text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2019 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef BITCOIN_VALIDATION_H
  #define BITCOIN_VALIDATION_H
  
  #if defined(HAVE_CONFIG_H)
  #include <config/bitcoin-config.h>
  #endif
  
  #include <amount.h>
  #include <coins.h>
  #include <crypto/common.h> // for ReadLE64
  #include <fs.h>
  #include <policy/feerate.h>
  #include <protocol.h> // For CMessageHeader::MessageStartChars
  #include <script/script_error.h>
  #include <sync.h>
  #include <txmempool.h> // For CTxMemPool::cs
  #include <txdb.h>
  #include <versionbits.h>
  
  #include <algorithm>
  #include <atomic>
  #include <exception>
  #include <map>
  #include <memory>
  #include <set>
  #include <stdint.h>
  #include <string>
  #include <utility>
  #include <vector>
  
  class CChainState;
  class CBlockIndex;
  class CBlockTreeDB;
  class CBlockUndo;
  class CChainParams;
  class CInv;
  class CConnman;
  class CScriptCheck;
  class CBlockPolicyEstimator;
  class CTxMemPool;
  class CValidationState;
  struct ChainTxData;
  
  struct DisconnectedBlockTransactions;
  struct PrecomputedTransactionData;
  struct LockPoints;
  
  /** Default for -minrelaytxfee, minimum relay fee for transactions */
  static const unsigned int DEFAULT_MIN_RELAY_TX_FEE = 1000;
  /** 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;
  /**
   * An extra transaction can be added to a package, as long as it only has one
   * ancestor and is no larger than this. Not really any reason to make this
   * configurable as it doesn't materially change DoS parameters.
   */
  static const unsigned int EXTRA_DESCENDANT_TX_SIZE_LIMIT = 10000;
  /** Default for -mempoolexpiry, expiration time for mempool transactions in hours */
  static const unsigned int DEFAULT_MEMPOOL_EXPIRY = 336;
  /** Maximum kilobytes for transactions to store for processing during reorg */
  static const unsigned int MAX_DISCONNECTED_TX_POOL_SIZE = 20000;
  /** 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 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;
  /** 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 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;
  
  static const bool DEFAULT_CHECKPOINTS_ENABLED = true;
  static const bool DEFAULT_TXINDEX = false;
  static const char* const DEFAULT_BLOCKFILTERINDEX = "0";
  static const unsigned int DEFAULT_BANSCORE_THRESHOLD = 100;
  /** Default for -persistmempool */
  static const bool DEFAULT_PERSIST_MEMPOOL = true;
  /** 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;
  
  /** Default for -stopatheight */
  static const int DEFAULT_STOPATHEIGHT = 0;
  
  struct BlockHasher
  {
      // this used to call `GetCheapHash()` in uint256, which was later moved; the
      // cheap hash function simply calls ReadLE64() however, so the end result is
      // identical
      size_t operator()(const uint256& hash) const { return ReadLE64(hash.begin()); }
  };
  
  extern CScript COINBASE_FLAGS;
  extern CCriticalSection cs_main;
  extern CBlockPolicyEstimator feeEstimator;
  extern CTxMemPool mempool;
  typedef std::unordered_map<uint256, CBlockIndex*, BlockHasher> BlockMap;
  extern Mutex g_best_block_mutex;
  extern std::condition_variable g_best_block_cv;
  extern uint256 g_best_block;
  extern std::atomic_bool fImporting;
  extern std::atomic_bool fReindex;
  extern int nScriptCheckThreads;
  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;
  /** 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;
  
  /** Minimum work we will assume exists on some valid chain. */
  extern arith_uint256 nMinimumChainWork;
  
  /** Best header we've seen so far (used for getheaders queries' starting points). */
  extern CBlockIndex *pindexBestHeader;
  
  /** 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;
  /** Minimum blocks required to signal NODE_NETWORK_LIMITED */
  static const unsigned int NODE_NETWORK_LIMITED_MIN_BLOCKS = 288;
  
  static const signed int DEFAULT_CHECKBLOCKS = 6;
  static const unsigned int DEFAULT_CHECKLEVEL = 3;
  
  // Require that user allocate at least 550 MiB 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 >= 550 MiB 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.
   *
   * May not be called in a
   * validationinterface callback.
   *
   * @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
   * @returns     If the block was processed, independently of block validity
   */
  bool ProcessNewBlock(const CChainParams& chainparams, const std::shared_ptr<const CBlock> pblock, bool fForceProcessing, bool* fNewBlock) LOCKS_EXCLUDED(cs_main);
  
  /**
   * Process incoming block headers.
   *
   * May not be called in a
   * validationinterface callback.
   *
   * @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
   * @param[out] first_invalid First header that fails validation, if one exists
   */
  bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& block, CValidationState& state, const CChainParams& chainparams, const CBlockIndex** ppindex = nullptr, CBlockHeader* first_invalid = nullptr) LOCKS_EXCLUDED(cs_main);
  
  /** Open a block file (blk?????.dat) */
  FILE* OpenBlockFile(const FlatFilePos &pos, bool fReadOnly = false);
  /** Translation to a filesystem path */
  fs::path GetBlockPosFilename(const FlatFilePos &pos);
  /** Import blocks from an external file */
  bool LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, FlatFilePos *dbp = nullptr);
  /** Ensures we have a genesis block in the block tree, possibly writing one to disk. */
  bool LoadGenesisBlock(const CChainParams& chainparams);
  /** Load the block tree and coins database from disk,
   * initializing state if we're running with -reindex. */
  bool LoadBlockIndex(const CChainParams& chainparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  /** Update the chain tip based on database information. */
  bool LoadChainTip(const CChainParams& chainparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  /** Unload database information */
  void UnloadBlockIndex();
  /** Run an instance of the script checking thread */
  void ThreadScriptCheck(int worker_num);
  /** Retrieve a transaction (from memory pool, or from disk, if possible) */
  bool GetTransaction(const uint256& hash, CTransactionRef& tx, const Consensus::Params& params, uint256& hashBlock, const CBlockIndex* const blockIndex = nullptr);
  /**
   * Find the best known block, and make it the tip of the block chain
   *
   * May not be called with cs_main held. May not be called in a
   * validationinterface callback.
   */
  bool ActivateBestChain(CValidationState& state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock = std::shared_ptr<const CBlock>());
  CAmount 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, const CBlockIndex* pindex);
  
  /** Calculate the amount of disk space the block & undo files currently use */
  uint64_t CalculateCurrentUsage();
  
  /**
   *  Mark one block file as pruned.
   */
  void PruneOneBlockFile(const int fileNumber) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /**
   *  Actually unlink the specified files
   */
  void UnlinkPrunedFiles(const std::set<int>& setFilesToPrune);
  
  /** Prune block files up to a given height */
  void PruneBlockFilesManual(int nManualPruneHeight);
  
  /** (try to) add transaction to memory pool
   * plTxnReplaced will be appended to with all transactions replaced from mempool **/
  bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransactionRef &tx,
                          bool* pfMissingInputs, std::list<CTransactionRef>* plTxnReplaced,
                          bool bypass_limits, const CAmount nAbsurdFee, bool test_accept=false) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /** Get the BIP9 state for a given deployment at the current tip. */
  ThresholdState VersionBitsTipState(const Consensus::Params& params, Consensus::DeploymentPos pos);
  
  /** Get the numerical statistics for the BIP9 state for a given deployment at the current tip. */
  BIP9Stats VersionBitsTipStatistics(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);
  
  
  /** Apply the effects of this transaction on the UTXO set represented by view */
  void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, int nHeight);
  
  /** Transaction validation functions */
  
  /**
   * Check if transaction will be final in the next block to be created.
   *
   * Calls IsFinalTx() with current block height and appropriate block time.
   *
   * See consensus/consensus.h for flag definitions.
   */
  bool CheckFinalTx(const CTransaction &tx, int flags = -1) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /**
   * Test whether the LockPoints height and time are still valid on the current chain
   */
  bool TestLockPointValidity(const LockPoints* lp) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /**
   * 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 CTxMemPool& pool, const CTransaction& tx, int flags, LockPoints* lp = nullptr, bool useExistingLockPoints = false) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /**
   * Closure representing one script verification
   * Note that this stores references to the spending transaction
   */
  class CScriptCheck
  {
  private:
      CTxOut m_tx_out;
      const CTransaction *ptxTo;
      unsigned int nIn;
      unsigned int nFlags;
      bool cacheStore;
      ScriptError error;
      PrecomputedTransactionData *txdata;
  
  public:
      CScriptCheck(): ptxTo(nullptr), nIn(0), nFlags(0), cacheStore(false), error(SCRIPT_ERR_UNKNOWN_ERROR) {}
      CScriptCheck(const CTxOut& outIn, const CTransaction& txToIn, unsigned int nInIn, unsigned int nFlagsIn, bool cacheIn, PrecomputedTransactionData* txdataIn) :
          m_tx_out(outIn), ptxTo(&txToIn), nIn(nInIn), nFlags(nFlagsIn), cacheStore(cacheIn), error(SCRIPT_ERR_UNKNOWN_ERROR), txdata(txdataIn) { }
  
      bool operator()();
  
      void swap(CScriptCheck &check) {
          std::swap(ptxTo, check.ptxTo);
          std::swap(m_tx_out, check.m_tx_out);
          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; }
  };
  
  /** Initializes the script-execution cache */
  void InitScriptExecutionCache();
  
  
  /** Functions for disk access for blocks */
  bool ReadBlockFromDisk(CBlock& block, const FlatFilePos& pos, const Consensus::Params& consensusParams);
  bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams);
  bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, const CMessageHeader::MessageStartChars& message_start);
  bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const CBlockIndex* pindex, const CMessageHeader::MessageStartChars& message_start);
  
  bool UndoReadFromDisk(CBlockUndo& blockundo, const CBlockIndex* pindex);
  
  /** Functions for validating blocks and updating the block tree */
  
  /** Context-independent validity checks */
  bool CheckBlock(const CBlock& block, CValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW = true, bool fCheckMerkleRoot = true);
  
  /** Check a block is completely valid from start to finish (only works on top of our current best block) */
  bool TestBlockValidity(CValidationState& state, const CChainParams& chainparams, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW = true, bool fCheckMerkleRoot = true) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /** Check whether witness commitments are required for a block, and whether to enforce NULLDUMMY (BIP 147) rules.
   *  Note that transaction witness validation rules are always enforced when P2SH is enforced. */
  bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params);
  
  /** When there are blocks in the active chain with missing data, rewind the chainstate and remove them from the block index */
  bool RewindBlockIndex(const CChainParams& params) LOCKS_EXCLUDED(cs_main);
  
  /** Update uncommitted block structures (currently: only the witness reserved value). This is safe for submitted blocks. */
  void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams);
  
  /** Produce the necessary coinbase commitment for a block (modifies the hash, don't call for mined blocks). */
  std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams);
  
  /** RAII wrapper for VerifyDB: Verify consistency of the block and coin databases */
  class CVerifyDB {
  public:
      CVerifyDB();
      ~CVerifyDB();
      bool VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview, int nCheckLevel, int nCheckDepth);
  };
  
  /** Replay blocks that aren't fully applied to the database. */
  bool ReplayBlocks(const CChainParams& params, CCoinsView* view);
  
  CBlockIndex* LookupBlockIndex(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /** Find the last common block between the parameter chain and a locator. */
  CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  enum DisconnectResult
  {
      DISCONNECT_OK,      // All good.
      DISCONNECT_UNCLEAN, // Rolled back, but UTXO set was inconsistent with block.
      DISCONNECT_FAILED   // Something else went wrong.
  };
  
  class ConnectTrace;
  
  /** @see CChainState::FlushStateToDisk */
  enum class FlushStateMode {
      NONE,
      IF_NEEDED,
      PERIODIC,
      ALWAYS
  };
  
  struct CBlockIndexWorkComparator
  {
      bool operator()(const CBlockIndex *pa, const CBlockIndex *pb) const;
  };
  
  /**
   * Maintains a tree of blocks (stored in `m_block_index`) which is consulted
   * to determine where the most-work tip is.
   *
   * This data is used mostly in `CChainState` - information about, e.g.,
   * candidate tips is not maintained here.
   */
  class BlockManager {
  public:
      BlockMap m_block_index GUARDED_BY(cs_main);
  
      /** In order to efficiently track invalidity of headers, we keep the set of
        * blocks which we tried to connect and found to be invalid here (ie which
        * were set to BLOCK_FAILED_VALID since the last restart). We can then
        * walk this set and check if a new header is a descendant of something in
        * this set, preventing us from having to walk m_block_index when we try
        * to connect a bad block and fail.
        *
        * While this is more complicated than marking everything which descends
        * from an invalid block as invalid at the time we discover it to be
        * invalid, doing so would require walking all of m_block_index to find all
        * descendants. Since this case should be very rare, keeping track of all
        * BLOCK_FAILED_VALID blocks in a set should be just fine and work just as
        * well.
        *
        * Because we already walk m_block_index in height-order at startup, we go
        * ahead and mark descendants of invalid blocks as FAILED_CHILD at that time,
        * instead of putting things in this set.
        */
      std::set<CBlockIndex*> m_failed_blocks;
  
      /**
       * All pairs A->B, where A (or one of its ancestors) misses transactions, but B has transactions.
       * Pruned nodes may have entries where B is missing data.
       */
      std::multimap<CBlockIndex*, CBlockIndex*> m_blocks_unlinked;
  
      /**
       * Load the blocktree off disk and into memory. Populate certain metadata
       * per index entry (nStatus, nChainWork, nTimeMax, etc.) as well as peripheral
       * collections like setDirtyBlockIndex.
       *
       * @param[out] block_index_candidates  Fill this set with any valid blocks for
       *                                     which we've downloaded all transactions.
       */
      bool LoadBlockIndex(
          const Consensus::Params& consensus_params,
          CBlockTreeDB& blocktree,
          std::set<CBlockIndex*, CBlockIndexWorkComparator>& block_index_candidates)
          EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      /** Clear all data members. */
      void Unload() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      CBlockIndex* AddToBlockIndex(const CBlockHeader& block) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
      /** Create a new block index entry for a given block hash */
      CBlockIndex* InsertBlockIndex(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      /**
       * If a block header hasn't already been seen, call CheckBlockHeader on it, ensure
       * that it doesn't descend from an invalid block, and then add it to m_block_index.
       */
      bool AcceptBlockHeader(
          const CBlockHeader& block,
          CValidationState& state,
          const CChainParams& chainparams,
          CBlockIndex** ppindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  };
  
  /**
   * A convenience class for constructing the CCoinsView* hierarchy used
   * to facilitate access to the UTXO set.
   *
   * This class consists of an arrangement of layered CCoinsView objects,
   * preferring to store and retrieve coins in memory via `m_cacheview` but
   * ultimately falling back on cache misses to the canonical store of UTXOs on
   * disk, `m_dbview`.
   */
  class CoinsViews {
  
  public:
      //! The lowest level of the CoinsViews cache hierarchy sits in a leveldb database on disk.
      //! All unspent coins reside in this store.
      CCoinsViewDB m_dbview GUARDED_BY(cs_main);
  
      //! This view wraps access to the leveldb instance and handles read errors gracefully.
      CCoinsViewErrorCatcher m_catcherview GUARDED_BY(cs_main);
  
      //! This is the top layer of the cache hierarchy - it keeps as many coins in memory as
      //! can fit per the dbcache setting.
      std::unique_ptr<CCoinsViewCache> m_cacheview GUARDED_BY(cs_main);
  
      //! This constructor initializes CCoinsViewDB and CCoinsViewErrorCatcher instances, but it
      //! *does not* create a CCoinsViewCache instance by default. This is done separately because the
      //! presence of the cache has implications on whether or not we're allowed to flush the cache's
      //! state to disk, which should not be done until the health of the database is verified.
      //!
      //! All arguments forwarded onto CCoinsViewDB.
      CoinsViews(std::string ldb_name, size_t cache_size_bytes, bool in_memory, bool should_wipe);
  
      //! Initialize the CCoinsViewCache member.
      void InitCache() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
  };
  
  /**
   * CChainState stores and provides an API to update our local knowledge of the
   * current best chain.
   *
   * Eventually, the API here is targeted at being exposed externally as a
   * consumable libconsensus library, so any functions added must only call
   * other class member functions, pure functions in other parts of the consensus
   * library, callbacks via the validation interface, or read/write-to-disk
   * functions (eventually this will also be via callbacks).
   *
   * Anything that is contingent on the current tip of the chain is stored here,
   * whereas block information and metadata independent of the current tip is
   * kept in `BlockMetadataManager`.
   */
  class CChainState {
  private:
  
      /**
       * Every received block is assigned a unique and increasing identifier, so we
       * know which one to give priority in case of a fork.
       */
      CCriticalSection cs_nBlockSequenceId;
      /** Blocks loaded from disk are assigned id 0, so start the counter at 1. */
      int32_t nBlockSequenceId = 1;
      /** Decreasing counter (used by subsequent preciousblock calls). */
      int32_t nBlockReverseSequenceId = -1;
      /** chainwork for the last block that preciousblock has been applied to. */
      arith_uint256 nLastPreciousChainwork = 0;
  
      /**
       * the ChainState CriticalSection
       * A lock that must be held when modifying this ChainState - held in ActivateBestChain()
       */
      CCriticalSection m_cs_chainstate;
  
      /**
       * Whether this chainstate is undergoing initial block download.
       *
       * Mutable because we need to be able to mark IsInitialBlockDownload()
       * const, which latches this for caching purposes.
       */
      mutable std::atomic<bool> m_cached_finished_ibd{false};
  
      //! Reference to a BlockManager instance which itself is shared across all
      //! CChainState instances. Keeping a local reference allows us to test more
      //! easily as opposed to referencing a global.
      BlockManager& m_blockman;
  
      //! Manages the UTXO set, which is a reflection of the contents of `m_chain`.
      std::unique_ptr<CoinsViews> m_coins_views;
  
  public:
      CChainState(BlockManager& blockman) : m_blockman(blockman) {}
      CChainState();
  
      /**
       * Initialize the CoinsViews UTXO set database management data structures. The in-memory
       * cache is initialized separately.
       *
       * All parameters forwarded to CoinsViews.
       */
      void InitCoinsDB(
          size_t cache_size_bytes,
          bool in_memory,
          bool should_wipe,
          std::string leveldb_name = "chainstate");
  
      //! Initialize the in-memory coins cache (to be done after the health of the on-disk database
      //! is verified).
      void InitCoinsCache() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
  
      //! @returns whether or not the CoinsViews object has been fully initialized and we can
      //!          safely flush this object to disk.
      bool CanFlushToDisk() EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
          return m_coins_views && m_coins_views->m_cacheview;
      }
  
      //! The current chain of blockheaders we consult and build on.
      //! @see CChain, CBlockIndex.
      CChain m_chain;
  
      /**
       * The set of all CBlockIndex entries with BLOCK_VALID_TRANSACTIONS (for itself and all ancestors) and
       * as good as our current tip or better. Entries may be failed, though, and pruning nodes may be
       * missing the data for the block.
       */
      std::set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexCandidates;
  
      //! @returns A reference to the in-memory cache of the UTXO set.
      CCoinsViewCache& CoinsTip() EXCLUSIVE_LOCKS_REQUIRED(cs_main)
      {
          assert(m_coins_views->m_cacheview);
          return *m_coins_views->m_cacheview.get();
      }
  
      //! @returns A reference to the on-disk UTXO set database.
      CCoinsViewDB& CoinsDB() EXCLUSIVE_LOCKS_REQUIRED(cs_main)
      {
          return m_coins_views->m_dbview;
      }
  
      //! @returns A reference to a wrapped view of the in-memory UTXO set that
      //!     handles disk read errors gracefully.
      CCoinsViewErrorCatcher& CoinsErrorCatcher() EXCLUSIVE_LOCKS_REQUIRED(cs_main)
      {
          return m_coins_views->m_catcherview;
      }
  
      //! Destructs all objects related to accessing the UTXO set.
      void ResetCoinsViews() { m_coins_views.reset(); }
  
      /**
       * Update the on-disk chain state.
       * The caches and indexes are flushed depending on the mode we're called with
       * if they're too large, if it's been a while since the last write,
       * or always and in all cases if we're in prune mode and are deleting files.
       *
       * If FlushStateMode::NONE is used, then FlushStateToDisk(...) won't do anything
       * besides checking if we need to prune.
       *
       * @returns true unless a system error occurred
       */
      bool FlushStateToDisk(
          const CChainParams& chainparams,
          CValidationState &state,
          FlushStateMode mode,
          int nManualPruneHeight = 0);
  
      //! Unconditionally flush all changes to disk.
      void ForceFlushStateToDisk();
  
      //! Prune blockfiles from the disk if necessary and then flush chainstate changes
      //! if we pruned.
      void PruneAndFlush();
  
      /**
       * Make the best chain active, in multiple steps. The result is either failure
       * or an activated best chain. pblock is either nullptr or a pointer to a block
       * that is already loaded (to avoid loading it again from disk).
       *
       * ActivateBestChain is split into steps (see ActivateBestChainStep) so that
       * we avoid holding cs_main for an extended period of time; the length of this
       * call may be quite long during reindexing or a substantial reorg.
       *
       * @returns true unless a system error occurred
       */
      bool ActivateBestChain(CValidationState& state,
          const CChainParams& chainparams,
          std::shared_ptr<const CBlock> pblock) LOCKS_EXCLUDED(cs_main);
  
      bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      // Block (dis)connection on a given view:
      DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view);
      bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pindex,
                        CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck = false) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      // Apply the effects of a block disconnection on the UTXO set.
      bool DisconnectTip(CValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions* disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs);
  
      // Manual block validity manipulation:
      bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
      bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
      void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      bool ReplayBlocks(const CChainParams& params, CCoinsView* view);
      bool RewindBlockIndex(const CChainParams& params) LOCKS_EXCLUDED(cs_main);
      bool LoadGenesisBlock(const CChainParams& chainparams);
  
      void PruneBlockIndexCandidates();
  
      void UnloadBlockIndex();
  
      /** Check whether we are doing an initial block download (synchronizing from disk or network) */
      bool IsInitialBlockDownload() const;
  
      /**
       * Make various assertions about the state of the block index.
       *
       * By default this only executes fully when using the Regtest chain; see: fCheckBlockIndex.
       */
      void CheckBlockIndex(const Consensus::Params& consensusParams);
  
  private:
      bool ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs);
      bool ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions& disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs);
  
      void InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
      CBlockIndex* FindMostWorkChain() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
      void ReceivedBlockTransactions(const CBlock& block, CBlockIndex* pindexNew, const FlatFilePos& pos, const Consensus::Params& consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      bool RollforwardBlock(const CBlockIndex* pindex, CCoinsViewCache& inputs, const CChainParams& params) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      //! Mark a block as not having block data
      void EraseBlockData(CBlockIndex* index) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  };
  
  /** Mark a block as precious and reorganize.
   *
   * May not be called in a
   * validationinterface callback.
   */
  bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIndex *pindex) LOCKS_EXCLUDED(cs_main);
  
  /** Mark a block as invalid. */
  bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
  
  /** Remove invalidity status from a block and its descendants. */
  void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
  /** @returns the most-work valid chainstate. */
  CChainState& ChainstateActive();
  
  /** @returns the most-work chain. */
  CChain& ChainActive();
  
  /** @returns the global block index map. */
  BlockMap& BlockIndex();
  
  // Most often ::ChainstateActive() should be used instead of this, but some code
  // may not be able to assume that this has been initialized yet and so must use it
  // directly, e.g. init.cpp.
  extern std::unique_ptr<CChainState> g_chainstate;
  
  /** Global variable that points to the active block tree (protected by cs_main) */
  extern std::unique_ptr<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;
  
  /** Get block file info entry for one block file */
  CBlockFileInfo* GetBlockFileInfo(size_t n);
  
  /** Dump the mempool to disk. */
  bool DumpMempool(const CTxMemPool& pool);
  
  /** Load the mempool from disk. */
  bool LoadMempool(CTxMemPool& pool);
  
  //! Check whether the block associated with this index entry is pruned or not.
  inline bool IsBlockPruned(const CBlockIndex* pblockindex)
  {
      return (fHavePruned && !(pblockindex->nStatus & BLOCK_HAVE_DATA) && pblockindex->nTx > 0);
  }
  
  #endif // BITCOIN_VALIDATION_H
  