watchtower: uses P2TR for sweep, delivery, and reward addresses

In this commit, we modify the watch tower to use P2TR addrs for just
about anything sweep related.

One eye sore in this diff are the changes to
`backup_task_internal_test.go`. All the values are hard coded, and now
either differ by a value of 48, or needed to be modified to account for
the new assumptions propagated to rewards values and fees.

watchtower/wtpolicy/policy.go

@@ -6,7 +6,6 @@ import (
 
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 	"github.com/lightningnetwork/lnd/watchtower/blob"
@@ -156,7 +155,7 @@ func (p Policy) Validate() error {
 // of the justice transaction and subtracting an amount that satisfies the
 // policy's fee rate.
 func (p *Policy) ComputeAltruistOutput(totalAmt btcutil.Amount,
-	txWeight int64) (btcutil.Amount, error) {
+	txWeight int64, sweepScript []byte) (btcutil.Amount, error) {
 
 	txFee := p.SweepFeeRate.FeeForWeight(txWeight)
 	if txFee > totalAmt {
@@ -165,10 +164,9 @@ func (p *Policy) ComputeAltruistOutput(totalAmt btcutil.Amount,
 
 	sweepAmt := totalAmt - txFee
 
-	// TODO(conner): replace w/ configurable dust limit
-	// Check that the created outputs won't be dusty. The sweep pkscript is
-	// currently a p2wpkh, so we'll use that script's dust limit.
-	if sweepAmt < lnwallet.DustLimitForSize(input.P2WPKHSize) {
+	// Check that the created outputs won't be dusty. We'll base the dust
+	// computation on the type of the script itself.
+	if sweepAmt < lnwallet.DustLimitForSize(len(sweepScript)) {
 		return 0, ErrCreatesDust
 	}
 
@@ -180,7 +178,8 @@ func (p *Policy) ComputeAltruistOutput(totalAmt btcutil.Amount,
 // and reward rate. The reward to he tower is subtracted first, before
 // splitting the remaining balance amongst the victim and fees.
 func (p *Policy) ComputeRewardOutputs(totalAmt btcutil.Amount,
-	txWeight int64) (btcutil.Amount, btcutil.Amount, error) {
+	txWeight int64,
+	rewardScript []byte) (btcutil.Amount, btcutil.Amount, error) {
 
 	txFee := p.SweepFeeRate.FeeForWeight(txWeight)
 	if txFee > totalAmt {
@@ -198,10 +197,9 @@ func (p *Policy) ComputeRewardOutputs(totalAmt btcutil.Amount,
 	// input value.
 	sweepAmt := totalAmt - rewardAmt - txFee
 
-	// TODO(conner): replace w/ configurable dust limit
-	// Check that the created outputs won't be dusty. The sweep pkscript is
-	// currently a p2wpkh, so we'll use that script's dust limit.
-	if sweepAmt < lnwallet.DustLimitForSize(input.P2WPKHSize) {
+	// Check that the created outputs won't be dusty. We'll base the dust
+	// computation on the type of the script itself.
+	if sweepAmt < lnwallet.DustLimitForSize(len(rewardScript)) {
 		return 0, 0, ErrCreatesDust
 	}
 
@@ -231,15 +229,16 @@ func ComputeRewardAmount(total btcutil.Amount, base, rate uint32) btcutil.Amount
 	return rewardBase + proportional
 }
 
-// ComputeJusticeTxOuts constructs the justice transaction outputs for the given
-// policy. If the policy specifies a reward for the tower, there will be two
-// outputs paying to the victim and the tower. Otherwise there will be a single
-// output sweeping funds back to the victim. The totalAmt should be the sum of
-// any inputs used in the transaction. The passed txWeight should include the
-// weight of the outputs for the justice transaction, which is dependent on
-// whether the justice transaction has a reward. The sweepPkScript should be the
-// pkScript of the victim to which funds will be recovered. The rewardPkScript
-// is the pkScript of the tower where its reward will be deposited, and will be
+// ComputeJusticeTxOuts constructs the justice transaction outputs for the
+// given policy. If the policy specifies a reward for the tower, there will be
+// two outputs paying to the victim and the tower. Otherwise there will be a
+// single output sweeping funds back to the victim. The totalAmt should be the
+// sum of any inputs used in the transaction. The passed txWeight should
+// include the weight of the outputs for the justice transaction, which is
+// dependent on whether the justice transaction has a reward. The sweepPkScript
+// should be the pkScript of the victim to which funds will be recovered. The
+// rewardPkScript is the pkScript of the tower where its reward will be
+// deposited, and will be
 // ignored if the blob type does not specify a reward.
 func (p *Policy) ComputeJusticeTxOuts(totalAmt btcutil.Amount, txWeight int64,
 	sweepPkScript, rewardPkScript []byte) ([]*wire.TxOut, error) {
@@ -247,19 +246,19 @@ func (p *Policy) ComputeJusticeTxOuts(totalAmt btcutil.Amount, txWeight int64,
 	var outputs []*wire.TxOut
 
 	// If the policy specifies a reward for the tower, compute a split of
-	// the funds based on the policy's parameters. Otherwise, we will use an
-	// the altruist output computation and sweep as much of the funds back
-	// to the victim as possible.
+	// the funds based on the policy's parameters. Otherwise, we will use
+	// the altruist output computation and sweep as much of the funds
+	// back to the victim as possible.
 	if p.BlobType.Has(blob.FlagReward) {
 		// Using the total input amount and the transaction's weight,
-		// compute the sweep and reward amounts. This corresponds to the
-		// amount returned to the victim and the amount paid to the
+		// compute the sweep and reward amounts. This corresponds to
+		// the amount returned to the victim and the amount paid to the
 		// tower, respectively. To do so, the required transaction fee
 		// is subtracted from the total, and the remaining amount is
-		// divided according to the prenegotiated reward rate from the
+		// divided according to the pre negotiated reward rate from the
 		// client's session info.
 		sweepAmt, rewardAmt, err := p.ComputeRewardOutputs(
-			totalAmt, txWeight,
+			totalAmt, txWeight, rewardPkScript,
 		)
 		if err != nil {
 			return nil, err
@@ -280,7 +279,7 @@ func (p *Policy) ComputeJusticeTxOuts(totalAmt btcutil.Amount, txWeight int64,
 		// returned to the victim. To do so, the required transaction
 		// fee is subtracted from the total input amount.
 		sweepAmt, err := p.ComputeAltruistOutput(
-			totalAmt, txWeight,
+			totalAmt, txWeight, sweepPkScript,
 		)
 		if err != nil {
 			return nil, err