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wallet: Update BnB upper bound to be consistent with tx building

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Use min_viable_change instead of cost_of_change as the upper limit of excess allowed when computing a changeless BnB solution.

This prevents a corner case where dust threshold > change_fee results in some changeless BnB solutions not being considered, despite change being dropped during tx building.

h/t @S3RK for identifying this issue in #26466 .
This commit is contained in:
Richard Myers 2024-09-16 12:09:40 +02:00
parent 17bc70f80a
commit 7df63761eb
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1 changed files with 2 additions and 6 deletions
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8
src/wallet/spend.cpp
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@ -1119,12 +1119,6 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal(
coin_selection_params.m_min_change_target = GenerateChangeTarget(std::floor(recipients_sum / vecSend.size()), coin_selection_params.m_change_fee, rng_fast);
if (coin_control.m_max_excess) {
coin_selection_params.m_max_excess = std::max(coin_control.m_max_excess.value(), coin_selection_params.m_cost_of_change);
} else {
coin_selection_params.m_max_excess = coin_selection_params.m_cost_of_change;
}
// The smallest change amount should be:
// 1. at least equal to dust threshold
// 2. at least 1 sat greater than fees to spend it at m_discard_feerate
@ -1132,6 +1126,8 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal(
const auto change_spend_fee = coin_selection_params.m_discard_feerate.GetFee(coin_selection_params.change_spend_size);
coin_selection_params.min_viable_change = std::max(change_spend_fee + 1, dust);
coin_selection_params.m_max_excess = std::max(coin_control.m_max_excess.value_or(0), coin_selection_params.min_viable_change);
// If set, do not add any excess from a changeless transaction to fees
coin_selection_params.m_add_excess_to_recipient_position = coin_control.m_add_excess_to_recipient_position;