lnd.xprv/sweep/weight_estimator.go

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package sweep
import (
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/lightningnetwork/lnd/input"
"github.com/lightningnetwork/lnd/lnwallet/chainfee"
)
// weightEstimator wraps a standard weight estimator instance and adds to that
// support for child-pays-for-parent.
type weightEstimator struct {
estimator input.TxWeightEstimator
feeRate chainfee.SatPerKWeight
parents map[chainhash.Hash]struct{}
parentsFee btcutil.Amount
parentsWeight int64
}
// newWeightEstimator instantiates a new sweeper weight estimator.
func newWeightEstimator(feeRate chainfee.SatPerKWeight) *weightEstimator {
return &weightEstimator{
feeRate: feeRate,
parents: make(map[chainhash.Hash]struct{}),
}
}
// add adds the weight of the given input to the weight estimate.
func (w *weightEstimator) add(inp input.Input) error {
// If there is a parent tx, add the parent's fee and weight.
w.tryAddParent(inp)
wt := inp.WitnessType()
return wt.AddWeightEstimation(&w.estimator)
}
// tryAddParent examines the input and updates parent tx totals if required for
// cpfp.
func (w *weightEstimator) tryAddParent(inp input.Input) {
// Get unconfirmed parent info from the input.
unconfParent := inp.UnconfParent()
// If there is no parent, there is nothing to add.
if unconfParent == nil {
return
}
// If we've already accounted for the parent tx, don't do it
// again. This can happens when two outputs of the parent tx are
// included in the same sweep tx.
parentHash := inp.OutPoint().Hash
if _, ok := w.parents[parentHash]; ok {
return
}
// Calculate parent fee rate.
parentFeeRate := chainfee.SatPerKWeight(unconfParent.Fee) * 1000 /
chainfee.SatPerKWeight(unconfParent.Weight)
// Ignore parents that pay at least the fee rate of this transaction.
// Parent pays for child is not happening.
if parentFeeRate >= w.feeRate {
return
}
// Include parent.
w.parents[parentHash] = struct{}{}
w.parentsFee += unconfParent.Fee
w.parentsWeight += unconfParent.Weight
}
// addP2WKHOutput updates the weight estimate to account for an additional
// native P2WKH output.
func (w *weightEstimator) addP2WKHOutput() {
w.estimator.AddP2WKHOutput()
}
// addOutput updates the weight estimate to account for the known
// output given.
func (w *weightEstimator) addOutput(txOut *wire.TxOut) {
w.estimator.AddTxOutput(txOut)
}
// weight gets the estimated weight of the transaction.
func (w *weightEstimator) weight() int {
return w.estimator.Weight()
}
// fee returns the tx fee to use for the aggregated inputs and outputs, taking
// into account unconfirmed parent transactions (cpfp).
func (w *weightEstimator) fee() btcutil.Amount {
// Calculate fee and weight for just this tx.
childWeight := int64(w.estimator.Weight())
// Add combined weight of unconfirmed parent txes.
totalWeight := childWeight + w.parentsWeight
// Subtract fee already paid by parents.
fee := w.feeRate.FeeForWeight(totalWeight) - w.parentsFee
// Clamp the fee to what would be required if no parent txes were paid
// for. This is to make sure no rounding errors can get us into trouble.
childFee := w.feeRate.FeeForWeight(childWeight)
if childFee > fee {
fee = childFee
}
return fee
}