tx_verify.cpp

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// Copyright (c) 2017-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.
 
#include <consensus/tx_verify.h>
 
#include <chain.h>
#include <coins.h>
#include <consensus/amount.h>
#include <consensus/consensus.h>
#include <consensus/validation.h>
#include <primitives/transaction.h>
#include <script/interpreter.h>
#include <script/script.h>
#include <tinyformat.h>
#include <util/check.h>
#include <util/moneystr.h>
 
#include <algorithm>
#include <cstddef>
#include <string>
 
bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
{
    if (tx.nLockTime == 0)
        return true;
    if ((int64_t)tx.nLockTime < ((int64_t)tx.nLockTime < LOCKTIME_THRESHOLD ? (int64_t)nBlockHeight : nBlockTime))
        return true;
 
    // Even if tx.nLockTime isn't satisfied by nBlockHeight/nBlockTime, a
    // transaction is still considered final if all inputs' nSequence ==
    // SEQUENCE_FINAL (0xffffffff), in which case nLockTime is ignored.
    //
    // Because of this behavior OP_CHECKLOCKTIMEVERIFY/CheckLockTime() will
    // also check that the spending input's nSequence != SEQUENCE_FINAL,
    // ensuring that an unsatisfied nLockTime value will actually cause
    // IsFinalTx() to return false here:
    for (const auto& txin : tx.vin) {
        if (!(txin.nSequence == CTxIn::SEQUENCE_FINAL))
            return false;
    }
    return true;
}
 
std::pair<int, int64_t> CalculateSequenceLocks(const CTransaction &tx, int flags, std::vector<int>& prevHeights, const CBlockIndex& block)
{
    assert(prevHeights.size() == tx.vin.size());
 
    // Will be set to the equivalent height- and time-based nLockTime
    // values that would be necessary to satisfy all relative lock-
    // time constraints given our view of block chain history.
    // The semantics of nLockTime are the last invalid height/time, so
    // use -1 to have the effect of any height or time being valid.
    int nMinHeight = -1;
    int64_t nMinTime = -1;
 
    bool fEnforceBIP68 = tx.version >= 2 && flags & LOCKTIME_VERIFY_SEQUENCE;
 
    // Do not enforce sequence numbers as a relative lock time
    // unless we have been instructed to
    if (!fEnforceBIP68) {
        return std::make_pair(nMinHeight, nMinTime);
    }
 
    for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
        const CTxIn& txin = tx.vin[txinIndex];
 
        // Sequence numbers with the most significant bit set are not
        // treated as relative lock-times, nor are they given any
        // consensus-enforced meaning at this point.
        if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_DISABLE_FLAG) {
            // The height of this input is not relevant for sequence locks
            prevHeights[txinIndex] = 0;
            continue;
        }
 
        int nCoinHeight = prevHeights[txinIndex];
 
        if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG) {
            const int64_t nCoinTime{Assert(block.GetAncestor(std::max(nCoinHeight - 1, 0)))->GetMedianTimePast()};
            // NOTE: Subtract 1 to maintain nLockTime semantics
            // BIP 68 relative lock times have the semantics of calculating
            // the first block or time at which the transaction would be
            // valid. When calculating the effective block time or height
            // for the entire transaction, we switch to using the
            // semantics of nLockTime which is the last invalid block
            // time or height.  Thus we subtract 1 from the calculated
            // time or height.
 
            // Time-based relative lock-times are measured from the
            // smallest allowed timestamp of the block containing the
            // txout being spent, which is the median time past of the
            // block prior.
            nMinTime = std::max(nMinTime, nCoinTime + (int64_t)((txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) << CTxIn::SEQUENCE_LOCKTIME_GRANULARITY) - 1);
        } else {
            nMinHeight = std::max(nMinHeight, nCoinHeight + (int)(txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) - 1);
        }
    }
 
    return std::make_pair(nMinHeight, nMinTime);
}
 
bool EvaluateSequenceLocks(const CBlockIndex& block, std::pair<int, int64_t> lockPair)
{
    assert(block.pprev);
    int64_t nBlockTime = block.pprev->GetMedianTimePast();
    if (lockPair.first >= block.nHeight || lockPair.second >= nBlockTime)
        return false;
 
    return true;
}
 
bool SequenceLocks(const CTransaction &tx, int flags, std::vector<int>& prevHeights, const CBlockIndex& block)
{
    return EvaluateSequenceLocks(block, CalculateSequenceLocks(tx, flags, prevHeights, block));
}
 
unsigned int GetLegacySigOpCount(const CTransaction& tx)
{
    unsigned int nSigOps = 0;
    for (const auto& txin : tx.vin)
    {
        nSigOps += txin.scriptSig.GetSigOpCount(false);
    }
    for (const auto& txout : tx.vout)
    {
        nSigOps += txout.scriptPubKey.GetSigOpCount(false);
    }
    return nSigOps;
}
 
unsigned int GetP2SHSigOpCount(const CTransaction& tx, const CCoinsViewCache& inputs)
{
    if (tx.IsCoinBase())
        return 0;
 
    unsigned int nSigOps = 0;
    for (unsigned int i = 0; i < tx.vin.size(); i++)
    {
        const Coin& coin = inputs.AccessCoin(tx.vin[i].prevout);
        assert(!coin.IsSpent());
        const CTxOut &prevout = coin.out;
        if (prevout.scriptPubKey.IsPayToScriptHash())
            nSigOps += prevout.scriptPubKey.GetSigOpCount(tx.vin[i].scriptSig);
    }
    return nSigOps;
}
 
int64_t GetTransactionSigOpCost(const CTransaction& tx, const CCoinsViewCache& inputs, script_verify_flags flags)
{
    int64_t nSigOps = GetLegacySigOpCount(tx) * WITNESS_SCALE_FACTOR;
 
    if (tx.IsCoinBase())
        return nSigOps;
 
    if (flags & SCRIPT_VERIFY_P2SH) {
        nSigOps += GetP2SHSigOpCount(tx, inputs) * WITNESS_SCALE_FACTOR;
    }
 
    for (unsigned int i = 0; i < tx.vin.size(); i++)
    {
        const Coin& coin = inputs.AccessCoin(tx.vin[i].prevout);
        assert(!coin.IsSpent());
        const CTxOut &prevout = coin.out;
        nSigOps += CountWitnessSigOps(tx.vin[i].scriptSig, prevout.scriptPubKey, tx.vin[i].scriptWitness, flags);
    }
    return nSigOps;
}
 
bool Consensus::CheckTxInputs(const CTransaction& tx, TxValidationState& state, const CCoinsViewCache& inputs, int nSpendHeight, CAmount& txfee)
{
    // are the actual inputs available?
    if (!inputs.HaveInputs(tx)) {
        return state.Invalid(TxValidationResult::TX_MISSING_INPUTS, "bad-txns-inputs-missingorspent",
                         strprintf("%s: inputs missing/spent", __func__));
    }
 
    CAmount nValueIn = 0;
    for (unsigned int i = 0; i < tx.vin.size(); ++i) {
        const COutPoint &prevout = tx.vin[i].prevout;
        const Coin& coin = inputs.AccessCoin(prevout);
        assert(!coin.IsSpent());
 
        // If prev is coinbase, check that it's matured
        if (coin.IsCoinBase() && nSpendHeight - coin.nHeight < COINBASE_MATURITY) {
            return state.Invalid(TxValidationResult::TX_PREMATURE_SPEND, "bad-txns-premature-spend-of-coinbase",
                strprintf("tried to spend coinbase at depth %d", nSpendHeight - coin.nHeight));
        }
 
        // Check for negative or overflow input values
        nValueIn += coin.out.nValue;
        if (!MoneyRange(coin.out.nValue) || !MoneyRange(nValueIn)) {
            return state.Invalid(TxValidationResult::TX_CONSENSUS, "bad-txns-inputvalues-outofrange");
        }
    }
 
    // `tx.GetValueOut()` won't throw in validation paths because output-range checks run first
    // (`bad-txns-vout-negative`, `bad-txns-vout-toolarge`, `bad-txns-txouttotal-toolarge`):
    // * `MemPoolAccept::PreChecks`: `CheckTransaction()` is called before this method;
    // * `Chainstate::ConnectBlock`: `CheckTransaction()` is called via `CheckBlock()` before this method.
    const CAmount value_out = tx.GetValueOut();
    if (nValueIn < value_out) {
        return state.Invalid(TxValidationResult::TX_CONSENSUS, "bad-txns-in-belowout",
            strprintf("value in (%s) < value out (%s)", FormatMoney(nValueIn), FormatMoney(value_out)));
    }
 
    // Tally transaction fees
    const CAmount txfee_aux = nValueIn - value_out;
    if (!MoneyRange(txfee_aux)) {
        // Unreachable, given the following preconditions:
        // * `value_out` comes from `tx.GetValueOut()`, which throws unless `MoneyRange(value_out)` and asserts `MoneyRange(nValueOut)` on return.
        // * `MoneyRange(nValueIn)` was enforced in the input loop.
        // * `nValueIn < value_out` was handled above, so `nValueIn >= value_out` here (and `txfee_aux >= 0`).
        // Therefore `0 <= txfee_aux = nValueIn - value_out <= nValueIn <= MAX_MONEY`.
        return state.Invalid(TxValidationResult::TX_CONSENSUS, "bad-txns-fee-outofrange");
    }
 
    txfee = txfee_aux;
    return true;
}