bitcoin/src/validation.h

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-present 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

#include <arith_uint256.h>
#include <attributes.h>
#include <chain.h>
#include <checkqueue.h>
#include <consensus/amount.h>
#include <cuckoocache.h>
#include <deploymentstatus.h>
#include <kernel/chain.h>
#include <kernel/chainparams.h>
#include <kernel/chainstatemanager_opts.h>
#include <kernel/cs_main.h> // IWYU pragma: export
#include <node/blockstorage.h>
#include <policy/feerate.h>
#include <policy/packages.h>
#include <policy/policy.h>
#include <script/script_error.h>
#include <script/sigcache.h>
#include <script/verify_flags.h>
#include <sync.h>
#include <txdb.h>
#include <txmempool.h>
#include <uint256.h>
#include <util/byte_units.h>
#include <util/check.h>
#include <util/fs.h>
#include <util/hasher.h>
#include <util/result.h>
#include <util/time.h>
#include <util/translation.h>
#include <versionbits.h>

#include <algorithm>
#include <atomic>
#include <cstdint>
#include <map>
#include <memory>
#include <optional>
#include <set>
#include <span>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>

class Chainstate;
class CTxMemPool;
class ChainstateManager;
struct ChainTxData;
class DisconnectedBlockTransactions;
struct PrecomputedTransactionData;
struct LockPoints;
struct AssumeutxoData;
namespace kernel {
struct ChainstateRole;
} // namespace kernel
namespace node {
class SnapshotMetadata;
} // namespace node
namespace Consensus {
struct Params;
} // namespace Consensus
namespace util {
class SignalInterrupt;
} // namespace util

/** Block files containing a block-height within MIN_BLOCKS_TO_KEEP of ActiveChain().Tip() will not be pruned. */
static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
static const signed int DEFAULT_CHECKBLOCKS = 6;
static constexpr 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;

/** Maximum number of dedicated script-checking threads allowed */
static constexpr int MAX_SCRIPTCHECK_THREADS{15};

/** Current sync state passed to tip changed callbacks. */
enum class SynchronizationState {
    INIT_REINDEX,
    INIT_DOWNLOAD,
    POST_INIT
};

/** Documentation for argument 'checklevel'. */
extern const std::vector<std::string> CHECKLEVEL_DOC;

CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams);

bool FatalError(kernel::Notifications& notifications, BlockValidationState& state, const bilingual_str& message);

/** Prune block files up to a given height */
void PruneBlockFilesManual(Chainstate& active_chainstate, int nManualPruneHeight);

/**
* Validation result for a transaction evaluated by MemPoolAccept (single or package).
* Here are the expected fields and properties of a result depending on its ResultType, applicable to
* results returned from package evaluation:
*+---------------------------+----------------+-------------------+------------------+----------------+-------------------+
*| Field or property         |    VALID       |                 INVALID              |  MEMPOOL_ENTRY | DIFFERENT_WITNESS |
*|                           |                |--------------------------------------|                |                   |
*|                           |                | TX_RECONSIDERABLE |     Other        |                |                   |
*+---------------------------+----------------+-------------------+------------------+----------------+-------------------+
*| txid in mempool?          | yes            | no                | no*              | yes            | yes               |
*| wtxid in mempool?         | yes            | no                | no*              | yes            | no                |
*| m_state                   | yes, IsValid() | yes, IsInvalid()  | yes, IsInvalid() | yes, IsValid() | yes, IsValid()    |
*| m_vsize                   | yes            | no                | no               | yes            | no                |
*| m_base_fees               | yes            | no                | no               | yes            | no                |
*| m_effective_feerate       | yes            | yes               | no               | no             | no                |
*| m_wtxids_fee_calculations | yes            | yes               | no               | no             | no                |
*| m_other_wtxid             | no             | no                | no               | no             | yes               |
*+---------------------------+----------------+-------------------+------------------+----------------+-------------------+
* (*) Individual transaction acceptance doesn't return MEMPOOL_ENTRY and DIFFERENT_WITNESS. It returns
* INVALID, with the errors txn-already-in-mempool and txn-same-nonwitness-data-in-mempool
* respectively. In those cases, the txid or wtxid may be in the mempool for a TX_CONFLICT.
*/
struct MempoolAcceptResult {
    /** Used to indicate the results of mempool validation. */
    enum class ResultType {
        VALID, //!> Fully validated, valid.
        INVALID, //!> Invalid.
        MEMPOOL_ENTRY, //!> Valid, transaction was already in the mempool.
        DIFFERENT_WITNESS, //!> Not validated. A same-txid-different-witness tx (see m_other_wtxid) already exists in the mempool and was not replaced.
    };
    /** Result type. Present in all MempoolAcceptResults. */
    const ResultType m_result_type;

    /** Contains information about why the transaction failed. */
    const TxValidationState m_state;

    /** Mempool transactions replaced by the tx. */
    const std::list<CTransactionRef> m_replaced_transactions;
    /** Virtual size as used by the mempool, calculated using serialized size and sigops. */
    const std::optional<int64_t> m_vsize;
    /** Raw base fees in satoshis. */
    const std::optional<CAmount> m_base_fees;
    /** The feerate at which this transaction was considered. This includes any fee delta added
     * using prioritisetransaction (i.e. modified fees). If this transaction was submitted as a
     * package, this is the package feerate, which may also include its descendants and/or
     * ancestors (see m_wtxids_fee_calculations below).
     */
    const std::optional<CFeeRate> m_effective_feerate;
    /** Contains the wtxids of the transactions used for fee-related checks. Includes this
     * transaction's wtxid and may include others if this transaction was validated as part of a
     * package. This is not necessarily equivalent to the list of transactions passed to
     * ProcessNewPackage().
     * Only present when m_result_type = ResultType::VALID. */
    const std::optional<std::vector<Wtxid>> m_wtxids_fee_calculations;

    /** The wtxid of the transaction in the mempool which has the same txid but different witness. */
    const std::optional<Wtxid> m_other_wtxid;

    static MempoolAcceptResult Failure(TxValidationState state) {
        return MempoolAcceptResult(state);
    }

    static MempoolAcceptResult FeeFailure(TxValidationState state,
                                          CFeeRate effective_feerate,
                                          const std::vector<Wtxid>& wtxids_fee_calculations) {
        return MempoolAcceptResult(state, effective_feerate, wtxids_fee_calculations);
    }

    static MempoolAcceptResult Success(std::list<CTransactionRef>&& replaced_txns,
                                       int64_t vsize,
                                       CAmount fees,
                                       CFeeRate effective_feerate,
                                       const std::vector<Wtxid>& wtxids_fee_calculations) {
        return MempoolAcceptResult(std::move(replaced_txns), vsize, fees,
                                   effective_feerate, wtxids_fee_calculations);
    }

    static MempoolAcceptResult MempoolTx(int64_t vsize, CAmount fees) {
        return MempoolAcceptResult(vsize, fees);
    }

    static MempoolAcceptResult MempoolTxDifferentWitness(const Wtxid& other_wtxid) {
        return MempoolAcceptResult(other_wtxid);
    }

// Private constructors. Use static methods MempoolAcceptResult::Success, etc. to construct.
private:
    /** Constructor for failure case */
    explicit MempoolAcceptResult(TxValidationState state)
        : m_result_type(ResultType::INVALID), m_state(state) {
            Assume(!state.IsValid()); // Can be invalid or error
        }

    /** Constructor for success case */
    explicit MempoolAcceptResult(std::list<CTransactionRef>&& replaced_txns,
                                 int64_t vsize,
                                 CAmount fees,
                                 CFeeRate effective_feerate,
                                 const std::vector<Wtxid>& wtxids_fee_calculations)
        : m_result_type(ResultType::VALID),
        m_replaced_transactions(std::move(replaced_txns)),
        m_vsize{vsize},
        m_base_fees(fees),
        m_effective_feerate(effective_feerate),
        m_wtxids_fee_calculations(wtxids_fee_calculations) {}

    /** Constructor for fee-related failure case */
    explicit MempoolAcceptResult(TxValidationState state,
                                 CFeeRate effective_feerate,
                                 const std::vector<Wtxid>& wtxids_fee_calculations)
        : m_result_type(ResultType::INVALID),
        m_state(state),
        m_effective_feerate(effective_feerate),
        m_wtxids_fee_calculations(wtxids_fee_calculations) {}

    /** Constructor for already-in-mempool case. It wouldn't replace any transactions. */
    explicit MempoolAcceptResult(int64_t vsize, CAmount fees)
        : m_result_type(ResultType::MEMPOOL_ENTRY), m_vsize{vsize}, m_base_fees(fees) {}

    /** Constructor for witness-swapped case. */
    explicit MempoolAcceptResult(const Wtxid& other_wtxid)
        : m_result_type(ResultType::DIFFERENT_WITNESS), m_other_wtxid(other_wtxid) {}
};

/**
* Validation result for package mempool acceptance.
*/
struct PackageMempoolAcceptResult
{
    PackageValidationState m_state;
    /**
    * Map from wtxid to finished MempoolAcceptResults. The client is responsible
    * for keeping track of the transaction objects themselves. If a result is not
    * present, it means validation was unfinished for that transaction. If there
    * was a package-wide error (see result in m_state), m_tx_results will be empty.
    */
    std::map<Wtxid, MempoolAcceptResult> m_tx_results;

    explicit PackageMempoolAcceptResult(PackageValidationState state,
                                        std::map<Wtxid, MempoolAcceptResult>&& results)
        : m_state{state}, m_tx_results(std::move(results)) {}

    explicit PackageMempoolAcceptResult(PackageValidationState state, CFeeRate feerate,
                                        std::map<Wtxid, MempoolAcceptResult>&& results)
        : m_state{state}, m_tx_results(std::move(results)) {}

    /** Constructor to create a PackageMempoolAcceptResult from a single MempoolAcceptResult */
    explicit PackageMempoolAcceptResult(const Wtxid& wtxid, const MempoolAcceptResult& result)
        : m_tx_results{ {wtxid, result} } {}
};

/**
 * Try to add a transaction to the mempool. This is an internal function and is exposed only for testing.
 * Client code should use ChainstateManager::ProcessTransaction()
 *
 * @param[in]  active_chainstate  Reference to the active chainstate.
 * @param[in]  tx                 The transaction to submit for mempool acceptance.
 * @param[in]  accept_time        The timestamp for adding the transaction to the mempool.
 *                                It is also used to determine when the entry expires.
 * @param[in]  bypass_limits      When true, don't enforce mempool fee and capacity limits,
 *                                and set entry_sequence to zero.
 * @param[in]  test_accept        When true, run validation checks but don't submit to mempool.
 *
 * @returns a MempoolAcceptResult indicating whether the transaction was accepted/rejected with reason.
 */
MempoolAcceptResult AcceptToMemoryPool(Chainstate& active_chainstate, const CTransactionRef& tx,
                                       int64_t accept_time, bool bypass_limits, bool test_accept)
    EXCLUSIVE_LOCKS_REQUIRED(cs_main);

/**
* Validate (and maybe submit) a package to the mempool. See doc/policy/packages.md for full details
* on package validation rules.
* @param[in]    test_accept         When true, run validation checks but don't submit to mempool.
* @param[in]    client_maxfeerate    If exceeded by an individual transaction, rest of (sub)package evaluation is aborted.
*                                   Only for sanity checks against local submission of transactions.
* @returns a PackageMempoolAcceptResult which includes a MempoolAcceptResult for each transaction.
* If a transaction fails, validation will exit early and some results may be missing. It is also
* possible for the package to be partially submitted.
*/
PackageMempoolAcceptResult ProcessNewPackage(Chainstate& active_chainstate, CTxMemPool& pool,
                                                   const Package& txns, bool test_accept, const std::optional<CFeeRate>& client_maxfeerate)
                                                   EXCLUSIVE_LOCKS_REQUIRED(cs_main);

/* Mempool validation helper functions */

/**
 * Check if transaction will be final in the next block to be created.
 */
bool CheckFinalTxAtTip(const CBlockIndex& active_chain_tip, const CTransaction& tx) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

/**
 * Calculate LockPoints required to check if transaction will be BIP68 final in the next block
 * to be created on top of tip.
 *
 * @param[in]   tip             Chain tip for which tx sequence locks are calculated. For
 *                              example, the tip of the current active chain.
 * @param[in]   coins_view      Any CCoinsView that provides access to the relevant coins for
 *                              checking sequence locks. For example, it can be a CCoinsViewCache
 *                              that isn't connected to anything but contains all the relevant
 *                              coins, or a CCoinsViewMemPool that is connected to the
 *                              mempool and chainstate UTXO set. In the latter case, the caller
 *                              is responsible for holding the appropriate locks to ensure that
 *                              calls to GetCoin() return correct coins.
 * @param[in]   tx              The transaction being evaluated.
 *
 * @returns The resulting height and time calculated and the hash of the block needed for
 *          calculation, or std::nullopt if there is an error.
 */
std::optional<LockPoints> CalculateLockPointsAtTip(
    CBlockIndex* tip,
    const CCoinsView& coins_view,
    const CTransaction& tx);

/**
 * Check if transaction will be BIP68 final in the next block to be created on top of tip.
 * @param[in]   tip             Chain tip to check tx sequence locks against. For example,
 *                              the tip of the current active chain.
 * @param[in]   lock_points     LockPoints containing the height and time at which this
 *                              transaction is final.
 * Simulates calling SequenceLocks() with data from the tip passed in.
 * The LockPoints should not be considered valid if CheckSequenceLocksAtTip returns false.
 */
bool CheckSequenceLocksAtTip(CBlockIndex* tip,
                             const LockPoints& lock_points);

/**
 * 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;
    script_verify_flags m_flags;
    bool cacheStore;
    PrecomputedTransactionData *txdata;
    SignatureCache* m_signature_cache;

public:
    CScriptCheck(const CTxOut& outIn, const CTransaction& txToIn, SignatureCache& signature_cache, unsigned int nInIn, script_verify_flags flags, bool cacheIn, PrecomputedTransactionData* txdataIn) :
        m_tx_out(outIn), ptxTo(&txToIn), nIn(nInIn), m_flags(flags), cacheStore(cacheIn), txdata(txdataIn), m_signature_cache(&signature_cache) { }

    CScriptCheck(const CScriptCheck&) = delete;
    CScriptCheck& operator=(const CScriptCheck&) = delete;
    CScriptCheck(CScriptCheck&&) = default;
    CScriptCheck& operator=(CScriptCheck&&) = default;

    std::optional<std::pair<ScriptError, std::string>> operator()();
};

// CScriptCheck is used a lot in std::vector, make sure that's efficient
static_assert(std::is_nothrow_move_assignable_v<CScriptCheck>);
static_assert(std::is_nothrow_move_constructible_v<CScriptCheck>);
static_assert(std::is_nothrow_destructible_v<CScriptCheck>);

/**
 * Convenience class for initializing and passing the script execution cache
 * and signature cache.
 */
class ValidationCache
{
private:
    //! Pre-initialized hasher to avoid having to recreate it for every hash calculation.
    CSHA256 m_script_execution_cache_hasher;

public:
    CuckooCache::cache<uint256, SignatureCacheHasher> m_script_execution_cache;
    SignatureCache m_signature_cache;

    ValidationCache(size_t script_execution_cache_bytes, size_t signature_cache_bytes);

    ValidationCache(const ValidationCache&) = delete;
    ValidationCache& operator=(const ValidationCache&) = delete;

    //! Return a copy of the pre-initialized hasher.
    CSHA256 ScriptExecutionCacheHasher() const { return m_script_execution_cache_hasher; }
};

/** Functions for validating blocks and updating the block tree */

/** Context-independent validity checks */
bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW = true, bool fCheckMerkleRoot = true);

/**
 * Verify a block, including transactions.
 *
 * @param[in]   block       The block we want to process. Must connect to the
 *                          current tip.
 * @param[in]   chainstate  The chainstate to connect to.
 * @param[in]   check_pow   perform proof-of-work check, nBits in the header
 *                          is always checked
 * @param[in]   check_merkle_root check the merkle root
 *
 * @return Valid or Invalid state. This doesn't currently return an Error state,
 *         and shouldn't unless there is something wrong with the existing
 *         chainstate. (This is different from functions like AcceptBlock which
 *         can fail trying to save new data.)
 *
 * For signets the challenge verification is skipped when check_pow is false.
 */
BlockValidationState TestBlockValidity(
    Chainstate& chainstate,
    const CBlock& block,
    bool check_pow,
    bool check_merkle_root) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

/** Check that the proof of work on each blockheader matches the value in nBits */
bool HasValidProofOfWork(std::span<const CBlockHeader> headers, const Consensus::Params& consensusParams);

/** Check if a block has been mutated (with respect to its merkle root and witness commitments). */
bool IsBlockMutated(const CBlock& block, bool check_witness_root);

/** Return the sum of the claimed work on a given set of headers. No verification of PoW is done. */
arith_uint256 CalculateClaimedHeadersWork(std::span<const CBlockHeader> headers);

enum class VerifyDBResult {
    SUCCESS,
    CORRUPTED_BLOCK_DB,
    INTERRUPTED,
    SKIPPED_L3_CHECKS,
    SKIPPED_MISSING_BLOCKS,
};

/** RAII wrapper for VerifyDB: Verify consistency of the block and coin databases */
class CVerifyDB
{
private:
    kernel::Notifications& m_notifications;

public:
    explicit CVerifyDB(kernel::Notifications& notifications);
    ~CVerifyDB();
    [[nodiscard]] VerifyDBResult VerifyDB(
        Chainstate& chainstate,
        const Consensus::Params& consensus_params,
        CCoinsView& coinsview,
        int nCheckLevel,
        int nCheckDepth) 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 Chainstate::FlushStateToDisk */
inline constexpr std::array FlushStateModeNames{"NONE", "IF_NEEDED", "PERIODIC", "ALWAYS"};
enum class FlushStateMode: uint8_t {
    NONE,
    IF_NEEDED,
    PERIODIC,
    ALWAYS
};

/**
 * 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(DBParams db_params, CoinsViewOptions options);

    //! Initialize the CCoinsViewCache member.
    void InitCache() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
};

enum class CoinsCacheSizeState
{
    //! The coins cache is in immediate need of a flush.
    CRITICAL = 2,
    //! The cache is at >= 90% capacity.
    LARGE = 1,
    OK = 0
};

constexpr int64_t LargeCoinsCacheThreshold(int64_t total_space) noexcept
{
    // No periodic flush needed if at least this much space is free
    constexpr int64_t MAX_BLOCK_COINSDB_USAGE_BYTES{int64_t(10_MiB)};
    return std::max((total_space * 9) / 10,
                    total_space - MAX_BLOCK_COINSDB_USAGE_BYTES);
}

//! Chainstate assumeutxo validity.
enum class Assumeutxo {
    //! Every block in the chain has been validated.
    VALIDATED,
    //! Blocks after an assumeutxo snapshot have been validated but the snapshot itself has not been validated.
    UNVALIDATED,
    //! The assumeutxo snapshot failed validation.
    INVALID,
};

/**
 * Chainstate 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 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 `BlockManager`.
 */
class Chainstate
{
protected:
    /**
     * The ChainState Mutex
     * A lock that must be held when modifying this ChainState - held in ActivateBestChain() and
     * InvalidateBlock()
     */
    Mutex m_chainstate_mutex;

    //! Optional mempool that is kept in sync with the chain.
    //! Only the active chainstate has a mempool.
    CTxMemPool* m_mempool;

    //! Manages the UTXO set, which is a reflection of the contents of `m_chain`.
    std::unique_ptr<CoinsViews> m_coins_views;

    //! Cached result of LookupBlockIndex(*m_from_snapshot_blockhash)
    mutable const CBlockIndex* m_cached_snapshot_base GUARDED_BY(::cs_main){nullptr};

    //! Cached result of LookupBlockIndex(*m_target_blockhash)
    mutable const CBlockIndex* m_cached_target_block GUARDED_BY(::cs_main){nullptr};

    std::optional<const char*> m_last_script_check_reason_logged GUARDED_BY(::cs_main){};

public:
    //! Reference to a BlockManager instance which itself is shared across all
    //! Chainstate instances.
    node::BlockManager& m_blockman;

    //! The chainstate manager that owns this chainstate. The reference is
    //! necessary so that this instance can check whether it is the active
    //! chainstate within deeply nested method calls.
    ChainstateManager& m_chainman;

    explicit Chainstate(
        CTxMemPool* mempool,
        node::BlockManager& blockman,
        ChainstateManager& chainman,
        std::optional<uint256> from_snapshot_blockhash = std::nullopt);

    //! Return path to chainstate leveldb directory.
    fs::path StoragePath() const;

    //! Return the current role of the chainstate. See `ChainstateManager`
    //! documentation for a description of the different types of chainstates.
    //!
    //! @sa ChainstateRole
    kernel::ChainstateRole GetRole() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    /**
     * 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);

    //! Initialize the in-memory coins cache (to be done after the health of the on-disk database
    //! is verified).
    void InitCoinsCache(size_t cache_size_bytes) 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() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
    {
        AssertLockHeld(::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;

    //! Assumeutxo state indicating whether all blocks in the chain were
    //! validated, or if the chainstate is based on an assumeutxo snapshot and
    //! the snapshot has not been validated.
    Assumeutxo m_assumeutxo GUARDED_BY(::cs_main);

    /**
     * The blockhash which is the base of the snapshot this chainstate was created from.
     *
     * std::nullopt if this chainstate was not created from a snapshot.
     */
    const std::optional<uint256> m_from_snapshot_blockhash;

    //! Target block for this chainstate. If this is not set, chainstate will
    //! target the most-work, valid block. If this is set, ChainstateManager
    //! considers this a "historical" chainstate since it will only contain old
    //! blocks up to the target block, not newer blocks.
    std::optional<uint256> m_target_blockhash GUARDED_BY(::cs_main);

    //! Hash of the UTXO set at the target block, computed when the chainstate
    //! reaches the target block, and null before then.
    std::optional<AssumeutxoHash> m_target_utxohash GUARDED_BY(::cs_main);

    /**
     * The base of the snapshot this chainstate was created from.
     *
     * nullptr if this chainstate was not created from a snapshot.
     */
    const CBlockIndex* SnapshotBase() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Return target block which chainstate tip is expected to reach, if this
    //! is a historic chainstate being used to validate a snapshot, or null if
    //! chainstate targets the most-work block.
    const CBlockIndex* TargetBlock() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
    //! Set target block for this chainstate. If null, chainstate will target
    //! the most-work valid block. If non-null chainstate will be a historic
    //! chainstate and target the specified block.
    void SetTargetBlock(CBlockIndex* block) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
    //! Set target block for this chainstate using just a block hash. Useful
    //! when the block database has not been loaded yet.
    void SetTargetBlockHash(uint256 block_hash) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Return true if chainstate reached target block.
    bool ReachedTarget() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
    {
        const CBlockIndex* target_block{TargetBlock()};
        assert(!target_block || target_block->GetAncestor(m_chain.Height()) == m_chain.Tip());
        return target_block && target_block == m_chain.Tip();
    }

    /**
     * The set of all CBlockIndex entries that have as much work as our current
     * tip or more, and transaction data needed to be validated (with
     * BLOCK_VALID_TRANSACTIONS for each block and its parents back to the
     * genesis block or an assumeutxo snapshot block). Entries may be failed,
     * though, and pruning nodes may be missing the data for the block.
     */
    std::set<CBlockIndex*, node::CBlockIndexWorkComparator> setBlockIndexCandidates;

    //! @returns A reference to the in-memory cache of the UTXO set.
    CCoinsViewCache& CoinsTip() EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
    {
        AssertLockHeld(::cs_main);
        Assert(m_coins_views);
        return *Assert(m_coins_views->m_cacheview);
    }

    //! @returns A reference to the on-disk UTXO set database.
    CCoinsViewDB& CoinsDB() EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
    {
        AssertLockHeld(::cs_main);
        return Assert(m_coins_views)->m_dbview;
    }

    //! @returns A pointer to the mempool.
    CTxMemPool* GetMempool()
    {
        return m_mempool;
    }

    //! @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)
    {
        AssertLockHeld(::cs_main);
        return Assert(m_coins_views)->m_catcherview;
    }

    //! Destructs all objects related to accessing the UTXO set.
    void ResetCoinsViews() { m_coins_views.reset(); }

    //! The cache size of the on-disk coins view.
    size_t m_coinsdb_cache_size_bytes{0};

    //! The cache size of the in-memory coins view.
    size_t m_coinstip_cache_size_bytes{0};

    //! Resize the CoinsViews caches dynamically and flush state to disk.
    //! @returns true unless an error occurred during the flush.
    bool ResizeCoinsCaches(size_t coinstip_size, size_t coinsdb_size)
        EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    /**
     * 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(
        BlockValidationState& 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();

    /**
     * Find the best known block, and make it the tip of the block chain. 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.
     *
     * May not be called with cs_main held. May not be called in a
     * validationinterface callback.
     *
     * Note that if this is called while a snapshot chainstate is active, and if
     * it is called on a validated chainstate whose tip has reached the base
     * block of the snapshot, its execution will take *MINUTES* while it hashes
     * the UTXO set to verify the assumeutxo value the snapshot was activated
     * with. `cs_main` will be held during this time.
     *
     * @returns true unless a system error occurred
     */
    bool ActivateBestChain(
        BlockValidationState& state,
        std::shared_ptr<const CBlock> pblock = nullptr)
        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
        LOCKS_EXCLUDED(::cs_main);

    // Block (dis)connection on a given view:
    DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view)
        EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
    bool ConnectBlock(const CBlock& block, BlockValidationState& state, CBlockIndex* pindex,
                      CCoinsViewCache& view, bool fJustCheck = false) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    // Apply the effects of a block disconnection on the UTXO set.
    bool DisconnectTip(BlockValidationState& state, DisconnectedBlockTransactions* disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_mempool->cs);

    // Manual block validity manipulation:
    /** Mark a block as precious and reorganize.
     *
     * May not be called in a validationinterface callback.
     */
    bool PreciousBlock(BlockValidationState& state, CBlockIndex* pindex)
        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
        LOCKS_EXCLUDED(::cs_main);

    /** Mark a block as invalid. */
    bool InvalidateBlock(BlockValidationState& state, CBlockIndex* pindex)
        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
        LOCKS_EXCLUDED(::cs_main);

    /** Set invalidity status to all descendants of a block */
    void SetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    /** Remove invalidity status from a block, its descendants and ancestors and reconsider them for activation */
    void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    /** Replay blocks that aren't fully applied to the database. */
    bool ReplayBlocks();

    /** Whether the chain state needs to be redownloaded due to lack of witness data */
    [[nodiscard]] bool NeedsRedownload() const EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    /** Ensures we have a genesis block in the block tree, possibly writing one to disk. */
    bool LoadGenesisBlock();

    void TryAddBlockIndexCandidate(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    void PruneBlockIndexCandidates();

    void ClearBlockIndexCandidates() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    /** Find the last common block of this chain and a locator. */
    const CBlockIndex* FindForkInGlobalIndex(const CBlockLocator& locator) const EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    /** Update the chain tip based on database information, i.e. CoinsTip()'s best block. */
    bool LoadChainTip() EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    //! Dictates whether we need to flush the cache to disk or not.
    //!
    //! @return the state of the size of the coins cache.
    CoinsCacheSizeState GetCoinsCacheSizeState() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    CoinsCacheSizeState GetCoinsCacheSizeState(
        size_t max_coins_cache_size_bytes,
        size_t max_mempool_size_bytes) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    std::string ToString() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Indirection necessary to make lock annotations work with an optional mempool.
    RecursiveMutex* MempoolMutex() const LOCK_RETURNED(m_mempool->cs)
    {
        return m_mempool ? &m_mempool->cs : nullptr;
    }

    //! Return the [start, end] (inclusive) of block heights we can prune.
    //!
    //! start > end is possible, meaning no blocks can be pruned.
    std::pair<int, int> GetPruneRange(int last_height_can_prune) const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

protected:
    bool ActivateBestChainStep(BlockValidationState& state, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_mempool->cs);
    bool ConnectTip(
        BlockValidationState& state,
        CBlockIndex* pindexNew,
        std::shared_ptr<const CBlock> block_to_connect,
        ConnectTrace& connectTrace,
        DisconnectedBlockTransactions& disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_mempool->cs);

    void InvalidBlockFound(CBlockIndex* pindex, const BlockValidationState& state) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    CBlockIndex* FindMostWorkChain() EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    bool RollforwardBlock(const CBlockIndex* pindex, CCoinsViewCache& inputs) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    void CheckForkWarningConditions() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    void InvalidChainFound(CBlockIndex* pindexNew) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    /**
     * 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.
     */
    void MaybeUpdateMempoolForReorg(
        DisconnectedBlockTransactions& disconnectpool,
        bool fAddToMempool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_mempool->cs);

    /** Check warning conditions and do some notifications on new chain tip set. */
    void UpdateTip(const CBlockIndex* pindexNew)
        EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    NodeClock::time_point m_next_write{NodeClock::time_point::max()};

    /**
     * In case of an invalid snapshot, rename the coins leveldb directory so
     * that it can be examined for issue diagnosis.
     */
    [[nodiscard]] util::Result<void> InvalidateCoinsDBOnDisk() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    friend ChainstateManager;
};

enum class SnapshotCompletionResult {
    SUCCESS,
    SKIPPED,

    // Expected assumeutxo configuration data is not found for the height of the
    // base block.
    MISSING_CHAINPARAMS,

    // Failed to generate UTXO statistics (to check UTXO set hash) for the
    // validated chainstate.
    STATS_FAILED,

    // The UTXO set hash of the validated chainstate does not match the one
    // expected by assumeutxo chainparams.
    HASH_MISMATCH,
};

/**
 * Interface for managing multiple \ref Chainstate objects, where each
 * chainstate is associated with chainstate* subdirectory in the data directory
 * and contains a database of UTXOs existing at a different point in history.
 * (See \ref Chainstate class for more information.)
 *
 * Normally there is exactly one Chainstate, which contains the UTXO set of
 * chain tip if syncing is completed, or the UTXO set the most recent validated
 * block if the initial sync is still in progress.
 *
 * However, if an assumeutxo snapshot is loaded before syncing is completed,
 * there will be two chainstates. The original fully validated chainstate will
 * continue to exist and download new blocks in the background. But the new
 * snapshot which is loaded will become a second chainstate. The second
 * chainstate will be used as the chain tip for the wallet and RPCs even though
 * it is only assumed to be valid. When the initial chainstate catches up to the
 * snapshot height and confirms that the assumeutxo snapshot is actually valid,
 * the second chainstate will be marked validated and become the only chainstate
 * again.
 */
class ChainstateManager
{
private:

    /** The last header for which a headerTip notification was issued. */
    CBlockIndex* m_last_notified_header GUARDED_BY(GetMutex()){nullptr};

    bool NotifyHeaderTip() LOCKS_EXCLUDED(GetMutex());

    //! Internal helper for ActivateSnapshot().
    //!
    //! De-serialization of a snapshot that is created with
    //! the dumptxoutset RPC.
    //! To reduce space the serialization format of the snapshot avoids
    //! duplication of tx hashes. The code takes advantage of the guarantee by
    //! leveldb that keys are lexicographically sorted.
    [[nodiscard]] util::Result<void> PopulateAndValidateSnapshot(
        Chainstate& snapshot_chainstate,
        AutoFile& coins_file,
        const node::SnapshotMetadata& metadata);

    /**
     * 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.
     * Caller must set min_pow_checked=true in order to add a new header to the
     * block index (permanent memory storage), indicating that the header is
     * known to be part of a sufficiently high-work chain (anti-dos check).
     */
    bool AcceptBlockHeader(
        const CBlockHeader& block,
        BlockValidationState& state,
        CBlockIndex** ppindex,
        bool min_pow_checked) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    friend Chainstate;

    /** Most recent headers presync progress update, for rate-limiting. */
    MockableSteadyClock::time_point m_last_presync_update GUARDED_BY(GetMutex()){};

    //! A queue for script verifications that have to be performed by worker threads.
    CCheckQueue<CScriptCheck> m_script_check_queue;

    //! Timers and counters used for benchmarking validation in both background
    //! and active chainstates.
    SteadyClock::duration GUARDED_BY(::cs_main) time_check{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_forks{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_connect{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_verify{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_undo{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_index{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_total{};
    int64_t GUARDED_BY(::cs_main) num_blocks_total{0};
    SteadyClock::duration GUARDED_BY(::cs_main) time_connect_total{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_flush{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_chainstate{};
    SteadyClock::duration GUARDED_BY(::cs_main) time_post_connect{};

protected:
    CBlockIndex* m_best_invalid GUARDED_BY(::cs_main){nullptr};

public:
    using Options = kernel::ChainstateManagerOpts;

    explicit ChainstateManager(const util::SignalInterrupt& interrupt, Options options, node::BlockManager::Options blockman_options);

    //! Function to restart active indexes; set dynamically to avoid a circular
    //! dependency on `base/index.cpp`.
    std::function<void()> snapshot_download_completed = std::function<void()>();

    const CChainParams& GetParams() const { return m_options.chainparams; }
    const Consensus::Params& GetConsensus() const { return m_options.chainparams.GetConsensus(); }
    bool ShouldCheckBlockIndex() const;
    const arith_uint256& MinimumChainWork() const { return *Assert(m_options.minimum_chain_work); }
    const uint256& AssumedValidBlock() const { return *Assert(m_options.assumed_valid_block); }
    kernel::Notifications& GetNotifications() const { return m_options.notifications; };

    /**
     * Make various assertions about the state of the block index.
     *
     * By default this only executes fully when using the Regtest chain; see: m_options.check_block_index.
     */
    void CheckBlockIndex() const;

    /**
     * Alias for ::cs_main.
     * Should be used in new code to make it easier to make ::cs_main a member
     * of this class.
     * Generally, methods of this class should be annotated to require this
     * mutex. This will make calling code more verbose, but also help to:
     * - Clarify that the method will acquire a mutex that heavily affects
     *   overall performance.
     * - Force call sites to think how long they need to acquire the mutex to
     *   get consistent results.
     */
    RecursiveMutex& GetMutex() const LOCK_RETURNED(::cs_main) { return ::cs_main; }

    const util::SignalInterrupt& m_interrupt;
    const Options m_options;
    //! A single BlockManager instance is shared across each constructed
    //! chainstate to avoid duplicating block metadata.
    node::BlockManager m_blockman;

    ValidationCache m_validation_cache;

    /**
     * Whether initial block download has ended and IsInitialBlockDownload
     * should return false from now on.
     *
     * 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};

    /**
     * Every received block is assigned a unique and increasing identifier, so we
     * know which one to give priority in case of a fork.
     */
    /** Blocks loaded from disk are assigned id SEQ_ID_INIT_FROM_DISK{1}
     * (SEQ_ID_BEST_CHAIN_FROM_DISK{0} if they belong to the best chain loaded from disk),
     * so start the counter after that. **/
    int32_t nBlockSequenceId GUARDED_BY(::cs_main) = SEQ_ID_INIT_FROM_DISK + 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;

    // Reset the memory-only sequence counters we use to track block arrival
    // (used by tests to reset state)
    void ResetBlockSequenceCounters() EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
    {
        AssertLockHeld(::cs_main);
        nBlockSequenceId = SEQ_ID_INIT_FROM_DISK + 1;
        nBlockReverseSequenceId = -1;
    }


    /** Best header we've seen so far for which the block is not known to be invalid
        (used, among others, for getheaders queries' starting points).
        In case of multiple best headers with the same work, it could point to any
        because CBlockIndexWorkComparator tiebreaker rules are not applied. */
    CBlockIndex* m_best_header GUARDED_BY(::cs_main){nullptr};

    //! The total number of bytes available for us to use across all in-memory
    //! coins caches. This will be split somehow across chainstates.
    size_t m_total_coinstip_cache{0};
    //
    //! The total number of bytes available for us to use across all leveldb
    //! coins databases. This will be split somehow across chainstates.
    size_t m_total_coinsdb_cache{0};

    //! Instantiate a new chainstate.
    //!
    //! @param[in] mempool              The mempool to pass to the chainstate
    //                                  constructor
    Chainstate& InitializeChainstate(CTxMemPool* mempool) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Construct and activate a Chainstate on the basis of UTXO snapshot data.
    //!
    //! Steps:
    //!
    //! - Initialize an unused Chainstate.
    //! - Load its `CoinsViews` contents from `coins_file`.
    //! - Verify that the hash of the resulting coinsdb matches the expected hash
    //!   per assumeutxo chain parameters.
    //! - Wait for our headers chain to include the base block of the snapshot.
    //! - "Fast forward" the tip of the new chainstate to the base of the snapshot.
    //! - Construct the new Chainstate and add it to m_chainstates.
    [[nodiscard]] util::Result<CBlockIndex*> ActivateSnapshot(
        AutoFile& coins_file, const node::SnapshotMetadata& metadata, bool in_memory);

    //! Try to validate an assumeutxo snapshot by using a validated historical
    //! chainstate targeted at the snapshot block. When the target block is
    //! reached, the UTXO hash is computed and saved to
    //! `validated_cs.m_target_utxohash`, and `unvalidated_cs.m_assumeutxo` will
    //! be updated from UNVALIDATED to either VALIDATED or INVALID depending on
    //! whether the hash matches. The INVALID case should not happen in practice
    //! because the software should refuse to load unrecognized snapshots, but
    //! if it does happen, it is a fatal error.
    SnapshotCompletionResult MaybeValidateSnapshot(Chainstate& validated_cs, Chainstate& unvalidated_cs) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Return current chainstate targeting the most-work, network tip.
    Chainstate& CurrentChainstate() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex())
    {
        for (auto& cs : m_chainstates) {
            if (cs && cs->m_assumeutxo != Assumeutxo::INVALID && !cs->m_target_blockhash) return *cs;
        }
        abort();
    }

    //! Return historical chainstate targeting a specific block, if any.
    Chainstate* HistoricalChainstate() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex())
    {
        for (auto& cs : m_chainstates) {
            if (cs && cs->m_assumeutxo != Assumeutxo::INVALID && cs->m_target_blockhash && !cs->m_target_utxohash) return cs.get();
        }
        return nullptr;
    }

    //! Return fully validated chainstate that should be used for indexing, to
    //! support indexes that need to index blocks in order and can't start from
    //! the snapshot block.
    Chainstate& ValidatedChainstate() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex())
    {
        for (auto* cs : {&CurrentChainstate(), HistoricalChainstate()}) {
            if (cs && cs->m_assumeutxo == Assumeutxo::VALIDATED) return *cs;
        }
        abort();
    }

    //! Remove a chainstate.
    std::unique_ptr<Chainstate> RemoveChainstate(Chainstate& chainstate) EXCLUSIVE_LOCKS_REQUIRED(GetMutex())
    {
        auto it{std::find_if(m_chainstates.begin(), m_chainstates.end(), [&](auto& cs) { return cs.get() == &chainstate; })};
        if (it != m_chainstates.end()) {
            auto ret{std::move(*it)};
            m_chainstates.erase(it);
            return ret;
        }
        return nullptr;
    }

    //! Alternatives to CurrentChainstate() used by older code to query latest
    //! chainstate information without locking cs_main. Newer code should avoid
    //! querying ChainstateManager and use Chainstate objects directly, or
    //! should use CurrentChainstate() instead.
    //! @{
    Chainstate& ActiveChainstate() const;
    CChain& ActiveChain() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex()) { return ActiveChainstate().m_chain; }
    int ActiveHeight() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex()) { return ActiveChain().Height(); }
    CBlockIndex* ActiveTip() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex()) { return ActiveChain().Tip(); }
    //! @}

    node::BlockMap& BlockIndex() EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
    {
        AssertLockHeld(::cs_main);
        return m_blockman.m_block_index;
    }

    /**
     * Track versionbit status
     */
    mutable VersionBitsCache m_versionbitscache;

    /** Check whether we are doing an initial block download (synchronizing from disk or network) */
    bool IsInitialBlockDownload() const;

    /** Guess verification progress (as a fraction between 0.0=genesis and 1.0=current tip). */
    double GuessVerificationProgress(const CBlockIndex* pindex) const EXCLUSIVE_LOCKS_REQUIRED(GetMutex());

    /**
     * Import blocks from an external file
     *
     * During reindexing, this function is called for each block file (datadir/blocks/blk?????.dat).
     * It reads all blocks contained in the given file and attempts to process them (add them to the
     * block index). The blocks may be out of order within each file and across files. Often this
     * function reads a block but finds that its parent hasn't been read yet, so the block can't be
     * processed yet. The function will add an entry to the blocks_with_unknown_parent map (which is
     * passed as an argument), so that when the block's parent is later read and processed, this
     * function can re-read the child block from disk and process it.
     *
     * Because a block's parent may be in a later file, not just later in the same file, the
     * blocks_with_unknown_parent map must be passed in and out with each call. It's a multimap,
     * rather than just a map, because multiple blocks may have the same parent (when chain splits
     * or stale blocks exist). It maps from parent-hash to child-disk-position.
     *
     * This function can also be used to read blocks from user-specified block files using the
     * -loadblock= option. There's no unknown-parent tracking, so the last two arguments are omitted.
     *
     *
     * @param[in]     file_in                       File containing blocks to read
     * @param[in]     dbp                           (optional) Disk block position (only for reindex)
     * @param[in,out] blocks_with_unknown_parent    (optional) Map of disk positions for blocks with
     *                                              unknown parent, key is parent block hash
     *                                              (only used for reindex)
     * */
    void LoadExternalBlockFile(
        AutoFile& file_in,
        FlatFilePos* dbp = nullptr,
        std::multimap<uint256, FlatFilePos>* blocks_with_unknown_parent = nullptr);

    /**
     * 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 block 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 block, or
     * (and possibly also) BlockChecked will have been called.
     *
     * May not be called in a validationinterface callback.
     *
     * @param[in]   block The block we want to process.
     * @param[in]   force_processing Process this block even if unrequested; used for non-network block sources.
     * @param[in]   min_pow_checked  True if proof-of-work anti-DoS checks have
     *                               been done by caller for headers chain
     *                               (note: only affects headers acceptance; if
     *                               block header is already present in block
     *                               index then this parameter has no effect)
     * @param[out]  new_block 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 std::shared_ptr<const CBlock>& block, bool force_processing, bool min_pow_checked, bool* new_block) LOCKS_EXCLUDED(cs_main);

    /**
     * Process incoming block headers.
     *
     * May not be called in a
     * validationinterface callback.
     *
     * @param[in]  headers The block headers themselves
     * @param[in]  min_pow_checked  True if proof-of-work anti-DoS checks have been done by caller for headers chain
     * @param[out] state This may be set to an Error state if any error occurred processing them
     * @param[out] ppindex If set, the pointer will be set to point to the last new block index object for the given headers
     * @returns false if AcceptBlockHeader fails on any of the headers, true otherwise (including if headers were already known)
     */
    bool ProcessNewBlockHeaders(std::span<const CBlockHeader> headers, bool min_pow_checked, BlockValidationState& state, const CBlockIndex** ppindex = nullptr) LOCKS_EXCLUDED(cs_main);

    /**
     * Sufficiently validate a block for disk storage (and store on disk).
     *
     * @param[in]   pblock          The block we want to process.
     * @param[in]   fRequested      Whether we requested this block from a
     *                              peer.
     * @param[in]   dbp             The location on disk, if we are importing
     *                              this block from prior storage.
     * @param[in]   min_pow_checked True if proof-of-work anti-DoS checks have
     *                              been done by caller for headers chain
     *
     * @param[out]  state       The state of the block validation.
     * @param[out]  ppindex     Optional return parameter to get the
     *                          CBlockIndex pointer for this block.
     * @param[out]  fNewBlock   Optional return parameter to indicate if the
     *                          block is new to our storage.
     *
     * @returns   False if the block or header is invalid, or if saving to disk fails (likely a fatal error); true otherwise.
     */
    bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock, bool min_pow_checked) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    void ReceivedBlockTransactions(const CBlock& block, CBlockIndex* pindexNew, const FlatFilePos& pos) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    /**
     * Try to add a transaction to the memory pool.
     *
     * @param[in]  tx              The transaction to submit for mempool acceptance.
     * @param[in]  test_accept     When true, run validation checks but don't submit to mempool.
     */
    [[nodiscard]] MempoolAcceptResult ProcessTransaction(const CTransactionRef& tx, bool test_accept=false)
        EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    //! Load the block tree and coins database from disk, initializing state if we're running with -reindex
    bool LoadBlockIndex() EXCLUSIVE_LOCKS_REQUIRED(cs_main);

    //! Check to see if caches are out of balance and if so, call
    //! ResizeCoinsCaches() as needed.
    void MaybeRebalanceCaches() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    /**
     * Update uncommitted block structures (currently: only the witness reserved
     * value). This is safe for submitted blocks as long as they honor
     * default_witness_commitment from the template.
     */
    void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev) const;

    /** 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;

    /** This is used by net_processing to report pre-synchronization progress of headers, as
     *  headers are not yet fed to validation during that time, but validation is (for now)
     *  responsible for logging and signalling through NotifyHeaderTip, so it needs this
     *  information. */
    void ReportHeadersPresync(int64_t height, int64_t timestamp);

    //! When starting up, search the datadir for a chainstate based on a UTXO
    //! snapshot that is in the process of being validated and load it if found.
    //! Return pointer to the Chainstate if it is loaded.
    Chainstate* LoadAssumeutxoChainstate() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Add new chainstate.
    Chainstate& AddChainstate(std::unique_ptr<Chainstate> chainstate) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    void ResetChainstates() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Remove the chainstate and all on-disk artifacts.
    //! Used when reindex{-chainstate} is called during snapshot use.
    [[nodiscard]] bool DeleteChainstate(Chainstate& chainstate) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! If we have validated a snapshot chain during this runtime, copy its
    //! chainstate directory over to the main `chainstate` location, completing
    //! validation of the snapshot.
    //!
    //! If the cleanup succeeds, the caller will need to ensure chainstates are
    //! reinitialized, since ResetChainstates() will be called before leveldb
    //! directories are moved or deleted.
    //!
    //! @sa node/chainstate:LoadChainstate()
    bool ValidatedSnapshotCleanup(Chainstate& validated_cs, Chainstate& unvalidated_cs) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Get range of historical blocks to download.
    std::optional<std::pair<const CBlockIndex*, const CBlockIndex*>> GetHistoricalBlockRange() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    //! Call ActivateBestChain() on every chainstate.
    util::Result<void> ActivateBestChains() LOCKS_EXCLUDED(::cs_main);

    //! If, due to invalidation / reconsideration of blocks, the previous
    //! best header is no longer valid / guaranteed to be the most-work
    //! header in our block-index not known to be invalid, recalculate it.
    void RecalculateBestHeader() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

    CCheckQueue<CScriptCheck>& GetCheckQueue() { return m_script_check_queue; }

    ~ChainstateManager();

    //! List of chainstates. Note: in general, it is not safe to delete
    //! Chainstate objects once they are added to this list because there is no
    //! mutex that can be locked to prevent Chainstate pointers from being used
    //! while they are deleted. (cs_main doesn't work because it is too narrow
    //! and is released in the middle of Chainstate::ActivateBestChain to let
    //! notifications be processed. m_chainstate_mutex doesn't work because it
    //! is not locked at other times when the chainstate is in use.)
    std::vector<std::unique_ptr<Chainstate>> m_chainstates GUARDED_BY(::cs_main);
};

/** Deployment* info via ChainstateManager */
template<typename DEP>
bool DeploymentActiveAfter(const CBlockIndex* pindexPrev, const ChainstateManager& chainman, DEP dep)
{
    return DeploymentActiveAfter(pindexPrev, chainman.GetConsensus(), dep, chainman.m_versionbitscache);
}

template<typename DEP>
bool DeploymentActiveAt(const CBlockIndex& index, const ChainstateManager& chainman, DEP dep)
{
    return DeploymentActiveAt(index, chainman.GetConsensus(), dep, chainman.m_versionbitscache);
}

template<typename DEP>
bool DeploymentEnabled(const ChainstateManager& chainman, DEP dep)
{
    return DeploymentEnabled(chainman.GetConsensus(), dep);
}

/** Identifies blocks that overwrote an existing coinbase output in the UTXO set (see BIP30) */
bool IsBIP30Repeat(const CBlockIndex& block_index);

/** Identifies blocks which coinbase output was subsequently overwritten in the UTXO set (see BIP30) */
bool IsBIP30Unspendable(const uint256& block_hash, int block_height);

// Returns the script flags which should be checked for a given block
script_verify_flags GetBlockScriptFlags(const CBlockIndex& block_index, const ChainstateManager& chainman);

#endif // BITCOIN_VALIDATION_H