waveterm/pkg/remote/remote.go

package remote

import (
	"bytes"
	"context"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/creack/pty"
	"github.com/google/uuid"
	"github.com/scripthaus-dev/mshell/pkg/base"
	"github.com/scripthaus-dev/mshell/pkg/packet"
	"github.com/scripthaus-dev/mshell/pkg/shexec"
	"github.com/scripthaus-dev/sh2-server/pkg/sstore"
)

const RemoteTypeMShell = "mshell"
const DefaultTermRows = 25
const DefaultTermCols = 80
const DefaultTerm = "xterm-256color"
const DefaultMaxPtySize = 1024 * 1024

const MShellServerCommand = `
PATH=$PATH:~/.mshell;
which mshell > /dev/null;
if [[ "$?" -ne 0 ]]
then
  printf "\n##N{\"type\": \"init\", \"notfound\": true, \"uname\": \"%s | %s\"}\n" "$(uname -s)" "$(uname -m)"
else
  mshell --server
fi
`

const (
	StatusInit         = "init"
	StatusConnected    = "connected"
	StatusDisconnected = "disconnected"
	StatusError        = "error"
)

var GlobalStore *Store

type Store struct {
	Lock *sync.Mutex
	Map  map[string]*MShellProc // key=remoteid
}

type RemoteRuntimeState struct {
	RemoteType          string              `json:"remotetype"`
	RemoteId            string              `json:"remoteid"`
	PhysicalId          string              `json:"physicalremoteid"`
	RemoteAlias         string              `json:"remotealias,omitempty"`
	RemoteCanonicalName string              `json:"remotecanonicalname"`
	RemoteVars          map[string]string   `json:"remotevars"`
	Status              string              `json:"status"`
	ErrorStr            string              `json:"errorstr,omitempty"`
	DefaultState        *sstore.RemoteState `json:"defaultstate"`
	ConnectMode         string              `json:"connectmode"`
}

func (state RemoteRuntimeState) IsConnected() bool {
	return state.Status == StatusConnected
}

func (state RemoteRuntimeState) GetBaseDisplayName() string {
	if state.RemoteAlias != "" {
		return state.RemoteAlias
	}
	return state.RemoteCanonicalName
}

func (state RemoteRuntimeState) GetDisplayName(rptr *sstore.RemotePtrType) string {
	name := state.GetBaseDisplayName()
	if rptr == nil {
		return name
	}
	if rptr.Name != "" {
		name = name + ":" + rptr.Name
	}
	if rptr.OwnerId != "" {
		name = "@" + rptr.OwnerId + ":" + name
	}
	return name
}

type MShellProc struct {
	Lock   *sync.Mutex
	Remote *sstore.RemoteType

	// runtime
	Status         string
	ServerProc     *shexec.ClientProc
	UName          string
	Err            error
	ControllingPty *os.File

	RunningCmds []base.CommandKey
}

func LoadRemotes(ctx context.Context) error {
	GlobalStore = &Store{
		Lock: &sync.Mutex{},
		Map:  make(map[string]*MShellProc),
	}
	allRemotes, err := sstore.GetAllRemotes(ctx)
	if err != nil {
		return err
	}
	for _, remote := range allRemotes {
		msh := MakeMShell(remote)
		GlobalStore.Map[remote.RemoteId] = msh
		if remote.ConnectMode == sstore.ConnectModeStartup {
			go msh.Launch()
		}
	}
	return nil
}

func GetRemoteByName(name string) *MShellProc {
	GlobalStore.Lock.Lock()
	defer GlobalStore.Lock.Unlock()
	for _, msh := range GlobalStore.Map {
		if msh.Remote.RemoteAlias == name || msh.Remote.GetName() == name {
			return msh
		}
	}
	return nil
}

func GetRemoteById(remoteId string) *MShellProc {
	GlobalStore.Lock.Lock()
	defer GlobalStore.Lock.Unlock()
	return GlobalStore.Map[remoteId]
}

func ResolveRemoteRef(remoteRef string) *RemoteRuntimeState {
	GlobalStore.Lock.Lock()
	defer GlobalStore.Lock.Unlock()

	_, err := uuid.Parse(remoteRef)
	if err == nil {
		msh := GlobalStore.Map[remoteRef]
		if msh != nil {
			state := msh.GetRemoteRuntimeState()
			return &state
		}
		return nil
	}
	for _, msh := range GlobalStore.Map {
		if msh.Remote.RemoteAlias == remoteRef || msh.Remote.RemoteCanonicalName == remoteRef {
			state := msh.GetRemoteRuntimeState()
			return &state
		}
	}
	return nil
}

func unquoteDQBashString(str string) (string, bool) {
	if len(str) < 2 {
		return str, false
	}
	if str[0] != '"' || str[len(str)-1] != '"' {
		return str, false
	}
	rtn := make([]byte, 0, len(str)-2)
	for idx := 1; idx < len(str)-1; idx++ {
		ch := str[idx]
		if ch == '"' {
			return str, false
		}
		if ch == '\\' {
			if idx == len(str)-2 {
				return str, false
			}
			nextCh := str[idx+1]
			if nextCh == '\n' {
				idx++
				continue
			}
			if nextCh == '$' || nextCh == '"' || nextCh == '\\' || nextCh == '`' {
				idx++
				rtn = append(rtn, nextCh)
				continue
			}
			rtn = append(rtn, '\\')
			continue
		} else {
			rtn = append(rtn, ch)
		}
	}
	return string(rtn), true
}

func makeShortHost(host string) string {
	dotIdx := strings.Index(host, ".")
	if dotIdx == -1 {
		return host
	}
	return host[0:dotIdx]
}

func (proc *MShellProc) GetRemoteRuntimeState() RemoteRuntimeState {
	proc.Lock.Lock()
	defer proc.Lock.Unlock()
	state := RemoteRuntimeState{
		RemoteType:          proc.Remote.RemoteType,
		RemoteId:            proc.Remote.RemoteId,
		RemoteAlias:         proc.Remote.RemoteAlias,
		RemoteCanonicalName: proc.Remote.RemoteCanonicalName,
		PhysicalId:          proc.Remote.PhysicalId,
		Status:              proc.Status,
		ConnectMode:         proc.Remote.ConnectMode,
	}
	if proc.Err != nil {
		state.ErrorStr = proc.Err.Error()
	}
	local := (proc.Remote.SSHOpts == nil || proc.Remote.SSHOpts.Local)
	vars := make(map[string]string)
	vars["user"] = proc.Remote.RemoteUser
	vars["bestuser"] = vars["user"]
	vars["host"] = proc.Remote.RemoteHost
	vars["shorthost"] = makeShortHost(proc.Remote.RemoteHost)
	vars["alias"] = proc.Remote.RemoteAlias
	vars["cname"] = proc.Remote.RemoteCanonicalName
	vars["physicalid"] = proc.Remote.PhysicalId
	vars["remoteid"] = proc.Remote.RemoteId
	vars["status"] = proc.Status
	vars["type"] = proc.Remote.RemoteType
	if proc.Remote.RemoteSudo {
		vars["sudo"] = "1"
	}
	if local {
		vars["local"] = "1"
	}
	if proc.ServerProc != nil && proc.ServerProc.InitPk != nil {
		state.DefaultState = &sstore.RemoteState{
			Cwd:  proc.ServerProc.InitPk.Cwd,
			Env0: proc.ServerProc.InitPk.Env0,
		}
		vars["home"] = proc.ServerProc.InitPk.HomeDir
		vars["remoteuser"] = proc.ServerProc.InitPk.User
		vars["bestuser"] = vars["remoteuser"]
		vars["remotehost"] = proc.ServerProc.InitPk.HostName
		vars["remoteshorthost"] = makeShortHost(proc.ServerProc.InitPk.HostName)
		vars["besthost"] = vars["remotehost"]
		vars["bestshorthost"] = vars["remoteshorthost"]
	}
	if local && proc.Remote.RemoteSudo {
		vars["bestuser"] = "sudo"
	} else if proc.Remote.RemoteSudo {
		vars["bestuser"] = "sudo@" + vars["bestuser"]
	}
	if local {
		vars["bestname"] = vars["bestuser"] + "@local"
		vars["bestshortname"] = vars["bestuser"] + "@local"
	} else {
		vars["bestname"] = vars["bestuser"] + "@" + vars["besthost"]
		vars["bestshortname"] = vars["bestuser"] + "@" + vars["bestshorthost"]
	}
	state.RemoteVars = vars
	return state
}

func (msh *MShellProc) NotifyUpdate() {
	rstate := msh.GetRemoteRuntimeState()
	update := &sstore.ModelUpdate{Remote: rstate}
	sstore.MainBus.SendUpdate("", update)
}

func GetAllRemoteRuntimeState() []RemoteRuntimeState {
	GlobalStore.Lock.Lock()
	defer GlobalStore.Lock.Unlock()

	var rtn []RemoteRuntimeState
	for _, proc := range GlobalStore.Map {
		state := proc.GetRemoteRuntimeState()
		rtn = append(rtn, state)
	}
	return rtn
}

func GetDefaultRemoteStateById(remoteId string) (*sstore.RemoteState, error) {
	remote := GetRemoteById(remoteId)
	if remote == nil {
		return nil, fmt.Errorf("remote not found")
	}
	if !remote.IsConnected() {
		return nil, fmt.Errorf("remote not connected")
	}
	state := remote.GetDefaultState()
	if state == nil {
		return nil, fmt.Errorf("could not get default remote state")
	}
	return state, nil
}

func MakeMShell(r *sstore.RemoteType) *MShellProc {
	rtn := &MShellProc{Lock: &sync.Mutex{}, Remote: r, Status: StatusInit}
	return rtn
}

func convertSSHOpts(opts *sstore.SSHOpts) shexec.SSHOpts {
	if opts == nil || opts.Local {
		opts = &sstore.SSHOpts{}
	}
	return shexec.SSHOpts{
		SSHHost:     opts.SSHHost,
		SSHOptsStr:  opts.SSHOptsStr,
		SSHIdentity: opts.SSHIdentity,
		SSHUser:     opts.SSHUser,
	}
}

func (msh *MShellProc) addControllingTty(ecmd *exec.Cmd) (*os.File, error) {
	msh.Lock.Lock()
	defer msh.Lock.Unlock()

	cmdPty, cmdTty, err := pty.Open()
	if err != nil {
		return nil, err
	}
	msh.ControllingPty = cmdPty
	ecmd.ExtraFiles = append(ecmd.ExtraFiles, cmdTty)
	if ecmd.SysProcAttr == nil {
		ecmd.SysProcAttr = &syscall.SysProcAttr{}
	}
	ecmd.SysProcAttr.Setsid = true
	ecmd.SysProcAttr.Setctty = true
	ecmd.SysProcAttr.Ctty = len(ecmd.ExtraFiles) + 3 - 1
	return cmdPty, nil
}

func (msh *MShellProc) setErrorStatus(err error) {
	msh.Lock.Lock()
	defer msh.Lock.Unlock()
	msh.Status = StatusError
	msh.Err = err
}

func (msh *MShellProc) getRemoteCopy() sstore.RemoteType {
	msh.Lock.Lock()
	defer msh.Lock.Unlock()
	return *msh.Remote
}

func (msh *MShellProc) Launch() {
	remote := msh.getRemoteCopy()
	ecmd := convertSSHOpts(remote.SSHOpts).MakeSSHExecCmd(MShellServerCommand)
	cmdPty, err := msh.addControllingTty(ecmd)
	if err != nil {
		msh.setErrorStatus(fmt.Errorf("cannot attach controlling tty to mshell command: %w", err))
		return
	}
	defer func() {
		if len(ecmd.ExtraFiles) > 0 {
			ecmd.ExtraFiles[len(ecmd.ExtraFiles)-1].Close()
		}
	}()
	remoteName := remote.GetName()
	go func() {
		fmt.Printf("[c-pty %s] starting...\n", remote.GetName())
		buf := make([]byte, 100)
		for {
			n, readErr := cmdPty.Read(buf)
			if readErr == io.EOF {
				break
			}
			if readErr != nil {
				fmt.Printf("[error] read from controlling-pty [%s]: %v\n", remoteName, readErr)
				break
			}
			readStr := string(buf[0:n])
			readStr = strings.ReplaceAll(readStr, "\r", "")
			readStr = strings.ReplaceAll(readStr, "\n", "\\n")
			fmt.Printf("[c-pty %s] %d '%s'\n", remoteName, n, readStr)
		}
	}()
	if remoteName == "test2" {
		go func() {
			time.Sleep(2 * time.Second)
			cmdPty.Write([]byte(Test2Pw))
			fmt.Printf("[c-pty %s] wrote password!\n", remoteName)
		}()
	}
	cproc, uname, err := shexec.MakeClientProc(ecmd)
	msh.WithLock(func() {
		msh.UName = uname
	})
	if err != nil {
		msh.setErrorStatus(err)
		fmt.Printf("[error] connecting remote %s (%s): %v\n", msh.Remote.GetName(), msh.UName, err)
		return
	}
	fmt.Printf("connected remote %s\n", msh.Remote.GetName())
	msh.WithLock(func() {
		msh.ServerProc = cproc
		msh.Status = StatusConnected
	})
	go func() {
		exitErr := cproc.Cmd.Wait()
		exitCode := shexec.GetExitCode(exitErr)
		msh.WithLock(func() {
			if msh.Status == StatusConnected {
				msh.Status = StatusDisconnected
			}
		})
		fmt.Printf("[error] RUNNER PROC EXITED code[%d]\n", exitCode)
	}()
	go msh.ProcessPackets()
	return
}

func (msh *MShellProc) IsConnected() bool {
	msh.Lock.Lock()
	defer msh.Lock.Unlock()
	return msh.Status == StatusConnected
}

func (msh *MShellProc) GetDefaultState() *sstore.RemoteState {
	msh.Lock.Lock()
	defer msh.Lock.Unlock()
	if msh.ServerProc == nil || msh.ServerProc.InitPk == nil {
		return nil
	}
	return &sstore.RemoteState{Cwd: msh.ServerProc.InitPk.HomeDir, Env0: msh.ServerProc.InitPk.Env0}
}

func replaceHomePath(pathStr string, homeDir string) string {
	if homeDir == "" {
		return pathStr
	}
	if pathStr == homeDir {
		return "~"
	}
	if strings.HasPrefix(pathStr, homeDir+"/") {
		return "~" + pathStr[len(homeDir):]
	}
	return pathStr
}

func (state RemoteRuntimeState) ExpandHomeDir(pathStr string) (string, error) {
	if pathStr != "~" && !strings.HasPrefix(pathStr, "~/") {
		return pathStr, nil
	}
	homeDir := state.RemoteVars["home"]
	if homeDir == "" {
		return "", fmt.Errorf("remote does not have HOME set, cannot do ~ expansion")
	}
	if pathStr == "~" {
		return homeDir, nil
	}
	return path.Join(homeDir, pathStr[2:]), nil
}

func (msh *MShellProc) IsCmdRunning(ck base.CommandKey) bool {
	msh.Lock.Lock()
	defer msh.Lock.Unlock()
	for _, runningCk := range msh.RunningCmds {
		if runningCk == ck {
			return true
		}
	}
	return false
}

func (msh *MShellProc) SendInput(pk *packet.InputPacketType) error {
	if !msh.IsConnected() {
		return fmt.Errorf("remote is not connected, cannot send input")
	}
	if !msh.IsCmdRunning(pk.CK) {
		return fmt.Errorf("cannot send input, cmd is not running")
	}
	dataPk := packet.MakeDataPacket()
	dataPk.CK = pk.CK
	dataPk.FdNum = 0 // stdin
	dataPk.Data64 = pk.InputData64
	return msh.ServerProc.Input.SendPacket(dataPk)
}

func makeTermOpts() sstore.TermOpts {
	return sstore.TermOpts{Rows: DefaultTermRows, Cols: DefaultTermCols, FlexRows: true, MaxPtySize: DefaultMaxPtySize}
}

func RunCommand(ctx context.Context, cmdId string, remotePtr sstore.RemotePtrType, remoteState *sstore.RemoteState, runPacket *packet.RunPacketType) (*sstore.CmdType, error) {
	if remotePtr.OwnerId != "" {
		return nil, fmt.Errorf("cannot run command against another user's remote '%s'", remotePtr.MakeFullRemoteRef())
	}
	msh := GetRemoteById(remotePtr.RemoteId)
	if msh == nil {
		return nil, fmt.Errorf("no remote id=%s found", remotePtr.RemoteId)
	}
	if !msh.IsConnected() {
		return nil, fmt.Errorf("remote '%s' is not connected", remotePtr.RemoteId)
	}
	if remoteState == nil {
		return nil, fmt.Errorf("no remote state passed to RunCommand")
	}
	msh.ServerProc.Output.RegisterRpc(runPacket.ReqId)
	err := shexec.SendRunPacketAndRunData(ctx, msh.ServerProc.Input, runPacket)
	if err != nil {
		return nil, fmt.Errorf("sending run packet to remote: %w", err)
	}
	rtnPk := msh.ServerProc.Output.WaitForResponse(ctx, runPacket.ReqId)
	if rtnPk == nil {
		return nil, ctx.Err()
	}
	startPk, ok := rtnPk.(*packet.CmdStartPacketType)
	if !ok {
		respPk, ok := rtnPk.(*packet.ResponsePacketType)
		if !ok {
			return nil, fmt.Errorf("invalid response received from server for run packet: %s", packet.AsString(rtnPk))
		}
		if respPk.Error != "" {
			return nil, errors.New(respPk.Error)
		}
		return nil, fmt.Errorf("invalid response received from server for run packet: %s", packet.AsString(rtnPk))
	}
	status := sstore.CmdStatusRunning
	if runPacket.Detached {
		status = sstore.CmdStatusDetached
	}
	cmd := &sstore.CmdType{
		SessionId:   runPacket.CK.GetSessionId(),
		CmdId:       startPk.CK.GetCmdId(),
		CmdStr:      runPacket.Command,
		Remote:      remotePtr,
		RemoteState: *remoteState,
		TermOpts:    makeTermOpts(),
		Status:      status,
		StartPk:     startPk,
		DonePk:      nil,
		RunOut:      nil,
	}
	err = sstore.CreateCmdPtyFile(ctx, cmd.SessionId, cmd.CmdId, cmd.TermOpts.MaxPtySize)
	if err != nil {
		return nil, err
	}
	msh.AddRunningCmd(startPk.CK)
	return cmd, nil
}

func (msh *MShellProc) AddRunningCmd(ck base.CommandKey) {
	msh.Lock.Lock()
	defer msh.Lock.Unlock()
	msh.RunningCmds = append(msh.RunningCmds, ck)
}

func (msh *MShellProc) PacketRpc(ctx context.Context, pk packet.RpcPacketType) (*packet.ResponsePacketType, error) {
	if !msh.IsConnected() {
		return nil, fmt.Errorf("runner is not connected")
	}
	if pk == nil {
		return nil, fmt.Errorf("PacketRpc passed nil packet")
	}
	reqId := pk.GetReqId()
	msh.ServerProc.Output.RegisterRpc(reqId)
	defer msh.ServerProc.Output.UnRegisterRpc(reqId)
	err := msh.ServerProc.Input.SendPacketCtx(ctx, pk)
	if err != nil {
		return nil, err
	}
	rtnPk := msh.ServerProc.Output.WaitForResponse(ctx, reqId)
	if rtnPk == nil {
		return nil, ctx.Err()
	}
	if respPk, ok := rtnPk.(*packet.ResponsePacketType); ok {
		return respPk, nil
	}
	return nil, fmt.Errorf("invalid response packet received: %s", packet.AsString(rtnPk))
}

func (runner *MShellProc) WithLock(fn func()) {
	runner.Lock.Lock()
	defer runner.Lock.Unlock()
	fn()
}

func makeDataAckPacket(ck base.CommandKey, fdNum int, ackLen int, err error) *packet.DataAckPacketType {
	ack := packet.MakeDataAckPacket()
	ack.CK = ck
	ack.FdNum = fdNum
	ack.AckLen = ackLen
	if err != nil {
		ack.Error = err.Error()
	}
	return ack
}

func (msh *MShellProc) handleCmdDonePacket(donePk *packet.CmdDonePacketType) {
	update, err := sstore.UpdateCmdDonePk(context.Background(), donePk)
	if err != nil {
		fmt.Printf("[error] updating cmddone: %v\n", err)
		return
	}
	if update != nil {
		// TODO fix timing issue (this update gets to the FE before run-command returns for short lived commands)
		go func() {
			time.Sleep(10 * time.Millisecond)
			sstore.MainBus.SendUpdate(donePk.CK.GetSessionId(), update)
		}()
	}
	return
}

func (msh *MShellProc) handleCmdErrorPacket(errPk *packet.CmdErrorPacketType) {
	err := sstore.AppendCmdErrorPk(context.Background(), errPk)
	if err != nil {
		fmt.Printf("[error] adding cmderr: %v\n", err)
		return
	}
	return
}

func (msh *MShellProc) notifyHangups_nolock() {
	for _, ck := range msh.RunningCmds {
		cmd, err := sstore.GetCmdById(context.Background(), ck.GetSessionId(), ck.GetCmdId())
		if err != nil {
			continue
		}
		update := sstore.ModelUpdate{Cmd: cmd}
		sstore.MainBus.SendUpdate(ck.GetSessionId(), update)
	}
	msh.RunningCmds = nil
}

func (runner *MShellProc) ProcessPackets() {
	defer runner.WithLock(func() {
		if runner.Status == StatusConnected {
			runner.Status = StatusDisconnected
		}
		err := sstore.HangupRunningCmdsByRemoteId(context.Background(), runner.Remote.RemoteId)
		if err != nil {
			fmt.Printf("[error] calling HUP on remoteid=%d cmds\n", runner.Remote.RemoteId)
		}
		runner.notifyHangups_nolock()
	})
	dataPosMap := make(map[base.CommandKey]int64)
	for pk := range runner.ServerProc.Output.MainCh {
		if pk.GetType() == packet.DataPacketStr {
			dataPk := pk.(*packet.DataPacketType)
			realData, err := base64.StdEncoding.DecodeString(dataPk.Data64)
			if err != nil {
				ack := makeDataAckPacket(dataPk.CK, dataPk.FdNum, 0, err)
				runner.ServerProc.Input.SendPacket(ack)
				continue
			}
			var ack *packet.DataAckPacketType
			if len(realData) > 0 {
				dataPos := dataPosMap[dataPk.CK]
				err = sstore.AppendToCmdPtyBlob(context.Background(), dataPk.CK.GetSessionId(), dataPk.CK.GetCmdId(), realData, dataPos)
				if err != nil {
					ack = makeDataAckPacket(dataPk.CK, dataPk.FdNum, 0, err)
				} else {
					ack = makeDataAckPacket(dataPk.CK, dataPk.FdNum, len(realData), nil)
				}
				dataPosMap[dataPk.CK] += int64(len(realData))
			}
			if ack != nil {
				runner.ServerProc.Input.SendPacket(ack)
			}
			// fmt.Printf("data %s fd=%d len=%d eof=%v err=%v\n", dataPk.CK, dataPk.FdNum, len(realData), dataPk.Eof, dataPk.Error)
			continue
		}
		if pk.GetType() == packet.CmdDataPacketStr {
			dataPacket := pk.(*packet.CmdDataPacketType)
			fmt.Printf("cmd-data %s pty=%d run=%d\n", dataPacket.CK, dataPacket.PtyDataLen, dataPacket.RunDataLen)
			continue
		}
		if pk.GetType() == packet.CmdDonePacketStr {
			runner.handleCmdDonePacket(pk.(*packet.CmdDonePacketType))
			continue
		}
		if pk.GetType() == packet.CmdErrorPacketStr {
			runner.handleCmdErrorPacket(pk.(*packet.CmdErrorPacketType))
			continue
		}
		if pk.GetType() == packet.MessagePacketStr {
			msgPacket := pk.(*packet.MessagePacketType)
			fmt.Printf("# %s\n", msgPacket.Message)
			continue
		}
		if pk.GetType() == packet.RawPacketStr {
			rawPacket := pk.(*packet.RawPacketType)
			fmt.Printf("stderr> %s\n", rawPacket.Data)
			continue
		}
		if pk.GetType() == packet.CmdStartPacketStr {
			startPk := pk.(*packet.CmdStartPacketType)
			fmt.Printf("start> reqid=%s (%p)\n", startPk.RespId, runner.ServerProc.Output)
			continue
		}
		fmt.Printf("MSH> %s\n", packet.AsString(pk))
	}
}

// returns number of chars (including braces) for brace-expr
func getBracedStr(runeStr []rune) int {
	if len(runeStr) < 3 {
		return 0
	}
	if runeStr[0] != '{' {
		return 0
	}
	for i := 1; i < len(runeStr); i++ {
		if runeStr[i] == '}' {
			if i == 1 { // cannot have {}
				return 0
			}
			return i + 1
		}
	}
	return 0
}

func isDigit(r rune) bool {
	return r >= '0' && r <= '9' // just check ascii digits (not unicode)
}

func EvalPrompt(promptFmt string, vars map[string]string, state *sstore.RemoteState) string {
	var buf bytes.Buffer
	promptRunes := []rune(promptFmt)
	for i := 0; i < len(promptRunes); i++ {
		ch := promptRunes[i]
		if ch == '\\' && i != len(promptRunes)-1 {
			nextCh := promptRunes[i+1]
			if nextCh == 'x' || nextCh == 'y' {
				nr := getBracedStr(promptRunes[i+2:])
				if nr > 0 {
					escCode := string(promptRunes[i+1 : i+1+nr+1]) // start at "x" or "y", extend nr+1 runes
					escStr := evalPromptEsc(escCode, vars, state)
					buf.WriteString(escStr)
					i += nr + 1
					continue
				} else {
					buf.WriteRune(ch) // invalid escape, so just write ch and move on
					continue
				}
			} else if isDigit(nextCh) {
				if len(promptRunes) >= i+4 && isDigit(promptRunes[i+2]) && isDigit(promptRunes[i+3]) {
					i += 3
					escStr := evalPromptEsc(string(promptRunes[i+1:i+4]), vars, state)
					buf.WriteString(escStr)
					continue
				} else {
					buf.WriteRune(ch) // invalid escape, so just write ch and move on
					continue
				}
			} else {
				i += 1
				escStr := evalPromptEsc(string(nextCh), vars, state)
				buf.WriteString(escStr)
				continue
			}
		}
		buf.WriteRune(ch)
	}
	return buf.String()
}

func evalPromptEsc(escCode string, vars map[string]string, state *sstore.RemoteState) string {
	if strings.HasPrefix(escCode, "x{") && strings.HasSuffix(escCode, "}") {
		varName := escCode[2 : len(escCode)-1]
		return vars[varName]
	}
	if strings.HasPrefix(escCode, "y{") && strings.HasSuffix(escCode, "}") {
		if state == nil {
			return ""
		}
		varName := escCode[2 : len(escCode)-1]
		varMap := shexec.ParseEnv0(state.Env0)
		return varMap[varName]
	}
	if escCode == "h" {
		return vars["remoteshorthost"]
	}
	if escCode == "H" {
		return vars["remotehost"]
	}
	if escCode == "s" {
		return "mshell"
	}
	if escCode == "u" {
		return vars["remoteuser"]
	}
	if escCode == "w" {
		if state == nil {
			return "?"
		}
		return replaceHomePath(state.Cwd, vars["home"])
	}
	if escCode == "W" {
		if state == nil {
			return "?"
		}
		return path.Base(replaceHomePath(state.Cwd, vars["home"]))
	}
	if escCode == "$" {
		if vars["remoteuser"] == "root" || vars["sudo"] == "1" {
			return "#"
		} else {
			return "$"
		}
	}
	if len(escCode) == 3 {
		// \nnn escape
		ival, err := strconv.ParseInt(escCode, 8, 32)
		if err != nil {
			return escCode
		}
		return string([]byte{byte(ival)})
	}
	if escCode == "e" {
		return "\033"
	}
	if escCode == "n" {
		return "\n"
	}
	if escCode == "r" {
		return "\r"
	}
	if escCode == "a" {
		return "\007"
	}
	if escCode == "\\" {
		return "\\"
	}
	if escCode == "[" {
		return ""
	}
	if escCode == "]" {
		return ""
	}

	// we don't support date/time escapes (d, t, T, @), version escapes (v, V), cmd number (#, !), terminal device (l), jobs (j)
	return "(" + escCode + ")"
}