txscript: backport tokenizer from dcrd

txscript/README.md

@@ -37,6 +37,10 @@ $ go get -u github.com/btcsuite/btcd/txscript
 * [Manually Signing a Transaction Output](http://godoc.org/github.com/btcsuite/btcd/txscript#example-SignTxOutput)  
   Demonstrates manually creating and signing a redeem transaction.
 
+* [Counting Opcodes in Scripts](http://godoc.org/github.com/decred/dcrd/txscript#example-ScriptTokenizer)  
+  Demonstrates creating a script tokenizer instance and using it to count the
+  number of opcodes a script contains.
+
 ## GPG Verification Key
 
 All official release tags are signed by Conformal so users can ensure the code

txscript/bench_test.go

@@ -0,0 +1,113 @@
+// Copyright (c) 2018-2019 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package txscript
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"testing"
+
+	"github.com/btcsuite/btcd/wire"
+)
+
+var (
+	// manyInputsBenchTx is a transaction that contains a lot of inputs which is
+	// useful for benchmarking signature hash calculation.
+	manyInputsBenchTx wire.MsgTx
+
+	// A mock previous output script to use in the signing benchmark.
+	prevOutScript = hexToBytes("a914f5916158e3e2c4551c1796708db8367207ed13bb87")
+)
+
+func init() {
+	// tx 620f57c92cf05a7f7e7f7d28255d5f7089437bc48e34dcfebf7751d08b7fb8f5
+	txHex, err := ioutil.ReadFile("data/many_inputs_tx.hex")
+	if err != nil {
+		panic(fmt.Sprintf("unable to read benchmark tx file: %v", err))
+	}
+
+	txBytes := hexToBytes(string(txHex))
+	err = manyInputsBenchTx.Deserialize(bytes.NewReader(txBytes))
+	if err != nil {
+		panic(err)
+	}
+}
+
+// BenchmarkCalcSigHash benchmarks how long it takes to calculate the signature
+// hashes for all inputs of a transaction with many inputs.
+func BenchmarkCalcSigHash(b *testing.B) {
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		for j := 0; j < len(manyInputsBenchTx.TxIn); j++ {
+			_, err := CalcSignatureHash(prevOutScript, SigHashAll,
+				&manyInputsBenchTx, j)
+			if err != nil {
+				b.Fatalf("failed to calc signature hash: %v", err)
+			}
+		}
+	}
+}
+
+// BenchmarkCalcWitnessSigHash benchmarks how long it takes to calculate the
+// witness signature hashes for all inputs of a transaction with many inputs.
+func BenchmarkCalcWitnessSigHash(b *testing.B) {
+	sigHashes := NewTxSigHashes(&manyInputsBenchTx)
+
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		for j := 0; j < len(manyInputsBenchTx.TxIn); j++ {
+			_, err := CalcWitnessSigHash(
+				prevOutScript, sigHashes, SigHashAll,
+				&manyInputsBenchTx, j, 5,
+			)
+			if err != nil {
+				b.Fatalf("failed to calc signature hash: %v", err)
+			}
+		}
+	}
+}
+
+// genComplexScript returns a script comprised of half as many opcodes as the
+// maximum allowed followed by as many max size data pushes fit without
+// exceeding the max allowed script size.
+func genComplexScript() ([]byte, error) {
+	var scriptLen int
+	builder := NewScriptBuilder()
+	for i := 0; i < MaxOpsPerScript/2; i++ {
+		builder.AddOp(OP_TRUE)
+		scriptLen++
+	}
+	maxData := bytes.Repeat([]byte{0x02}, MaxScriptElementSize)
+	for i := 0; i < (MaxScriptSize-scriptLen)/(MaxScriptElementSize+3); i++ {
+		builder.AddData(maxData)
+	}
+	return builder.Script()
+}
+
+// BenchmarkScriptParsing benchmarks how long it takes to parse a very large
+// script.
+func BenchmarkScriptParsing(b *testing.B) {
+	script, err := genComplexScript()
+	if err != nil {
+		b.Fatalf("failed to create benchmark script: %v", err)
+	}
+
+	const scriptVersion = 0
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		tokenizer := MakeScriptTokenizer(scriptVersion, script)
+		for tokenizer.Next() {
+			_ = tokenizer.Opcode()
+			_ = tokenizer.Data()
+			_ = tokenizer.ByteIndex()
+		}
+		if err := tokenizer.Err(); err != nil {
+			b.Fatalf("failed to parse script: %v", err)
+		}
+	}
+}

txscript/error.go

@@ -1,4 +1,5 @@
 // Copyright (c) 2013-2017 The btcsuite developers
+// Copyright (c) 2015-2019 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -47,6 +48,10 @@ const (
 	// the provided data exceeds MaxDataCarrierSize.
 	ErrTooMuchNullData
 
+	// ErrUnsupportedScriptVersion is returned when an unsupported script
+	// version is passed to a function which deals with script analysis.
+	ErrUnsupportedScriptVersion
+
 	// ------------------------------------------
 	// Failures related to final execution state.
 	// ------------------------------------------
@@ -352,6 +357,7 @@ var errorCodeStrings = map[ErrorCode]string{
 	ErrNotMultisigScript:                  "ErrNotMultisigScript",
 	ErrTooManyRequiredSigs:                "ErrTooManyRequiredSigs",
 	ErrTooMuchNullData:                    "ErrTooMuchNullData",
+	ErrUnsupportedScriptVersion:           "ErrUnsupportedScriptVersion",
 	ErrEarlyReturn:                        "ErrEarlyReturn",
 	ErrEmptyStack:                         "ErrEmptyStack",
 	ErrEvalFalse:                          "ErrEvalFalse",

txscript/error_test.go

@@ -1,4 +1,5 @@
 // Copyright (c) 2017 The btcsuite developers
+// Copyright (c) 2015-2019 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -22,6 +23,7 @@ func TestErrorCodeStringer(t *testing.T) {
 		{ErrUnsupportedAddress, "ErrUnsupportedAddress"},
 		{ErrTooManyRequiredSigs, "ErrTooManyRequiredSigs"},
 		{ErrTooMuchNullData, "ErrTooMuchNullData"},
+		{ErrUnsupportedScriptVersion, "ErrUnsupportedScriptVersion"},
 		{ErrNotMultisigScript, "ErrNotMultisigScript"},
 		{ErrEarlyReturn, "ErrEarlyReturn"},
 		{ErrEmptyStack, "ErrEmptyStack"},

txscript/example_test.go

@@ -1,4 +1,5 @@
 // Copyright (c) 2014-2016 The btcsuite developers
+// Copyright (c) 2015-2019 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -180,3 +181,34 @@ func ExampleSignTxOutput() {
 	// Output:
 	// Transaction successfully signed
 }
+
+// This example demonstrates creating a script tokenizer instance and using it
+// to count the number of opcodes a script contains.
+func ExampleScriptTokenizer() {
+	// Create a script to use in the example.  Ordinarily this would come from
+	// some other source.
+	hash160 := btcutil.Hash160([]byte("example"))
+	script, err := txscript.NewScriptBuilder().AddOp(txscript.OP_DUP).
+		AddOp(txscript.OP_HASH160).AddData(hash160).
+		AddOp(txscript.OP_EQUALVERIFY).AddOp(txscript.OP_CHECKSIG).Script()
+	if err != nil {
+		fmt.Printf("failed to build script: %v\n", err)
+		return
+	}
+
+	// Create a tokenizer to iterate the script and count the number of opcodes.
+	const scriptVersion = 0
+	var numOpcodes int
+	tokenizer := txscript.MakeScriptTokenizer(scriptVersion, script)
+	for tokenizer.Next() {
+		numOpcodes++
+	}
+	if tokenizer.Err() != nil {
+		fmt.Printf("script failed to parse: %v\n", err)
+	} else {
+		fmt.Printf("script contains %d opcode(s)\n", numOpcodes)
+	}
+
+	// Output:
+	// script contains 5 opcode(s)
+}

txscript/tokenizer.go

@@ -0,0 +1,183 @@
+// Copyright (c) 2019 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package txscript
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+// opcodeArrayRef is used to break initialization cycles.
+var opcodeArrayRef *[256]opcode
+
+func init() {
+	opcodeArrayRef = &opcodeArray
+}
+
+// ScriptTokenizer provides a facility for easily and efficiently tokenizing
+// transaction scripts without creating allocations.  Each successive opcode is
+// parsed with the Next function, which returns false when iteration is
+// complete, either due to successfully tokenizing the entire script or
+// encountering a parse error.  In the case of failure, the Err function may be
+// used to obtain the specific parse error.
+//
+// Upon successfully parsing an opcode, the opcode and data associated with it
+// may be obtained via the Opcode and Data functions, respectively.
+//
+// The ByteIndex function may be used to obtain the tokenizer's current offset
+// into the raw script.
+type ScriptTokenizer struct {
+	script  []byte
+	version uint16
+	offset  int32
+	op      *opcode
+	data    []byte
+	err     error
+}
+
+// Done returns true when either all opcodes have been exhausted or a parse
+// failure was encountered and therefore the state has an associated error.
+func (t *ScriptTokenizer) Done() bool {
+	return t.err != nil || t.offset >= int32(len(t.script))
+}
+
+// Next attempts to parse the next opcode and returns whether or not it was
+// successful.  It will not be successful if invoked when already at the end of
+// the script, a parse failure is encountered, or an associated error already
+// exists due to a previous parse failure.
+//
+// In the case of a true return, the parsed opcode and data can be obtained with
+// the associated functions and the offset into the script will either point to
+// the next opcode or the end of the script if the final opcode was parsed.
+//
+// In the case of a false return, the parsed opcode and data will be the last
+// successfully parsed values (if any) and the offset into the script will
+// either point to the failing opcode or the end of the script if the function
+// was invoked when already at the end of the script.
+//
+// Invoking this function when already at the end of the script is not
+// considered an error and will simply return false.
+func (t *ScriptTokenizer) Next() bool {
+	if t.Done() {
+		return false
+	}
+
+	op := &opcodeArrayRef[t.script[t.offset]]
+	switch {
+	// No additional data.  Note that some of the opcodes, notably OP_1NEGATE,
+	// OP_0, and OP_[1-16] represent the data themselves.
+	case op.length == 1:
+		t.offset++
+		t.op = op
+		t.data = nil
+		return true
+
+	// Data pushes of specific lengths -- OP_DATA_[1-75].
+	case op.length > 1:
+		script := t.script[t.offset:]
+		if len(script) < op.length {
+			str := fmt.Sprintf("opcode %s requires %d bytes, but script only "+
+				"has %d remaining", op.name, op.length, len(script))
+			t.err = scriptError(ErrMalformedPush, str)
+			return false
+		}
+
+		// Move the offset forward and set the opcode and data accordingly.
+		t.offset += int32(op.length)
+		t.op = op
+		t.data = script[1:op.length]
+		return true
+
+	// Data pushes with parsed lengths -- OP_PUSHDATA{1,2,4}.
+	case op.length < 0:
+		script := t.script[t.offset+1:]
+		if len(script) < -op.length {
+			str := fmt.Sprintf("opcode %s requires %d bytes, but script only "+
+				"has %d remaining", op.name, -op.length, len(script))
+			t.err = scriptError(ErrMalformedPush, str)
+			return false
+		}
+
+		// Next -length bytes are little endian length of data.
+		var dataLen int32
+		switch op.length {
+		case -1:
+			dataLen = int32(script[0])
+		case -2:
+			dataLen = int32(binary.LittleEndian.Uint16(script[:2]))
+		case -4:
+			dataLen = int32(binary.LittleEndian.Uint32(script[:4]))
+		default:
+			str := fmt.Sprintf("invalid opcode length %d", op.length)
+			t.err = scriptError(ErrMalformedPush, str)
+			return false
+		}
+
+		// Move to the beginning of the data.
+		script = script[-op.length:]
+
+		// Disallow entries that do not fit script or were sign extended.
+		if dataLen > int32(len(script)) || dataLen < 0 {
+			str := fmt.Sprintf("opcode %s pushes %d bytes, but script only "+
+				"has %d remaining", op.name, dataLen, len(script))
+			t.err = scriptError(ErrMalformedPush, str)
+			return false
+		}
+
+		// Move the offset forward and set the opcode and data accordingly.
+		t.offset += 1 + int32(-op.length) + dataLen
+		t.op = op
+		t.data = script[:dataLen]
+		return true
+	}
+
+	// The only remaining case is an opcode with length zero which is
+	// impossible.
+	panic("unreachable")
+}
+
+// Script returns the full script associated with the tokenizer.
+func (t *ScriptTokenizer) Script() []byte {
+	return t.script
+}
+
+// ByteIndex returns the current offset into the full script that will be parsed
+// next and therefore also implies everything before it has already been parsed.
+func (t *ScriptTokenizer) ByteIndex() int32 {
+	return t.offset
+}
+
+// Opcode returns the current opcode associated with the tokenizer.
+func (t *ScriptTokenizer) Opcode() byte {
+	return t.op.value
+}
+
+// Data returns the data associated with the most recently successfully parsed
+// opcode.
+func (t *ScriptTokenizer) Data() []byte {
+	return t.data
+}
+
+// Err returns any errors currently associated with the tokenizer.  This will
+// only be non-nil in the case a parsing error was encountered.
+func (t *ScriptTokenizer) Err() error {
+	return t.err
+}
+
+// MakeScriptTokenizer returns a new instance of a script tokenizer.  Passing
+// an unsupported script version will result in the returned tokenizer
+// immediately having an err set accordingly.
+//
+// See the docs for ScriptTokenizer for more details.
+func MakeScriptTokenizer(scriptVersion uint16, script []byte) ScriptTokenizer {
+	// Only version 0 scripts are currently supported.
+	var err error
+	if scriptVersion != 0 {
+		str := fmt.Sprintf("script version %d is not supported", scriptVersion)
+		err = scriptError(ErrUnsupportedScriptVersion, str)
+
+	}
+	return ScriptTokenizer{version: scriptVersion, script: script, err: err}
+}