universe: add new CommitPoint() and TapscriptRoot() methods to RootCommitment

Author: Roasbeef

universe/supplycommit/env.go

@@ -35,6 +35,7 @@ const (
 type SupplySubTree uint8
 
 const (
+
 	// MintTreeType is the sub tree that tracks mints.
 	MintTreeType SupplySubTree = iota
 
@@ -235,6 +236,39 @@ func (r *RootCommitment) TxOut() (*wire.TxOut, error) {
 	return txOut, err
 }
 
+// CommitPoint returns the outpoint that corresponds to the root commitment.
+func (r *RootCommitment) CommitPoint() wire.OutPoint {
+	return wire.OutPoint{
+		Hash:  r.Txn.TxHash(),
+		Index: r.TxOutIdx,
+	}
+}
+
+// computeSupplyCommitTapscriptRoot creates the tapscript root hash for a supply
+// commitment with the given supply root hash.
+func computeSupplyCommitTapscriptRoot(supplyRootHash mssmt.NodeHash,
+) ([]byte, error) {
+
+	// Create a non-spendable script leaf that commits to the supply root.
+	tapLeaf, err := asset.NewNonSpendableScriptLeaf(
+		asset.PedersenVersion, supplyRootHash[:],
+	)
+	if err != nil {
+		return nil, fmt.Errorf("unable to create leaf: %w", err)
+	}
+
+	tapscriptTree := txscript.AssembleTaprootScriptTree(tapLeaf)
+	rootHash := tapscriptTree.RootNode.TapHash()
+	return rootHash[:], nil
+}
+
+// TapscriptRoot returns the tapscript root hash that commits to the supply
+// root. This is tweaked with the internal key to derive the output key.
+func (r *RootCommitment) TapscriptRoot() ([]byte, error) {
+	supplyRootHash := r.SupplyRoot.NodeHash()
+	return computeSupplyCommitTapscriptRoot(supplyRootHash)
+}
+
 // RootCommitTxOut returns the transaction output that corresponds to the root
 // commitment. This is used to create a new commitment output.
 func RootCommitTxOut(internalKey *btcec.PublicKey,
@@ -245,21 +279,13 @@ func RootCommitTxOut(internalKey *btcec.PublicKey,
 	if tapOutKey == nil {
 		// We'll create a new unspendable output that contains a
 		// commitment to the root.
-		//
-		// TODO(roasbeef): need other version info here/
-		tapLeaf, err := asset.NewNonSpendableScriptLeaf(
-			asset.PedersenVersion, supplyRootHash[:],
-		)
+		rootHash, err := computeSupplyCommitTapscriptRoot(supplyRootHash)
 		if err != nil {
-			return nil, nil, fmt.Errorf("unable to create leaf: %w",
-				err)
+			return nil, nil, err
 		}
 
-		tapscriptTree := txscript.AssembleTaprootScriptTree(tapLeaf)
-
-		rootHash := tapscriptTree.RootNode.TapHash()
 		taprootOutputKey = txscript.ComputeTaprootOutputKey(
-			internalKey, rootHash[:],
+			internalKey, rootHash,
 		)
 	} else {
 		taprootOutputKey = tapOutKey