asset: function asset.TapCommitmentKey takes an asset specifier as arg

This commit modifies the `asset.TapCommitmentKey` function such that it
takes the asset specifier as an argument.

Author: ffranr

address/address.go

@@ -276,7 +276,11 @@ func (a *Tap) AttachGenesis(gen asset.Genesis) {
 // TapCommitmentKey is the key that maps to the root commitment for the asset
 // group specified by a Taproot Asset address.
 func (a *Tap) TapCommitmentKey() [32]byte {
-	return asset.TapCommitmentKey(a.AssetID, a.GroupKey)
+	assetSpecifier := asset.NewSpecifierOptionalGroupPubKey(
+		a.AssetID, a.GroupKey,
+	)
+
+	return asset.TapCommitmentKey(assetSpecifier)
 }
 
 // AssetCommitmentKey is the key that maps to the asset leaf for the asset

asset/asset.go

@@ -1552,23 +1552,38 @@ func New(genesis Genesis, amount, locktime, relativeLocktime uint64,
 }
 
 // TapCommitmentKey is the key that maps to the root commitment for a specific
-// asset group within a TapCommitment.
+// asset within a TapCommitment.
 //
 // NOTE: This function is also used outside the asset package.
-func TapCommitmentKey(assetID ID, groupKey *btcec.PublicKey) [32]byte {
-	if groupKey == nil {
-		return assetID
+func TapCommitmentKey(assetSpecifier Specifier) [32]byte {
+	var commitmentKey [32]byte
+
+	switch {
+	case assetSpecifier.HasGroupPubKey():
+		assetSpecifier.WhenGroupPubKey(func(pubKey btcec.PublicKey) {
+			serializedPubKey := schnorr.SerializePubKey(&pubKey)
+			commitmentKey = sha256.Sum256(serializedPubKey)
+		})
+
+	case assetSpecifier.HasId():
+		assetSpecifier.WhenId(func(id ID) {
+			commitmentKey = id
+		})
+
+	default:
+		// We should never reach this point as the asset specifier
+		// should always have either a group public key, an asset ID, or
+		// both.
+		panic("invalid asset specifier")
 	}
-	return sha256.Sum256(schnorr.SerializePubKey(groupKey))
+
+	return commitmentKey
 }
 
 // TapCommitmentKey is the key that maps to the root commitment for a specific
 // asset group within a TapCommitment.
 func (a *Asset) TapCommitmentKey() [32]byte {
-	if a.GroupKey == nil {
-		return TapCommitmentKey(a.Genesis.ID(), nil)
-	}
-	return TapCommitmentKey(a.Genesis.ID(), &a.GroupKey.GroupPubKey)
+	return TapCommitmentKey(a.Specifier())
 }
 
 // AssetCommitmentKey returns a key which can be used to locate an

commitment/asset.go

@@ -8,7 +8,6 @@ import (
 	"errors"
 	"fmt"
 
-	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/lightninglabs/taproot-assets/asset"
 	"github.com/lightninglabs/taproot-assets/fn"
 	"github.com/lightninglabs/taproot-assets/mssmt"
@@ -151,16 +150,15 @@ func parseCommon(assets ...*asset.Asset) (*AssetCommitment, error) {
 		assetsMap[key] = newAsset
 	}
 
-	var groupPubKey *btcec.PublicKey
-	if assetGroupKey != nil {
-		groupPubKey = &assetGroupKey.GroupPubKey
-	}
-
 	// The tapKey here is what will be used to place this asset commitment
 	// into the top-level Taproot Asset commitment. For assets without a
 	// group key, then this will be the normal asset ID. Otherwise, this'll
 	// be the sha256 of the group key.
-	tapKey := asset.TapCommitmentKey(firstAssetID, groupPubKey)
+	assetSpecifier := asset.NewSpecifierOptionalGroupKey(
+		firstAssetID, assetGroupKey,
+	)
+
+	tapKey := asset.TapCommitmentKey(assetSpecifier)
 
 	return &AssetCommitment{
 		Version:   maxVersion,

tapsend/send.go

@@ -172,7 +172,12 @@ type FundingDescriptor struct {
 // TapCommitmentKey is the key that maps to the root commitment for the asset
 // group specified by a recipient descriptor.
 func (r *FundingDescriptor) TapCommitmentKey() [32]byte {
-	return asset.TapCommitmentKey(r.ID, r.GroupKey)
+	assetSpecifier := asset.NewIdSpecifier(r.ID)
+	if r.GroupKey != nil {
+		assetSpecifier = asset.NewSpecifier(r.ID, *r.GroupKey)
+	}
+
+	return asset.TapCommitmentKey(assetSpecifier)
 }
 
 // DescribeRecipients extracts the recipient descriptors from a Taproot Asset