refactor(types): centralise to-key target extraction

Co-Authored-By: Charon <charon@lethean.io>

chain/ring.go

@@ -55,9 +55,11 @@ func (c *Chain) GetRingOutputs(height, amount uint64, offsets []uint64) ([]types
 // TxOutHTLC selects redeem vs refund based on whether the spending height is
 // before or after the contract expiration.
 func ringOutputSpendKey(height uint64, target types.TxOutTarget) (types.PublicKey, error) {
-	switch t := target.(type) {
-	case types.TxOutToKey:
+	if t, ok := types.AsTxOutToKey(target); ok {
 		return t.Key, nil
+	}
+
+	switch t := target.(type) {
 	case types.TxOutMultisig:
 		if len(t.Keys) == 0 {
 			return types.PublicKey{}, fmt.Errorf("unsupported multisig target with no keys")

tui/explorer_model.go

@@ -325,7 +325,7 @@ func (m *ExplorerModel) viewTxDetail() string {
 		for i, output := range tx.Vout {
 			switch v := output.(type) {
 			case types.TxOutputBare:
-				if targetKey, ok := v.Target.(types.TxOutToKey); ok {
+				if targetKey, ok := types.AsTxOutToKey(v.Target); ok {
 					b.WriteString(fmt.Sprintf("  [%d] bare amount=%d key=%x\n", i, v.Amount, targetKey.Key[:4]))
 				} else {
 					b.WriteString(fmt.Sprintf("  [%d] bare amount=%d target=%T\n", i, v.Amount, v.Target))

types/transaction.go

@@ -121,6 +121,13 @@ type TxOutTarget interface {
 	TargetType() uint8
 }
 
+// AsTxOutToKey returns target as a TxOutToKey when it is a standard
+// transparent output target.
+func AsTxOutToKey(target TxOutTarget) (TxOutToKey, bool) {
+	v, ok := target.(TxOutToKey)
+	return v, ok
+}
+
 // TxOutToKey is the txout_to_key target variant. On the wire it is
 // serialised as a 33-byte packed blob: 32-byte public key + 1-byte mix_attr.
 type TxOutToKey struct {
@@ -219,7 +226,7 @@ func (t TxInputHTLC) InputType() uint8 { return InputTypeHTLC }
 // TxInputMultisig spends from a multisig output (HF1+).
 type TxInputMultisig struct {
 	Amount        uint64
-	MultisigOutID Hash   // 32-byte hash identifying the multisig output
+	MultisigOutID Hash // 32-byte hash identifying the multisig output
 	SigsCount     uint64
 	EtcDetails    []byte // opaque variant vector
 }

types/transaction_test.go

@@ -14,6 +14,25 @@ func TestTxOutToKey_TargetType_Good(t *testing.T) {
 	}
 }
 
+func TestAsTxOutToKey_Good(t *testing.T) {
+	target, ok := AsTxOutToKey(TxOutToKey{Key: PublicKey{1}, MixAttr: 7})
+	if !ok {
+		t.Fatal("AsTxOutToKey: expected true for TxOutToKey target")
+	}
+	if target.Key != (PublicKey{1}) {
+		t.Errorf("Key: got %x, want %x", target.Key, PublicKey{1})
+	}
+	if target.MixAttr != 7 {
+		t.Errorf("MixAttr: got %d, want %d", target.MixAttr, 7)
+	}
+}
+
+func TestAsTxOutToKey_Bad(t *testing.T) {
+	if _, ok := AsTxOutToKey(TxOutHTLC{}); ok {
+		t.Fatal("AsTxOutToKey: expected false for non-to-key target")
+	}
+}
+
 func TestTxOutMultisig_TargetType_Good(t *testing.T) {
 	var target TxOutTarget = TxOutMultisig{MinimumSigs: 2, Keys: []PublicKey{{1}, {2}}}
 	if target.TargetType() != TargetTypeMultisig {

wallet/scanner.go

@@ -64,7 +64,7 @@ func (s *V1Scanner) ScanTransaction(tx *types.Transaction, txHash types.Hash,
 			continue
 		}
 
-		targetKey, ok := bare.Target.(types.TxOutToKey)
+		targetKey, ok := types.AsTxOutToKey(bare.Target)
 		if !ok {
 			continue
 		}