watchtower: add new TaprootCommit Type and flag

This commit adds a new FlagTaprootChannel Flag which is then used to
construct a new blob Type: TypeAltruistTaprootCommit. New watchtower
feature bits are also added (4/5).

watchtower/blob/type.go

@@ -26,6 +26,10 @@ const (
 	// channel, and therefore must expect a P2WSH-style to-remote output if
 	// one exists.
 	FlagAnchorChannel Flag = 1 << 2
+
+	// FlagTaprootChannel signals that this blob is meant to spend a
+	// taproot channel and therefore must expect P2TR outputs.
+	FlagTaprootChannel Flag = 1 << 3
 )
 
 // Type returns a Type consisting solely of this flag enabled.
@@ -42,6 +46,8 @@ func (f Flag) String() string {
 		return "FlagCommitOutputs"
 	case FlagAnchorChannel:
 		return "FlagAnchorChannel"
+	case FlagTaprootChannel:
+		return "FlagTaprootChannel"
 	default:
 		return "FlagUnknown"
 	}
@@ -67,6 +73,11 @@ const (
 	// TypeRewardCommit sweeps only commitment outputs to a sweep address
 	// controlled by the user, and pays a negotiated reward to the tower.
 	TypeRewardCommit = Type(FlagCommitOutputs | FlagReward)
+
+	// TypeAltruistTaprootCommit sweeps only the commitment outputs from a
+	// taproot channel commitment to a sweep address controlled by the user,
+	// and does not give the tower a reward.
+	TypeAltruistTaprootCommit = Type(FlagCommitOutputs | FlagTaprootChannel)
 )
 
 // Identifier returns a unique, stable string identifier for the blob Type.
@@ -78,6 +89,8 @@ func (t Type) Identifier() (string, error) {
 		return "anchor", nil
 	case TypeRewardCommit:
 		return "reward", nil
+	case TypeAltruistTaprootCommit:
+		return "taproot", nil
 	default:
 		return "", fmt.Errorf("unknown blob type: %v", t)
 	}
@@ -124,14 +137,20 @@ func (t Type) IsAnchorChannel() bool {
 	return t.Has(FlagAnchorChannel)
 }
 
-// knownFlags maps the supported flags to their name.
-var knownFlags = map[Flag]struct{}{
-	FlagReward:        {},
-	FlagCommitOutputs: {},
-	FlagAnchorChannel: {},
+// IsTaprootChannel returns true if the blob type is for a taproot channel.
+func (t Type) IsTaprootChannel() bool {
+	return t.Has(FlagTaprootChannel)
 }
 
-// String returns a human readable description of a Type.
+// knownFlags maps the supported flags to their name.
+var knownFlags = map[Flag]struct{}{
+	FlagReward:         {},
+	FlagCommitOutputs:  {},
+	FlagAnchorChannel:  {},
+	FlagTaprootChannel: {},
+}
+
+// String returns a human-readable description of a Type.
 func (t Type) String() string {
 	var (
 		hrPieces        []string
@@ -175,9 +194,10 @@ func (t Type) String() string {
 // supportedTypes is the set of all configurations known to be supported by the
 // package.
 var supportedTypes = map[Type]struct{}{
-	TypeAltruistCommit:       {},
-	TypeRewardCommit:         {},
-	TypeAltruistAnchorCommit: {},
+	TypeAltruistCommit:        {},
+	TypeRewardCommit:          {},
+	TypeAltruistAnchorCommit:  {},
+	TypeAltruistTaprootCommit: {},
 }
 
 // IsSupportedType returns true if the given type is supported by the package.

watchtower/blob/type_test.go

@@ -16,19 +16,28 @@ type typeStringTest struct {
 
 var typeStringTests = []typeStringTest{
 	{
-		name:   "commit no-reward",
-		typ:    blob.TypeAltruistCommit,
-		expStr: "[No-FlagAnchorChannel|FlagCommitOutputs|No-FlagReward]",
+		name: "commit no-reward",
+		typ:  blob.TypeAltruistCommit,
+		expStr: "[No-FlagTaprootChannel|" +
+			"No-FlagAnchorChannel|" +
+			"FlagCommitOutputs|" +
+			"No-FlagReward]",
 	},
 	{
-		name:   "commit reward",
-		typ:    blob.TypeRewardCommit,
-		expStr: "[No-FlagAnchorChannel|FlagCommitOutputs|FlagReward]",
+		name: "commit reward",
+		typ:  blob.TypeRewardCommit,
+		expStr: "[No-FlagTaprootChannel|" +
+			"No-FlagAnchorChannel|" +
+			"FlagCommitOutputs|" +
+			"FlagReward]",
 	},
 	{
-		name:   "unknown flag",
-		typ:    unknownFlag.Type(),
-		expStr: "0000000000010000[No-FlagAnchorChannel|No-FlagCommitOutputs|No-FlagReward]",
+		name: "unknown flag",
+		typ:  unknownFlag.Type(),
+		expStr: "0000000000010000[No-FlagTaprootChannel|" +
+			"No-FlagAnchorChannel|" +
+			"No-FlagCommitOutputs|" +
+			"No-FlagReward]",
 	},
 }
 

watchtower/wtpolicy/policy.go

@@ -125,6 +125,12 @@ func (p Policy) IsAnchorChannel() bool {
 	return p.TxPolicy.BlobType.IsAnchorChannel()
 }
 
+// IsTaprootChannel returns true if the session policy requires taproot
+// channels.
+func (p Policy) IsTaprootChannel() bool {
+	return p.TxPolicy.BlobType.IsTaprootChannel()
+}
+
 // Validate ensures that the policy satisfies some minimal correctness
 // constraints.
 func (p Policy) Validate() error {

watchtower/wtpolicy/policy_test.go

@@ -93,20 +93,32 @@ func TestPolicyValidate(t *testing.T) {
 	}
 }
 
-// TestPolicyIsAnchorChannel asserts that the IsAnchorChannel helper properly
-// reflects the anchor bit of the policy's blob type.
-func TestPolicyIsAnchorChannel(t *testing.T) {
-	policyNoAnchor := wtpolicy.Policy{
+// TestPolicyIsChannelType asserts that the IsAnchorChannel and IsTaprootChannel
+// helpers properly reflect the anchor bit of the policy's blob type.
+func TestPolicyIsChannelType(t *testing.T) {
+	t.Parallel()
+
+	policyLegacy := wtpolicy.Policy{
 		TxPolicy: wtpolicy.TxPolicy{
 			BlobType: blob.TypeAltruistCommit,
 		},
 	}
-	require.Equal(t, false, policyNoAnchor.IsAnchorChannel())
+	require.False(t, policyLegacy.IsAnchorChannel())
+	require.False(t, policyLegacy.IsTaprootChannel())
 
 	policyAnchor := wtpolicy.Policy{
 		TxPolicy: wtpolicy.TxPolicy{
 			BlobType: blob.TypeAltruistAnchorCommit,
 		},
 	}
-	require.Equal(t, true, policyAnchor.IsAnchorChannel())
+	require.True(t, policyAnchor.IsAnchorChannel())
+	require.False(t, policyAnchor.IsTaprootChannel())
+
+	policyTaproot := wtpolicy.Policy{
+		TxPolicy: wtpolicy.TxPolicy{
+			BlobType: blob.TypeAltruistTaprootCommit,
+		},
+	}
+	require.True(t, policyTaproot.IsTaprootChannel())
+	require.False(t, policyTaproot.IsAnchorChannel())
 }

watchtower/wtwire/features.go

@@ -9,6 +9,8 @@ var FeatureNames = map[lnwire.FeatureBit]string{
 	AltruistSessionsOptional: "altruist-sessions",
 	AnchorCommitRequired:     "anchor-commit",
 	AnchorCommitOptional:     "anchor-commit",
+	TaprootCommitRequired:    "taproot-commit",
+	TaprootCommitOptional:    "taproot-commit",
 }
 
 const (
@@ -30,4 +32,13 @@ const (
 	// AnchorCommitOptional specifies that the advertising tower allows the
 	// remote party to negotiate sessions for protecting anchor channels.
 	AnchorCommitOptional lnwire.FeatureBit = 3
+
+	// TaprootCommitRequired specifies that the advertising tower requires
+	// the remote party to negotiate sessions for protecting taproot
+	// channels.
+	TaprootCommitRequired lnwire.FeatureBit = 4
+
+	// TaprootCommitOptional specifies that the advertising tower allows the
+	// remote party to negotiate sessions for protecting taproot channels.
+	TaprootCommitOptional lnwire.FeatureBit = 5
 )