sweep: move tx generation to separate file

sweep/sweeper.go

@@ -1,11 +1,7 @@
 package sweep
 
 import (
-	"fmt"
-	"github.com/btcsuite/btcd/blockchain"
-	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/lnwallet"
 )
 
@@ -69,169 +65,7 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []Input, confTarget uint32,
 		return nil, err
 	}
 
-	inputs, txWeight, csvCount, cltvCount := getWeightEstimate(inputs)
+	return createSweepTx(
-	log.Infof("Creating sweep transaction for %v inputs (%v CSV, %v CLTV) "+
+		inputs, pkScript, currentBlockHeight, feePerKw, s.cfg.Signer,
-		"using %v sat/kw", len(inputs), csvCount, cltvCount,
-		int64(feePerKw))
-
-	txFee := feePerKw.FeeForWeight(txWeight)
-
-	// Sum up the total value contained in the inputs.
-	var totalSum btcutil.Amount
-	for _, o := range inputs {
-		totalSum += btcutil.Amount(o.SignDesc().Output.Value)
-	}
-
-	// Sweep as much possible, after subtracting txn fees.
-	sweepAmt := int64(totalSum - txFee)
-
-	// Create the sweep transaction that we will be building. We use
-	// version 2 as it is required for CSV. The txn will sweep the amount
-	// after fees to the pkscript generated above.
-	sweepTx := wire.NewMsgTx(2)
-	sweepTx.AddTxOut(&wire.TxOut{
-		PkScript: pkScript,
-		Value:    sweepAmt,
-	})
-
-	sweepTx.LockTime = currentBlockHeight
-
-	// Add all inputs to the sweep transaction. Ensure that for each
-	// csvInput, we set the sequence number properly.
-	for _, input := range inputs {
-		sweepTx.AddTxIn(&wire.TxIn{
-			PreviousOutPoint: *input.OutPoint(),
-			Sequence:         input.BlocksToMaturity(),
-		})
-	}
-
-	// Before signing the transaction, check to ensure that it meets some
-	// basic validity requirements.
-	//
-	// TODO(conner): add more control to sanity checks, allowing us to
-	// delay spending "problem" outputs, e.g. possibly batching with other
-	// classes if fees are too low.
-	btx := btcutil.NewTx(sweepTx)
-	if err := blockchain.CheckTransactionSanity(btx); err != nil {
-		return nil, err
-	}
-
-	hashCache := txscript.NewTxSigHashes(sweepTx)
-
-	// With all the inputs in place, use each output's unique witness
-	// function to generate the final witness required for spending.
-	addWitness := func(idx int, tso Input) error {
-		witness, err := tso.BuildWitness(
-			s.cfg.Signer, sweepTx, hashCache, idx,
 	)
-		if err != nil {
-			return err
-		}
-
-		sweepTx.TxIn[idx].Witness = witness
-
-		return nil
-	}
-
-	// Finally we'll attach a valid witness to each csv and cltv input
-	// within the sweeping transaction.
-	for i, input := range inputs {
-		if err := addWitness(i, input); err != nil {
-			return nil, err
-		}
-	}
-
-	return sweepTx, nil
-}
-
-// getInputWitnessSizeUpperBound returns the maximum length of the witness for
-// the given input if it would be included in a tx.
-func getInputWitnessSizeUpperBound(input Input) (int, error) {
-	switch input.WitnessType() {
-
-	// Outputs on a remote commitment transaction that pay directly
-	// to us.
-	case lnwallet.CommitmentNoDelay:
-		return lnwallet.P2WKHWitnessSize, nil
-
-	// Outputs on a past commitment transaction that pay directly
-	// to us.
-	case lnwallet.CommitmentTimeLock:
-		return lnwallet.ToLocalTimeoutWitnessSize, nil
-
-	// Outgoing second layer HTLC's that have confirmed within the
-	// chain, and the output they produced is now mature enough to
-	// sweep.
-	case lnwallet.HtlcOfferedTimeoutSecondLevel:
-		return lnwallet.ToLocalTimeoutWitnessSize, nil
-
-	// Incoming second layer HTLC's that have confirmed within the
-	// chain, and the output they produced is now mature enough to
-	// sweep.
-	case lnwallet.HtlcAcceptedSuccessSecondLevel:
-		return lnwallet.ToLocalTimeoutWitnessSize, nil
-
-	// An HTLC on the commitment transaction of the remote party,
-	// that has had its absolute timelock expire.
-	case lnwallet.HtlcOfferedRemoteTimeout:
-		return lnwallet.AcceptedHtlcTimeoutWitnessSize, nil
-
-	// An HTLC on the commitment transaction of the remote party,
-	// that can be swept with the preimage.
-	case lnwallet.HtlcAcceptedRemoteSuccess:
-		return lnwallet.OfferedHtlcSuccessWitnessSize, nil
-
-	}
-
-	return 0, fmt.Errorf("unexpected witness type: %v", input.WitnessType())
-}
-
-// getWeightEstimate returns a weight estimate for the given inputs.
-// Additionally, it returns counts for the number of csv and cltv inputs.
-func getWeightEstimate(inputs []Input) ([]Input, int64, int, int) {
-	// We initialize a weight estimator so we can accurately asses the
-	// amount of fees we need to pay for this sweep transaction.
-	//
-	// TODO(roasbeef): can be more intelligent about buffering outputs to
-	// be more efficient on-chain.
-	var weightEstimate lnwallet.TxWeightEstimator
-
-	// Our sweep transaction will pay to a single segwit p2wkh address,
-	// ensure it contributes to our weight estimate.
-	weightEstimate.AddP2WKHOutput()
-
-	// For each output, use its witness type to determine the estimate
-	// weight of its witness, and add it to the proper set of spendable
-	// outputs.
-	var (
-		sweepInputs         []Input
-		csvCount, cltvCount int
-	)
-	for i := range inputs {
-		input := inputs[i]
-
-		size, err := getInputWitnessSizeUpperBound(input)
-		if err != nil {
-			log.Warn(err)
-
-			// Skip inputs for which no weight estimate can be
-			// given.
-			continue
-		}
-		weightEstimate.AddWitnessInput(size)
-
-		switch input.WitnessType() {
-		case lnwallet.CommitmentTimeLock,
-			lnwallet.HtlcOfferedTimeoutSecondLevel,
-			lnwallet.HtlcAcceptedSuccessSecondLevel:
-			csvCount++
-		case lnwallet.HtlcOfferedRemoteTimeout:
-			cltvCount++
-		}
-		sweepInputs = append(sweepInputs, input)
-	}
-
-	txWeight := int64(weightEstimate.Weight())
-
-	return sweepInputs, txWeight, csvCount, cltvCount
 }

sweep/txgenerator.go

@@ -0,0 +1,183 @@
+package sweep
+
+import (
+	"fmt"
+	"github.com/btcsuite/btcd/blockchain"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
+	"github.com/lightningnetwork/lnd/lnwallet"
+)
+
+// createSweepTx builds a signed tx spending the inputs to a the output script.
+func createSweepTx(inputs []Input, outputPkScript []byte,
+	currentBlockHeight uint32, feePerKw lnwallet.SatPerKWeight,
+	signer lnwallet.Signer) (*wire.MsgTx, error) {
+
+	inputs, txWeight, csvCount, cltvCount := getWeightEstimate(inputs)
+
+	log.Infof("Creating sweep transaction for %v inputs (%v CSV, %v CLTV) "+
+		"using %v sat/kw", len(inputs), csvCount, cltvCount,
+		int64(feePerKw))
+
+	txFee := feePerKw.FeeForWeight(txWeight)
+
+	// Sum up the total value contained in the inputs.
+	var totalSum btcutil.Amount
+	for _, o := range inputs {
+		totalSum += btcutil.Amount(o.SignDesc().Output.Value)
+	}
+
+	// Sweep as much possible, after subtracting txn fees.
+	sweepAmt := int64(totalSum - txFee)
+
+	// Create the sweep transaction that we will be building. We use
+	// version 2 as it is required for CSV. The txn will sweep the amount
+	// after fees to the pkscript generated above.
+	sweepTx := wire.NewMsgTx(2)
+	sweepTx.AddTxOut(&wire.TxOut{
+		PkScript: outputPkScript,
+		Value:    sweepAmt,
+	})
+
+	sweepTx.LockTime = currentBlockHeight
+
+	// Add all inputs to the sweep transaction. Ensure that for each
+	// csvInput, we set the sequence number properly.
+	for _, input := range inputs {
+		sweepTx.AddTxIn(&wire.TxIn{
+			PreviousOutPoint: *input.OutPoint(),
+			Sequence:         input.BlocksToMaturity(),
+		})
+	}
+
+	// Before signing the transaction, check to ensure that it meets some
+	// basic validity requirements.
+	//
+	// TODO(conner): add more control to sanity checks, allowing us to
+	// delay spending "problem" outputs, e.g. possibly batching with other
+	// classes if fees are too low.
+	btx := btcutil.NewTx(sweepTx)
+	if err := blockchain.CheckTransactionSanity(btx); err != nil {
+		return nil, err
+	}
+
+	hashCache := txscript.NewTxSigHashes(sweepTx)
+
+	// With all the inputs in place, use each output's unique witness
+	// function to generate the final witness required for spending.
+	addWitness := func(idx int, tso Input) error {
+		witness, err := tso.BuildWitness(
+			signer, sweepTx, hashCache, idx,
+		)
+		if err != nil {
+			return err
+		}
+
+		sweepTx.TxIn[idx].Witness = witness
+
+		return nil
+	}
+
+	// Finally we'll attach a valid witness to each csv and cltv input
+	// within the sweeping transaction.
+	for i, input := range inputs {
+		if err := addWitness(i, input); err != nil {
+			return nil, err
+		}
+	}
+
+	return sweepTx, nil
+}
+
+// getInputWitnessSizeUpperBound returns the maximum length of the witness for
+// the given input if it would be included in a tx.
+func getInputWitnessSizeUpperBound(input Input) (int, error) {
+	switch input.WitnessType() {
+
+	// Outputs on a remote commitment transaction that pay directly
+	// to us.
+	case lnwallet.CommitmentNoDelay:
+		return lnwallet.P2WKHWitnessSize, nil
+
+	// Outputs on a past commitment transaction that pay directly
+	// to us.
+	case lnwallet.CommitmentTimeLock:
+		return lnwallet.ToLocalTimeoutWitnessSize, nil
+
+	// Outgoing second layer HTLC's that have confirmed within the
+	// chain, and the output they produced is now mature enough to
+	// sweep.
+	case lnwallet.HtlcOfferedTimeoutSecondLevel:
+		return lnwallet.ToLocalTimeoutWitnessSize, nil
+
+	// Incoming second layer HTLC's that have confirmed within the
+	// chain, and the output they produced is now mature enough to
+	// sweep.
+	case lnwallet.HtlcAcceptedSuccessSecondLevel:
+		return lnwallet.ToLocalTimeoutWitnessSize, nil
+
+	// An HTLC on the commitment transaction of the remote party,
+	// that has had its absolute timelock expire.
+	case lnwallet.HtlcOfferedRemoteTimeout:
+		return lnwallet.AcceptedHtlcTimeoutWitnessSize, nil
+
+	// An HTLC on the commitment transaction of the remote party,
+	// that can be swept with the preimage.
+	case lnwallet.HtlcAcceptedRemoteSuccess:
+		return lnwallet.OfferedHtlcSuccessWitnessSize, nil
+
+	}
+
+	return 0, fmt.Errorf("unexpected witness type: %v", input.WitnessType())
+}
+
+// getWeightEstimate returns a weight estimate for the given inputs.
+// Additionally, it returns counts for the number of csv and cltv inputs.
+func getWeightEstimate(inputs []Input) ([]Input, int64, int, int) {
+	// We initialize a weight estimator so we can accurately asses the
+	// amount of fees we need to pay for this sweep transaction.
+	//
+	// TODO(roasbeef): can be more intelligent about buffering outputs to
+	// be more efficient on-chain.
+	var weightEstimate lnwallet.TxWeightEstimator
+
+	// Our sweep transaction will pay to a single segwit p2wkh address,
+	// ensure it contributes to our weight estimate.
+	weightEstimate.AddP2WKHOutput()
+
+	// For each output, use its witness type to determine the estimate
+	// weight of its witness, and add it to the proper set of spendable
+	// outputs.
+	var (
+		sweepInputs         []Input
+		csvCount, cltvCount int
+	)
+	for i := range inputs {
+		input := inputs[i]
+
+		size, err := getInputWitnessSizeUpperBound(input)
+		if err != nil {
+			log.Warn(err)
+
+			// Skip inputs for which no weight estimate can be
+			// given.
+			continue
+		}
+		weightEstimate.AddWitnessInput(size)
+
+		switch input.WitnessType() {
+		case lnwallet.CommitmentTimeLock,
+			lnwallet.HtlcOfferedTimeoutSecondLevel,
+			lnwallet.HtlcAcceptedSuccessSecondLevel:
+			csvCount++
+		case lnwallet.HtlcOfferedRemoteTimeout:
+			cltvCount++
+		}
+		sweepInputs = append(sweepInputs, input)
+	}
+
+	txWeight := int64(weightEstimate.Weight())
+
+	return sweepInputs, txWeight, csvCount, cltvCount
+}