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Take into account the segwit tx header when...

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...selecting coins

We take into account the larger segwit tx header for every
transaction, not just the segwit ones. The reason for this is that
we prefer to overestimate the fees for the transaction than
underestimating them - the former might create txs with a slightly
higher feerate than the requested one, while the latter might
create txs with a slightly lower one - or worse, invalid (<1 sat/vbyte)!
This commit is contained in:
Daniela Brozzoni 2022-07-12 15:51:27 +02:00
parent 7ac87b8f99
commit ae919061e2
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1 changed files with 11 additions and 0 deletions
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11
src/wallet/mod.rs
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@ -759,6 +759,17 @@ where
fee_amount += fee_rate.fee_wu(tx.weight()); fee_amount += fee_rate.fee_wu(tx.weight());
// Segwit transactions' header is 2WU larger than legacy txs' header,
// as they contain a witness marker (1WU) and a witness flag (1WU) (see BIP144).
// At this point we really don't know if the resulting transaction will be segwit
// or legacy, so we just add this 2WU to the fee_amount - overshooting the fee amount
// is better than undershooting it.
// If we pass a fee_amount that is slightly higher than the final fee_amount, we
// end up with a transaction with a slightly higher fee rate than the requested one.
// If, instead, we undershoot, we may end up with a feerate lower than the requested one
// - we might come up with non broadcastable txs!
fee_amount += fee_rate.fee_wu(2);
if params.change_policy != tx_builder::ChangeSpendPolicy::ChangeAllowed if params.change_policy != tx_builder::ChangeSpendPolicy::ChangeAllowed
&& self.change_descriptor.is_none() && self.change_descriptor.is_none()
{ {