tappsbt: add AltLeaves to VInput and VOutput

Author: jharveyb

tappsbt/decode.go

@@ -179,6 +179,9 @@ func (i *VInput) decode(pIn psbt.PInput) error {
 	}, {
 		key:     PsbtKeyTypeInputTapAssetProof,
 		decoder: proofDecoder(&i.Proof),
+	}, {
+		key:     PsbtKeyTypeInputAltLeaves,
+		decoder: altLeavesDecoder(&i.AltLeaves),
 	}}
 
 	for idx := range mapping {
@@ -308,8 +311,10 @@ func (o *VOutput) decode(pOut psbt.POutput, txOut *wire.TxOut) error {
 		{
 			key:     PsbtKeyTypeOutputTapAssetRelativeLockTime,
 			decoder: tlvDecoder(&o.RelativeLockTime, tlv.DUint64),
-		},
-	}
+		}, {
+			key:     PsbtKeyTypeOutputTapAltLeaves,
+			decoder: altLeavesDecoder(&o.AltLeaves),
+		}}
 
 	for idx := range mapping {
 		unknown, err := findCustomFieldsByKeyPrefix(
@@ -366,6 +371,17 @@ func proofDecoder(p **proof.Proof) decoderFunc {
 	}
 }
 
+// altLeavesDecoder returns a decoder function that can handle nil alt leaves.
+func altLeavesDecoder(a *[]AltLeafAsset) decoderFunc {
+	return func(key, byteVal []byte) error {
+		if len(byteVal) == 0 {
+			return nil
+		}
+
+		return tlvDecoder(a, asset.AltLeavesDecoder)(key, byteVal)
+	}
+}
+
 // assetDecoder returns a decoder function that can handle nil assets.
 func assetDecoder(a **asset.Asset) decoderFunc {
 	return func(key, byteVal []byte) error {

tappsbt/encode.go

@@ -185,6 +185,9 @@ func (i *VInput) encode() (psbt.PInput, error) {
 		{
 			key:     PsbtKeyTypeInputTapAssetProof,
 			encoder: proofEncoder(i.Proof),
+		}, {
+			key:     PsbtKeyTypeInputAltLeaves,
+			encoder: altLeavesEncoder(i.AltLeaves),
 		},
 	}
 
@@ -300,6 +303,9 @@ func (o *VOutput) encode(coinType uint32) (psbt.POutput, *wire.TxOut, error) {
 		{
 			key:     PsbtKeyTypeOutputTapAssetRelativeLockTime,
 			encoder: tlvEncoder(&o.RelativeLockTime, tlv.EUint64),
+		}, {
+			key:     PsbtKeyTypeOutputTapAltLeaves,
+			encoder: altLeavesEncoder(o.AltLeaves),
 		},
 	}
 
@@ -377,6 +383,18 @@ func proofEncoder(p *proof.Proof) encoderFunc {
 	}
 }
 
+// altLeavesEncoder is an encoder that does nothing if the given alt leaf slice
+// is nil.
+func altLeavesEncoder(a []AltLeafAsset) encoderFunc {
+	if a == nil {
+		return func([]byte) ([]*customPsbtField, error) {
+			return nil, nil
+		}
+	}
+
+	return tlvEncoder(&a, asset.AltLeavesEncoder)
+}
+
 // assetEncoder is an encoder that does nothing if the given asset is nil.
 func assetEncoder(a *asset.Asset) encoderFunc {
 	if a == nil {

tappsbt/interface.go

@@ -42,6 +42,7 @@ var (
 	PsbtKeyTypeInputTapAnchorTapscriptSibling             = []byte{0x78}
 	PsbtKeyTypeInputTapAsset                              = []byte{0x79}
 	PsbtKeyTypeInputTapAssetProof                         = []byte{0x7a}
+	PsbtKeyTypeInputAltLeaves                             = []byte{0x7b}
 
 	PsbtKeyTypeOutputTapType                               = []byte{0x70}
 	PsbtKeyTypeOutputTapIsInteractive                      = []byte{0x71}
@@ -57,6 +58,7 @@ var (
 	PsbtKeyTypeOutputTapAssetProofSuffix                   = []byte{0x7b}
 	PsbtKeyTypeOutputTapAssetLockTime                      = []byte{0x7c}
 	PsbtKeyTypeOutputTapAssetRelativeLockTime              = []byte{0x7d}
+	PsbtKeyTypeOutputTapAltLeaves                          = []byte{0x7e}
 )
 
 // The following keys are used as custom fields on the BTC level anchor
@@ -104,6 +106,9 @@ type bip32DerivationPredicate func(*psbt.Bip32Derivation) bool
 // BIP-0032 derivation paths.
 type taprootBip32DerivationPredicate func(*psbt.TaprootBip32Derivation) bool
 
+// AltLeafAsset is an AltLeaf backed by an Asset object.
+type AltLeafAsset = asset.AltLeaf[*asset.Asset]
+
 var (
 	// VOutIsSplitRoot is a predicate that returns true if the virtual
 	// output is a split root output.
@@ -370,6 +375,12 @@ type VInput struct {
 	// Proof is a transition proof that proves the asset being spent was
 	// committed to in the anchor transaction above.
 	Proof *proof.Proof
+
+	// AltLeaves represent data used to construct an Asset commitment, that
+	// will be inserted in the input anchor Tap commitment. These
+	// data-carrying leaves are used for a purpose distinct from
+	// representing individual Taproot Assets.
+	AltLeaves []AltLeafAsset
 }
 
 // Copy creates a deep copy of the VInput.
@@ -382,7 +393,8 @@ func (i *VInput) Copy() *VInput {
 		// We never expect the individual fields of the proof to change
 		// while it is assigned to a virtual input. So not deep copying
 		// it here is fine.
-		Proof: i.Proof,
+		Proof:     i.Proof,
+		AltLeaves: asset.CopyAltLeaves(i.AltLeaves),
 	}
 }
 
@@ -563,6 +575,12 @@ type VOutput struct {
 	// since the header information needs to be added once the anchor
 	// transaction was confirmed in a block.
 	ProofSuffix *proof.Proof
+
+	// AltLeaves represent data used to construct an Asset commitment, that
+	// will be inserted in the output anchor Tap commitment. These
+	// data-carrying leaves are used for a purpose distinct from
+	// representing individual Taproot Assets.
+	AltLeaves []AltLeafAsset
 }
 
 // Copy creates a deep copy of the VOutput.
@@ -590,6 +608,7 @@ func (o *VOutput) Copy() *VOutput {
 		ScriptKey:                    o.ScriptKey,
 		ProofDeliveryAddress:         o.ProofDeliveryAddress,
 		ProofSuffix:                  o.ProofSuffix,
+		AltLeaves:                    asset.CopyAltLeaves(o.AltLeaves),
 	}
 }