Function PaysForRBF

src/policy/rbf.cpp:151–176

}

std::optional<std::string> PaysForRBF(CAmount original_fees,
                                      CAmount replacement_fees,
                                      size_t replacement_vsize,
                                      CFeeRate relay_fee,
                                      const uint256& txid)
{
    // BIP125 Rule #3: The replacement fees must be greater than or equal to fees of the
    // transactions it replaces, otherwise the bandwidth used by those conflicting transactions
    // would not be paid for.
    if (replacement_fees < original_fees) {
        return strprintf("rejecting replacement %s, less fees than conflicting txs; %s < %s",
                         txid.ToString(), FormatMoney(replacement_fees), FormatMoney(original_fees));
    }

    // BIP125 Rule #4: The new transaction must pay for its own bandwidth. Otherwise, we have a DoS
    // vector where attackers can cause a transaction to be replaced (and relayed) repeatedly by
    // increasing the fee by tiny amounts.
    CAmount additional_fees = replacement_fees - original_fees;
    if (additional_fees < relay_fee.GetFee(replacement_vsize)) {
        return strprintf("rejecting replacement %s, not enough additional fees to relay; %s < %s",
                         txid.ToString(),
                         FormatMoney(additional_fees),
                         FormatMoney(relay_fee.GetFee(replacement_vsize)));
    }
    return std::nullopt;
}