Method DisconnectBlock

src/validation.cpp:2185–2254

Undo the effects of this block (with given index) on the UTXO set represented by coins. * When FAILED is returned, view is left in an indeterminate state. */

/** Undo the effects of this block (with given index) on the UTXO set represented by coins.
 *  When FAILED is returned, view is left in an indeterminate state. */
DisconnectResult Chainstate::DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view)
{
    AssertLockHeld(::cs_main);
    bool fClean = true;

    CBlockUndo blockUndo;
    if (!m_blockman.ReadBlockUndo(blockUndo, *pindex)) {
        LogError("DisconnectBlock(): failure reading undo data\n");
        return DISCONNECT_FAILED;
    }

    if (blockUndo.vtxundo.size() + 1 != block.vtx.size()) {
        LogError("DisconnectBlock(): block and undo data inconsistent\n");
        return DISCONNECT_FAILED;
    }

    // Ignore blocks that contain transactions which are 'overwritten' by later transactions,
    // unless those are already completely spent.
    // See https://github.com/bitcoin/bitcoin/issues/22596 for additional information.
    // Note: the blocks specified here are different than the ones used in ConnectBlock because DisconnectBlock
    // unwinds the blocks in reverse. As a result, the inconsistency is not discovered until the earlier
    // blocks with the duplicate coinbase transactions are disconnected.
    bool fEnforceBIP30 = !((pindex->nHeight==91722 && pindex->GetBlockHash() == uint256{"00000000000271a2dc26e7667f8419f2e15416dc6955e5a6c6cdf3f2574dd08e"}) ||
                           (pindex->nHeight==91812 && pindex->GetBlockHash() == uint256{"00000000000af0aed4792b1acee3d966af36cf5def14935db8de83d6f9306f2f"}));

    // undo transactions in reverse order
    for (int i = block.vtx.size() - 1; i >= 0; i--) {
        const CTransaction &tx = *(block.vtx[i]);
        Txid hash = tx.GetHash();
        bool is_coinbase = tx.IsCoinBase();
        bool is_bip30_exception = (is_coinbase && !fEnforceBIP30);

        // Check that all outputs are available and match the outputs in the block itself
        // exactly.
        for (size_t o = 0; o < tx.vout.size(); o++) {
            if (!tx.vout[o].scriptPubKey.IsUnspendable()) {
                COutPoint out(hash, o);
                Coin coin;
                bool is_spent = view.SpendCoin(out, &coin);
                if (!is_spent || tx.vout[o] != coin.out || pindex->nHeight != coin.nHeight || is_coinbase != coin.IsCoinBase()) {
                    if (!is_bip30_exception) {
                        fClean = false; // transaction output mismatch
                    }
                }
            }
        }

        // restore inputs
        if (i > 0) { // not coinbases
            CTxUndo &txundo = blockUndo.vtxundo[i-1];
            if (txundo.vprevout.size() != tx.vin.size()) {
                LogError("DisconnectBlock(): transaction and undo data inconsistent\n");
                return DISCONNECT_FAILED;
            }
            for (unsigned int j = tx.vin.size(); j > 0;) {
                --j;
                const COutPoint& out = tx.vin[j].prevout;
                int res = ApplyTxInUndo(std::move(txundo.vprevout[j]), view, out);