0cba47dac0
If inputs require outputs to be added at the same time, this will change the weight and amount calculations, so we must account for that. We wait to get the weight estimator for the sweep tx until needed, such that we can easily choose whether to include a change output or not in the estimate. This is needed for the case where the second level transactions can pay for their own fee, so no change output is needed.
112 lines
3.2 KiB
Go
112 lines
3.2 KiB
Go
package sweep
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import (
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"github.com/btcsuite/btcd/chaincfg/chainhash"
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"github.com/btcsuite/btcd/wire"
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"github.com/btcsuite/btcutil"
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"github.com/lightningnetwork/lnd/input"
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"github.com/lightningnetwork/lnd/lnwallet/chainfee"
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)
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// weightEstimator wraps a standard weight estimator instance and adds to that
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// support for child-pays-for-parent.
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type weightEstimator struct {
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estimator input.TxWeightEstimator
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feeRate chainfee.SatPerKWeight
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parents map[chainhash.Hash]struct{}
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parentsFee btcutil.Amount
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parentsWeight int64
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}
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// newWeightEstimator instantiates a new sweeper weight estimator.
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func newWeightEstimator(feeRate chainfee.SatPerKWeight) *weightEstimator {
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return &weightEstimator{
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feeRate: feeRate,
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parents: make(map[chainhash.Hash]struct{}),
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}
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}
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// add adds the weight of the given input to the weight estimate.
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func (w *weightEstimator) add(inp input.Input) error {
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// If there is a parent tx, add the parent's fee and weight.
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w.tryAddParent(inp)
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wt := inp.WitnessType()
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return wt.AddWeightEstimation(&w.estimator)
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}
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// tryAddParent examines the input and updates parent tx totals if required for
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// cpfp.
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func (w *weightEstimator) tryAddParent(inp input.Input) {
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// Get unconfirmed parent info from the input.
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unconfParent := inp.UnconfParent()
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// If there is no parent, there is nothing to add.
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if unconfParent == nil {
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return
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}
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// If we've already accounted for the parent tx, don't do it
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// again. This can happens when two outputs of the parent tx are
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// included in the same sweep tx.
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parentHash := inp.OutPoint().Hash
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if _, ok := w.parents[parentHash]; ok {
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return
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}
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// Calculate parent fee rate.
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parentFeeRate := chainfee.SatPerKWeight(unconfParent.Fee) * 1000 /
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chainfee.SatPerKWeight(unconfParent.Weight)
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// Ignore parents that pay at least the fee rate of this transaction.
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// Parent pays for child is not happening.
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if parentFeeRate >= w.feeRate {
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return
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}
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// Include parent.
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w.parents[parentHash] = struct{}{}
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w.parentsFee += unconfParent.Fee
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w.parentsWeight += unconfParent.Weight
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}
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// addP2WKHOutput updates the weight estimate to account for an additional
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// native P2WKH output.
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func (w *weightEstimator) addP2WKHOutput() {
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w.estimator.AddP2WKHOutput()
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}
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// addOutput updates the weight estimate to account for the known
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// output given.
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func (w *weightEstimator) addOutput(txOut *wire.TxOut) {
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w.estimator.AddTxOutput(txOut)
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}
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// weight gets the estimated weight of the transaction.
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func (w *weightEstimator) weight() int {
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return w.estimator.Weight()
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}
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// fee returns the tx fee to use for the aggregated inputs and outputs, taking
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// into account unconfirmed parent transactions (cpfp).
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func (w *weightEstimator) fee() btcutil.Amount {
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// Calculate fee and weight for just this tx.
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childWeight := int64(w.estimator.Weight())
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// Add combined weight of unconfirmed parent txes.
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totalWeight := childWeight + w.parentsWeight
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// Subtract fee already paid by parents.
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fee := w.feeRate.FeeForWeight(totalWeight) - w.parentsFee
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// Clamp the fee to what would be required if no parent txes were paid
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// for. This is to make sure no rounding errors can get us into trouble.
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childFee := w.feeRate.FeeForWeight(childWeight)
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if childFee > fee {
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fee = childFee
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}
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return fee
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}
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