Return scriptPos in checkParseableInScript

txscript/opcode.go

@@ -658,7 +658,8 @@ func (pop *parsedOpcode) isDisabled() bool {
 
 // checkParseableInScript checks whether or not the current opcode is able to be
 // parsed at a certain position in a script.
-func (pop *parsedOpcode) checkParseableInScript(script []byte, scriptPos int) (error) {
+// This returns the position of the next opcode to be parsed in the script.
+func (pop *parsedOpcode) checkParseableInScript(script []byte, scriptPos int) (int, error) {
 	// Parse data out of instruction.
 	switch {
 	// No additional data.  Note that some of the opcodes, notably
@@ -673,7 +674,7 @@ func (pop *parsedOpcode) checkParseableInScript(script []byte, scriptPos int) (e
 			str := fmt.Sprintf("opcode %s requires %d "+
 				"bytes, but script only has %d remaining",
 				pop.opcode.name, pop.opcode.length, len(script[scriptPos:]))
-			return scriptError(ErrMalformedPush, str)
+			return 0, scriptError(ErrMalformedPush, str)
 		}
 
 		// Slice out the data.
@@ -685,11 +686,11 @@ func (pop *parsedOpcode) checkParseableInScript(script []byte, scriptPos int) (e
 		var l uint
 		off := scriptPos + 1
 
-		if len(script[off:]) < - pop.opcode.length {
+		if len(script[off:]) < -pop.opcode.length {
 			str := fmt.Sprintf("opcode %s requires %d "+
 				"bytes, but script only has %d remaining",
-				pop.opcode.name, - pop.opcode.length, len(script[off:]))
-			return scriptError(ErrMalformedPush, str)
+				pop.opcode.name, -pop.opcode.length, len(script[off:]))
+			return 0, scriptError(ErrMalformedPush, str)
 		}
 
 		// Next -length bytes are little endian length of data.
@@ -707,7 +708,7 @@ func (pop *parsedOpcode) checkParseableInScript(script []byte, scriptPos int) (e
 		default:
 			str := fmt.Sprintf("invalid opcode length %d",
 				pop.opcode.length)
-			return scriptError(ErrMalformedPush, str)
+			return 0, scriptError(ErrMalformedPush, str)
 		}
 
 		// Move offset to beginning of the data.
@@ -719,13 +720,13 @@ func (pop *parsedOpcode) checkParseableInScript(script []byte, scriptPos int) (e
 			str := fmt.Sprintf("opcode %s pushes %d bytes, "+
 				"but script only has %d remaining",
 				pop.opcode.name, int(l), len(script[off:]))
-			return scriptError(ErrMalformedPush, str)
+			return 0, scriptError(ErrMalformedPush, str)
 		}
 
 		pop.data = script[off : off+int(l)]
 		scriptPos += 1 - pop.opcode.length + int(l)
 	}
-	return nil
+	return scriptPos, nil
 }
 
 // alwaysIllegal returns whether or not the opcode is always illegal when passed

txscript/script.go

@@ -196,11 +196,12 @@ func IsPushOnlyScript(script []byte) bool {
 // the list of parsed opcodes up to the point of failure along with the error.
 func parseScriptTemplate(script []byte, opcodes *[256]opcode) ([]parsedOpcode, error) {
 	retScript := make([]parsedOpcode, 0, len(script))
+	var err error
 	for i := 0; i < len(script); {
 		instr := script[i]
 		op := &opcodes[instr]
 		pop := parsedOpcode{opcode: op}
-		err := pop.checkParseableInScript(script, i)
+		i, err = pop.checkParseableInScript(script, i)
 		if err != nil {
 			return retScript, err
 		}
@@ -223,6 +224,8 @@ func parseScriptTemplate(script []byte, opcodes *[256]opcode) ([]parsedOpcode, e
 // Not returning the full opcode list up until failure also has the benefit of
 // reducing GC pressure, as the list would get immediately thrown away.
 func checkScriptTemplateParseable(script []byte, opcodes *[256]opcode) (*byte, error) {
+	var err error
+
 	// A script of length zero is an unspendable script but it is parseable.
 	var firstOpcode byte
 	var numParsedInstr uint = 0
@@ -231,7 +234,7 @@ func checkScriptTemplateParseable(script []byte, opcodes *[256]opcode) (*byte, e
 		instr := script[i]
 		op := &opcodes[instr]
 		pop := parsedOpcode{opcode: op}
-		err := pop.checkParseableInScript(script, i)
+		i, err = pop.checkParseableInScript(script, i)
 		if err != nil {
 			return nil, err
 		}

txscript/script_test.go

@@ -4315,12 +4315,12 @@ func TestIsUnspendable(t *testing.T) {
 		},
 		{
 			// Spendable
-			pkScript: []byte{0x51},
+			pkScript: []byte{OP_TRUE},
 			expected: false,
 		},
 		{
 			// Unspendable
-			pkScript: []byte{0x6a},
+			pkScript: []byte{OP_RETURN},
 			expected: true,
 		},
 	}