package sweep import ( "context" "fmt" "github.com/btcsuite/btcd/btcec" "github.com/btcsuite/btcd/txscript" "github.com/btcsuite/btcd/wire" "github.com/btcsuite/btcutil" "github.com/lightninglabs/loop/lndclient" "github.com/lightninglabs/loop/swap" "github.com/lightningnetwork/lnd/input" "github.com/lightningnetwork/lnd/keychain" ) // Sweeper creates htlc sweep txes. type Sweeper struct { Lnd *lndclient.LndServices } // CreateSweepTx creates an htlc sweep tx. func (s *Sweeper) CreateSweepTx( globalCtx context.Context, height int32, htlc *swap.Htlc, htlcOutpoint wire.OutPoint, keyBytes [33]byte, witnessFunc func(sig []byte) (wire.TxWitness, error), amount, fee btcutil.Amount, destAddr btcutil.Address) (*wire.MsgTx, error) { // Compose tx. sweepTx := wire.NewMsgTx(2) sweepTx.LockTime = uint32(height) // Add HTLC input. sweepTx.AddTxIn(&wire.TxIn{ PreviousOutPoint: htlcOutpoint, SignatureScript: htlc.SigScript, }) // Add output for the destination address. sweepPkScript, err := txscript.PayToAddrScript(destAddr) if err != nil { return nil, err } sweepTx.AddTxOut(&wire.TxOut{ PkScript: sweepPkScript, Value: int64(amount - fee), }) // Generate a signature for the swap htlc transaction. key, err := btcec.ParsePubKey(keyBytes[:], btcec.S256()) if err != nil { return nil, err } signDesc := input.SignDescriptor{ WitnessScript: htlc.Script, Output: &wire.TxOut{ Value: int64(amount), }, HashType: txscript.SigHashAll, InputIndex: 0, KeyDesc: keychain.KeyDescriptor{ PubKey: key, }, } rawSigs, err := s.Lnd.Signer.SignOutputRaw( globalCtx, sweepTx, []*input.SignDescriptor{&signDesc}, ) if err != nil { return nil, fmt.Errorf("signing: %v", err) } sig := rawSigs[0] // Add witness stack to the tx input. sweepTx.TxIn[0].Witness, err = witnessFunc(sig) if err != nil { return nil, err } return sweepTx, nil } // GetSweepFee calculates the required tx fee to spend to P2WKH. It takes a // function that is expected to add the weight of the input to the weight // estimator. func (s *Sweeper) GetSweepFee(ctx context.Context, addInputEstimate func(*input.TxWeightEstimator), sweepConfTarget int32) ( btcutil.Amount, error) { // Get fee estimate from lnd. feeRate, err := s.Lnd.WalletKit.EstimateFee(ctx, sweepConfTarget) if err != nil { return 0, fmt.Errorf("estimate fee: %v", err) } // Calculate weight for this tx. var weightEstimate input.TxWeightEstimator weightEstimate.AddP2WKHOutput() addInputEstimate(&weightEstimate) weight := weightEstimate.Weight() return feeRate.FeeForWeight(int64(weight)), nil }