_modify =
        is_snapshot ? m_snapshot_chainstate : m_ibd_chainstate;

    if (to_modify) {
        throw std::logic_error("should not be overwriting a chainstate");
    }
    to_modify.reset(new CChainState(mempool, m_blockman, snapshot_blockhash));

    // Snapshot chainstates and initial IBD chaintates always become active.
    if (is_snapshot || (!is_snapshot && !m_active_chainstate)) {
        LogPrintf("Switching active chainstate to %s\n", to_modify->ToString());
        m_active_chainstate = to_modify.get();
    } else {
        throw std::logic_error("unexpected chainstate activation");
    }

    return *to_modify;
}

CChainState& ChainstateManager::ActiveChainstate() const
{
    assert(m_active_chainstate);
    return *m_active_chainstate;
}

bool ChainstateManager::IsSnapshotActive() const
{
    return m_snapshot_chainstate && m_active_chainstate == m_snapshot_chainstate.get();
}

CChainState& ChainstateManager::ValidatedChainstate() const
{
    if (m_snapshot_chainstate && IsSnapshotValidated()) {
        return *m_snapshot_chainstate.get();
    }
    assert(m_ibd_chainstate);
    return *m_ibd_chainstate.get();
}

bool ChainstateManager::IsBackgroundIBD(CChainState* chainstate) const
{
    return (m_snapshot_chainstate && chainstate == m_ibd_chainstate.get());
}

void ChainstateManager::Unload()
{
    for (CChainState* chainstate : this->GetAll()) {
        chainstate->m_chain.SetTip(nullptr);
        chainstate->UnloadBlockIndex();
    }

    m_blockman.Unload();
}

void ChainstateManager::Reset()
{
    m_ibd_chainstate.reset();
    m_snapshot_chainstate.reset();
    m_active_chainstate = nullptr;
    m_snapshot_validated = false;
}

void ChainstateManager::MaybeRebalanceCaches()
{
    if (m_ibd_chainstate && !m_snapshot_chainstate) {
        LogPrintf("[snapshot] allocating all cache to the IBD chainstate\n");
        // Allocate everything to the IBD chainstate.
        m_ibd_chainstate->ResizeCoinsCaches(m_total_coinstip_cache, m_total_coinsdb_cache);
    }
    else if (m_snapshot_chainstate && !m_ibd_chainstate) {
        LogPrintf("[snapshot] allocating all cache to the snapshot chainstate\n");
        // Allocate everything to the snapshot chainstate.
        m_snapshot_chainstate->ResizeCoinsCaches(m_total_coinstip_cache, m_total_coinsdb_cache);
    }
    else if (m_ibd_chainstate && m_snapshot_chainstate) {
        // If both chainstates exist, determine who needs more cache based on IBD status.
        //
        // Note: shrink caches first so that we don't inadvertently overwhelm available memory.
        if (m_snapshot_chainstate->IsInitialBlockDownload()) {
            m_ibd_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.05, m_total_coinsdb_cache * 0.05);
            m_snapshot_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.95, m_total_coinsdb_cache * 0.95);
        } else {
            m_snapshot_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.05, m_total_coinsdb_cache * 0.05);
            m_ibd_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.95, m_total_coinsdb_cache * 0.95);
        }
    }
}