add anchor output in vtxo tree and async redeem transaction

common/bitcointree/builder.go

@@ -15,8 +15,12 @@ import (
 
 // CraftSharedOutput returns the taproot script and the amount of the initial root output
 func CraftSharedOutput(
-	cosigners []*secp256k1.PublicKey, aspPubkey *secp256k1.PublicKey, receivers []Receiver,
-	feeSatsPerNode uint64, roundLifetime int64,
+	cosigners []*secp256k1.PublicKey,
+	aspPubkey *secp256k1.PublicKey,
+	receivers []Receiver,
+	feeSatsPerNode,
+	dustAmount uint64,
+	roundLifetime int64,
 ) ([]byte, int64, error) {
 	aggregatedKey, _, err := createAggregatedKeyWithSweep(
 		cosigners, aspPubkey, roundLifetime,
@@ -25,7 +29,7 @@ func CraftSharedOutput(
 		return nil, 0, err
 	}
 
-	root, err := createRootNode(aggregatedKey, cosigners, receivers, feeSatsPerNode)
+	root, err := createRootNode(aggregatedKey, cosigners, receivers, feeSatsPerNode, dustAmount)
 	if err != nil {
 		return nil, 0, err
 	}
@@ -42,8 +46,13 @@ func CraftSharedOutput(
 
 // CraftCongestionTree creates all the tree's transactions
 func CraftCongestionTree(
-	initialInput *wire.OutPoint, cosigners []*secp256k1.PublicKey, aspPubkey *secp256k1.PublicKey, receivers []Receiver,
-	feeSatsPerNode uint64, roundLifetime int64,
+	initialInput *wire.OutPoint,
+	cosigners []*secp256k1.PublicKey,
+	aspPubkey *secp256k1.PublicKey,
+	receivers []Receiver,
+	feeSatsPerNode,
+	dustAmount uint64,
+	roundLifetime int64,
 ) (tree.CongestionTree, error) {
 	aggregatedKey, sweepTapLeaf, err := createAggregatedKeyWithSweep(
 		cosigners, aspPubkey, roundLifetime,
@@ -52,7 +61,7 @@ func CraftCongestionTree(
 		return nil, err
 	}
 
-	root, err := createRootNode(aggregatedKey, cosigners, receivers, feeSatsPerNode)
+	root, err := createRootNode(aggregatedKey, cosigners, receivers, feeSatsPerNode, dustAmount)
 	if err != nil {
 		return nil, err
 	}
@@ -110,6 +119,7 @@ type node interface {
 type leaf struct {
 	vtxoScript VtxoScript
 	amount     int64
+	dustAmount int64
 }
 
 type branch struct {
@@ -152,12 +162,22 @@ func (l *leaf) getOutputs() ([]*wire.TxOut, error) {
 		return nil, err
 	}
 
-	output := &wire.TxOut{
-		Value:    l.amount,
+	vtxoOutputAmount := l.amount - l.dustAmount
+	if vtxoOutputAmount <= l.dustAmount {
+		return nil, fmt.Errorf("vtxo output amount must be greater than dust amount")
+	}
+
+	vtxoOutput := &wire.TxOut{
+		Value:    l.amount - l.dustAmount,
 		PkScript: script,
 	}
 
-	return []*wire.TxOut{output}, nil
+	anchorOutput := &wire.TxOut{
+		Value:    l.dustAmount,
+		PkScript: ANCHOR_PKSCRIPT,
+	}
+
+	return []*wire.TxOut{vtxoOutput, anchorOutput}, nil
 }
 
 func (b *branch) getOutputs() ([]*wire.TxOut, error) {
@@ -247,7 +267,8 @@ func createRootNode(
 	aggregatedKey *musig2.AggregateKey,
 	cosigners []*secp256k1.PublicKey,
 	receivers []Receiver,
-	feeSatsPerNode uint64,
+	feeSatsPerNode,
+	dustAmount uint64,
 ) (root node, err error) {
 	if len(receivers) == 0 {
 		return nil, fmt.Errorf("no receivers provided")
@@ -258,6 +279,7 @@ func createRootNode(
 		leafNode := &leaf{
 			vtxoScript: r.Script,
 			amount:     int64(r.Amount),
+			dustAmount: int64(dustAmount),
 		}
 		nodes = append(nodes, leafNode)
 	}

common/bitcointree/musig2_test.go

@@ -17,6 +17,7 @@ import (
 )
 
 const (
+	dustAmount  = 100
 	minRelayFee = 1000
 	exitDelay   = 512
 	lifetime    = 1024
@@ -46,6 +47,7 @@ func TestRoundTripSignTree(t *testing.T) {
 			asp.PubKey(),
 			castReceivers(f.Receivers, asp.PubKey()),
 			minRelayFee,
+			dustAmount,
 			lifetime,
 		)
 		require.NoError(t, err)
@@ -60,6 +62,7 @@ func TestRoundTripSignTree(t *testing.T) {
 			asp.PubKey(),
 			castReceivers(f.Receivers, asp.PubKey()),
 			minRelayFee,
+			dustAmount,
 			lifetime,
 		)
 		require.NoError(t, err)

common/bitcointree/psbt.go

@@ -11,6 +11,9 @@ var (
 	COSIGNER_PSBT_KEY_PREFIX = []byte("cosigner")
 )
 
+// p2wsh(OP_TRUE)
+var ANCHOR_PKSCRIPT = []byte{0, 32, 74, 232, 21, 114, 240, 110, 27, 136, 253, 92, 237, 122, 26, 0, 9, 69, 67, 46, 131, 225, 85, 30, 111, 114, 30, 233, 192, 11, 140, 195, 50, 96}
+
 func AddCosignerKey(inIndex int, ptx *psbt.Packet, key *secp256k1.PublicKey) error {
 	currentCosigners, err := GetCosignerKeys(ptx.Inputs[inIndex])
 	if err != nil {

pkg/client-sdk/covenantless_client.go

@@ -1886,24 +1886,30 @@ func (a *covenantlessArkClient) validateOffChainReceiver(
 			return err
 		}
 
+		var amount uint64
+
 		for _, output := range tx.UnsignedTx.TxOut {
 			if len(output.PkScript) == 0 {
 				continue
 			}
 
-			if bytes.Equal(
-				output.PkScript[2:], schnorr.SerializePubKey(outputTapKey),
-			) {
-				if output.Value != int64(receiver.Amount) {
-					continue
-				}
+			if bytes.Equal(output.PkScript, bitcointree.ANCHOR_PKSCRIPT) {
+				amount += uint64(output.Value)
+				continue
+			}
 
-				found = true
-				break
+			if len(output.PkScript) == 34 {
+				if bytes.Equal(output.PkScript[2:], schnorr.SerializePubKey(outputTapKey)) {
+					found = true
+					amount += uint64(output.Value)
+				}
 			}
 		}
 
 		if found {
+			if amount != receiver.Amount {
+				continue
+			}
 			break
 		}
 	}

server/internal/core/application/covenantless.go

@@ -260,6 +260,10 @@ func (s *covenantlessService) CompleteAsyncPayment(
 	vtxos := make([]domain.Vtxo, 0, len(asyncPayData.receivers))
 
 	for outIndex, out := range redeemPtx.UnsignedTx.TxOut {
+		if bytes.Equal(out.PkScript, bitcointree.ANCHOR_PKSCRIPT) {
+			continue // skip anchor output
+		}
+
 		desc := asyncPayData.receivers[outIndex].Descriptor
 		_, _, _, _, err := descriptor.ParseReversibleVtxoDescriptor(desc)
 		isPending := err == nil

server/internal/infrastructure/tx-builder/covenantless/builder.go

@@ -281,9 +281,16 @@ func (b *txBuilder) BuildRoundTx(
 		return "", nil, "", err
 	}
 
+	var dustAmount uint64
+
 	if !isOnchainOnly(payments) {
+		dustAmount, err = b.wallet.GetDustAmount(context.Background())
+		if err != nil {
+			return "", nil, "", err
+		}
+
 		sharedOutputScript, sharedOutputAmount, err = bitcointree.CraftSharedOutput(
-			cosigners, aspPubkey, receivers, feeAmount, b.roundLifetime,
+			cosigners, aspPubkey, receivers, feeAmount, dustAmount, b.roundLifetime,
 		)
 		if err != nil {
 			return
@@ -314,7 +321,7 @@ func (b *txBuilder) BuildRoundTx(
 		}
 
 		congestionTree, err = bitcointree.CraftCongestionTree(
-			initialOutpoint, cosigners, aspPubkey, receivers, feeAmount, b.roundLifetime,
+			initialOutpoint, cosigners, aspPubkey, receivers, feeAmount, dustAmount, b.roundLifetime,
 		)
 		if err != nil {
 			return
@@ -497,6 +504,11 @@ func (b *txBuilder) BuildAsyncPaymentTransactions(
 		return "", fmt.Errorf("redeem tx fee is higher than the amount of the change receiver")
 	}
 
+	dustAmount, err := b.wallet.GetDustAmount(context.Background())
+	if err != nil {
+		return "", err
+	}
+
 	for i, receiver := range receivers {
 		offchainScript, err := bitcointree.ParseVtxoScript(receiver.Descriptor)
 		if err != nil {
@@ -518,6 +530,9 @@ func (b *txBuilder) BuildAsyncPaymentTransactions(
 		value := receiver.Amount
 		if i == len(receivers)-1 {
 			value -= redeemTxMinRelayFee
+			if value <= dustAmount {
+				return "", fmt.Errorf("change amount is dust amount")
+			}
 		}
 		outs = append(outs, &wire.TxOut{
 			Value:    int64(value),

server/internal/infrastructure/tx-builder/covenantless/builder_test.go

@@ -47,7 +47,7 @@ func TestMain(m *testing.M) {
 	wallet.On("MinRelayFee", mock.Anything, mock.Anything).
 		Return(uint64(30), nil)
 	wallet.On("GetDustAmount", mock.Anything).
-		Return(uint64(1000), nil)
+		Return(uint64(100), nil)
 	wallet.On("GetForfeitAddress", mock.Anything).
 		Return(forfeitAddress, nil)