sweep: update sweeper to use AuxSweeper to add extra change addr

In this commit, we start to use the AuxSweeper (if present) to obtain a
new extra change addr we should add to the sweeping transaction. With
this, we'll take the set of inputs and our change addr, and then maybe
gain a new change addr to add to the sweep transaction.

The extra change addr will be treated as an extra required tx out,
shared across all the relevant inputs. This'll also be used in
NeedWalletInput to make sure that we add an extra input if needed to be
able to pay for the change addr.

sweep/txgenerator.go

@@ -38,7 +38,7 @@ func createSweepTx(inputs []input.Input, outputs []*wire.TxOut,
 	signer input.Signer) (*wire.MsgTx, btcutil.Amount, error) {
 
 	inputs, estimator, err := getWeightEstimate(
-		inputs, outputs, feeRate, maxFeeRate, changePkScript,
+		inputs, outputs, feeRate, maxFeeRate, [][]byte{changePkScript},
 	)
 	if err != nil {
 		return nil, 0, err
@@ -221,7 +221,7 @@ func createSweepTx(inputs []input.Input, outputs []*wire.TxOut,
 // Additionally, it returns counts for the number of csv and cltv inputs.
 func getWeightEstimate(inputs []input.Input, outputs []*wire.TxOut,
 	feeRate, maxFeeRate chainfee.SatPerKWeight,
-	outputPkScript []byte) ([]input.Input, *weightEstimator, error) {
+	outputPkScripts [][]byte) ([]input.Input, *weightEstimator, error) {
 
 	// We initialize a weight estimator so we can accurately asses the
 	// amount of fees we need to pay for this sweep transaction.
@@ -237,31 +237,33 @@ func getWeightEstimate(inputs []input.Input, outputs []*wire.TxOut,
 
 	// If there is any leftover change after paying to the given outputs
 	// and required outputs, it will go to a single segwit p2wkh or p2tr
-	// 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.
-	switch {
-	case txscript.IsPayToTaproot(outputPkScript):
-		weightEstimate.addP2TROutput()
+	// 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.
+	for _, outputPkScript := range outputPkScripts {
+		switch {
+		case txscript.IsPayToTaproot(outputPkScript):
+			weightEstimate.addP2TROutput()
 
-	case txscript.IsPayToWitnessScriptHash(outputPkScript):
-		weightEstimate.addP2WSHOutput()
+		case txscript.IsPayToWitnessScriptHash(outputPkScript):
+			weightEstimate.addP2WSHOutput()
 
-	case txscript.IsPayToWitnessPubKeyHash(outputPkScript):
-		weightEstimate.addP2WKHOutput()
+		case txscript.IsPayToWitnessPubKeyHash(outputPkScript):
+			weightEstimate.addP2WKHOutput()
 
-	case txscript.IsPayToPubKeyHash(outputPkScript):
-		weightEstimate.estimator.AddP2PKHOutput()
+		case txscript.IsPayToPubKeyHash(outputPkScript):
+			weightEstimate.estimator.AddP2PKHOutput()
 
-	case txscript.IsPayToScriptHash(outputPkScript):
-		weightEstimate.estimator.AddP2SHOutput()
+		case txscript.IsPayToScriptHash(outputPkScript):
+			weightEstimate.estimator.AddP2SHOutput()
 
-	default:
-		// Unknown script type.
-		return nil, nil, errors.New("unknown script type")
+		default:
+			// Unknown script type.
+			return nil, nil, errors.New("unknown script type")
+		}
 	}
 
 	// For each output, use its witness type to determine the estimate