txscript: Remove unneeded param from NewScript.

This commit removes the unnecessary sigScript parameter from the
txscript.NewScript function.  This has bothered me for a while because it
can and really should be obtained from the provided transaction and input
index.  The way it was, the passed script could technically be different
than what is in the transaction.  Obviously that would be an improper use
of the API, but it's safer and more convenient to simply pull it from the
provided transaction and index.

Also, since the function signature is changing anyways, make the input
index parameter come after the transaction which it references.

blockchain/scriptval.go

@@ -83,8 +83,8 @@ out:
 			// Create a new script engine for the script pair.
 			sigScript := txIn.SignatureScript
 			pkScript := originMsgTx.TxOut[originTxIndex].PkScript
-			engine, err := txscript.NewScript(sigScript, pkScript,
-				txVI.txInIndex, txVI.tx.MsgTx(), v.flags)
+			engine, err := txscript.NewScript(pkScript,
+				txVI.tx.MsgTx(), txVI.txInIndex, v.flags)
 			if err != nil {
 				str := fmt.Sprintf("failed to parse input "+
 					"%s:%d which references output %s:%d - "+

txscript/example_test.go

@@ -164,8 +164,8 @@ func ExampleSignTxOutput() {
 	flags := txscript.ScriptBip16 | txscript.ScriptVerifyDERSignatures |
 		txscript.ScriptStrictMultiSig |
 		txscript.ScriptDiscourageUpgradableNops
-	s, err := txscript.NewScript(redeemTx.TxIn[0].SignatureScript,
-		originTx.TxOut[0].PkScript, 0, redeemTx, flags)
+	s, err := txscript.NewScript(originTx.TxOut[0].PkScript, redeemTx, 0,
+		flags)
 	if err != nil {
 		fmt.Println(err)
 		return

txscript/internal_test.go

@@ -4202,7 +4202,7 @@ func TestBitcoindInvalidTests(t *testing.T) {
 			continue
 		}
 		tx := createSpendingTx(scriptSig, scriptPubKey)
-		s, err := NewScript(scriptSig, scriptPubKey, 0, tx, flags)
+		s, err := NewScript(scriptPubKey, tx, 0, flags)
 		if err == nil {
 			if err := s.Execute(); err == nil {
 				t.Errorf("%s test succeeded when it "+
@@ -4254,7 +4254,7 @@ func TestBitcoindValidTests(t *testing.T) {
 			continue
 		}
 		tx := createSpendingTx(scriptSig, scriptPubKey)
-		s, err := NewScript(scriptSig, scriptPubKey, 0, tx, flags)
+		s, err := NewScript(scriptPubKey, tx, 0, flags)
 		if err != nil {
 			t.Errorf("%s failed to create script: %v", name, err)
 			continue
@@ -4391,8 +4391,7 @@ testloop:
 					k, i, test)
 				continue testloop
 			}
-			s, err := NewScript(txin.SignatureScript, pkScript, k,
-				tx.MsgTx(), flags)
+			s, err := NewScript(pkScript, tx.MsgTx(), k, flags)
 			if err != nil {
 				t.Errorf("test (%d:%v:%d) failed to create "+
 					"script: %v", i, test, k, err)
@@ -4537,8 +4536,7 @@ testloop:
 			// These are meant to fail, so as soon as the first
 			// input fails the transaction has failed. (some of the
 			// test txns have good inputs, too..
-			s, err := NewScript(txin.SignatureScript, pkScript, k,
-				tx.MsgTx(), flags)
+			s, err := NewScript(pkScript, tx.MsgTx(), k, flags)
 			if err != nil {
 				continue testloop
 			}

txscript/opcode_test.go

@@ -507,9 +507,7 @@ func TestScripts(t *testing.T) {
 			flags = txscript.ScriptVerifyDERSignatures
 		}
 		mockTx.TxOut[0].PkScript = test.script
-		sigScript := mockTx.TxIn[0].SignatureScript
-		engine, err := txscript.NewScript(sigScript, test.script, 0,
-			mockTx, flags)
+		engine, err := txscript.NewScript(test.script, mockTx, 0, flags)
 		if err == nil {
 			err = engine.Execute()
 		}
@@ -4285,8 +4283,7 @@ func testOpcode(t *testing.T, test *detailedTest) {
 
 	tx.TxOut[0].PkScript = test.script
 
-	engine, err := txscript.NewScript(tx.TxIn[0].SignatureScript,
-		tx.TxOut[0].PkScript, 0, tx, 0)
+	engine, err := txscript.NewScript(tx.TxOut[0].PkScript, tx, 0, 0)
 	if err != nil {
 		if err != test.expectedReturn {
 			t.Errorf("Error return not expected %s: %v %v",

txscript/script.go

@@ -146,6 +146,10 @@ var (
 	// ErrInvalidFlags is returned when the passed flags to NewScript contain
 	// an invalid combination.
 	ErrInvalidFlags = errors.New("invalid flags combination")
+
+	// ErrInvalidIndex is returned when the passed input index for the
+	// provided transaction is out of range.
+	ErrInvalidIndex = errors.New("invalid input index")
 )
 
 const (
@@ -699,10 +703,15 @@ const (
 )
 
 // NewScript returns a new script engine for the provided tx and input idx with
-// a signature script scriptSig and a pubkeyscript scriptPubKey. If bip16 is
-// true then it will be treated as if the bip16 threshhold has passed and thus
-// pay-to-script hash transactions will be fully validated.
-func NewScript(scriptSig []byte, scriptPubKey []byte, txidx int, tx *wire.MsgTx, flags ScriptFlags) (*Script, error) {
+// with a pubkeyscript scriptPubKey. If bip16 is true then it will be treated as
+// if the bip16 threshhold has passed and thus pay-to-script hash transactions
+// will be fully validated.
+func NewScript(scriptPubKey []byte, tx *wire.MsgTx, txidx int, flags ScriptFlags) (*Script, error) {
+	if txidx < 0 || txidx >= len(tx.TxIn) {
+		return nil, ErrInvalidIndex
+	}
+	scriptSig := tx.TxIn[txidx].SignatureScript
+
 	var m Script
 	if flags&ScriptVerifySigPushOnly == ScriptVerifySigPushOnly && !IsPushOnlyScript(scriptSig) {
 		return nil, ErrStackNonPushOnly

txscript/script_test.go

@@ -1636,9 +1636,8 @@ func testTx(t *testing.T, test txTest) {
 	if test.strictSigs {
 		flags |= txscript.ScriptVerifyDERSignatures
 	}
-	engine, err := txscript.NewScript(
-		test.tx.TxIn[test.idx].SignatureScript, test.pkScript,
-		test.idx, test.tx, flags)
+	engine, err := txscript.NewScript(test.pkScript, test.tx, test.idx,
+		flags)
 	if err != nil {
 		if err != test.parseErr {
 			t.Errorf("Failed to parse %s: got \"%v\" expected "+
@@ -2470,8 +2469,7 @@ func TestBadPC(t *testing.T) {
 	pkScript := []byte{txscript.OP_NOP}
 
 	for _, test := range pcTests {
-		engine, err := txscript.NewScript(tx.TxIn[0].SignatureScript,
-			pkScript, 0, tx, 0)
+		engine, err := txscript.NewScript(pkScript, tx, 0, 0)
 		if err != nil {
 			t.Errorf("Failed to create script: %v", err)
 		}
@@ -2542,8 +2540,7 @@ func TestCheckErrorCondition(t *testing.T) {
 		txscript.OP_TRUE,
 	}
 
-	engine, err := txscript.NewScript(tx.TxIn[0].SignatureScript, pkScript,
-		0, tx, 0)
+	engine, err := txscript.NewScript(pkScript, tx, 0, 0)
 	if err != nil {
 		t.Errorf("failed to create script: %v", err)
 	}
@@ -2892,10 +2889,9 @@ nexttest:
 
 		// Validate tx input scripts
 		scriptFlags := txscript.ScriptBip16 | txscript.ScriptVerifyDERSignatures
-		for j, txin := range tx.TxIn {
-			engine, err := txscript.NewScript(txin.SignatureScript,
-				SigScriptTests[i].inputs[j].txout.PkScript,
-				j, tx, scriptFlags)
+		for j := range tx.TxIn {
+			engine, err := txscript.NewScript(SigScriptTests[i].
+				inputs[j].txout.PkScript, tx, j, scriptFlags)
 			if err != nil {
 				t.Errorf("cannot create script vm for test %v: %v",
 					SigScriptTests[i].name, err)
@@ -3307,9 +3303,8 @@ func signAndCheck(msg string, tx *wire.MsgTx, idx int, pkScript []byte,
 	hashType txscript.SigHashType, kdb txscript.KeyDB, sdb txscript.ScriptDB,
 	previousScript []byte) error {
 
-	sigScript, err := txscript.SignTxOutput(
-		&chaincfg.TestNet3Params, tx, idx, pkScript, hashType,
-		kdb, sdb, []byte{})
+	sigScript, err := txscript.SignTxOutput(&chaincfg.TestNet3Params, tx,
+		idx, pkScript, hashType, kdb, sdb, []byte{})
 	if err != nil {
 		return fmt.Errorf("failed to sign output %s: %v", msg, err)
 	}
@@ -3317,11 +3312,10 @@ func signAndCheck(msg string, tx *wire.MsgTx, idx int, pkScript []byte,
 	return checkScripts(msg, tx, idx, sigScript, pkScript)
 }
 
-func checkScripts(msg string, tx *wire.MsgTx, idx int,
-	sigScript, pkScript []byte) error {
-	engine, err := txscript.NewScript(sigScript, pkScript, idx, tx,
-		txscript.ScriptBip16|
-			txscript.ScriptVerifyDERSignatures)
+func checkScripts(msg string, tx *wire.MsgTx, idx int, sigScript, pkScript []byte) error {
+	tx.TxIn[idx].SignatureScript = sigScript
+	engine, err := txscript.NewScript(pkScript, tx, idx,
+		txscript.ScriptBip16|txscript.ScriptVerifyDERSignatures)
 	if err != nil {
 		return fmt.Errorf("failed to make script engine for %s: %v",
 			msg, err)
@@ -4857,9 +4851,7 @@ func TestInvalidFlagCombinations(t *testing.T) {
 	pkScript := []byte{txscript.OP_NOP}
 
 	for i, test := range tests {
-		_, err := txscript.NewScript(tx.TxIn[0].SignatureScript,
-			pkScript, 0, tx, test)
-
+		_, err := txscript.NewScript(pkScript, tx, 0, test)
 		if err != txscript.ErrInvalidFlags {
 			t.Fatalf("TestInvalidFlagCombinations #%d unexpected "+
 				"error: %v", i, err)