text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2016 The Bitcoin Core developers
  // Copyright (c) 2017 The Bitcoin developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef BITCOIN_VALIDATION_H
  #define BITCOIN_VALIDATION_H
  
  #if defined(HAVE_CONFIG_H)
  #include "config/bitcoin-config.h"
  #endif
  
  #include "amount.h"
  #include "chain.h"
  #include "coins.h"
  #include "protocol.h" // For CMessageHeader::MessageMagic
  #include "script/script_error.h"
  #include "sync.h"
  #include "versionbits.h"
  
  #include <boost/filesystem/path.hpp>
  
  #include <algorithm>
  #include <atomic>
  #include <cstdint>
  #include <exception>
  #include <map>
  #include <set>
  #include <string>
  #include <utility>
  #include <vector>
  
  class CBlockIndex;
  class CBlockTreeDB;
  class CBloomFilter;
  class CChainParams;
  class CConnman;
  class CInv;
  class Config;
  class CScriptCheck;
  class CTxMemPool;
  class CTxUndo;
  class CValidationInterface;
  class CValidationState;
  struct ChainTxData;
  
  struct PrecomputedTransactionData;
  struct LockPoints;
  
  #define MIN_TRANSACTION_SIZE                                                   \
      (::GetSerializeSize(CTransaction(), SER_NETWORK, PROTOCOL_VERSION))
  
  /** Default for DEFAULT_WHITELISTRELAY. */
  static const bool DEFAULT_WHITELISTRELAY = true;
  /** Default for DEFAULT_WHITELISTFORCERELAY. */
  static const bool DEFAULT_WHITELISTFORCERELAY = true;
  /** Default for -minrelaytxfee, minimum relay fee for transactions */
  static const Amount DEFAULT_MIN_RELAY_TX_FEE(1000);
  //! -maxtxfee default
  static const Amount DEFAULT_TRANSACTION_MAXFEE(COIN / 10);
  //! Discourage users to set fees higher than this amount (in satoshis) per kB
  static const Amount HIGH_TX_FEE_PER_KB(COIN / 100);
  /** -maxtxfee will warn if called with a higher fee than this amount (in
   * satoshis */
  static const Amount HIGH_MAX_TX_FEE(100 * HIGH_TX_FEE_PER_KB);
  /** Default for -limitancestorcount, max number of in-mempool ancestors */
  static const unsigned int DEFAULT_ANCESTOR_LIMIT = 25;
  /** Default for -limitancestorsize, maximum kilobytes of tx + all in-mempool
   * ancestors */
  static const unsigned int DEFAULT_ANCESTOR_SIZE_LIMIT = 101;
  /** Default for -limitdescendantcount, max number of in-mempool descendants */
  static const unsigned int DEFAULT_DESCENDANT_LIMIT = 25;
  /** Default for -limitdescendantsize, maximum kilobytes of in-mempool
   * descendants */
  static const unsigned int DEFAULT_DESCENDANT_SIZE_LIMIT = 101;
  /** Default for -mempoolexpiry, expiration time for mempool transactions in
   * hours */
  static const unsigned int DEFAULT_MEMPOOL_EXPIRY = 336;
  /** The maximum size of a blk?????.dat file (since 0.8) */
  static const unsigned int MAX_BLOCKFILE_SIZE = 0x8000000; // 128 MiB
  /** The pre-allocation chunk size for blk?????.dat files (since 0.8) */
  static const unsigned int BLOCKFILE_CHUNK_SIZE = 0x1000000; // 16 MiB
  /** The pre-allocation chunk size for rev?????.dat files (since 0.8) */
  static const unsigned int UNDOFILE_CHUNK_SIZE = 0x100000; // 1 MiB
  
  /** Maximum number of script-checking threads allowed */
  static const int MAX_SCRIPTCHECK_THREADS = 16;
  /** -par default (number of script-checking threads, 0 = auto) */
  static const int DEFAULT_SCRIPTCHECK_THREADS = 0;
  /** Number of blocks that can be requested at any given time from a single peer.
   */
  static const int MAX_BLOCKS_IN_TRANSIT_PER_PEER = 16;
  /** Timeout in seconds during which a peer must stall block download progress
   * before being disconnected. */
  static const unsigned int BLOCK_STALLING_TIMEOUT = 2;
  /** Number of headers sent in one getheaders result. We rely on the assumption
   * that if a peer sends
   *  less than this number, we reached its tip. Changing this value is a protocol
   * upgrade. */
  static const unsigned int MAX_HEADERS_RESULTS = 2000;
  /** Maximum depth of blocks we're willing to serve as compact blocks to peers
   *  when requested. For older blocks, a regular BLOCK response will be sent. */
  static const int MAX_CMPCTBLOCK_DEPTH = 5;
  /** Maximum depth of blocks we're willing to respond to GETBLOCKTXN requests
   * for. */
  static const int MAX_BLOCKTXN_DEPTH = 10;
  /** Size of the "block download window": how far ahead of our current height do
   * we fetch ? Larger windows tolerate larger download speed differences between
   * peer, but increase the potential degree of disordering of blocks on disk
   * (which make reindexing and in the future perhaps pruning harder). We'll
   * probably want to make this a per-peer adaptive value at some point. */
  static const unsigned int BLOCK_DOWNLOAD_WINDOW = 1024;
  /** Time to wait (in seconds) between writing blocks/block index to disk. */
  static const unsigned int DATABASE_WRITE_INTERVAL = 60 * 60;
  /** Time to wait (in seconds) between flushing chainstate to disk. */
  static const unsigned int DATABASE_FLUSH_INTERVAL = 24 * 60 * 60;
  /** Maximum length of reject messages. */
  static const unsigned int MAX_REJECT_MESSAGE_LENGTH = 111;
  /** Average delay between local address broadcasts in seconds. */
  static const unsigned int AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL = 24 * 24 * 60;
  /** Average delay between peer address broadcasts in seconds. */
  static const unsigned int AVG_ADDRESS_BROADCAST_INTERVAL = 30;
  /** Average delay between trickled inventory transmissions in seconds.
   *  Blocks and whitelisted receivers bypass this, outbound peers get half this
   * delay. */
  static const unsigned int INVENTORY_BROADCAST_INTERVAL = 5;
  /** Maximum number of inventory items to send per transmission.
   *  Limits the impact of low-fee transaction floods. */
  static const unsigned int INVENTORY_BROADCAST_MAX =
      7 * INVENTORY_BROADCAST_INTERVAL;
  /** Average delay between feefilter broadcasts in seconds. */
  static const unsigned int AVG_FEEFILTER_BROADCAST_INTERVAL = 10 * 60;
  /** Maximum feefilter broadcast delay after significant change. */
  static const unsigned int MAX_FEEFILTER_CHANGE_DELAY = 5 * 60;
  /** Block download timeout base, expressed in millionths of the block interval
   * (i.e. 10 min) */
  static const int64_t BLOCK_DOWNLOAD_TIMEOUT_BASE = 1000000;
  /** Additional block download timeout per parallel downloading peer (i.e. 5 min)
   */
  static const int64_t BLOCK_DOWNLOAD_TIMEOUT_PER_PEER = 500000;
  
  static const unsigned int DEFAULT_LIMITFREERELAY = 0;
  static const bool DEFAULT_RELAYPRIORITY = true;
  static const int64_t DEFAULT_MAX_TIP_AGE = 24 * 60 * 60;
  /** Maximum age of our tip in seconds for us to be considered current for fee
   * estimation */
  static const int64_t MAX_FEE_ESTIMATION_TIP_AGE = 3 * 60 * 60;
  
  /** Default for -permitbaremultisig */
  static const bool DEFAULT_PERMIT_BAREMULTISIG = true;
  static const bool DEFAULT_CHECKPOINTS_ENABLED = true;
  static const bool DEFAULT_TXINDEX = false;
  static const unsigned int DEFAULT_BANSCORE_THRESHOLD = 100;
  
  /** Default for using fee filter */
  static const bool DEFAULT_FEEFILTER = true;
  
  /** Maximum number of headers to announce when relaying blocks with headers
   * message.*/
  static const unsigned int MAX_BLOCKS_TO_ANNOUNCE = 8;
  
  /** Maximum number of unconnecting headers announcements before DoS score */
  static const int MAX_UNCONNECTING_HEADERS = 10;
  
  static const bool DEFAULT_PEERBLOOMFILTERS = true;
  
  extern CScript COINBASE_FLAGS;
  extern CCriticalSection cs_main;
  extern CTxMemPool mempool;
  extern uint64_t nLastBlockTx;
  extern uint64_t nLastBlockSize;
  extern const std::string strMessageMagic;
  extern CWaitableCriticalSection csBestBlock;
  extern CConditionVariable cvBlockChange;
  extern std::atomic_bool fImporting;
  extern bool fReindex;
  extern int nScriptCheckThreads;
  extern bool fTxIndex;
  extern bool fIsBareMultisigStd;
  extern bool fRequireStandard;
  extern bool fCheckBlockIndex;
  extern bool fCheckpointsEnabled;
  extern size_t nCoinCacheUsage;
  
  /** A fee rate smaller than this is considered zero fee (for relaying, mining
   * and transaction creation) */
  extern CFeeRate minRelayTxFee;
  /** Absolute maximum transaction fee (in satoshis) used by wallet and mempool
   * (rejects high fee in sendrawtransaction) */
  extern Amount maxTxFee;
  /** If the tip is older than this (in seconds), the node is considered to be in
   * initial block download. */
  extern int64_t nMaxTipAge;
  
  /** Block hash whose ancestors we will assume to have valid scripts without
   * checking them. */
  extern uint256 hashAssumeValid;
  
  /** Best header we've seen so far (used for getheaders queries' starting
   * points). */
  extern CBlockIndex *pindexBestHeader;
  
  /** Minimum disk space required - used in CheckDiskSpace() */
  static const uint64_t nMinDiskSpace = 52428800;
  
  /** Pruning-related variables and constants */
  /** True if any block files have ever been pruned. */
  extern bool fHavePruned;
  /** True if we're running in -prune mode. */
  extern bool fPruneMode;
  /** Number of MiB of block files that we're trying to stay below. */
  extern uint64_t nPruneTarget;
  /** Block files containing a block-height within MIN_BLOCKS_TO_KEEP of
   * chainActive.Tip() will not be pruned. */
  static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
  
  static const signed int DEFAULT_CHECKBLOCKS = 6;
  static const unsigned int DEFAULT_CHECKLEVEL = 3;
  
  // Require that user allocate at least 550MB for block & undo files (blk???.dat
  // and rev???.dat)
  // At 1MB per block, 288 blocks = 288MB.
  // Add 15% for Undo data = 331MB
  // Add 20% for Orphan block rate = 397MB
  // We want the low water mark after pruning to be at least 397 MB and since we
  // prune in full block file chunks, we need the high water mark which triggers
  // the prune to be one 128MB block file + added 15% undo data = 147MB greater
  // for a total of 545MB. Setting the target to > than 550MB will make it likely
  // we can respect the target.
  static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
  
  /**
   * Process an incoming block. This only returns after the best known valid
   * block is made active. Note that it does not, however, guarantee that the
   * specific block passed to it has been checked for validity!
   *
   * If you want to *possibly* get feedback on whether pblock is valid, you must
   * install a CValidationInterface (see validationinterface.h) - this will have
   * its BlockChecked method called whenever *any* block completes validation.
   *
   * Note that we guarantee that either the proof-of-work is valid on pblock, or
   * (and possibly also) BlockChecked will have been called.
   *
   * Call without cs_main held.
   *
   * @param[in]   pblock  The block we want to process.
   * @param[in]   fForceProcessing Process this block even if unrequested; used
   * for non-network block sources and whitelisted peers.
   * @param[out]  fNewBlock A boolean which is set to indicate if the block was
   * first received via this call
   * @return True if state.IsValid()
   */
  bool ProcessNewBlock(const Config &config,
                       const std::shared_ptr<const CBlock> pblock,
                       bool fForceProcessing, bool *fNewBlock);
  
  /**
   * Process incoming block headers.
   *
   * Call without cs_main held.
   *
   * @param[in]  block The block headers themselves
   * @param[out] state This may be set to an Error state if any error occurred
   * processing them
   * @param[in]  chainparams The params for the chain we want to connect to
   * @param[out] ppindex If set, the pointer will be set to point to the last new
   * block index object for the given headers
   */
  bool ProcessNewBlockHeaders(const Config &config,
                              const std::vector<CBlockHeader> &block,
                              CValidationState &state,
                              const CBlockIndex **ppindex = nullptr);
  
  /** Check whether enough disk space is available for an incoming block */
  bool CheckDiskSpace(uint64_t nAdditionalBytes = 0);
  /** Open a block file (blk?????.dat) */
  FILE *OpenBlockFile(const CDiskBlockPos &pos, bool fReadOnly = false);
  /** Open an undo file (rev?????.dat) */
  FILE *OpenUndoFile(const CDiskBlockPos &pos, bool fReadOnly = false);
  /** Translation to a filesystem path */
  boost::filesystem::path GetBlockPosFilename(const CDiskBlockPos &pos,
                                              const char *prefix);
  /** Import blocks from an external file */
  bool LoadExternalBlockFile(const Config &config, FILE *fileIn,
                             CDiskBlockPos *dbp = nullptr);
  /** Initialize a new block tree database + block data on disk */
  bool InitBlockIndex(const Config &config);
  /** Load the block tree and coins database from disk */
  bool LoadBlockIndex(const CChainParams &chainparams);
  /** Unload database information */
  void UnloadBlockIndex();
  /** Run an instance of the script checking thread */
  void ThreadScriptCheck();
  /** Check whether we are doing an initial block download (synchronizing from
   * disk or network) */
  bool IsInitialBlockDownload();
  /** Format a string that describes several potential problems detected by the
   * core.
   * strFor can have three values:
   * - "rpc": get critical warnings, which should put the client in safe mode if
   * non-empty
   * - "statusbar": get all warnings
   * - "gui": get all warnings, translated (where possible) for GUI
   * This function only returns the highest priority warning of the set selected
   * by strFor.
   */
  std::string GetWarnings(const std::string &strFor);
  /** Retrieve a transaction (from memory pool, or from disk, if possible) */
  bool GetTransaction(const Config &config, const uint256 &hash,
                      CTransactionRef &tx, uint256 &hashBlock,
                      bool fAllowSlow = false);
  /** Find the best known block, and make it the tip of the block chain */
  bool ActivateBestChain(
      const Config &config, CValidationState &state,
      std::shared_ptr<const CBlock> pblock = std::shared_ptr<const CBlock>());
  Amount GetBlockSubsidy(int nHeight, const Consensus::Params &consensusParams);
  
  /** Guess verification progress (as a fraction between 0.0=genesis and
   * 1.0=current tip). */
  double GuessVerificationProgress(const ChainTxData &data, CBlockIndex *pindex);
  
  /**
   * 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
   */
  void FindFilesToPrune(std::set<int> &setFilesToPrune,
                        uint64_t nPruneAfterHeight);
  
  /**
   *  Mark one block file as pruned.
   */
  void PruneOneBlockFile(const int fileNumber);
  
  /**
   *  Actually unlink the specified files
   */
  void UnlinkPrunedFiles(const std::set<int> &setFilesToPrune);
  
  /** Create a new block index entry for a given block hash */
  CBlockIndex *InsertBlockIndex(uint256 hash);
  /** Flush all state, indexes and buffers to disk. */
  void FlushStateToDisk();
  /** Prune block files and flush state to disk. */
  void PruneAndFlush();
  /** Prune block files up to a given height */
  void PruneBlockFilesManual(int nPruneUpToHeight);
  
  /** Check is UAHF has activated. */
  bool IsUAHFenabled(const Config &config, const CBlockIndex *pindexPrev);
  
  /** Check is DAA HF has activated. */
  bool IsDAAEnabled(const Config &config, const CBlockIndex *pindexPrev);
  
  /** (try to) add transaction to memory pool
   * plTxnReplaced will be appended to with all transactions replaced from mempool
   * **/
  bool AcceptToMemoryPool(const Config &config, CTxMemPool &pool,
                          CValidationState &state, const CTransactionRef &tx,
                          bool fLimitFree, bool *pfMissingInputs,
                          std::list<CTransactionRef> *plTxnReplaced = nullptr,
                          bool fOverrideMempoolLimit = false,
                          const Amount nAbsurdFee = Amount(0));
  
  /** Convert CValidationState to a human-readable message for logging */
  std::string FormatStateMessage(const CValidationState &state);
  
  /** Get the BIP9 state for a given deployment at the current tip. */
  ThresholdState VersionBitsTipState(const Consensus::Params &params,
                                     Consensus::DeploymentPos pos);
  
  /** Get the block height at which the BIP9 deployment switched into the state
   * for the block building on the current tip. */
  int VersionBitsTipStateSinceHeight(const Consensus::Params &params,
                                     Consensus::DeploymentPos pos);
  
  /**
   * Count ECDSA signature operations the old-fashioned (pre-0.6) way
   * @return number of sigops this transaction's outputs will produce when spent
   * @see CTransaction::FetchInputs
   */
  uint64_t GetSigOpCountWithoutP2SH(const CTransaction &tx);
  
  /**
   * Count ECDSA signature operations in pay-to-script-hash inputs.
   *
   * @param[in] mapInputs Map of previous transactions that have outputs we're
   * spending
   * @return maximum number of sigops required to validate this transaction's
   * inputs
   * @see CTransaction::FetchInputs
   */
  uint64_t GetP2SHSigOpCount(const CTransaction &tx,
                             const CCoinsViewCache &mapInputs);
  
  /**
   * Compute total signature operation of a transaction.
   * @param[in] tx     Transaction for which we are computing the cost
   * @param[in] inputs Map of previous transactions that have outputs we're
   * spending
   * @param[out] flags Script verification flags
   * @return Total signature operation cost of tx
   */
  uint64_t GetTransactionSigOpCount(const CTransaction &tx,
                                    const CCoinsViewCache &inputs, int flags);
  
  /**
   * 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 sigCacheStore/scriptCacheStore 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.
   */
  bool CheckInputs(const CTransaction &tx, CValidationState &state,
                   const CCoinsViewCache &view, bool fScriptChecks,
                   uint32_t flags, bool sigCacheStore, bool scriptCacheStore,
                   const PrecomputedTransactionData &txdata,
                   std::vector<CScriptCheck> *pvChecks = nullptr);
  
  /** Apply the effects of this transaction on the UTXO set represented by view */
  void UpdateCoins(const CTransaction &tx, CCoinsViewCache &inputs, int nHeight);
  void UpdateCoins(const CTransaction &tx, CCoinsViewCache &inputs,
                   CTxUndo &txundo, int nHeight);
  
  /** Transaction validation functions */
  
  /** Context-independent validity checks for coinbase and non-coinbase
   * transactions */
  bool CheckRegularTransaction(const CTransaction &tx, CValidationState &state,
                               bool fCheckDuplicateInputs = true);
  bool CheckCoinbase(const CTransaction &tx, CValidationState &state,
                     bool fCheckDuplicateInputs = true);
  
  namespace Consensus {
  
  /**
   * Check whether all inputs of this transaction are valid (no double spends and
   * amounts). This does not modify the UTXO set. This does not check scripts and
   * sigs. Preconditions: tx.IsCoinBase() is false.
   */
  bool CheckTxInputs(const CTransaction &tx, CValidationState &state,
                     const CCoinsViewCache &inputs, int nSpendHeight);
  
  } // namespace Consensus
  
  /**
   * Test whether the LockPoints height and time are still valid on the current
   * chain.
   */
  bool TestLockPointValidity(const LockPoints *lp);
  
  /**
   * Check if transaction is final per BIP 68 sequence numbers and can be included
   * in a block. Consensus critical. Takes as input a list of heights at which
   * tx's inputs (in order) confirmed.
   */
  bool SequenceLocks(const CTransaction &tx, int flags,
                     std::vector<int> *prevHeights, const CBlockIndex &block);
  
  /**
   * Check if transaction will be BIP 68 final in the next block to be created.
   *
   * Simulates calling SequenceLocks() with data from the tip of the current
   * active chain. Optionally stores in LockPoints the resulting height and time
   * calculated and the hash of the block needed for calculation or skips the
   * calculation and uses the LockPoints passed in for evaluation. The LockPoints
   * should not be considered valid if CheckSequenceLocks returns false.
   *
   * See consensus/consensus.h for flag definitions.
   */
  bool CheckSequenceLocks(const CTransaction &tx, int flags,
                          LockPoints *lp = nullptr,
                          bool useExistingLockPoints = false);
  
  /**
   * Closure representing one script verification.
   * Note that this stores references to the spending transaction.
   */
  class CScriptCheck {
  private:
      CScript scriptPubKey;
      Amount amount;
      const CTransaction *ptxTo;
      unsigned int nIn;
      uint32_t nFlags;
      bool cacheStore;
      ScriptError error;
      PrecomputedTransactionData txdata;
  
  public:
      CScriptCheck()
          : amount(0), ptxTo(0), nIn(0), nFlags(0), cacheStore(false),
            error(SCRIPT_ERR_UNKNOWN_ERROR), txdata() {}
  
      CScriptCheck(const CScript &scriptPubKeyIn, const Amount amountIn,
                   const CTransaction &txToIn, unsigned int nInIn,
                   uint32_t nFlagsIn, bool cacheIn,
                   const PrecomputedTransactionData &txdataIn)
          : scriptPubKey(scriptPubKeyIn), amount(amountIn), ptxTo(&txToIn),
            nIn(nInIn), nFlags(nFlagsIn), cacheStore(cacheIn),
            error(SCRIPT_ERR_UNKNOWN_ERROR), txdata(txdataIn) {}
  
      bool operator()();
  
      void swap(CScriptCheck &check) {
          scriptPubKey.swap(check.scriptPubKey);
          std::swap(ptxTo, check.ptxTo);
          std::swap(amount, check.amount);
          std::swap(nIn, check.nIn);
          std::swap(nFlags, check.nFlags);
          std::swap(cacheStore, check.cacheStore);
          std::swap(error, check.error);
          std::swap(txdata, check.txdata);
      }
  
      ScriptError GetScriptError() const { return error; }
  };
  
  /** Functions for disk access for blocks */
  bool WriteBlockToDisk(const CBlock &block, CDiskBlockPos &pos,
                        const CMessageHeader::MessageMagic &messageStart);
  bool ReadBlockFromDisk(CBlock &block, const CDiskBlockPos &pos,
                         const Config &config);
  bool ReadBlockFromDisk(CBlock &block, const CBlockIndex *pindex,
                         const Config &config);
  
  /** Functions for validating blocks and updating the block tree */
  
  /** Context-independent validity checks */
  bool CheckBlock(const Config &Config, const CBlock &block,
                  CValidationState &state, bool fCheckPOW = true,
                  bool fCheckMerkleRoot = true);
  
  /**
   * Context dependent validity checks for non coinbase transactions. This
   * doesn't check the validity of the transaction against the UTXO set, but
   * simply characteristic that are suceptible to change over time such as feature
   * activation/deactivation and CLTV.
   */
  bool ContextualCheckTransaction(const Config &config, const CTransaction &tx,
                                  CValidationState &state, int nHeight,
                                  int64_t nLockTimeCutoff);
  
  /**
   * This is a variant of ContextualCheckTransaction which computes the contextual
   * check for a transaction based on the chain tip.
   *
   * See consensus/consensus.h for flag definitions.
   */
  bool ContextualCheckTransactionForCurrentBlock(const Config &config,
                                                 const CTransaction &tx,
                                                 CValidationState &state,
                                                 int flags = -1);
  
  /**
   * 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().
   */
  bool ContextualCheckBlock(const Config &config, const CBlock &block,
                            CValidationState &state,
                            const Consensus::Params &consensusParams,
                            const CBlockIndex *pindexPrev);
  
  /**
   * Check a block is completely valid from start to finish (only works on top of
   * our current best block, with cs_main held)
   */
  bool TestBlockValidity(const Config &config, CValidationState &state,
                         const CBlock &block, CBlockIndex *pindexPrev,
                         bool fCheckPOW = true, bool fCheckMerkleRoot = true);
  
  /**
   * When there are blocks in the active chain with missing data, rewind the
   * chainstate and remove them from the block index.
   */
  bool RewindBlockIndex(const Config &config);
  
  /**
   * RAII wrapper for VerifyDB: Verify consistency of the block and coin
   * databases.
   */
  class CVerifyDB {
  public:
      CVerifyDB();
      ~CVerifyDB();
      bool VerifyDB(const Config &config, CCoinsView *coinsview, int nCheckLevel,
                    int nCheckDepth);
  };
  
  /** Find the last common block between the parameter chain and a locator. */
  CBlockIndex *FindForkInGlobalIndex(const CChain &chain,
                                     const CBlockLocator &locator);
  
  /** Mark a block as precious and reorganize. */
  bool PreciousBlock(const Config &config, CValidationState &state,
                     CBlockIndex *pindex);
  
  /** Mark a block as invalid. */
  bool InvalidateBlock(const Config &config, CValidationState &state,
                       CBlockIndex *pindex);
  
  /** Remove invalidity status from a block and its descendants. */
  bool ResetBlockFailureFlags(CBlockIndex *pindex);
  
  /** The currently-connected chain of blocks (protected by cs_main). */
  extern CChain chainActive;
  
  /** Global variable that points to the active CCoinsView (protected by cs_main)
   */
  extern CCoinsViewCache *pcoinsTip;
  
  /** Global variable that points to the active block tree (protected by cs_main)
   */
  extern CBlockTreeDB *pblocktree;
  
  /**
   * Return the spend height, which is one more than the inputs.GetBestBlock().
   * While checking, GetBestBlock() refers to the parent block. (protected by
   * cs_main)
   * This is also true for mempool checks.
   */
  int GetSpendHeight(const CCoinsViewCache &inputs);
  
  extern VersionBitsCache versionbitscache;
  
  /**
   * Determine what nVersion a new block should use.
   */
  int32_t ComputeBlockVersion(const CBlockIndex *pindexPrev,
                              const Consensus::Params &params);
  
  /**
   * Reject codes greater or equal to this can be returned by AcceptToMemPool for
   * transactions, to signal internal conditions. They cannot and should not be
   * sent over the P2P network.
   */
  static const unsigned int REJECT_INTERNAL = 0x100;
  /** Too high fee. Can not be triggered by P2P transactions */
  static const unsigned int REJECT_HIGHFEE = 0x100;
  /** Transaction is already known (either in mempool or blockchain) */
  static const unsigned int REJECT_ALREADY_KNOWN = 0x101;
  /** Transaction conflicts with a transaction already known */
  static const unsigned int REJECT_CONFLICT = 0x102;
  
  /** Get block file info entry for one block file */
  CBlockFileInfo *GetBlockFileInfo(size_t n);
  
  /** Dump the mempool to disk. */
  void DumpMempool();
  
  /** Load the mempool from disk. */
  bool LoadMempool(const Config &config);
  
  #endif // BITCOIN_VALIDATION_H
  