+++ /dev/null
-// Copyright (c) 2013-2015 The btcsuite 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"
-)
-
-const (
- // defaultScriptAlloc is the default size used for the backing array
- // for a script being built by the ScriptBuilder. The array will
- // dynamically grow as needed, but this figure is intended to provide
- // enough space for vast majority of scripts without needing to grow the
- // backing array multiple times.
- defaultScriptAlloc = 500
-)
-
-// ErrScriptNotCanonical identifies a non-canonical script. The caller can use
-// a type assertion to detect this error type.
-type ErrScriptNotCanonical string
-
-// Error implements the error interface.
-func (e ErrScriptNotCanonical) Error() string {
- return string(e)
-}
-
-// ScriptBuilder provides a facility for building custom scripts. It allows
-// you to push opcodes, ints, and data while respecting canonical encoding. In
-// general it does not ensure the script will execute correctly, however any
-// data pushes which would exceed the maximum allowed script engine limits and
-// are therefore guaranteed not to execute will not be pushed and will result in
-// the Script function returning an error.
-//
-// For example, the following would build a 2-of-3 multisig script for usage in
-// a pay-to-script-hash (although in this situation MultiSigScript() would be a
-// better choice to generate the script):
-// builder := txscript.NewScriptBuilder()
-// builder.AddOp(txscript.OP_2).AddData(pubKey1).AddData(pubKey2)
-// builder.AddData(pubKey3).AddOp(txscript.OP_3)
-// builder.AddOp(txscript.OP_CHECKMULTISIG)
-// script, err := builder.Script()
-// if err != nil {
-// // Handle the error.
-// return
-// }
-// fmt.Printf("Final multi-sig script: %x\n", script)
-type ScriptBuilder struct {
- script []byte
- err error
-}
-
-// AddOp pushes the passed opcode to the end of the script. The script will not
-// be modified if pushing the opcode would cause the script to exceed the
-// maximum allowed script engine size.
-func (b *ScriptBuilder) AddOp(opcode byte) *ScriptBuilder {
- if b.err != nil {
- return b
- }
-
- // Pushes that would cause the script to exceed the largest allowed
- // script size would result in a non-canonical script.
- if len(b.script)+1 > MaxScriptSize {
- str := fmt.Sprintf("adding an opcode would exceed the maximum "+
- "allowed canonical script length of %d", MaxScriptSize)
- b.err = ErrScriptNotCanonical(str)
- return b
- }
-
- b.script = append(b.script, opcode)
- return b
-}
-
-// AddOps pushes the passed opcodes to the end of the script. The script will
-// not be modified if pushing the opcodes would cause the script to exceed the
-// maximum allowed script engine size.
-func (b *ScriptBuilder) AddOps(opcodes []byte) *ScriptBuilder {
- if b.err != nil {
- return b
- }
-
- // Pushes that would cause the script to exceed the largest allowed
- // script size would result in a non-canonical script.
- if len(b.script)+len(opcodes) > MaxScriptSize {
- str := fmt.Sprintf("adding opcodes would exceed the maximum "+
- "allowed canonical script length of %d", MaxScriptSize)
- b.err = ErrScriptNotCanonical(str)
- return b
- }
-
- b.script = append(b.script, opcodes...)
- return b
-}
-
-// canonicalDataSize returns the number of bytes the canonical encoding of the
-// data will take.
-func canonicalDataSize(data []byte) int {
- dataLen := len(data)
-
- // When the data consists of a single number that can be represented
- // by one of the "small integer" opcodes, that opcode will be instead
- // of a data push opcode followed by the number.
- if dataLen == 0 {
- return 1
- } else if dataLen == 1 && data[0] <= 16 {
- return 1
- } else if dataLen == 1 && data[0] == 0x81 {
- return 1
- }
-
- if dataLen < OP_PUSHDATA1 {
- return 1 + dataLen
- } else if dataLen <= 0xff {
- return 2 + dataLen
- } else if dataLen <= 0xffff {
- return 3 + dataLen
- }
-
- return 5 + dataLen
-}
-
-// addData is the internal function that actually pushes the passed data to the
-// end of the script. It automatically chooses canonical opcodes depending on
-// the length of the data. A zero length buffer will lead to a push of empty
-// data onto the stack (OP_0). No data limits are enforced with this function.
-func (b *ScriptBuilder) addData(data []byte) *ScriptBuilder {
- dataLen := len(data)
-
- // When the data consists of a single number that can be represented
- // by one of the "small integer" opcodes, use that opcode instead of
- // a data push opcode followed by the number.
- if dataLen == 0 || dataLen == 1 && data[0] == 0 {
- b.script = append(b.script, OP_0)
- return b
- } else if dataLen == 1 && data[0] <= 16 {
- b.script = append(b.script, (OP_1-1)+data[0])
- return b
- } else if dataLen == 1 && data[0] == 0x81 {
- b.script = append(b.script, byte(OP_1NEGATE))
- return b
- }
-
- // Use one of the OP_DATA_# opcodes if the length of the data is small
- // enough so the data push instruction is only a single byte.
- // Otherwise, choose the smallest possible OP_PUSHDATA# opcode that
- // can represent the length of the data.
- if dataLen < OP_PUSHDATA1 {
- b.script = append(b.script, byte((OP_DATA_1-1)+dataLen))
- } else if dataLen <= 0xff {
- b.script = append(b.script, OP_PUSHDATA1, byte(dataLen))
- } else if dataLen <= 0xffff {
- buf := make([]byte, 2)
- binary.LittleEndian.PutUint16(buf, uint16(dataLen))
- b.script = append(b.script, OP_PUSHDATA2)
- b.script = append(b.script, buf...)
- } else {
- buf := make([]byte, 4)
- binary.LittleEndian.PutUint32(buf, uint32(dataLen))
- b.script = append(b.script, OP_PUSHDATA4)
- b.script = append(b.script, buf...)
- }
-
- // Append the actual data.
- b.script = append(b.script, data...)
-
- return b
-}
-
-// AddFullData should not typically be used by ordinary users as it does not
-// include the checks which prevent data pushes larger than the maximum allowed
-// sizes which leads to scripts that can't be executed. This is provided for
-// testing purposes such as regression tests where sizes are intentionally made
-// larger than allowed.
-//
-// Use AddData instead.
-func (b *ScriptBuilder) AddFullData(data []byte) *ScriptBuilder {
- if b.err != nil {
- return b
- }
-
- return b.addData(data)
-}
-
-// AddData pushes the passed data to the end of the script. It automatically
-// chooses canonical opcodes depending on the length of the data. A zero length
-// buffer will lead to a push of empty data onto the stack (OP_0) and any push
-// of data greater than MaxScriptElementSize will not modify the script since
-// that is not allowed by the script engine. Also, the script will not be
-// modified if pushing the data would cause the script to exceed the maximum
-// allowed script engine size.
-func (b *ScriptBuilder) AddData(data []byte) *ScriptBuilder {
- if b.err != nil {
- return b
- }
-
- // Pushes that would cause the script to exceed the largest allowed
- // script size would result in a non-canonical script.
- dataSize := canonicalDataSize(data)
- if len(b.script)+dataSize > MaxScriptSize {
- str := fmt.Sprintf("adding %d bytes of data would exceed the "+
- "maximum allowed canonical script length of %d",
- dataSize, MaxScriptSize)
- b.err = ErrScriptNotCanonical(str)
- return b
- }
-
- // Pushes larger than the max script element size would result in a
- // script that is not canonical.
- dataLen := len(data)
- if dataLen > MaxScriptElementSize {
- str := fmt.Sprintf("adding a data element of %d bytes would "+
- "exceed the maximum allowed script element size of %d",
- dataLen, MaxScriptElementSize)
- b.err = ErrScriptNotCanonical(str)
- return b
- }
-
- return b.addData(data)
-}
-
-// AddInt64 pushes the passed integer to the end of the script. The script will
-// not be modified if pushing the data would cause the script to exceed the
-// maximum allowed script engine size.
-func (b *ScriptBuilder) AddInt64(val int64) *ScriptBuilder {
- if b.err != nil {
- return b
- }
-
- // Pushes that would cause the script to exceed the largest allowed
- // script size would result in a non-canonical script.
- if len(b.script)+1 > MaxScriptSize {
- str := fmt.Sprintf("adding an integer would exceed the "+
- "maximum allow canonical script length of %d",
- MaxScriptSize)
- b.err = ErrScriptNotCanonical(str)
- return b
- }
-
- // Fast path for small integers and OP_1NEGATE.
- if val == 0 {
- b.script = append(b.script, OP_0)
- return b
- }
- if val == -1 || (val >= 1 && val <= 16) {
- b.script = append(b.script, byte((OP_1-1)+val))
- return b
- }
-
- return b.AddData(scriptNum(val).Bytes())
-}
-
-// Reset resets the script so it has no content.
-func (b *ScriptBuilder) Reset() *ScriptBuilder {
- b.script = b.script[0:0]
- b.err = nil
- return b
-}
-
-// Script returns the currently built script. When any errors occurred while
-// building the script, the script will be returned up the point of the first
-// error along with the error.
-func (b *ScriptBuilder) Script() ([]byte, error) {
- return b.script, b.err
-}
-
-// NewScriptBuilder returns a new instance of a script builder. See
-// ScriptBuilder for details.
-func NewScriptBuilder() *ScriptBuilder {
- return &ScriptBuilder{
- script: make([]byte, 0, defaultScriptAlloc),
- }
-}
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