Example of stepping through a script using the txscript API.

example_txscript_step.go

package main

import (
	"encoding/hex"
	"fmt"
	"os"

	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/txscript"
	"github.com/btcsuite/btcd/wire"
)

// createSpendTx generates a basic spending transaction given the passed
// signature and public key scripts.
func createSpendingTx(sigScript, pkScript []byte) (*wire.MsgTx, error) {
	coinbaseTx := wire.NewMsgTx(wire.TxVersion)

	outPoint := wire.NewOutPoint(&chainhash.Hash{}, ^uint32(0))
	txIn := wire.NewTxIn(outPoint, []byte{txscript.OP_0, txscript.OP_0})
	txOut := wire.NewTxOut(0, pkScript)
	coinbaseTx.AddTxIn(txIn)
	coinbaseTx.AddTxOut(txOut)

	spendingTx := wire.NewMsgTx(wire.TxVersion)
	coinbaseTxSha := coinbaseTx.TxHash()
	outPoint = wire.NewOutPoint(&coinbaseTxSha, 0)
	txIn = wire.NewTxIn(outPoint, sigScript)
	txOut = wire.NewTxOut(0, nil)

	spendingTx.AddTxIn(txIn)
	spendingTx.AddTxOut(txOut)

	return spendingTx, nil
}

func main() {
	txscript.SetLogWriter(os.Stdout, "trace")
	sigScript, err := hex.DecodeString("47304402202f7505132be14872581f35d74b759212d9da40482653f1ffa3116c3294a4a51702206adbf347a2240ca41c66522b1a22a41693610b76a8e7770645dc721d1635854f0143410479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8ac")
	if err != nil {
		fmt.Println(err)
		return
	}
	pkScript, err := hex.DecodeString("a91431edc23bdafda4639e669f89ad6b2318dd79d03287")
	if err != nil {
		fmt.Println(err)
		return
	}

	tx, err := createSpendingTx(sigScript, pkScript)
	if err != nil {
		fmt.Println(err)
		return
	}

	vm, err := txscript.NewEngine(pkScript, tx, 0, txscript.StandardVerifyFlags, nil)
	if err != nil {
		fmt.Println(err)
		return
	}

	if err := vm.Execute(); err != nil {
		fmt.Println(err)
		return
	}

	// Alternatively, you can comment out the execute above, step through
	// it manually, and examine the stack.
	/*
		done := false
		for !done {
			// Display the instruction and associated data at the program
			// counter.
			dis, err := vm.DisasmPC()
			if err != nil {
				fmt.Printf("stepping (%v)\n", err)
			}
			fmt.Printf("stepping %v\n", dis)

			// Execute the next instruction.
			done, err = vm.Step()
			if err != nil {
				fmt.Println(err)
				return
			}

			// Display the stacks.
			dataStack := vm.GetStack()
			if len(dataStack) != 0 {
				fmt.Println("Data stack:")
				spew.Dump(dataStack)
				fmt.Println("")
			}
			altStack := vm.GetAltStack()
			if len(altStack) != 0 {
				fmt.Println("Alternate stack:")
				spew.Dump(altStack)
				fmt.Println("")
			}
		}
	*/
}