add cached version of HasWitness

tx.go

@@ -25,6 +25,7 @@ type Tx struct {
 	msgTx         *wire.MsgTx     // Underlying MsgTx
 	txHash        *chainhash.Hash // Cached transaction hash
 	txHashWitness *chainhash.Hash // Cached transaction witness hash
+	txHasWitness  *bool           // If the transaction has witness data
 	txIndex       int             // Position within a block or TxIndexUnknown
 }
 
@@ -64,6 +65,20 @@ func (t *Tx) WitnessHash() *chainhash.Hash {
 	return &hash
 }
 
+// HasWitness returns false if none of the inputs within the transaction
+// contain witness data, true false otherwise. This equivalent to calling
+// HasWitness on the underlying wire.MsgTx, however it caches the result so
+// subsequent calls are more efficient.
+func (t *Tx) HasWitness() bool {
+	if t.txHashWitness != nil {
+		return *t.txHasWitness
+	}
+
+	hasWitness := t.msgTx.HasWitness()
+	t.txHasWitness = &hasWitness
+	return hasWitness
+}
+
 // Index returns the saved index of the transaction within a block.  This value
 // will be TxIndexUnknown if it hasn't already explicitly been set.
 func (t *Tx) Index() int {