Function ApplyTxInUndo

src/validation.cpp:1591–1616

* Restore the UTXO in a Coin at a given COutPoint * @param undo The Coin to be restored. * @param view The coins view to which to apply the changes. * @param out The out point that corresponds to the tx input. * @return A DisconnectResult as an int */

 * @return A DisconnectResult as an int
 */
int ApplyTxInUndo(Coin&& undo, CCoinsViewCache& view, const COutPoint& out)
{
    bool fClean = true;

    if (view.HaveCoin(out)) fClean = false; // overwriting transaction output

    if (undo.nHeight == 0) {
        // Missing undo metadata (height and coinbase). Older versions included this
        // information only in undo records for the last spend of a transactions'
        // outputs. This implies that it must be present for some other output of the same tx.
        const Coin& alternate = AccessByTxid(view, out.hash);
        if (!alternate.IsSpent()) {
            undo.nHeight = alternate.nHeight;
            undo.fCoinBase = alternate.fCoinBase;
        } else {
            return DISCONNECT_FAILED; // adding output for transaction without known metadata
        }
    }
    // The potential_overwrite parameter to AddCoin is only allowed to be false if we know for
    // sure that the coin did not already exist in the cache. As we have queried for that above
    // using HaveCoin, we don't need to guess. When fClean is false, a coin already existed and
    // it is an overwrite.
    view.AddCoin(out, std::move(undo), !fClean);

    return fClean ? DISCONNECT_OK : DISCONNECT_UNCLEAN;
}

/** 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. */