refactor(types): centralise transparent spend-key lookup

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

chain/ring.go

@@ -56,8 +56,8 @@ func (c *Chain) GetRingOutputs(height, amount uint64, offsets []uint64) ([]types
 // before or after the contract expiration. The refund path only opens after
 // the expiration height has passed.
 func ringOutputSpendKey(height uint64, target types.TxOutTarget) (types.PublicKey, error) {
-	if t, ok := types.AsTxOutToKey(target); ok {
+	if key, ok := (types.TxOutputBare{Target: target}).SpendKey(); ok {
-		return t.Key, nil
+		return key, nil
 	}
 
 	switch t := target.(type) {

tui/explorer_model.go

@@ -325,8 +325,8 @@ func (m *ExplorerModel) viewTxDetail() string {
 		for i, output := range tx.Vout {
 			switch v := output.(type) {
 			case types.TxOutputBare:
-				if targetKey, ok := types.AsTxOutToKey(v.Target); ok {
+				if targetKey, ok := v.SpendKey(); ok {
-					b.WriteString(fmt.Sprintf("  [%d] bare amount=%d key=%x\n", i, v.Amount, targetKey.Key[:4]))
+					b.WriteString(fmt.Sprintf("  [%d] bare amount=%d key=%x\n", i, v.Amount, targetKey[:4]))
 				} else {
 					b.WriteString(fmt.Sprintf("  [%d] bare amount=%d target=%T\n", i, v.Amount, v.Target))
 				}

types/transaction.go

@@ -244,6 +244,17 @@ type TxOutputBare struct {
 	Target TxOutTarget
 }
 
+// SpendKey returns the standard transparent spend key when the target is
+// TxOutToKey. Callers that only care about transparent key outputs can use
+// this instead of repeating a type assertion.
+func (t TxOutputBare) SpendKey() (PublicKey, bool) {
+	target, ok := AsTxOutToKey(t.Target)
+	if !ok {
+		return PublicKey{}, false
+	}
+	return target.Key, true
+}
+
 // OutputType returns the wire variant tag for bare outputs.
 func (t TxOutputBare) OutputType() uint8 { return OutputTypeBare }
 

types/transaction_test.go

@@ -33,6 +33,27 @@ func TestAsTxOutToKey_Bad(t *testing.T) {
 	}
 }
 
+func TestTxOutputBare_SpendKey_Good(t *testing.T) {
+	out := TxOutputBare{
+		Amount: 10,
+		Target: TxOutToKey{Key: PublicKey{0xAA, 0xBB}, MixAttr: 3},
+	}
+	key, ok := out.SpendKey()
+	if !ok {
+		t.Fatal("SpendKey: expected true for TxOutToKey target")
+	}
+	if key != (PublicKey{0xAA, 0xBB}) {
+		t.Errorf("SpendKey: got %x, want %x", key, PublicKey{0xAA, 0xBB})
+	}
+}
+
+func TestTxOutputBare_SpendKey_Bad(t *testing.T) {
+	out := TxOutputBare{Target: TxOutHTLC{Expiration: 100}}
+	if key, ok := out.SpendKey(); ok || key != (PublicKey{}) {
+		t.Fatalf("SpendKey: got (%x, %v), want zero key and false", key, ok)
+	}
+}
+
 func TestTxOutMultisig_TargetType_Good(t *testing.T) {
 	var target TxOutTarget = TxOutMultisig{MinimumSigs: 2, Keys: []PublicKey{{1}, {2}}}
 	if target.TargetType() != TargetTypeMultisig {

wallet/scanner.go

@@ -64,11 +64,11 @@ func (s *V1Scanner) ScanTransaction(tx *types.Transaction, txHash types.Hash,
 			continue
 		}
 
-		targetKey, ok := types.AsTxOutToKey(bare.Target)
+		targetKey, ok := bare.SpendKey()
 		if !ok {
 			continue
 		}
-		if types.PublicKey(expectedPublicKey) != targetKey.Key {
+		if types.PublicKey(expectedPublicKey) != targetKey {
 			continue
 		}