sweep: allow specified outputs to sweep tx

We'll use this to attach an output for the value reserved for anchor
commitments fee bumping if the user requests a send_all transaction.

rpcserver.go

@@ -1256,7 +1256,7 @@ func (r *rpcServer) SendCoins(ctx context.Context,
 		// safe manner, so no need to worry about locking.
 		sweepTxPkg, err := sweep.CraftSweepAllTx(
 			feePerKw, lnwallet.DefaultDustLimit(),
-			uint32(bestHeight), targetAddr, wallet,
+			uint32(bestHeight), nil, targetAddr, wallet,
 			wallet.WalletController, wallet.WalletController,
 			r.server.cc.FeeEstimator, r.server.cc.Signer,
 		)

sweep/sweeper.go

@@ -1192,8 +1192,8 @@ func (s *UtxoSweeper) sweep(inputs inputSet, feeRate chainfee.SatPerKWeight,
 
 	// Create sweep tx.
 	tx, err := createSweepTx(
-		inputs, s.currentOutputScript, uint32(currentHeight), feeRate,
-		dustLimit(s.relayFeeRate), s.cfg.Signer,
+		inputs, nil, s.currentOutputScript, uint32(currentHeight),
+		feeRate, dustLimit(s.relayFeeRate), s.cfg.Signer,
 	)
 	if err != nil {
 		return fmt.Errorf("create sweep tx: %v", err)
@@ -1487,7 +1487,7 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []input.Input, feePref FeePreference,
 	}
 
 	return createSweepTx(
-		inputs, pkScript, currentBlockHeight, feePerKw,
+		inputs, nil, pkScript, currentBlockHeight, feePerKw,
 		dustLimit(s.relayFeeRate), s.cfg.Signer,
 	)
 }

sweep/sweeper_test.go

@@ -354,7 +354,7 @@ func assertTxFeeRate(t *testing.T, tx *wire.MsgTx,
 	outputAmt := tx.TxOut[0].Value
 
 	fee := btcutil.Amount(inputAmt - outputAmt)
-	_, estimator := getWeightEstimate(inputs, 0)
+	_, estimator := getWeightEstimate(inputs, nil, 0)
 	txWeight := estimator.weight()
 
 	expectedFee := expectedFeeRate.FeeForWeight(int64(txWeight))

sweep/txgenerator.go

@@ -131,12 +131,14 @@ func generateInputPartitionings(sweepableInputs []txInput,
 	return sets, nil
 }
 
-// createSweepTx builds a signed tx spending the inputs to a the output script.
-func createSweepTx(inputs []input.Input, outputPkScript []byte,
-	currentBlockHeight uint32, feePerKw chainfee.SatPerKWeight,
-	dustLimit btcutil.Amount, signer input.Signer) (*wire.MsgTx, error) {
+// createSweepTx builds a signed tx spending the inputs to the given outputs,
+// sending any leftover change to the change script.
+func createSweepTx(inputs []input.Input, outputs []*wire.TxOut,
+	changePkScript []byte, currentBlockHeight uint32,
+	feePerKw chainfee.SatPerKWeight, dustLimit btcutil.Amount,
+	signer input.Signer) (*wire.MsgTx, error) {
 
-	inputs, estimator := getWeightEstimate(inputs, feePerKw)
+	inputs, estimator := getWeightEstimate(inputs, outputs, feePerKw)
 	txFee := estimator.fee()
 
 	var (
@@ -210,6 +212,16 @@ func createSweepTx(inputs []input.Input, outputPkScript []byte,
 		totalInput += btcutil.Amount(o.SignDesc().Output.Value)
 	}
 
+	// Add the outputs given, if any.
+	for _, o := range outputs {
+		sweepTx.AddTxOut(o)
+		requiredOutput += btcutil.Amount(o.Value)
+	}
+
+	if requiredOutput+txFee > totalInput {
+		return nil, fmt.Errorf("insufficient input to create sweep tx")
+	}
+
 	// The value remaining after the required output and fees, go to
 	// change. Not that this fee is what we would have to pay in case the
 	// sweep tx has a change output.
@@ -219,7 +231,7 @@ func createSweepTx(inputs []input.Input, outputPkScript []byte,
 	// above.
 	if changeAmt >= dustLimit {
 		sweepTx.AddTxOut(&wire.TxOut{
-			PkScript: outputPkScript,
+			PkScript: changePkScript,
 			Value:    int64(changeAmt),
 		})
 	} else {
@@ -287,8 +299,8 @@ func createSweepTx(inputs []input.Input, outputPkScript []byte,
 
 // 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, feeRate chainfee.SatPerKWeight) (
-	[]input.Input, *weightEstimator) {
+func getWeightEstimate(inputs []input.Input, outputs []*wire.TxOut,
+	feeRate chainfee.SatPerKWeight) ([]input.Input, *weightEstimator) {
 
 	// We initialize a weight estimator so we can accurately asses the
 	// amount of fees we need to pay for this sweep transaction.
@@ -297,13 +309,19 @@ func getWeightEstimate(inputs []input.Input, feeRate chainfee.SatPerKWeight) (
 	// be more efficient on-chain.
 	weightEstimate := newWeightEstimator(feeRate)
 
-	// Our sweep transaction will pay to a single segwit p2wkh address,
-	// ensure it contributes to our weight estimate. If the inputs we add
-	// have required TxOuts, then this will be our change address. Note
-	// that if we have required TxOuts, we might end up creating a sweep tx
-	// without a change output. It is okay to add the change output to the
-	// weight estimate regardless, since the estimated fee will just be
-	// subtracted from this already dust output, and trimmed.
+	// Our sweep transaction will always pay to the given set of outputs.
+	for _, o := range outputs {
+		weightEstimate.addOutput(o)
+	}
+
+	// If there is any leftover change after paying to the given outputs
+	// and required outputs, it will go to a single segwit p2wkh address.
+	// This will be our change address, so ensure it contributes to our
+	// weight estimate. Note that if we have other outputs, we might end up
+	// creating a sweep tx without a change output. It is okay to add the
+	// change output to the weight estimate regardless, since the estimated
+	// fee will just be subtracted from this already dust output, and
+	// trimmed.
 	weightEstimate.addP2WKHOutput()
 
 	// For each output, use its witness type to determine the estimate

sweep/txgenerator_test.go

@@ -39,7 +39,7 @@ func TestWeightEstimate(t *testing.T) {
 		))
 	}
 
-	_, estimator := getWeightEstimate(inputs, 0)
+	_, estimator := getWeightEstimate(inputs, nil, 0)
 	weight := int64(estimator.weight())
 	if weight != expectedWeight {
 		t.Fatalf("unexpected weight. expected %d but got %d.",

sweep/walletsweep.go

@@ -148,13 +148,24 @@ type WalletSweepPackage struct {
 	CancelSweepAttempt func()
 }
 
+// DeliveryAddr is a pair of (address, amount) used to craft a transaction
+// paying to more than one specified address.
+type DeliveryAddr struct {
+	// Addr is the address to pay to.
+	Addr btcutil.Address
+
+	// Amt is the amount to pay to the given address.
+	Amt btcutil.Amount
+}
+
 // CraftSweepAllTx attempts to craft a WalletSweepPackage which will allow the
-// caller to sweep ALL outputs within the wallet to a single UTXO, as specified
-// by the delivery address. The sweep transaction will be crafted with the
-// target fee rate, and will use the utxoSource and outpointLocker as sources
-// for wallet funds.
+// caller to sweep ALL outputs within the wallet to a list of outputs. Any
+// leftover amount after these outputs and transaction fee, is sent to a single
+// output, as specified by the change address. The sweep transaction will be
+// crafted with the target fee rate, and will use the utxoSource and
+// outpointLocker as sources for wallet funds.
 func CraftSweepAllTx(feeRate chainfee.SatPerKWeight, dustLimit btcutil.Amount,
-	blockHeight uint32, deliveryAddr btcutil.Address,
+	blockHeight uint32, deliveryAddrs []DeliveryAddr, changeAddr btcutil.Address,
 	coinSelectLocker CoinSelectionLocker, utxoSource UtxoSource,
 	outpointLocker OutpointLocker, feeEstimator chainfee.Estimator,
 	signer input.Signer) (*WalletSweepPackage, error) {
@@ -261,9 +272,25 @@ func CraftSweepAllTx(feeRate chainfee.SatPerKWeight, dustLimit btcutil.Amount,
 		inputsToSweep = append(inputsToSweep, &input)
 	}
 
-	// Next, we'll convert the delivery addr to a pkScript that we can use
+	// Create a list of TxOuts from the given delivery addresses.
+	var txOuts []*wire.TxOut
+	for _, d := range deliveryAddrs {
+		pkScript, err := txscript.PayToAddrScript(d.Addr)
+		if err != nil {
+			unlockOutputs()
+
+			return nil, err
+		}
+
+		txOuts = append(txOuts, &wire.TxOut{
+			PkScript: pkScript,
+			Value:    int64(d.Amt),
+		})
+	}
+
+	// Next, we'll convert the change addr to a pkScript that we can use
 	// to create the sweep transaction.
-	deliveryPkScript, err := txscript.PayToAddrScript(deliveryAddr)
+	changePkScript, err := txscript.PayToAddrScript(changeAddr)
 	if err != nil {
 		unlockOutputs()
 
@@ -273,7 +300,7 @@ func CraftSweepAllTx(feeRate chainfee.SatPerKWeight, dustLimit btcutil.Amount,
 	// Finally, we'll ask the sweeper to craft a sweep transaction which
 	// respects our fee preference and targets all the UTXOs of the wallet.
 	sweepTx, err := createSweepTx(
-		inputsToSweep, deliveryPkScript, blockHeight, feeRate,
+		inputsToSweep, txOuts, changePkScript, blockHeight, feeRate,
 		dustLimit, signer,
 	)
 	if err != nil {

sweep/walletsweep_test.go

@@ -288,7 +288,8 @@ func TestCraftSweepAllTxCoinSelectFail(t *testing.T) {
 	utxoLocker := newMockOutpointLocker()
 
 	_, err := CraftSweepAllTx(
-		0, 100, 10, nil, coinSelectLocker, utxoSource, utxoLocker, nil, nil,
+		0, 100, 10, nil, nil, coinSelectLocker, utxoSource,
+		utxoLocker, nil, nil,
 	)
 
 	// Since we instructed the coin select locker to fail above, we should
@@ -313,7 +314,8 @@ func TestCraftSweepAllTxUnknownWitnessType(t *testing.T) {
 	utxoLocker := newMockOutpointLocker()
 
 	_, err := CraftSweepAllTx(
-		0, 100, 10, nil, coinSelectLocker, utxoSource, utxoLocker, nil, nil,
+		0, 100, 10, nil, nil, coinSelectLocker, utxoSource,
+		utxoLocker, nil, nil,
 	)
 
 	// Since passed in a p2wsh output, which is unknown, we should fail to
@@ -347,8 +349,8 @@ func TestCraftSweepAllTx(t *testing.T) {
 	utxoLocker := newMockOutpointLocker()
 
 	sweepPkg, err := CraftSweepAllTx(
-		0, 100, 10, deliveryAddr, coinSelectLocker, utxoSource, utxoLocker,
-		feeEstimator, signer,
+		0, 100, 10, nil, deliveryAddr, coinSelectLocker, utxoSource,
+		utxoLocker, feeEstimator, signer,
 	)
 	if err != nil {
 		t.Fatalf("unable to make sweep tx: %v", err)