neoneo-go/pkg/vm/cli/cli.go

829 lines
22 KiB
Go

package cli
import (
"bytes"
"crypto/elliptic"
"encoding/base64"
"encoding/hex"
"encoding/json"
"errors"
"fmt"
"io"
"math/big"
"os"
"strconv"
"strings"
"text/tabwriter"
"github.com/chzyer/readline"
"github.com/kballard/go-shellquote"
"github.com/nspcc-dev/neo-go/pkg/compiler"
"github.com/nspcc-dev/neo-go/pkg/config"
"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
"github.com/nspcc-dev/neo-go/pkg/encoding/address"
"github.com/nspcc-dev/neo-go/pkg/encoding/bigint"
"github.com/nspcc-dev/neo-go/pkg/smartcontract/callflag"
"github.com/nspcc-dev/neo-go/pkg/smartcontract/manifest"
"github.com/nspcc-dev/neo-go/pkg/util"
"github.com/nspcc-dev/neo-go/pkg/util/slice"
"github.com/nspcc-dev/neo-go/pkg/vm"
"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
"github.com/urfave/cli"
)
const (
vmKey = "vm"
manifestKey = "manifest"
exitFuncKey = "exitFunc"
readlineInstanceKey = "readlineKey"
printLogoKey = "printLogoKey"
boolType = "bool"
boolFalse = "false"
boolTrue = "true"
intType = "int"
stringType = "string"
)
var commands = []cli.Command{
{
Name: "exit",
Usage: "Exit the VM prompt",
Description: "Exit the VM prompt",
Action: handleExit,
},
{
Name: "ip",
Usage: "Show current instruction",
Description: "Show current instruction",
Action: handleIP,
},
{
Name: "break",
Usage: "Place a breakpoint",
UsageText: `break <ip>`,
Description: `break <ip>
<ip> is mandatory parameter, example:
> break 12`,
Action: handleBreak,
},
{
Name: "estack",
Usage: "Show evaluation stack contents",
Description: "Show evaluation stack contents",
Action: handleXStack,
},
{
Name: "istack",
Usage: "Show invocation stack contents",
Description: "Show invocation stack contents",
Action: handleXStack,
},
{
Name: "sslot",
Usage: "Show static slot contents",
Description: "Show static slot contents",
Action: handleSlots,
},
{
Name: "lslot",
Usage: "Show local slot contents",
Description: "Show local slot contents",
Action: handleSlots,
},
{
Name: "aslot",
Usage: "Show arguments slot contents",
Description: "Show arguments slot contents",
Action: handleSlots,
},
{
Name: "loadnef",
Usage: "Load a NEF-consistent script into the VM",
UsageText: `loadnef <file> <manifest>`,
Description: `loadnef <file> <manifest>
both parameters are mandatory, example:
> loadnef /path/to/script.nef /path/to/manifest.json`,
Action: handleLoadNEF,
},
{
Name: "loadbase64",
Usage: "Load a base64-encoded script string into the VM",
UsageText: `loadbase64 <string>`,
Description: `loadbase64 <string>
<string> is mandatory parameter, example:
> loadbase64 AwAQpdToAAAADBQV9ehtQR1OrVZVhtHtoUHRfoE+agwUzmFvf3Rhfg/EuAVYOvJgKiON9j8TwAwIdHJhbnNmZXIMFDt9NxHG8Mz5sdypA9G/odiW8SOMQWJ9W1I4`,
Action: handleLoadBase64,
},
{
Name: "loadhex",
Usage: "Load a hex-encoded script string into the VM",
UsageText: `loadhex <string>`,
Description: `loadhex <string>
<string> is mandatory parameter, example:
> loadhex 0c0c48656c6c6f20776f726c6421`,
Action: handleLoadHex,
},
{
Name: "loadgo",
Usage: "Compile and load a Go file with the manifest into the VM",
UsageText: `loadgo <file>`,
Description: `loadgo <file>
<file> is mandatory parameter, example:
> loadgo /path/to/file.go`,
Action: handleLoadGo,
},
{
Name: "reset",
Usage: "Unload compiled script from the VM",
Action: handleReset,
},
{
Name: "parse",
Usage: "Parse provided argument and convert it into other possible formats",
UsageText: `parse <arg>`,
Description: `parse <arg>
<arg> is an argument which is tried to be interpreted as an item of different types
and converted to other formats. Strings are escaped and output in quotes.`,
Action: handleParse,
},
{
Name: "run",
Usage: "Execute the current loaded script",
UsageText: `run [<method> [<parameter>...]]`,
Description: `run [<method> [<parameter>...]]
<method> is a contract method, specified in manifest. It can be '_' which will push
parameters onto the stack and execute from the current offset.
<parameter> is a parameter (can be repeated multiple times) that can be specified
as <type>:<value>, where type can be:
'` + boolType + `': supports '` + boolFalse + `' and '` + boolTrue + `' values
'` + intType + `': supports integers as values
'` + stringType + `': supports strings as values (that are pushed as a byte array
values to the stack)
or can be just <value>, for which the type will be detected automatically
following these rules: '` + boolTrue + `' and '` + boolFalse + `' are treated as respective
boolean values, everything that can be converted to integer is treated as
integer and everything else is treated like a string.
Example:
> run put ` + stringType + `:"Something to put"`,
Action: handleRun,
},
{
Name: "cont",
Usage: "Continue execution of the current loaded script",
Description: "Continue execution of the current loaded script",
Action: handleCont,
},
{
Name: "step",
Usage: "Step (n) instruction in the program",
UsageText: `step [<n>]`,
Description: `step [<n>]
<n> is optional parameter to specify number of instructions to run, example:
> step 10`,
Action: handleStep,
},
{
Name: "stepinto",
Usage: "Stepinto instruction to take in the debugger",
Description: `Usage: stepInto
example:
> stepinto`,
Action: handleStepInto,
},
{
Name: "stepout",
Usage: "Stepout instruction to take in the debugger",
Description: `stepOut
example:
> stepout`,
Action: handleStepOut,
},
{
Name: "stepover",
Usage: "Stepover instruction to take in the debugger",
Description: `stepOver
example:
> stepover`,
Action: handleStepOver,
},
{
Name: "ops",
Usage: "Dump opcodes of the current loaded program",
Description: "Dump opcodes of the current loaded program",
Action: handleOps,
},
}
var completer *readline.PrefixCompleter
func init() {
var pcItems []readline.PrefixCompleterInterface
for _, c := range commands {
if !c.Hidden {
var flagsItems []readline.PrefixCompleterInterface
for _, f := range c.Flags {
names := strings.SplitN(f.GetName(), ", ", 2) // only long name will be offered
flagsItems = append(flagsItems, readline.PcItem("--"+names[0]))
}
pcItems = append(pcItems, readline.PcItem(c.Name, flagsItems...))
}
}
completer = readline.NewPrefixCompleter(pcItems...)
}
// Various errors.
var (
ErrMissingParameter = errors.New("missing argument")
ErrInvalidParameter = errors.New("can't parse argument")
)
// VMCLI object for interacting with the VM.
type VMCLI struct {
vm *vm.VM
shell *cli.App
}
// New returns a new VMCLI object.
func New() *VMCLI {
return NewWithConfig(true, os.Exit, &readline.Config{
Prompt: "\033[32mNEO-GO-VM >\033[0m ", // green prompt ^^
})
}
// NewWithConfig returns new VMCLI instance using provided config.
func NewWithConfig(printLogotype bool, onExit func(int), c *readline.Config) *VMCLI {
if c.AutoComplete == nil {
// Autocomplete commands/flags on TAB.
c.AutoComplete = completer
}
l, err := readline.NewEx(c)
if err != nil {
panic(err)
}
ctl := cli.NewApp()
ctl.Name = "VM CLI"
// Note: need to set empty `ctl.HelpName` and `ctl.UsageText`, otherwise
// `filepath.Base(os.Args[0])` will be used which is `neo-go`.
ctl.HelpName = ""
ctl.UsageText = ""
ctl.Writer = l.Stdout()
ctl.ErrWriter = l.Stderr()
ctl.Version = config.Version
ctl.Usage = "Official VM CLI for Neo-Go"
// Override default error handler in order not to exit on error.
ctl.ExitErrHandler = func(context *cli.Context, err error) {}
ctl.Commands = commands
vmcli := VMCLI{
vm: vm.New(),
shell: ctl,
}
vmcli.shell.Metadata = map[string]interface{}{
vmKey: vmcli.vm,
manifestKey: new(manifest.Manifest),
exitFuncKey: onExit,
readlineInstanceKey: l,
printLogoKey: printLogotype,
}
changePrompt(vmcli.shell)
return &vmcli
}
func getExitFuncFromContext(app *cli.App) func(int) {
return app.Metadata[exitFuncKey].(func(int))
}
func getReadlineInstanceFromContext(app *cli.App) *readline.Instance {
return app.Metadata[readlineInstanceKey].(*readline.Instance)
}
func getVMFromContext(app *cli.App) *vm.VM {
return app.Metadata[vmKey].(*vm.VM)
}
func setVMInContext(app *cli.App, v *vm.VM) {
old := getVMFromContext(app)
*old = *v
}
func getManifestFromContext(app *cli.App) *manifest.Manifest {
return app.Metadata[manifestKey].(*manifest.Manifest)
}
func getPrintLogoFromContext(app *cli.App) bool {
return app.Metadata[printLogoKey].(bool)
}
func setManifestInContext(app *cli.App, m *manifest.Manifest) {
old := getManifestFromContext(app)
*old = *m
}
func checkVMIsReady(app *cli.App) bool {
v := getVMFromContext(app)
if v == nil || !v.Ready() {
writeErr(app.Writer, errors.New("VM is not ready: no program loaded"))
return false
}
return true
}
func handleExit(c *cli.Context) error {
l := getReadlineInstanceFromContext(c.App)
_ = l.Close()
exit := getExitFuncFromContext(c.App)
fmt.Fprintln(c.App.Writer, "Bye!")
exit(0)
return nil
}
func handleIP(c *cli.Context) error {
if !checkVMIsReady(c.App) {
return nil
}
v := getVMFromContext(c.App)
ctx := v.Context()
if ctx.NextIP() < ctx.LenInstr() {
ip, opcode := v.Context().NextInstr()
fmt.Fprintf(c.App.Writer, "instruction pointer at %d (%s)\n", ip, opcode)
} else {
fmt.Fprintln(c.App.Writer, "execution has finished")
}
return nil
}
func handleBreak(c *cli.Context) error {
if !checkVMIsReady(c.App) {
return nil
}
v := getVMFromContext(c.App)
args := c.Args()
if len(args) != 1 {
return fmt.Errorf("%w: <ip>", ErrMissingParameter)
}
n, err := strconv.Atoi(args[0])
if err != nil {
return fmt.Errorf("%w: %s", ErrInvalidParameter, err)
}
v.AddBreakPoint(n)
fmt.Fprintf(c.App.Writer, "breakpoint added at instruction %d\n", n)
return nil
}
func handleXStack(c *cli.Context) error {
v := getVMFromContext(c.App)
var stackDump string
switch c.Command.Name {
case "estack":
stackDump = v.DumpEStack()
case "istack":
stackDump = v.DumpIStack()
default:
return errors.New("unknown stack")
}
fmt.Fprintln(c.App.Writer, stackDump)
return nil
}
func handleSlots(c *cli.Context) error {
v := getVMFromContext(c.App)
vmCtx := v.Context()
if vmCtx == nil {
return errors.New("no program loaded")
}
var rawSlot string
switch c.Command.Name {
case "sslot":
rawSlot = vmCtx.DumpStaticSlot()
case "lslot":
rawSlot = vmCtx.DumpLocalSlot()
case "aslot":
rawSlot = vmCtx.DumpArgumentsSlot()
default:
return errors.New("unknown slot")
}
fmt.Fprintln(c.App.Writer, rawSlot)
return nil
}
func handleLoadNEF(c *cli.Context) error {
v := getVMFromContext(c.App)
args := c.Args()
if len(args) < 2 {
return fmt.Errorf("%w: <file> <manifest>", ErrMissingParameter)
}
if err := v.LoadFileWithFlags(args[0], callflag.All); err != nil {
return fmt.Errorf("failed to read nef: %w", err)
}
m, err := getManifestFromFile(args[1])
if err != nil {
return fmt.Errorf("failed to read manifest: %w", err)
}
fmt.Fprintf(c.App.Writer, "READY: loaded %d instructions\n", v.Context().LenInstr())
setManifestInContext(c.App, m)
changePrompt(c.App)
return nil
}
func handleLoadBase64(c *cli.Context) error {
v := getVMFromContext(c.App)
args := c.Args()
if len(args) < 1 {
return fmt.Errorf("%w: <string>", ErrMissingParameter)
}
b, err := base64.StdEncoding.DecodeString(args[0])
if err != nil {
return fmt.Errorf("%w: %s", ErrInvalidParameter, err)
}
v.LoadWithFlags(b, callflag.All)
fmt.Fprintf(c.App.Writer, "READY: loaded %d instructions\n", v.Context().LenInstr())
changePrompt(c.App)
return nil
}
func handleLoadHex(c *cli.Context) error {
v := getVMFromContext(c.App)
args := c.Args()
if len(args) < 1 {
return fmt.Errorf("%w: <string>", ErrMissingParameter)
}
b, err := hex.DecodeString(args[0])
if err != nil {
return fmt.Errorf("%w: %s", ErrInvalidParameter, err)
}
v.LoadWithFlags(b, callflag.All)
fmt.Fprintf(c.App.Writer, "READY: loaded %d instructions\n", v.Context().LenInstr())
changePrompt(c.App)
return nil
}
func handleLoadGo(c *cli.Context) error {
v := getVMFromContext(c.App)
args := c.Args()
if len(args) < 1 {
return fmt.Errorf("%w: <file>", ErrMissingParameter)
}
name := strings.TrimSuffix(args[0], ".go")
b, di, err := compiler.CompileWithOptions(args[0], nil, &compiler.Options{Name: name})
if err != nil {
return fmt.Errorf("failed to compile: %w", err)
}
// Don't perform checks, just load.
m, err := di.ConvertToManifest(&compiler.Options{})
if err != nil {
return fmt.Errorf("can't create manifest: %w", err)
}
setManifestInContext(c.App, m)
v.LoadWithFlags(b.Script, callflag.All)
fmt.Fprintf(c.App.Writer, "READY: loaded %d instructions\n", v.Context().LenInstr())
changePrompt(c.App)
return nil
}
func handleReset(c *cli.Context) error {
setVMInContext(c.App, vm.New())
changePrompt(c.App)
return nil
}
func getManifestFromFile(name string) (*manifest.Manifest, error) {
bs, err := os.ReadFile(name)
if err != nil {
return nil, fmt.Errorf("%w: can't read manifest", ErrInvalidParameter)
}
var m manifest.Manifest
if err := json.Unmarshal(bs, &m); err != nil {
return nil, fmt.Errorf("%w: can't unmarshal manifest", ErrInvalidParameter)
}
return &m, nil
}
func handleRun(c *cli.Context) error {
v := getVMFromContext(c.App)
m := getManifestFromContext(c.App)
args := c.Args()
if len(args) != 0 {
var (
params []stackitem.Item
offset int
err error
runCurrent = args[0] != "_"
)
params, err = parseArgs(args[1:])
if err != nil {
return err
}
if runCurrent {
md := m.ABI.GetMethod(args[0], len(params))
if md == nil {
return fmt.Errorf("%w: method not found", ErrInvalidParameter)
}
offset = md.Offset
}
for i := len(params) - 1; i >= 0; i-- {
v.Estack().PushVal(params[i])
}
if runCurrent {
if !v.Ready() {
return errors.New("no program loaded")
}
v.Context().Jump(offset)
if initMD := m.ABI.GetMethod(manifest.MethodInit, 0); initMD != nil {
v.Call(initMD.Offset)
}
}
}
runVMWithHandling(c)
changePrompt(c.App)
return nil
}
// runVMWithHandling runs VM with handling errors and additional state messages.
func runVMWithHandling(c *cli.Context) {
v := getVMFromContext(c.App)
err := v.Run()
if err != nil {
writeErr(c.App.ErrWriter, err)
}
var message string
switch {
case v.HasFailed():
message = "" // the error will be printed on return
case v.HasHalted():
message = v.DumpEStack()
case v.AtBreakpoint():
ctx := v.Context()
if ctx.NextIP() < ctx.LenInstr() {
i, op := ctx.NextInstr()
message = fmt.Sprintf("at breakpoint %d (%s)", i, op)
} else {
message = "execution has finished"
}
}
if message != "" {
fmt.Fprintln(c.App.Writer, message)
}
}
func handleCont(c *cli.Context) error {
if !checkVMIsReady(c.App) {
return nil
}
runVMWithHandling(c)
changePrompt(c.App)
return nil
}
func handleStep(c *cli.Context) error {
var (
n = 1
err error
)
if !checkVMIsReady(c.App) {
return nil
}
v := getVMFromContext(c.App)
args := c.Args()
if len(args) > 0 {
n, err = strconv.Atoi(args[0])
if err != nil {
return fmt.Errorf("%w: %s", ErrInvalidParameter, err)
}
}
v.AddBreakPointRel(n)
runVMWithHandling(c)
changePrompt(c.App)
return nil
}
func handleStepInto(c *cli.Context) error {
return handleStepType(c, "into")
}
func handleStepOut(c *cli.Context) error {
return handleStepType(c, "out")
}
func handleStepOver(c *cli.Context) error {
return handleStepType(c, "over")
}
func handleStepType(c *cli.Context, stepType string) error {
if !checkVMIsReady(c.App) {
return nil
}
v := getVMFromContext(c.App)
var err error
switch stepType {
case "into":
err = v.StepInto()
case "out":
err = v.StepOut()
case "over":
err = v.StepOver()
}
if err != nil {
return err
}
_ = handleIP(c)
changePrompt(c.App)
return nil
}
func handleOps(c *cli.Context) error {
if !checkVMIsReady(c.App) {
return nil
}
v := getVMFromContext(c.App)
out := bytes.NewBuffer(nil)
v.PrintOps(out)
fmt.Fprintln(c.App.Writer, out.String())
return nil
}
func changePrompt(app *cli.App) {
v := getVMFromContext(app)
l := getReadlineInstanceFromContext(app)
if v.Ready() && v.Context().NextIP() >= 0 && v.Context().NextIP() < v.Context().LenInstr() {
l.SetPrompt(fmt.Sprintf("\033[32mNEO-GO-VM %d >\033[0m ", v.Context().NextIP()))
} else {
l.SetPrompt("\033[32mNEO-GO-VM >\033[0m ")
}
}
// Run waits for user input from Stdin and executes the passed command.
func (c *VMCLI) Run() error {
if getPrintLogoFromContext(c.shell) {
printLogo(c.shell.Writer)
}
l := getReadlineInstanceFromContext(c.shell)
for {
line, err := l.Readline()
if errors.Is(err, io.EOF) || errors.Is(err, readline.ErrInterrupt) {
return nil // OK, stop execution.
}
if err != nil {
return fmt.Errorf("failed to read input: %w", err) // Critical error, stop execution.
}
args, err := shellquote.Split(line)
if err != nil {
writeErr(c.shell.ErrWriter, fmt.Errorf("failed to parse arguments: %w", err))
continue // Not a critical error, continue execution.
}
err = c.shell.Run(append([]string{"vm"}, args...))
if err != nil {
writeErr(c.shell.ErrWriter, err) // Various command/flags parsing errors and execution errors.
}
}
}
func handleParse(c *cli.Context) error {
res, err := Parse(c.Args())
if err != nil {
return err
}
fmt.Fprintln(c.App.Writer, res)
return nil
}
// Parse converts it's argument to other formats.
func Parse(args []string) (string, error) {
if len(args) < 1 {
return "", ErrMissingParameter
}
arg := args[0]
buf := bytes.NewBuffer(nil)
if val, err := strconv.ParseInt(arg, 10, 64); err == nil {
bs := bigint.ToBytes(big.NewInt(val))
buf.WriteString(fmt.Sprintf("Integer to Hex\t%s\n", hex.EncodeToString(bs)))
buf.WriteString(fmt.Sprintf("Integer to Base64\t%s\n", base64.StdEncoding.EncodeToString(bs)))
}
noX := strings.TrimPrefix(arg, "0x")
if rawStr, err := hex.DecodeString(noX); err == nil {
if val, err := util.Uint160DecodeBytesBE(rawStr); err == nil {
buf.WriteString(fmt.Sprintf("BE ScriptHash to Address\t%s\n", address.Uint160ToString(val)))
buf.WriteString(fmt.Sprintf("LE ScriptHash to Address\t%s\n", address.Uint160ToString(val.Reverse())))
}
if pub, err := keys.NewPublicKeyFromBytes(rawStr, elliptic.P256()); err == nil {
sh := pub.GetScriptHash()
buf.WriteString(fmt.Sprintf("Public key to BE ScriptHash\t%s\n", sh))
buf.WriteString(fmt.Sprintf("Public key to LE ScriptHash\t%s\n", sh.Reverse()))
buf.WriteString(fmt.Sprintf("Public key to Address\t%s\n", address.Uint160ToString(sh)))
}
buf.WriteString(fmt.Sprintf("Hex to String\t%s\n", fmt.Sprintf("%q", string(rawStr))))
buf.WriteString(fmt.Sprintf("Hex to Integer\t%s\n", bigint.FromBytes(rawStr)))
buf.WriteString(fmt.Sprintf("Swap Endianness\t%s\n", hex.EncodeToString(slice.CopyReverse(rawStr))))
}
if addr, err := address.StringToUint160(arg); err == nil {
buf.WriteString(fmt.Sprintf("Address to BE ScriptHash\t%s\n", addr))
buf.WriteString(fmt.Sprintf("Address to LE ScriptHash\t%s\n", addr.Reverse()))
buf.WriteString(fmt.Sprintf("Address to Base64 (BE)\t%s\n", base64.StdEncoding.EncodeToString(addr.BytesBE())))
buf.WriteString(fmt.Sprintf("Address to Base64 (LE)\t%s\n", base64.StdEncoding.EncodeToString(addr.BytesLE())))
}
if rawStr, err := base64.StdEncoding.DecodeString(arg); err == nil {
buf.WriteString(fmt.Sprintf("Base64 to String\t%s\n", fmt.Sprintf("%q", string(rawStr))))
buf.WriteString(fmt.Sprintf("Base64 to BigInteger\t%s\n", bigint.FromBytes(rawStr)))
if u, err := util.Uint160DecodeBytesBE(rawStr); err == nil {
buf.WriteString(fmt.Sprintf("Base64 to BE ScriptHash\t%s\n", u.StringBE()))
buf.WriteString(fmt.Sprintf("Base64 to LE ScriptHash\t%s\n", u.StringLE()))
buf.WriteString(fmt.Sprintf("Base64 to Address (BE)\t%s\n", address.Uint160ToString(u)))
buf.WriteString(fmt.Sprintf("Base64 to Address (LE)\t%s\n", address.Uint160ToString(u.Reverse())))
}
}
buf.WriteString(fmt.Sprintf("String to Hex\t%s\n", hex.EncodeToString([]byte(arg))))
buf.WriteString(fmt.Sprintf("String to Base64\t%s\n", base64.StdEncoding.EncodeToString([]byte(arg))))
out := buf.Bytes()
buf = bytes.NewBuffer(nil)
w := tabwriter.NewWriter(buf, 0, 4, 4, '\t', 0)
if _, err := w.Write(out); err != nil {
return "", err
}
if err := w.Flush(); err != nil {
return "", err
}
return buf.String(), nil
}
func parseArgs(args []string) ([]stackitem.Item, error) {
items := make([]stackitem.Item, len(args))
for i, arg := range args {
var typ, value string
typeAndVal := strings.Split(arg, ":")
if len(typeAndVal) < 2 {
if typeAndVal[0] == boolFalse || typeAndVal[0] == boolTrue {
typ = boolType
} else if _, err := strconv.Atoi(typeAndVal[0]); err == nil {
typ = intType
} else {
typ = stringType
}
value = typeAndVal[0]
} else {
typ = typeAndVal[0]
value = typeAndVal[1]
}
switch typ {
case boolType:
if value == boolFalse {
items[i] = stackitem.NewBool(false)
} else if value == boolTrue {
items[i] = stackitem.NewBool(true)
} else {
return nil, fmt.Errorf("%w: invalid bool value", ErrInvalidParameter)
}
case intType:
val, err := strconv.ParseInt(value, 10, 64)
if err != nil {
return nil, fmt.Errorf("%w: invalid integer value", ErrInvalidParameter)
}
items[i] = stackitem.NewBigInteger(big.NewInt(val))
case stringType:
items[i] = stackitem.NewByteArray([]byte(value))
}
}
return items, nil
}
const logo = `
_ ____________ __________ _ ____ ___
/ | / / ____/ __ \ / ____/ __ \ | | / / |/ /
/ |/ / __/ / / / /_____/ / __/ / / /____| | / / /|_/ /
/ /| / /___/ /_/ /_____/ /_/ / /_/ /_____/ |/ / / / /
/_/ |_/_____/\____/ \____/\____/ |___/_/ /_/
`
func printLogo(w io.Writer) {
fmt.Fprint(w, logo)
fmt.Fprintln(w)
fmt.Fprintln(w)
fmt.Fprintln(w)
}
func writeErr(w io.Writer, err error) {
fmt.Fprintf(w, "Error: %s\n", err)
}