text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2018 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 <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 <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 <timedata.h>
  #include <tinyformat.h>
  #include <txdb.h>
  #include <txmempool.h>
  #include <ui_interface.h>
  #include <uint256.h>
  #include <undo.h>
  #include <util/moneystr.h>
  #include <util/rbf.h>
  #include <util/strencodings.h>
  #include <util/system.h>
  #include <util/translation.h>
  #include <util/validation.h>
  #include <validationinterface.h>
  #include <warnings.h>
  
  #include <string>
  
  #include <boost/algorithm/string/replace.hpp>
  #include <boost/thread.hpp>
  
  #if defined(NDEBUG)
  # error "Bitcoin cannot be compiled without assertions."
  #endif
  
  #define MICRO 0.000001
  #define MILLI 0.001
  
  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;
  }
  
  namespace {
  BlockManager g_blockman;
  } // anon namespace
  
  std::unique_ptr<CChainState> g_chainstate;
  
  CChainState& ChainstateActive() {
      assert(g_chainstate);
      return *g_chainstate;
  }
  
  CChain& ChainActive() {
      assert(g_chainstate);
      return g_chainstate->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;
  int nScriptCheckThreads = 0;
  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;
  size_t nCoinCacheUsage = 5000 * 300;
  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;
  CTxMemPool mempool(&feeEstimator);
  
  /** Constant stuff for coinbase transactions we create: */
  CScript COINBASE_FLAGS;
  
  // Internal stuff
  namespace {
      CBlockIndex* pindexBestInvalid = nullptr;
  
      CCriticalSection 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_blockman.m_block_index.find(hash);
      return it == g_blockman.m_block_index.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;
  
  // See definition for documentation
  static void FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight);
  static void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight);
  bool CheckInputs(const CTransaction& tx, CValidationState &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() < (GetTime() - 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(DisconnectedBlockTransactions& disconnectpool, bool fAddToMempool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs)
  {
      AssertLockHeld(cs_main);
      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
          CValidationState stateDummy;
          if (!fAddToMempool || (*it)->IsCoinBase() ||
              !AcceptToMemoryPool(mempool, stateDummy, *it, nullptr /* pfMissingInputs */,
                                  nullptr /* plTxnReplaced */, true /* bypass_limits */, 0 /* nAbsurdFee */)) {
              // 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, CValidationState& 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 CheckInputs
      LOCK(pool.cs);
  
      assert(!tx.IsCoinBase());
      for (const CTxIn& txin : tx.vin) {
          const Coin& coin = view.AccessCoin(txin.prevout);
  
          // At this point we haven't actually checked if the coins are all
          // available (or shouldn't assume we have, since CheckInputs does).
          // So we just return failure if the inputs are not available here,
          // and then only have to check equivalence for available inputs.
          if (coin.IsSpent()) return false;
  
          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 CheckInputs() to cache signature and script validity against current tip consensus rules.
      return CheckInputs(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;
          CValidationState &m_state;
          bool* m_missing_inputs;
          const int64_t m_accept_time;
          std::list<CTransactionRef>* m_replaced_transactions;
          const bool m_bypass_limits;
          const CAmount& m_absurd_fee;
          /*
           * 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;
      };
  
      // 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, CValidationState& 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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "mempool min fee not met", strprintf("%d < %d", package_fee, mempoolRejectFee));
          }
  
          if (package_fee < ::minRelayTxFee.GetFee(package_size)) {
              return state.Invalid(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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
      CValidationState &state = args.m_state;
      bool* pfMissingInputs = args.m_missing_inputs;
      const int64_t nAcceptTime = args.m_accept_time;
      const bool bypass_limits = args.m_bypass_limits;
      const CAmount& nAbsurdFee = args.m_absurd_fee;
      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 (pfMissingInputs) {
          *pfMissingInputs = false;
      }
  
      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(ValidationInvalidReason::CONSENSUS, false, "coinbase");
  
      // Rather not work on nonstandard transactions (unless -testnet/-regtest)
      std::string reason;
      if (fRequireStandard && !IsStandardTx(tx, reason))
          return state.Invalid(ValidationInvalidReason::TX_NOT_STANDARD, false, 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(ValidationInvalidReason::TX_NOT_STANDARD, false, "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(ValidationInvalidReason::TX_PREMATURE_SPEND, false, "non-final");
  
      // is it already in the memory pool?
      if (m_pool.exists(hash)) {
          return state.Invalid(ValidationInvalidReason::TX_CONFLICT, false, "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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "txn-mempool-conflict");
                  }
  
                  setConflicts.insert(ptxConflicting->GetHash());
              }
          }
      }
  
      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++) {
                  // Optimistically just do efficient check of cache for outputs
                  if (coins_cache.HaveCoinInCache(COutPoint(hash, out))) {
                      return state.Invalid(ValidationInvalidReason::TX_CONFLICT, false, "txn-already-known");
                  }
              }
              // Otherwise assume this might be an orphan tx for which we just haven't seen parents yet
              if (pfMissingInputs) {
                  *pfMissingInputs = true;
              }
              return false; // fMissingInputs and !state.IsInvalid() is used to detect this condition, don't set state.Invalid()
          }
      }
  
      // Bring the best block into scope
      m_view.GetBestBlock();
  
      // 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(ValidationInvalidReason::TX_PREMATURE_SPEND, false, "non-BIP68-final");
  
      CAmount nFees = 0;
      if (!Consensus::CheckTxInputs(tx, state, m_view, GetSpendHeight(m_view), nFees)) {
          return error("%s: Consensus::CheckTxInputs: %s, %s", __func__, tx.GetHash().ToString(), FormatStateMessage(state));
      }
  
      // Check for non-standard pay-to-script-hash in inputs
      if (fRequireStandard && !AreInputsStandard(tx, m_view))
          return state.Invalid(ValidationInvalidReason::TX_NOT_STANDARD, false, "bad-txns-nonstandard-inputs");
  
      // Check for non-standard witness in P2WSH
      if (tx.HasWitness() && fRequireStandard && !IsWitnessStandard(tx, m_view))
          return state.Invalid(ValidationInvalidReason::TX_WITNESS_MUTATED, false, "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(ValidationInvalidReason::TX_NOT_STANDARD, false, "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;
  
      if (nAbsurdFee && nFees > nAbsurdFee)
          return state.Invalid(ValidationInvalidReason::TX_NOT_STANDARD, false,
                  "absurdly-high-fee", strprintf("%d > %d", nFees, nAbsurdFee));
  
      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 dependant 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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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(ValidationInvalidReason::CONSENSUS, false, "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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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;
  
      CValidationState &state = args.m_state;
  
      constexpr unsigned int scriptVerifyFlags = STANDARD_SCRIPT_VERIFY_FLAGS;
  
      // Check against previous transactions
      // This is done last to help prevent CPU exhaustion denial-of-service attacks.
      if (!CheckInputs(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.
          CValidationState stateDummy; // Want reported failures to be from first CheckInputs
          if (!tx.HasWitness() && CheckInputs(tx, stateDummy, m_view, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, false, txdata) &&
                  !CheckInputs(tx, stateDummy, m_view, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, false, txdata)) {
              // Only the witness is missing, so the transaction itself may be fine.
              state.Invalid(ValidationInvalidReason::TX_WITNESS_MUTATED, false,
                      state.GetRejectReason(), state.GetDebugMessage());
          }
          assert(IsTransactionReason(state.GetReason()));
          return false; // state filled in by CheckInputs
      }
  
      return true;
  }
  
  bool MemPoolAccept::ConsensusScriptChecks(ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata)
  {
      const CTransaction& tx = *ws.m_ptx;
      const uint256& hash = ws.m_hash;
  
      CValidationState &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.
      unsigned int currentBlockScriptVerifyFlags = GetBlockScriptFlags(::ChainActive().Tip(), chainparams.GetConsensus());
      if (!CheckInputsFromMempoolAndCache(tx, state, m_view, m_pool, currentBlockScriptVerifyFlags, txdata)) {
          return error("%s: BUG! PLEASE REPORT THIS! CheckInputs failed against latest-block but not STANDARD flags %s, %s",
                  __func__, hash.ToString(), FormatStateMessage(state));
      }
  
      return true;
  }
  
  bool MemPoolAccept::Finalize(ATMPArgs& args, Workspace& ws)
  {
      const CTransaction& tx = *ws.m_ptx;
      const uint256& hash = ws.m_hash;
      CValidationState &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 BTC 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(ValidationInvalidReason::TX_MEMPOOL_POLICY, false, "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(*ptx);
  
      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);
  
      return true;
  }
  
  } // anon namespace
  
  /** (try to) add transaction to memory pool with a specified acceptance time **/
  static bool AcceptToMemoryPoolWithTime(const CChainParams& chainparams, CTxMemPool& pool, CValidationState &state, const CTransactionRef &tx,
                          bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
                          bool bypass_limits, const CAmount nAbsurdFee, bool test_accept) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      std::vector<COutPoint> coins_to_uncache;
      MemPoolAccept::ATMPArgs args { chainparams, state, pfMissingInputs, nAcceptTime, plTxnReplaced, bypass_limits, nAbsurdFee, coins_to_uncache, test_accept };
      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
      CValidationState stateDummy;
      ::ChainstateActive().FlushStateToDisk(chainparams, stateDummy, FlushStateMode::PERIODIC);
      return res;
  }
  
  bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransactionRef &tx,
                          bool* pfMissingInputs, std::list<CTransactionRef>* plTxnReplaced,
                          bool bypass_limits, const CAmount nAbsurdFee, bool test_accept)
  {
      const CChainParams& chainparams = Params();
      return AcceptToMemoryPoolWithTime(chainparams, pool, state, tx, pfMissingInputs, GetTime(), plTxnReplaced, bypass_limits, nAbsurdFee, test_accept);
  }
  
  /**
   * Return transaction in txOut, and if it was found inside a block, its hash is placed in hashBlock.
   * If blockIndex is provided, the transaction is fetched from the corresponding block.
   */
  bool GetTransaction(const uint256& hash, CTransactionRef& txOut, const Consensus::Params& consensusParams, uint256& hashBlock, const CBlockIndex* const block_index)
  {
      LOCK(cs_main);
  
      if (!block_index) {
          CTransactionRef ptx = mempool.get(hash);
          if (ptx) {
              txOut = ptx;
              return true;
          }
  
          if (g_txindex) {
              return g_txindex->FindTx(hash, hashBlock, txOut);
          }
      } else {
          CBlock block;
          if (ReadBlockFromDisk(block, block_index, consensusParams)) {
              for (const auto& tx : block.vtx) {
                  if (tx->GetHash() == hash) {
                      txOut = tx;
                      hashBlock = block_index->GetBlockHash();
                      return true;
                  }
              }
          }
      }
  
      return false;
  }
  
  
  
  
  
  
  //////////////////////////////////////////////////////////////////////////////
  //
  // CBlock and CBlockIndex
  //
  
  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;
  }
  
  bool ReadBlockFromDisk(CBlock& 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.GetHash(), block.nBits, consensusParams))
          return error("ReadBlockFromDisk: Errors in block header at %s", pos.ToString());
  
      return true;
  }
  
  bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
  {
      FlatFilePos blockPos;
      {
          LOCK(cs_main);
          blockPos = pindex->GetBlockPos();
      }
  
      if (!ReadBlockFromDisk(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 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, blk_start + CMessageHeader::MESSAGE_START_SIZE),
                      HexStr(message_start, message_start + CMessageHeader::MESSAGE_START_SIZE));
          }
  
          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);
  }
  
  // NOTE: for now m_blockman is set to a global, but this will be changed
  // in a future commit.
  CChainState::CChainState() : m_blockman(g_blockman) {}
  
  
  void CChainState::InitCoinsDB(
      size_t cache_size_bytes,
      bool in_memory,
      bool should_wipe,
      std::string leveldb_name)
  {
      m_coins_views = MakeUnique<CoinsViews>(
          leveldb_name, cache_size_bytes, in_memory, should_wipe);
  }
  
  void CChainState::InitCoinsCache()
  {
      assert(m_coins_views != nullptr);
      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;
  
  BlockMap& BlockIndex()
  {
      return g_blockman.m_block_index;
  }
  
  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();
  }
  
  void static InvalidChainFound(CBlockIndex* pindexNew) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      if (!pindexBestInvalid || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
          pindexBestInvalid = pindexNew;
  
      LogPrintf("%s: invalid block=%s  height=%d  log2_work=%.8g  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=%.8g  date=%s\n", __func__,
        tip->GetBlockHash().ToString(), ::ChainActive().Height(), log(tip->nChainWork.getdouble())/log(2.0),
        FormatISO8601DateTime(tip->GetBlockTime()));
      CheckForkWarningConditions();
  }
  
  void CChainState::InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state) {
      if (state.GetReason() != ValidationInvalidReason::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> scriptExecutionCache;
  static uint256 scriptExecutionCacheNonce(GetRandHash());
  
  void InitScriptExecutionCache() {
      // 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 = 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 inputs of this transaction are valid (no double spends, scripts & sigs, amounts)
   * This does not modify the UTXO set.
   *
   * 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 CheckInputs(const CTransaction& tx, CValidationState &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;
      // We only use the first 19 bytes of nonce to avoid a second SHA
      // round - giving us 19 + 32 + 4 = 55 bytes (+ 8 + 1 = 64)
      static_assert(55 - sizeof(flags) - 32 >= 128/8, "Want at least 128 bits of nonce for script execution cache");
      CSHA256().Write(scriptExecutionCacheNonce.begin(), 55 - sizeof(flags) - 32).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 (scriptExecutionCache.contains(hashCacheEntry, !cacheFullScriptStore)) {
          return true;
      }
  
      for (unsigned int i = 0; i < tx.vin.size(); i++) {
          const COutPoint &prevout = tx.vin[i].prevout;
          const Coin& coin = inputs.AccessCoin(prevout);
          assert(!coin.IsSpent());
  
          // 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(coin.out, 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(coin.out, tx, i,
                          flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheSigStore, &txdata);
                  if (check2())
                      return state.Invalid(ValidationInvalidReason::TX_NOT_STANDARD, false, strprintf("non-mandatory-script-verify-flag (%s)", ScriptErrorString(check.GetScriptError())));
              }
              // MANDATORY flag failures correspond to
              // ValidationInvalidReason::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(ValidationInvalidReason::CONSENSUS, false, 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.
          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, const std::string& userMessage = "", unsigned int prefix = 0)
  {
      SetMiscWarning(strMessage);
      LogPrintf("*** %s\n", strMessage);
      if (!userMessage.empty()) {
          uiInterface.ThreadSafeMessageBox(userMessage, "", CClientUIInterface::MSG_ERROR | prefix);
      } else {
          uiInterface.ThreadSafeMessageBox(_("Error: A fatal internal error occurred, see debug.log for details").translated, "", CClientUIInterface::MSG_ERROR | CClientUIInterface::MSG_NOPREFIX);
      }
      StartShutdown();
      return false;
  }
  
  static bool AbortNode(CValidationState& state, const std::string& strMessage, const std::string& userMessage = "", unsigned int prefix = 0)
  {
      AbortNode(strMessage, userMessage, prefix);
      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
          }
      }
      // The potential_overwrite parameter to AddCoin is only allowed to be false if we know for
      // sure that the coin did not already exist in the cache. As we have queried for that above
      // using HaveCoin, we don't need to guess. When fClean is false, a 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)
  {
      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 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) {
                      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.
          }
      }
  
      // move best block pointer to prevout block
      view.SetBestBlock(pindex->pprev->GetBlockHash());
  
      return fClean ? DISCONNECT_OK : DISCONNECT_UNCLEAN;
  }
  
  void static FlushBlockFile(bool fFinalize = false)
  {
      LOCK(cs_LastBlockFile);
  
      FlatFilePos block_pos_old(nLastBlockFile, vinfoBlockFile[nLastBlockFile].nSize);
      FlatFilePos undo_pos_old(nLastBlockFile, vinfoBlockFile[nLastBlockFile].nUndoSize);
  
      bool status = true;
      status &= BlockFileSeq().Flush(block_pos_old, fFinalize);
      status &= UndoFileSeq().Flush(undo_pos_old, fFinalize);
      if (!status) {
          AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");
      }
  }
  
  static bool FindUndoPos(CValidationState &state, int nFile, FlatFilePos &pos, unsigned int nAddSize);
  
  static bool WriteUndoDataForBlock(const CBlockUndo& blockundo, CValidationState& 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");
  
          // 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);
  
  // 0.13.0 was shipped with a segwit deployment defined for testnet, but not for
  // mainnet. We no longer need to support disabling the segwit deployment
  // except for testing purposes, due to limitations of the functional test
  // environment. See test/functional/p2p-segwit.py.
  static bool IsScriptWitnessEnabled(const Consensus::Params& params)
  {
      return params.SegwitHeight != std::numeric_limits<int>::max();
  }
  
  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;
  
      // BIP16 didn't become active until Apr 1 2012 (on mainnet, and
      // retroactively applied to testnet)
      // However, only one historical block violated the P2SH rules (on both
      // mainnet and testnet), so for simplicity, always leave P2SH
      // on except for the one violating block.
      if (consensusparams.BIP16Exception.IsNull() || // no bip16 exception on this chain
          pindex->phashBlock == nullptr || // this is a new candidate block, eg from TestBlockValidity()
          *pindex->phashBlock != consensusparams.BIP16Exception) // this block isn't the historical exception
      {
          flags |= SCRIPT_VERIFY_P2SH;
      }
  
      // Enforce WITNESS rules whenever P2SH is in effect (and the segwit
      // deployment is defined).
      if (flags & SCRIPT_VERIFY_P2SH && IsScriptWitnessEnabled(consensusparams)) {
          flags |= SCRIPT_VERIFY_WITNESS;
      }
  
      // 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 BIP147 NULLDUMMY (activated simultaneously with segwit)
      if (IsWitnessEnabled(pindex->pprev, consensusparams)) {
          flags |= SCRIPT_VERIFY_NULLDUMMY;
      }
  
      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, CValidationState& state, CBlockIndex* pindex,
                    CCoinsViewCache& view, 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.GetReason() == ValidationInvalidReason::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__, FormatStateMessage(state));
      }
  
      // 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());
  
      // 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;
      }
  
      nBlocksTotal++;
  
      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.
      // This rule was originally applied to all blocks with a timestamp after March 15, 2012, 0:00 UTC.
      // Now that the whole chain is irreversibly beyond that time it is applied to all blocks except the
      // two in the chain that violate it. This prevents exploiting the issue against nodes during their
      // initial block download.
      bool fEnforceBIP30 = !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256S("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
                             (pindex->nHeight==91880 && pindex->GetBlockHash() == uint256S("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721")));
  
      // Once BIP34 activated it was not possible to create new duplicate coinbases and thus other than starting
      // with the 2 existing duplicate coinbase pairs, not possible to create overwriting txs.  But by the
      // time BIP34 activated, in each of the existing pairs the duplicate coinbase had overwritten the first
      // before the first had been spent.  Since those coinbases are sufficiently buried it's no longer possible to create further
      // duplicate transactions descending from the known pairs either.
      // If we're on the known chain at height greater than where BIP34 activated, we can save the db accesses needed for the BIP30 check.
  
      // BIP34 requires that a block at height X (block X) has its coinbase
      // scriptSig start with a CScriptNum of X (indicated height X).  The above
      // logic of no longer requiring BIP30 once BIP34 activates is flawed in the
      // case that there is a block X before the BIP34 height of 227,931 which has
      // an indicated height Y where Y is greater than X.  The coinbase for block
      // X would also be a valid coinbase for block Y, which could be a BIP30
      // violation.  An exhaustive search of all mainnet coinbases before the
      // BIP34 height which have an indicated height greater than the block height
      // reveals many occurrences. The 3 lowest indicated heights found are
      // 209,921, 490,897, and 1,983,702 and thus coinbases for blocks at these 3
      // heights would be the first opportunity for BIP30 to be violated.
  
      // The search reveals a great many blocks which have an indicated height
      // greater than 1,983,702, so we simply remove the optimization to skip
      // BIP30 checking for blocks at height 1,983,702 or higher.  Before we reach
      // that block in another 25 years or so, we should take advantage of a
      // future consensus change to do a new and improved version of BIP34 that
      // will actually prevent ever creating any duplicate coinbases in the
      // future.
      static constexpr int BIP34_IMPLIES_BIP30_LIMIT = 1983702;
  
      // There is no potential to create a duplicate coinbase at block 209,921
      // because this is still before the BIP34 height and so explicit BIP30
      // checking is still active.
  
      // The final case is block 176,684 which has an indicated height of
      // 490,897. Unfortunately, this issue was not discovered until about 2 weeks
      // before block 490,897 so there was not much opportunity to address this
      // case other than to carefully analyze it and determine it would not be a
      // problem. Block 490,897 was, in fact, mined with a different coinbase than
      // block 176,684, but it is important to note that even if it hadn't been or
      // is remined on an alternate fork with a duplicate coinbase, we would still
      // not run into a BIP30 violation.  This is because the coinbase for 176,684
      // is spent in block 185,956 in transaction
      // d4f7fbbf92f4a3014a230b2dc70b8058d02eb36ac06b4a0736d9d60eaa9e8781.  This
      // spending transaction can't be duplicated because it also spends coinbase
      // 0328dd85c331237f18e781d692c92de57649529bd5edf1d01036daea32ffde29.  This
      // coinbase has an indicated height of over 4.2 billion, and wouldn't be
      // duplicatable until that height, and it's currently impossible to create a
      // chain that long. Nevertheless we may wish to consider a future soft fork
      // which retroactively prevents block 490,897 from creating a duplicate
      // coinbase. The two historical BIP30 violations often provide a confusing
      // edge case when manipulating the UTXO and it would be simpler not to have
      // another edge case to deal with.
  
      // testnet3 has no blocks before the BIP34 height with indicated heights
      // post BIP34 before approximately height 486,000,000 and presumably will
      // be reset before it reaches block 1,983,702 and starts doing unnecessary
      // BIP30 checking again.
      assert(pindex->pprev);
      CBlockIndex *pindexBIP34height = pindex->pprev->GetAncestor(chainparams.GetConsensus().BIP34Height);
      //Only continue to enforce if we're below BIP34 activation height or the block hash at that height doesn't correspond.
      fEnforceBIP30 = fEnforceBIP30 && (!pindexBIP34height || !(pindexBIP34height->GetBlockHash() == chainparams.GetConsensus().BIP34Hash));
  
      // TODO: Remove BIP30 checking from block height 1,983,702 on, once we have a
      // consensus change that ensures coinbases at those heights can not
      // duplicate earlier coinbases.
      if (fEnforceBIP30 || pindex->nHeight >= BIP34_IMPLIES_BIP30_LIMIT) {
          for (const auto& tx : block.vtx) {
              for (size_t o = 0; o < tx->vout.size(); o++) {
                  if (view.HaveCoin(COutPoint(tx->GetHash(), o))) {
                      return state.Invalid(ValidationInvalidReason::CONSENSUS, error("ConnectBlock(): tried to overwrite transaction"),
                                       "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;
  
      CCheckQueueControl<CScriptCheck> control(fScriptChecks && nScriptCheckThreads ? &scriptcheckqueue : nullptr);
  
      std::vector<int> prevheights;
      CAmount nFees = 0;
      int nInputs = 0;
      int64_t nSigOpsCost = 0;
      blockundo.vtxundo.reserve(block.vtx.size() - 1);
      std::vector<PrecomputedTransactionData> txdata;
      txdata.reserve(block.vtx.size()); // Required so that pointers to individual PrecomputedTransactionData don't get invalidated
      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;
              if (!Consensus::CheckTxInputs(tx, state, view, pindex->nHeight, txfee)) {
                  if (!IsBlockReason(state.GetReason())) {
                      // CheckTxInputs may return MISSING_INPUTS or
                      // PREMATURE_SPEND but we can't return that, as it's not
                      // defined for a block, so we reset the reason flag to
                      // CONSENSUS here.
                      state.Invalid(ValidationInvalidReason::CONSENSUS, false,
                              state.GetRejectReason(), state.GetDebugMessage());
                  }
                  return error("%s: Consensus::CheckTxInputs: %s, %s", __func__, tx.GetHash().ToString(), FormatStateMessage(state));
              }
              nFees += txfee;
              if (!MoneyRange(nFees)) {
                  return state.Invalid(ValidationInvalidReason::CONSENSUS, error("%s: accumulated fee in the block out of range.", __func__),
                                   "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)) {
                  return state.Invalid(ValidationInvalidReason::CONSENSUS, error("%s: contains a non-BIP68-final transaction", __func__),
                                   "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)
              return state.Invalid(ValidationInvalidReason::CONSENSUS, error("ConnectBlock(): too many sigops"),
                               "bad-blk-sigops");
  
          txdata.emplace_back(tx);
          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) */
              if (fScriptChecks && !CheckInputs(tx, state, view, flags, fCacheResults, fCacheResults, txdata[i], nScriptCheckThreads ? &vChecks : nullptr)) {
                  if (state.GetReason() == ValidationInvalidReason::TX_NOT_STANDARD) {
                      // CheckInputs may return NOT_STANDARD for extra flags we passed,
                      // but we can't return that, as it's not defined for a block, so
                      // we reset the reason flag to CONSENSUS here.
                      // In the event of a future soft-fork, we may need to
                      // consider whether rewriting to CONSENSUS or
                      // RECENT_CONSENSUS_CHANGE would be more appropriate.
                      state.Invalid(ValidationInvalidReason::CONSENSUS, false,
                                state.GetRejectReason(), state.GetDebugMessage());
                  }
                  return error("ConnectBlock(): CheckInputs on %s failed with %s",
                      tx.GetHash().ToString(), FormatStateMessage(state));
              }
              control.Add(vChecks);
          }
  
          CTxUndo undoDummy;
          if (i > 0) {
              blockundo.vtxundo.push_back(CTxUndo());
          }
          UpdateCoins(tx, view, i == 0 ? undoDummy : blockundo.vtxundo.back(), pindex->nHeight);
      }
      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)
          return state.Invalid(ValidationInvalidReason::CONSENSUS,
                           error("ConnectBlock(): coinbase pays too much (actual=%d vs limit=%d)",
                                 block.vtx[0]->GetValueOut(), blockReward),
                                 "bad-cb-amount");
  
      if (!control.Wait())
          return state.Invalid(ValidationInvalidReason::CONSENSUS, error("%s: CheckQueue failed", __func__), "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;
  
      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;
  }
  
  bool CChainState::FlushStateToDisk(
      const CChainParams& chainparams,
      CValidationState &state,
      FlushStateMode mode,
      int nManualPruneHeight)
  {
      int64_t nMempoolUsage = mempool.DynamicMemoryUsage();
      LOCK(cs_main);
      assert(this->CanFlushToDisk());
      static int64_t nLastWrite = 0;
      static int64_t nLastFlush = 0;
      std::set<int> setFilesToPrune;
      bool full_flush_completed = false;
      try {
      {
          bool fFlushForPrune = false;
          bool fDoFullFlush = false;
          LOCK(cs_LastBlockFile);
          if (fPruneMode && (fCheckForPruning || nManualPruneHeight > 0) && !fReindex) {
              if (nManualPruneHeight > 0) {
                  FindFilesToPruneManual(setFilesToPrune, nManualPruneHeight);
              } else {
                  FindFilesToPrune(setFilesToPrune, chainparams.PruneAfterHeight());
                  fCheckForPruning = false;
              }
              if (!setFilesToPrune.empty()) {
                  fFlushForPrune = true;
                  if (!fHavePruned) {
                      pblocktree->WriteFlag("prunedblockfiles", true);
                      fHavePruned = true;
                  }
              }
          }
          int64_t nNow = GetTimeMicros();
          // Avoid writing/flushing immediately after startup.
          if (nLastWrite == 0) {
              nLastWrite = nNow;
          }
          if (nLastFlush == 0) {
              nLastFlush = nNow;
          }
          int64_t nMempoolSizeMax = gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000;
          int64_t cacheSize = CoinsTip().DynamicMemoryUsage();
          int64_t nTotalSpace = nCoinCacheUsage + std::max<int64_t>(nMempoolSizeMax - nMempoolUsage, 0);
          // 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 && cacheSize > std::max((9 * nTotalSpace) / 10, nTotalSpace - MAX_BLOCK_COINSDB_USAGE * 1024 * 1024);
          // The cache is over the limit, we have to write now.
          bool fCacheCritical = mode == FlushStateMode::IF_NEEDED && cacheSize > nTotalSpace;
          // 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 + (int64_t)DATABASE_WRITE_INTERVAL * 1000000;
          // It's been very long since we flushed the cache. Do this infrequently, to optimize cache usage.
          bool fPeriodicFlush = mode == FlushStateMode::PERIODIC && nNow > nLastFlush + (int64_t)DATABASE_FLUSH_INTERVAL * 1000000;
          // 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!", _("Error: Disk space is too low!").translated, CClientUIInterface::MSG_NOPREFIX);
              }
              // 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).
              {
                  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)
                  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()) {
              // 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!", _("Error: Disk space is too low!").translated, CClientUIInterface::MSG_NOPREFIX);
              }
              // 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() {
      CValidationState state;
      const CChainParams& chainparams = Params();
      if (!this->FlushStateToDisk(chainparams, state, FlushStateMode::ALWAYS)) {
          LogPrintf("%s: failed to flush state (%s)\n", __func__, FormatStateMessage(state));
      }
  }
  
  void CChainState::PruneAndFlush() {
      CValidationState state;
      fCheckForPruning = true;
      const CChainParams& chainparams = Params();
  
      if (!this->FlushStateToDisk(chainparams, state, FlushStateMode::NONE)) {
          LogPrintf("%s: failed to flush state (%s)\n", __func__, FormatStateMessage(state));
      }
  }
  
  static void DoWarning(const std::string& strWarning)
  {
      static bool fWarned = false;
      SetMiscWarning(strWarning);
      if (!fWarned) {
          AlertNotify(strWarning);
          fWarned = true;
      }
  }
  
  /** Private helper function that concatenates warning messages. */
  static void AppendWarning(std::string& res, const std::string& warn)
  {
      if (!res.empty()) res += ", ";
      res += warn;
  }
  
  /** Check warning conditions and do some notifications on new chain tip set. */
  void static UpdateTip(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();
      }
  
      std::string warningMessages;
      if (!::ChainstateActive().IsInitialBlockDownload())
      {
          int nUpgraded = 0;
          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 std::string strWarning = strprintf(_("Warning: unknown new rules activated (versionbit %i)").translated, bit);
                  if (state == ThresholdState::ACTIVE) {
                      DoWarning(strWarning);
                  } else {
                      AppendWarning(warningMessages, strWarning);
                  }
              }
          }
          // 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->nVersion > VERSIONBITS_LAST_OLD_BLOCK_VERSION && (pindex->nVersion & ~nExpectedVersion) != 0)
                  ++nUpgraded;
              pindex = pindex->pprev;
          }
          if (nUpgraded > 0)
              AppendWarning(warningMessages, strprintf(_("%d of last 100 blocks have unexpected version").translated, nUpgraded));
      }
      LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%.8g 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(),
        !warningMessages.empty() ? strprintf(" warning='%s'", warningMessages) : "");
  
  }
  
  /** 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(CValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions *disconnectpool)
  {
      CBlockIndex *pindexDelete = m_chain.Tip();
      assert(pindexDelete);
      // 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.
      int64_t nStart = GetTimeMicros();
      {
          CCoinsViewCache view(&CoinsTip());
          assert(view.GetBestBlock() == pindexDelete->GetBlockHash());
          if (DisconnectBlock(block, pindexDelete, view) != 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;
  
      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();
              mempool.removeRecursive(**it, MemPoolRemovalReason::REORG);
              disconnectpool->removeEntry(it);
          }
      }
  
      m_chain.SetTip(pindexDelete->pprev);
  
      UpdateTip(pindexDelete->pprev, chainparams);
      // Let wallets know transactions went from 1-confirmed to
      // 0-confirmed or conflicted:
      GetMainSignals().BlockDisconnected(pblock);
      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;
      std::shared_ptr<std::vector<CTransactionRef>> conflictedTxs;
      PerBlockConnectTrace() : conflictedTxs(std::make_shared<std::vector<CTransactionRef>>()) {}
  };
  /**
   * Used to track blocks whose transactions were applied to the UTXO state as a
   * part of a single ActivateBestChainStep call.
   *
   * This class also tracks transactions that are removed from the mempool as
   * conflicts (per block) and can be used to pass all those transactions
   * through SyncTransaction.
   *
   * This class assumes (and asserts) that the conflicted transactions for a given
   * block are added via mempool callbacks prior to the BlockConnected() associated
   * with those transactions. If any transactions are marked conflicted, it is
   * assumed that an associated block will always be added.
   *
   * 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;
      CTxMemPool &pool;
      boost::signals2::scoped_connection m_connNotifyEntryRemoved;
  
  public:
      explicit ConnectTrace(CTxMemPool &_pool) : blocksConnected(1), pool(_pool) {
          m_connNotifyEntryRemoved = pool.NotifyEntryRemoved.connect(std::bind(&ConnectTrace::NotifyEntryRemoved, this, std::placeholders::_1, std::placeholders::_2));
      }
  
      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);
          assert(blocksConnected.back().conflictedTxs->empty());
          blocksConnected.pop_back();
          return blocksConnected;
      }
  
      void NotifyEntryRemoved(CTransactionRef txRemoved, MemPoolRemovalReason reason) {
          assert(!blocksConnected.back().pindex);
          if (reason == MemPoolRemovalReason::CONFLICT) {
              blocksConnected.back().conflictedTxs->emplace_back(std::move(txRemoved));
          }
      }
  };
  
  /**
   * 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(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions &disconnectpool)
  {
      assert(pindexNew->pprev == m_chain.Tip());
      // 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.
      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, chainparams);
          GetMainSignals().BlockChecked(blockConnecting, state);
          if (!rv) {
              if (state.IsInvalid())
                  InvalidBlockFound(pindexNew, state);
              return error("%s: ConnectBlock %s failed, %s", __func__, pindexNew->GetBlockHash().ToString(), FormatStateMessage(state));
          }
          nTime3 = GetTimeMicros(); nTimeConnectTotal += nTime3 - nTime2;
          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.;
      mempool.removeForBlock(blockConnecting.vtx, pindexNew->nHeight);
      disconnectpool.removeForBlock(blockConnecting.vtx);
      // Update m_chain & related variables.
      m_chain.SetTip(pindexNew);
      UpdateTip(pindexNew, chainparams);
  
      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(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace)
  {
      AssertLockHeld(cs_main);
  
      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(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.GetReason() != ValidationInvalidReason::BLOCK_MUTATED) {
                          InvalidChainFound(vpindexToConnect.front());
                      }
                      state = CValidationState();
                      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(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(disconnectpool, true);
      }
      mempool.check(&CoinsTip());
  
      // Callbacks/notifications for a new best chain.
      if (fInvalidFound)
          CheckForkWarningConditionsOnNewFork(vpindexToConnect.back());
      else
          CheckForkWarningConditions();
  
      return true;
  }
  
  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(fInitialBlockDownload, pindexHeader);
      }
      return fNotify;
  }
  
  static void LimitValidationInterfaceQueue() LOCKS_EXCLUDED(cs_main) {
      AssertLockNotHeld(cs_main);
  
      if (GetMainSignals().CallbacksPending() > 10) {
          SyncWithValidationInterfaceQueue();
      }
  }
  
  bool CChainState::ActivateBestChain(CValidationState &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 {
          boost::this_thread::interruption_point();
  
          // 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();
  
          {
              LOCK2(cs_main, ::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(mempool); // 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, trace.conflictedTxs);
                  }
              } 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(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(CValidationState &state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock) {
      return ::ChainstateActive().ActivateBestChain(state, chainparams, std::move(pblock));
  }
  
  bool CChainState::PreciousBlock(CValidationState& 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(CValidationState& state, const CChainParams& params, CBlockIndex *pindex) {
      return ::ChainstateActive().PreciousBlock(state, params, pindex);
  }
  
  bool CChainState::InvalidateBlock(CValidationState& 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(::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(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(IsInitialBlockDownload(), to_mark_failed->pprev);
      }
      return true;
  }
  
  bool InvalidateBlock(CValidationState& 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);
      }
  
      if (!fKnown) {
          while (vinfoBlockFile[nFile].nSize + nAddSize >= MAX_BLOCKFILE_SIZE) {
              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);
          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!", _("Error: Disk space is too low!").translated, CClientUIInterface::MSG_NOPREFIX);
          }
          if (bytes_allocated != 0 && fPruneMode) {
              fCheckForPruning = true;
          }
      }
  
      setDirtyFileInfo.insert(nFile);
      return true;
  }
  
  static bool FindUndoPos(CValidationState &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!", _("Error: Disk space is too low!").translated, CClientUIInterface::MSG_NOPREFIX);
      }
      if (bytes_allocated != 0 && fPruneMode) {
          fCheckForPruning = true;
      }
  
      return true;
  }
  
  static bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW = true)
  {
      // Check proof of work matches claimed amount
      if (fCheckPOW && !CheckProofOfWork(block.GetHash(), block.nBits, consensusParams))
          return state.Invalid(ValidationInvalidReason::BLOCK_INVALID_HEADER, false, "high-hash", "proof of work failed");
  
      return true;
  }
  
  bool CheckBlock(const CBlock& block, CValidationState& 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;
  
      // Check the merkle root.
      if (fCheckMerkleRoot) {
          bool mutated;
          uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated);
          if (block.hashMerkleRoot != hashMerkleRoot2)
              return state.Invalid(ValidationInvalidReason::BLOCK_MUTATED, false, "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(ValidationInvalidReason::BLOCK_MUTATED, false, "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(ValidationInvalidReason::CONSENSUS, false, "bad-blk-length", "size limits failed");
  
      // First transaction must be coinbase, the rest must not be
      if (block.vtx.empty() || !block.vtx[0]->IsCoinBase())
          return state.Invalid(ValidationInvalidReason::CONSENSUS, false, "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(ValidationInvalidReason::CONSENSUS, false, "bad-cb-multiple", "more than one coinbase");
  
      // Check transactions
      for (const auto& tx : block.vtx)
          if (!CheckTransaction(*tx, state))
              return state.Invalid(state.GetReason(), false, state.GetRejectReason(),
                                   strprintf("Transaction check failed (tx hash %s) %s", tx->GetHash().ToString(), 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(ValidationInvalidReason::CONSENSUS, false, "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);
  }
  
  int GetWitnessCommitmentIndex(const CBlock& block)
  {
      int commitpos = -1;
      if (!block.vtx.empty()) {
          for (size_t o = 0; o < block.vtx[0]->vout.size(); o++) {
              if (block.vtx[0]->vout[o].scriptPubKey.size() >= 38 && block.vtx[0]->vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0]->vout[o].scriptPubKey[1] == 0x24 && block.vtx[0]->vout[o].scriptPubKey[2] == 0xaa && block.vtx[0]->vout[o].scriptPubKey[3] == 0x21 && block.vtx[0]->vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0]->vout[o].scriptPubKey[5] == 0xed) {
                  commitpos = o;
              }
          }
      }
      return commitpos;
  }
  
  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 != -1 && 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 == -1) {
              uint256 witnessroot = BlockWitnessMerkleRoot(block, nullptr);
              CHash256().Write(witnessroot.begin(), 32).Write(ret.data(), 32).Finalize(witnessroot.begin());
              CTxOut out;
              out.nValue = 0;
              out.scriptPubKey.resize(38);
              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, CValidationState& state, const CChainParams& params, const CBlockIndex* pindexPrev, int64_t nAdjustedTime) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      assert(pindexPrev != nullptr);
      const int nHeight = pindexPrev->nHeight + 1;
  
      // Check proof of work
      const Consensus::Params& consensusParams = params.GetConsensus();
      if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))
          return state.Invalid(ValidationInvalidReason::BLOCK_INVALID_HEADER, false, "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
          // g_blockman.m_block_index.
          CBlockIndex* pcheckpoint = GetLastCheckpoint(params.Checkpoints());
          if (pcheckpoint && nHeight < pcheckpoint->nHeight)
              return state.Invalid(ValidationInvalidReason::BLOCK_CHECKPOINT, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight), "bad-fork-prior-to-checkpoint");
      }
  
      // Check timestamp against prev
      if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
          return state.Invalid(ValidationInvalidReason::BLOCK_INVALID_HEADER, false, "time-too-old", "block's timestamp is too early");
  
      // Check timestamp
      if (block.GetBlockTime() > nAdjustedTime + MAX_FUTURE_BLOCK_TIME)
          return state.Invalid(ValidationInvalidReason::BLOCK_TIME_FUTURE, false, "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.nVersion < 2 && nHeight >= consensusParams.BIP34Height) ||
         (block.nVersion < 3 && nHeight >= consensusParams.BIP66Height) ||
         (block.nVersion < 4 && nHeight >= consensusParams.BIP65Height))
              return state.Invalid(ValidationInvalidReason::BLOCK_INVALID_HEADER, false, 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, CValidationState& 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(ValidationInvalidReason::CONSENSUS, false, "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(ValidationInvalidReason::CONSENSUS, false, "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 != -1) {
              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(ValidationInvalidReason::BLOCK_MUTATED, false, "bad-witness-nonce-size", strprintf("%s : invalid witness reserved value size", __func__));
              }
              CHash256().Write(hashWitness.begin(), 32).Write(&block.vtx[0]->vin[0].scriptWitness.stack[0][0], 32).Finalize(hashWitness.begin());
              if (memcmp(hashWitness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) {
                  return state.Invalid(ValidationInvalidReason::BLOCK_MUTATED, false, "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(ValidationInvalidReason::BLOCK_MUTATED, false, "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(ValidationInvalidReason::CONSENSUS, false, "bad-blk-weight", strprintf("%s : weight limit failed", __func__));
      }
  
      return true;
  }
  
  bool BlockManager::AcceptBlockHeader(const CBlockHeader& block, CValidationState& 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)
                  return state.Invalid(ValidationInvalidReason::CACHED_INVALID, error("%s: block %s is marked invalid", __func__, hash.ToString()), "duplicate");
              return true;
          }
  
          if (!CheckBlockHeader(block, state, chainparams.GetConsensus()))
              return error("%s: Consensus::CheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
  
          // Get prev block index
          CBlockIndex* pindexPrev = nullptr;
          BlockMap::iterator mi = m_block_index.find(block.hashPrevBlock);
          if (mi == m_block_index.end())
              return state.Invalid(ValidationInvalidReason::BLOCK_MISSING_PREV, error("%s: prev block not found", __func__), "prev-blk-not-found");
          pindexPrev = (*mi).second;
          if (pindexPrev->nStatus & BLOCK_FAILED_MASK)
              return state.Invalid(ValidationInvalidReason::BLOCK_INVALID_PREV, error("%s: prev block invalid", __func__), "bad-prevblk");
          if (!ContextualCheckBlockHeader(block, state, chainparams, pindexPrev, GetAdjustedTime()))
              return error("%s: Consensus::ContextualCheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
  
          /* 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;
                      }
                      return state.Invalid(ValidationInvalidReason::BLOCK_INVALID_PREV, error("%s: prev block invalid", __func__), "bad-prevblk");
                  }
              }
          }
      }
      if (pindex == nullptr)
          pindex = AddToBlockIndex(block);
  
      if (ppindex)
          *ppindex = pindex;
  
      return true;
  }
  
  // Exposed wrapper for AcceptBlockHeader
  bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, CValidationState& state, const CChainParams& chainparams, const CBlockIndex** ppindex, CBlockHeader *first_invalid)
  {
      if (first_invalid != nullptr) first_invalid->SetNull();
      {
          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 = g_blockman.AcceptBlockHeader(header, state, chainparams, &pindex);
              ::ChainstateActive().CheckBlockIndex(chainparams.GetConsensus());
  
              if (!accepted) {
                  if (first_invalid) *first_invalid = header;
                  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, CValidationState& 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)) {
          assert(IsBlockReason(state.GetReason()));
          if (state.IsInvalid() && state.GetReason() != ValidationInvalidReason::BLOCK_MUTATED) {
              pindex->nStatus |= BLOCK_FAILED_VALID;
              setDirtyBlockIndex.insert(pindex);
          }
          return error("%s: %s", __func__, FormatStateMessage(state));
      }
  
      // 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 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;
          CValidationState 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__, FormatStateMessage(state));
          }
      }
  
      NotifyHeaderTip();
  
      CValidationState state; // Only used to report errors, not invalidity - ignore it
      if (!::ChainstateActive().ActivateBestChain(state, chainparams, pblock))
          return error("%s: ActivateBestChain failed (%s)", __func__, FormatStateMessage(state));
  
      return true;
  }
  
  bool TestBlockValidity(CValidationState& state, const CChainParams& chainparams, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW, bool fCheckMerkleRoot)
  {
      AssertLockHeld(cs_main);
      assert(pindexPrev && pindexPrev == ::ChainActive().Tip());
      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__, FormatStateMessage(state));
      if (!CheckBlock(block, state, chainparams.GetConsensus(), fCheckPOW, fCheckMerkleRoot))
          return error("%s: Consensus::CheckBlock: %s", __func__, FormatStateMessage(state));
      if (!ContextualCheckBlock(block, state, chainparams.GetConsensus(), pindexPrev))
          return error("%s: Consensus::ContextualCheckBlock: %s", __func__, FormatStateMessage(state));
      if (!::ChainstateActive().ConnectBlock(block, state, &indexDummy, viewNew, 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;
  }
  
  /* Prune a block file (modify associated database entries)*/
  void PruneOneBlockFile(const int fileNumber)
  {
      LOCK(cs_LastBlockFile);
  
      for (const auto& entry : g_blockman.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 = g_blockman.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) {
                      g_blockman.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);
      }
  }
  
  /* Calculate the block/rev files to delete based on height specified by user with RPC command pruneblockchain */
  static void FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight)
  {
      assert(fPruneMode && nManualPruneHeight > 0);
  
      LOCK2(cs_main, cs_LastBlockFile);
      if (::ChainActive().Tip() == nullptr)
          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, ::ChainActive().Tip()->nHeight - 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)
  {
      CValidationState state;
      const CChainParams& chainparams = Params();
      if (!::ChainstateActive().FlushStateToDisk(
              chainparams, state, FlushStateMode::NONE, nManualPruneHeight)) {
          LogPrintf("%s: failed to flush state (%s)\n", __func__, FormatStateMessage(state));
      }
  }
  
  /**
   * Prune block and undo files (blk???.dat and undo???.dat) so that the disk space used is less than a user-defined target.
   * The user sets the target (in MB) on the command line or in config file.  This will be run on startup and whenever new
   * space is allocated in a block or undo file, staying below the target. Changing back to unpruned requires a reindex
   * (which in this case means the blockchain must be re-downloaded.)
   *
   * Pruning functions are called from FlushStateToDisk when the global fCheckForPruning flag has been set.
   * Block and undo files are deleted in lock-step (when blk00003.dat is deleted, so is rev00003.dat.)
   * Pruning cannot take place until the longest chain is at least a certain length (100000 on mainnet, 1000 on testnet, 1000 on regtest).
   * Pruning will never delete a block within a defined distance (currently 288) from the active chain's tip.
   * The block index is updated by unsetting HAVE_DATA and HAVE_UNDO for any blocks that were stored in the deleted files.
   * A db flag records the fact that at least some block files have been pruned.
   *
   * @param[out]   setFilesToPrune   The set of file indices that can be unlinked will be returned
   */
  static void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight)
  {
      LOCK2(cs_main, cs_LastBlockFile);
      if (::ChainActive().Tip() == nullptr || nPruneTarget == 0) {
          return;
      }
      if ((uint64_t)::ChainActive().Tip()->nHeight <= nPruneAfterHeight) {
          return;
      }
  
      unsigned int nLastBlockWeCanPrune = ::ChainActive().Tip()->nHeight - 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 (::ChainstateActive().IsInitialBlockDownload()) {
              // 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(const CChainParams& chainparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      if (!g_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 : g_blockman.m_block_index)
      {
          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;
  
      return true;
  }
  
  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);
      CBlockIndex* pindex;
      CBlockIndex* pindexFailure = nullptr;
      int nGoodTransactions = 0;
      CValidationState state;
      int reportDone = 0;
      LogPrintf("[0%%]..."); /* Continued */
      for (pindex = ::ChainActive().Tip(); pindex && pindex->pprev; pindex = pindex->pprev) {
          boost::this_thread::interruption_point();
          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(), FormatStateMessage(state));
          // 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()) <= nCoinCacheUsage) {
              assert(coins.GetBestBlock() == pindex->GetBlockHash());
              DisconnectResult res = ::ChainstateActive().DisconnectBlock(block, pindex, coins);
              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()) {
              boost::this_thread::interruption_point();
              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, chainparams))
                  return error("VerifyDB(): *** found unconnectable block at %d, hash=%s (%s)", pindex->nHeight, pindex->GetBlockHash().ToString(), FormatStateMessage(state));
          }
      }
  
      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);
              DisconnectResult res = DisconnectBlock(block, pindexOld, cache);
              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
  
      CValidationState state;
      // Loop until the tip is below nHeight, or we reach a pruned block.
      while (!ShutdownRequested()) {
          {
              LOCK2(cs_main, ::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, FormatStateMessage(state));
              }
  
              // 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", FormatStateMessage(state));
              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());
          }
      }
  
      return true;
  }
  
  bool RewindBlockIndex(const CChainParams& params) {
      if (!::ChainstateActive().RewindBlockIndex(params)) {
          return false;
      }
  
      LOCK(cs_main);
      if (::ChainActive().Tip() != nullptr) {
          // 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.
          CValidationState state;
          if (!::ChainstateActive().FlushStateToDisk(params, state, FlushStateMode::ALWAYS)) {
              LogPrintf("RewindBlockIndex: unable to flush state to disk (%s)\n", FormatStateMessage(state));
              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()
  {
      LOCK(cs_main);
      ::ChainActive().SetTip(nullptr);
      g_blockman.Unload();
      pindexBestInvalid = nullptr;
      pindexBestHeader = nullptr;
      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;
  
      ::ChainstateActive().UnloadBlockIndex();
  }
  
  bool LoadBlockIndex(const CChainParams& chainparams)
  {
      // Load block index from databases
      bool needs_init = fReindex;
      if (!fReindex) {
          bool ret = LoadBlockIndexDB(chainparams);
          if (!ret) return false;
          needs_init = g_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");
      }
      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);
  }
  
  bool 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()) {
              boost::this_thread::interruption_point();
  
              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);
                  blkdat.SetPos(nBlockPos);
                  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) {
                        CValidationState 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) {
                      CValidationState state;
                      if (!ActivateBestChain(state, chainparams)) {
                          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);
                              CValidationState 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());
      }
      if (nLoaded > 0)
          LogPrintf("Loaded %i blocks from external file in %dms\n", nLoaded, GetTimeMillis() - nStart);
      return nLoaded > 0;
  }
  
  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 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 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);
              }
              CValidationState state;
              if (nTime + nExpiryTimeout > nNow) {
                  LOCK(cs_main);
                  AcceptToMemoryPoolWithTime(chainparams, pool, state, tx, nullptr /* pfMissingInputs */, nTime,
                                             nullptr /* plTxnReplaced */, false /* bypass_limits */, 0 /* nAbsurdFee */,
                                             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);
          }
      } 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\n", count, failed, expired, already_there);
      return true;
  }
  
  bool DumpMempool(const CTxMemPool& pool)
  {
      int64_t start = GetTimeMicros();
  
      std::map<uint256, CAmount> mapDeltas;
      std::vector<TxMempoolInfo> vinfo;
  
      static Mutex dump_mutex;
      LOCK(dump_mutex);
  
      {
          LOCK(pool.cs);
          for (const auto &i : pool.mapDeltas) {
              mapDeltas[i.first] = i.second;
          }
          vinfo = pool.infoAll();
      }
  
      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;
          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 pindex->nChainTx / fTxTotal;
  }
  
  class CMainCleanup
  {
  public:
      CMainCleanup() {}
      ~CMainCleanup() {
          // block headers
          BlockMap::iterator it1 = g_blockman.m_block_index.begin();
          for (; it1 != g_blockman.m_block_index.end(); it1++)
              delete (*it1).second;
          g_blockman.m_block_index.clear();
      }
  };
  static CMainCleanup instance_of_cmaincleanup;
  