Add 0-value P2A output to offchain transactions (#566)

* P2A in vtxo tree and redeem txs

* update validation.go

* fix conflict

* fix linter error

* fix test unilateral exit

* fix bitcoin_wallet.go

* e2e test: faucet onchain

* fixes

* NewAddresses returns onchain P2TR addresses

* e2e tests: add TODOs

* fixes after reviews

Author: louisinger

client/main.go

@@ -306,13 +306,14 @@ func dumpPrivKey(ctx *cli.Context) error {
 }
 
 func receive(ctx *cli.Context) error {
-	offchainAddr, boardingAddr, err := arkSdkClient.Receive(ctx.Context)
+	onchainAddr, offchainAddr, boardingAddr, err := arkSdkClient.Receive(ctx.Context)
 	if err != nil {
 		return err
 	}
 	return printJSON(map[string]interface{}{
 		"boarding_address": boardingAddr,
 		"offchain_address": offchainAddr,
+		"onchain_address":  onchainAddr,
 	})
 }
 
@@ -397,10 +398,6 @@ func redeem(ctx *cli.Context) error {
 		return arkSdkClient.StartUnilateralExit(ctx.Context)
 	}
 
-	if address == "" {
-		return fmt.Errorf("missing destination address")
-	}
-
 	if complete {
 		txID, err := arkSdkClient.CompleteUnilateralExit(ctx.Context, address)
 		if err != nil {

common/fees.go

@@ -11,20 +11,6 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 )
 
-var TreeTxSize = (&input.TxWeightEstimator{}).
-	AddTaprootKeySpendInput(txscript.SigHashDefault). // parent
-	AddP2TROutput().                                  // left child
-	AddP2TROutput().                                  // right child
-	VSize()
-
-var ConnectorTxSize = (&input.TxWeightEstimator{}).
-	AddTaprootKeySpendInput(txscript.SigHashDefault).
-	AddP2TROutput().
-	AddP2TROutput().
-	AddP2TROutput().
-	AddP2TROutput().
-	VSize()
-
 func ComputeForfeitTxFee(
 	feeRate chainfee.SatPerKVByte,
 	tapscript *waddrmgr.Tapscript,
@@ -56,32 +42,3 @@ func ComputeForfeitTxFee(
 
 	return uint64(feeRate.FeeForVSize(lntypes.VByte(txWeightEstimator.VSize())).ToUnit(btcutil.AmountSatoshi)), nil
 }
-
-func ComputeRedeemTxFee(
-	feeRate chainfee.SatPerKVByte,
-	vtxos []VtxoInput,
-	numOutputs int,
-) (int64, error) {
-	if len(vtxos) <= 0 {
-		return 0, fmt.Errorf("missing vtxos")
-	}
-
-	redeemTxWeightEstimator := &input.TxWeightEstimator{}
-
-	// Estimate inputs
-	for _, vtxo := range vtxos {
-		if vtxo.Tapscript == nil {
-			txid := vtxo.Outpoint.Hash.String()
-			return 0, fmt.Errorf("missing tapscript for vtxo %s", txid)
-		}
-
-		redeemTxWeightEstimator.AddTapscriptInput(lntypes.WeightUnit(vtxo.WitnessSize), vtxo.Tapscript)
-	}
-
-	// Estimate outputs
-	for i := 0; i < numOutputs; i++ {
-		redeemTxWeightEstimator.AddP2TROutput()
-	}
-
-	return int64(feeRate.FeeForVSize(lntypes.VByte(redeemTxWeightEstimator.VSize())).ToUnit(btcutil.AmountSatoshi)), nil
-}

common/tree/anchor.go

@@ -0,0 +1,66 @@
+package tree
+
+import (
+	"bytes"
+
+	"github.com/btcsuite/btcd/btcutil/psbt"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+)
+
+var (
+	ANCHOR_PKSCRIPT = []byte{
+		0x51, 0x02, 0x4e, 0x73,
+	}
+	ANCHOR_VALUE = int64(0)
+)
+
+func AnchorOutput() *wire.TxOut {
+	return &wire.TxOut{
+		Value:    ANCHOR_VALUE,
+		PkScript: ANCHOR_PKSCRIPT,
+	}
+}
+
+// ExtractWithAnchors extracts the final witness and scriptSig from psbt fields and ignores anchor inputs without failing.
+func ExtractWithAnchors(p *psbt.Packet) (*wire.MsgTx, error) {
+	finalTx := p.UnsignedTx.Copy()
+
+	for i, tin := range finalTx.TxIn {
+		pInput := p.Inputs[i]
+
+		// ignore anchor outputs
+		if pInput.WitnessUtxo != nil && bytes.Equal(pInput.WitnessUtxo.PkScript, ANCHOR_PKSCRIPT) {
+			continue
+		}
+
+		if pInput.FinalScriptSig != nil {
+			tin.SignatureScript = pInput.FinalScriptSig
+		}
+
+		if pInput.FinalScriptWitness != nil {
+			witnessReader := bytes.NewReader(
+				pInput.FinalScriptWitness,
+			)
+
+			witCount, err := wire.ReadVarInt(witnessReader, 0)
+			if err != nil {
+				return nil, err
+			}
+
+			tin.Witness = make(wire.TxWitness, witCount)
+			for j := uint64(0); j < witCount; j++ {
+				wit, err := wire.ReadVarBytes(
+					witnessReader, 0,
+					txscript.MaxScriptSize, "witness",
+				)
+				if err != nil {
+					return nil, err
+				}
+				tin.Witness[j] = wit
+			}
+		}
+	}
+
+	return finalTx, nil
+}

common/tree/builder.go

@@ -22,15 +22,14 @@ const (
 // radix is hardcoded to 2
 func CraftSharedOutput(
 	receivers []Leaf,
-	feeSatsPerNode uint64,
 	sweepTapTreeRoot []byte,
 ) ([]byte, int64, error) {
-	root, err := createTxTree(receivers, feeSatsPerNode, sweepTapTreeRoot, vtxoTreeRadix)
+	root, err := createTxTree(receivers, sweepTapTreeRoot, vtxoTreeRadix)
 	if err != nil {
 		return nil, 0, err
 	}
 
-	amount := root.getAmount() + int64(feeSatsPerNode)
+	amount := root.getAmount() + ANCHOR_VALUE
 
 	aggregatedKey, err := AggregateKeys(root.getCosigners(), sweepTapTreeRoot)
 	if err != nil {
@@ -50,11 +49,10 @@ func CraftSharedOutput(
 func BuildVtxoTree(
 	initialInput *wire.OutPoint,
 	receivers []Leaf,
-	feeSatsPerNode uint64,
 	sweepTapTreeRoot []byte,
 	vtxoTreeExpiry common.RelativeLocktime,
 ) (TxTree, error) {
-	root, err := createTxTree(receivers, feeSatsPerNode, sweepTapTreeRoot, vtxoTreeRadix)
+	root, err := createTxTree(receivers, sweepTapTreeRoot, vtxoTreeRadix)
 	if err != nil {
 		return nil, err
 	}
@@ -66,14 +64,13 @@ func BuildVtxoTree(
 // radix is hardcoded to 4
 func CraftConnectorsOutput(
 	receivers []Leaf,
-	feeSatsPerNode uint64,
 ) ([]byte, int64, error) {
-	root, err := createTxTree(receivers, feeSatsPerNode, nil, connectorsTreeRadix)
+	root, err := createTxTree(receivers, nil, connectorsTreeRadix)
 	if err != nil {
 		return nil, 0, err
 	}
 
-	amount := root.getAmount() + int64(feeSatsPerNode)
+	amount := root.getAmount() + ANCHOR_VALUE
 
 	aggregatedKey, err := AggregateKeys(root.getCosigners(), nil)
 	if err != nil {
@@ -93,9 +90,8 @@ func CraftConnectorsOutput(
 func BuildConnectorsTree(
 	initialInput *wire.OutPoint,
 	receivers []Leaf,
-	feeSatsPerNode uint64,
 ) (TxTree, error) {
-	root, err := createTxTree(receivers, feeSatsPerNode, nil, connectorsTreeRadix)
+	root, err := createTxTree(receivers, nil, connectorsTreeRadix)
 	if err != nil {
 		return nil, err
 	}
@@ -150,7 +146,7 @@ func toTxTree(root node, initialInput *wire.OutPoint, expiry *common.RelativeLoc
 }
 
 type node interface {
-	getAmount() int64 // returns the input amount of the node = sum of all receivers' amounts + fees
+	getAmount() int64 // returns the input amount of the node = sum of all receivers' amounts
 	getOutputs() ([]*wire.TxOut, error)
 	getChildren() []node
 	getCosigners() []*secp256k1.PublicKey
@@ -167,7 +163,6 @@ type branch struct {
 	cosigners []*secp256k1.PublicKey
 	pkScript  []byte
 	children  []node
-	feeAmount int64
 }
 
 func (b *branch) getCosigners() []*secp256k1.PublicKey {
@@ -190,7 +185,7 @@ func (b *branch) getAmount() int64 {
 	amount := int64(0)
 	for _, child := range b.children {
 		amount += child.getAmount()
-		amount += b.feeAmount
+		amount += ANCHOR_VALUE
 	}
 
 	return amount
@@ -206,6 +201,7 @@ func (l *leaf) getOutputs() ([]*wire.TxOut, error) {
 			Value:    l.amount,
 			PkScript: l.pkScript,
 		},
+		AnchorOutput(),
 	}, nil
 }
 
@@ -214,12 +210,12 @@ func (b *branch) getOutputs() ([]*wire.TxOut, error) {
 
 	for _, child := range b.children {
 		outputs = append(outputs, &wire.TxOut{
-			Value:    child.getAmount() + b.feeAmount,
+			Value:    child.getAmount(),
 			PkScript: b.pkScript,
 		})
 	}
 
-	return outputs, nil
+	return append(outputs, AnchorOutput()), nil
 }
 
 func getTreeNode(
@@ -257,7 +253,7 @@ func getTx(
 		return nil, err
 	}
 
-	tx, err := psbt.New([]*wire.OutPoint{input}, outputs, 2, 0, []uint32{wire.MaxTxInSequenceNum})
+	tx, err := psbt.New([]*wire.OutPoint{input}, outputs, 3, 0, []uint32{wire.MaxTxInSequenceNum})
 	if err != nil {
 		return nil, err
 	}
@@ -290,7 +286,6 @@ func getTx(
 // from the leaves to the root.
 func createTxTree(
 	receivers []Leaf,
-	feeSatsPerNode uint64,
 	tapTreeRoot []byte,
 	radix int,
 ) (root node, err error) {
@@ -372,7 +367,7 @@ func createTxTree(
 	}
 
 	for len(nodes) > 1 {
-		nodes, err = createUpperLevel(nodes, int64(feeSatsPerNode), tapTreeRoot, radix)
+		nodes, err = createUpperLevel(nodes, tapTreeRoot, radix)
 		if err != nil {
 			return nil, fmt.Errorf("failed to create tx tree: %w", err)
 		}
@@ -381,20 +376,20 @@ func createTxTree(
 	return nodes[0], nil
 }
 
-func createUpperLevel(nodes []node, feeAmount int64, tapTreeRoot []byte, radix int) ([]node, error) {
+func createUpperLevel(nodes []node, tapTreeRoot []byte, radix int) ([]node, error) {
 	if len(nodes) <= 1 {
 		return nodes, nil
 	}
 
 	if len(nodes) < radix {
-		return createUpperLevel(nodes, feeAmount, tapTreeRoot, len(nodes))
+		return createUpperLevel(nodes, tapTreeRoot, len(nodes))
 	}
 
 	remainder := len(nodes) % radix
 	if remainder != 0 {
 		// Handle nodes that don't form a complete group
 		last := nodes[len(nodes)-remainder:]
-		groups, err := createUpperLevel(nodes[:len(nodes)-remainder], feeAmount, tapTreeRoot, radix)
+		groups, err := createUpperLevel(nodes[:len(nodes)-remainder], tapTreeRoot, radix)
 		if err != nil {
 			return nil, err
 		}
@@ -425,7 +420,6 @@ func createUpperLevel(nodes []node, feeAmount int64, tapTreeRoot []byte, radix i
 		branchNode := &branch{
 			pkScript:  pkScript,
 			cosigners: cosigners,
-			feeAmount: feeAmount,
 			children:  children,
 		}
 

common/tree/musig2_test.go

@@ -14,11 +14,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-const (
-	minRelayFee = 1000
-	exitDelay   = 512
-)
-
 var (
 	vtxoTreeExpiry   = common.RelativeLocktime{Type: common.LocktimeTypeBlock, Value: 144}
 	rootInput, _     = wire.NewOutPointFromString("49f8664acc899be91902f8ade781b7eeb9cbe22bdd9efbc36e56195de21bcd12:0")
@@ -41,14 +36,14 @@ func TestBuildAndSignVtxoTree(t *testing.T) {
 	for _, v := range testVectors {
 		t.Run(v.name, func(t *testing.T) {
 			sharedOutScript, sharedOutAmount, err := tree.CraftSharedOutput(
-				v.receivers, minRelayFee, sweepRoot[:],
+				v.receivers, sweepRoot[:],
 			)
 			require.NoError(t, err)
 			require.NotNil(t, sharedOutScript)
 			require.NotZero(t, sharedOutAmount)
 
 			vtxoTree, err := tree.BuildVtxoTree(
-				rootInput, v.receivers, minRelayFee, sweepRoot[:], vtxoTreeExpiry,
+				rootInput, v.receivers, sweepRoot[:], vtxoTreeExpiry,
 			)
 			require.NoError(t, err)
 			require.NotNil(t, vtxoTree)

common/tree/pending.go

@@ -14,6 +14,9 @@ const (
 	cltvSequence = wire.MaxTxInSequenceNum - 1
 )
 
+// BuildRedeemTx builds a redeem tx for the given vtxos and outputs.
+// The redeem tx is spending VTXOs using collaborative taproot path.
+// An anchor output is added to the transaction
 func BuildRedeemTx(
 	vtxos []common.VtxoInput,
 	outputs []*wire.TxOut,
@@ -95,7 +98,7 @@ func BuildRedeemTx(
 	}
 
 	redeemPtx, err := psbt.New(
-		ins, outputs, 2, uint32(txLocktime), sequences,
+		ins, append(outputs, AnchorOutput()), 3, uint32(txLocktime), sequences,
 	)
 	if err != nil {
 		return "", err

common/tree/validation.go

@@ -112,7 +112,7 @@ func ValidateVtxoTree(
 		sumRootValue += output.Value
 	}
 
-	if sumRootValue >= roundTxAmount {
+	if sumRootValue != roundTxAmount {
 		return ErrInvalidAmount
 	}
 
@@ -220,7 +220,7 @@ func validateNodeTransaction(node Node, tree TxTree, tapTreeRoot []byte) error {
 			sumChildAmount += output.Value
 		}
 
-		if sumChildAmount >= parentOutput.Value {
+		if sumChildAmount != parentOutput.Value {
 			return ErrInvalidAmount
 		}
 	}

pkg/client-sdk/ark_sdk.go

@@ -20,7 +20,7 @@ type ArkClient interface {
 	Unlock(ctx context.Context, password string) error
 	Lock(ctx context.Context) error
 	Balance(ctx context.Context, computeExpiryDetails bool) (*Balance, error)
-	Receive(ctx context.Context) (offchainAddr, boardingAddr string, err error)
+	Receive(ctx context.Context) (onchainAddr, offchainAddr, boardingAddr string, err error)
 	SendOffChain(
 		ctx context.Context, withExpiryCoinselect bool, receivers []Receiver,
 		withZeroFees bool,