sweep: create new Input interface

This commit introduces a common interface for sweep
inputs. It eliminates the type checking from UtxoSweeper.

Also the formerly present Amount() getter is removed. It was redundant
because this value is present in SignDesc().Output.Value as well.

sweep/sweeper.go

@@ -53,7 +53,7 @@ func New(cfg *UtxoSweeperConfig) *UtxoSweeper {
 // - Make handling re-orgs easier.
 // - Thwart future possible fee sniping attempts.
 // - Make us blend in with the bitcoind wallet.
-func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
+func (s *UtxoSweeper) CreateSweepTx(inputs []Input,
 	currentBlockHeight uint32) (*wire.MsgTx, error) {
 
 	// Create a transaction which sweeps all the newly mature outputs into
@@ -62,18 +62,7 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 	// TODO(roasbeef): can be more intelligent about buffering outputs to
 	// be more efficient on-chain.
 
-	// Assemble the inputs into a slice csv spendable outputs, and also a
-	// set of regular spendable outputs. The set of regular outputs are CLTV
-	// locked outputs that have had their timelocks expire.
-	var (
-		csvOutputs     []CsvSpendableOutput
-		cltvOutputs    []SpendableOutput
-		weightEstimate lnwallet.TxWeightEstimator
-	)
-
-	// Allocate enough room for both types of outputs.
-	csvOutputs = make([]CsvSpendableOutput, 0, len(inputs))
-	cltvOutputs = make([]SpendableOutput, 0, len(inputs))
+	var weightEstimate lnwallet.TxWeightEstimator
 
 	// Our sweep transaction will pay to a single segwit p2wkh address,
 	// ensure it contributes to our weight estimate.
@@ -82,6 +71,8 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 	// 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.
+	csvCount := 0
+	cltvCount := 0
 	for i := range inputs {
 		input := inputs[i]
 
@@ -93,7 +84,7 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 			weightEstimate.AddWitnessInput(
 				lnwallet.ToLocalTimeoutWitnessSize,
 			)
-			csvOutputs = append(csvOutputs, input)
+			csvCount++
 
 		// Outgoing second layer HTLC's that have confirmed within the
 		// chain, and the output they produced is now mature enough to
@@ -102,7 +93,7 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 			weightEstimate.AddWitnessInput(
 				lnwallet.ToLocalTimeoutWitnessSize,
 			)
-			csvOutputs = append(csvOutputs, input)
+			csvCount++
 
 		// Incoming second layer HTLC's that have confirmed within the
 		// chain, and the output they produced is now mature enough to
@@ -111,7 +102,7 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 			weightEstimate.AddWitnessInput(
 				lnwallet.ToLocalTimeoutWitnessSize,
 			)
-			csvOutputs = append(csvOutputs, input)
+			csvCount++
 
 		// An HTLC on the commitment transaction of the remote party,
 		// that has had its absolute timelock expire.
@@ -119,9 +110,11 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 			weightEstimate.AddWitnessInput(
 				lnwallet.AcceptedHtlcTimeoutWitnessSize,
 			)
-			cltvOutputs = append(cltvOutputs, input)
+			cltvCount++
 
 		default:
+			// TODO: Also add non-timelocked outputs
+
 			log.Warnf("kindergarten output in nursery store "+
 				"contains unexpected witness type: %v",
 				input.WitnessType())
@@ -129,11 +122,11 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 		}
 	}
 
-	log.Infof("Creating sweep transaction for %v CSV inputs, %v CLTV "+
-		"inputs", len(csvOutputs), len(cltvOutputs))
+	log.Infof("Creating sweep transaction for %v inputs (%v CSV, %v CLTV)",
+		csvCount+cltvCount, csvCount, cltvCount)
 
 	txWeight := int64(weightEstimate.Weight())
-	return s.populateSweepTx(txWeight, currentBlockHeight, csvOutputs, cltvOutputs)
+	return s.populateSweepTx(txWeight, currentBlockHeight, inputs)
 }
 
 // populateSweepTx populate the final sweeping transaction with all witnesses
@@ -141,8 +134,7 @@ func (s *UtxoSweeper) CreateSweepTx(inputs []CsvSpendableOutput,
 // has a single output sending all the funds back to the source wallet, after
 // accounting for the fee estimate.
 func (s *UtxoSweeper) populateSweepTx(txWeight int64, currentBlockHeight uint32,
-	csvInputs []CsvSpendableOutput,
-	cltvInputs []SpendableOutput) (*wire.MsgTx, error) {
+	inputs []Input) (*wire.MsgTx, error) {
 
 	// Generate the receiving script to which the funds will be swept.
 	pkScript, err := s.cfg.GenSweepScript()
@@ -152,11 +144,8 @@ func (s *UtxoSweeper) populateSweepTx(txWeight int64, currentBlockHeight uint32,
 
 	// Sum up the total value contained in the inputs.
 	var totalSum btcutil.Amount
-	for _, o := range csvInputs {
-		totalSum += o.Amount()
-	}
-	for _, o := range cltvInputs {
-		totalSum += o.Amount()
+	for _, o := range inputs {
+		totalSum += btcutil.Amount(o.SignDesc().Output.Value)
 	}
 
 	// Using the txn weight estimate, compute the required txn fee.
@@ -181,25 +170,16 @@ func (s *UtxoSweeper) populateSweepTx(txWeight int64, currentBlockHeight uint32,
 		Value:    sweepAmt,
 	})
 
-	// We'll also ensure that the transaction has the required lock time if
-	// we're sweeping any cltvInputs.
-	if len(cltvInputs) > 0 {
-		sweepTx.LockTime = currentBlockHeight
-	}
+	sweepTx.LockTime = currentBlockHeight
 
 	// Add all inputs to the sweep transaction. Ensure that for each
 	// csvInput, we set the sequence number properly.
-	for _, input := range csvInputs {
+	for _, input := range inputs {
 		sweepTx.AddTxIn(&wire.TxIn{
 			PreviousOutPoint: *input.OutPoint(),
 			Sequence:         input.BlocksToMaturity(),
 		})
 	}
-	for _, input := range cltvInputs {
-		sweepTx.AddTxIn(&wire.TxIn{
-			PreviousOutPoint: *input.OutPoint(),
-		})
-	}
 
 	// Before signing the transaction, check to ensure that it meets some
 	// basic validity requirements.
@@ -215,7 +195,7 @@ func (s *UtxoSweeper) populateSweepTx(txWeight int64, currentBlockHeight uint32,
 
 	// 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 SpendableOutput) error {
+	addWitness := func(idx int, tso Input) error {
 		witness, err := tso.BuildWitness(
 			s.cfg.Signer, sweepTx, hashCache, idx,
 		)
@@ -230,20 +210,11 @@ func (s *UtxoSweeper) populateSweepTx(txWeight int64, currentBlockHeight uint32,
 
 	// Finally we'll attach a valid witness to each csv and cltv input
 	// within the sweeping transaction.
-	for i, input := range csvInputs {
+	for i, input := range inputs {
 		if err := addWitness(i, input); err != nil {
 			return nil, err
 		}
 	}
 
-	// Add offset to relative indexes so cltv witnesses don't overwrite csv
-	// witnesses.
-	offset := len(csvInputs)
-	for i, input := range cltvInputs {
-		if err := addWitness(offset+i, input); err != nil {
-			return nil, err
-		}
-	}
-
 	return sweepTx, nil
 }