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package askpass
import (
"bufio"
"bytes"
"errors"
"fmt"
"log/slog"
"os"
"os/exec"
"strings"
"syscall"
"golang.org/x/sys/unix"
"golang.org/x/term"
)
// Most of this is copied from OpenSSH readpassphrase.
// State for the ReadPassphrase function
type ReadPassFlags uint8
const (
RP_ECHO = 1 << iota /* echo stuff or something 8 */
RP_ALLOW_STDIN /* Allow stdin and not askpass */
RP_ALLOW_EOF /* not used */
RP_USE_ASKPASS /* Use SSH_ASKPASS */
RP_ASK_PERMISSION /* Ask for permission, yes/no prompt */
RP_NEWLINE /* Print newline after answer. */
RPP_ECHO_OFF /* Turn off echo (default). */
RPP_ECHO_ON /* Leave echo on. */
RPP_REQUIRE_TTY /* Fail if there is no tty. */
RPP_FORCELOWER /* Force input to lower case. */
RPP_FORCEUPPER /* Force input to upper case. */
RPP_SEVENBIT /* Strip the high bit from input. */
RPP_STDIN /* Read from stdin, not /dev/tty */
)
var (
ErrNoAskpass = errors.New("system does not have an askpass program")
// Default ASKPASS programs
SSH_ASKPASS_DEFAULTS = []string{
"/usr/lib/ssh/x11-ssh-askpass",
"/usr/lib/ssh/gnome-ssh-askpass3",
"/usr/lib/ssh/gnome-ssh-askpass",
"/usr/libexec/openssh/gnome-ssh-askpass",
"/usr/bin/ksshaskpass",
"/usr/libexec/seahorse/ssh-askpass",
"/usr/lib/seahorse/ssh-askpass",
}
)
func findAskPass() (string, error) {
for _, s := range SSH_ASKPASS_DEFAULTS {
if _, err := os.Stat(s); errors.Is(err, os.ErrNotExist) {
continue
}
return s, nil
}
return "", ErrNoAskpass
}
func isTerminal(fd uintptr) bool {
_, err := unix.IoctlGetTermios(int(fd), unix.TCGETS)
return err == nil
}
func ReadPassphrase(prompt string, flags ReadPassFlags) ([]byte, error) {
var allow_askpass bool
var use_askpass bool
var askpass_hint string
if _, ok := os.LookupEnv("DISPLAY"); ok {
allow_askpass = true
} else if _, ok2 := os.LookupEnv("WAYLAND_DISPLAY"); ok2 {
allow_askpass = true
}
if s, ok := os.LookupEnv("SSH_ASKPASS_REQUIRE"); ok {
switch s {
case "force":
use_askpass = true
allow_askpass = true
case "prefer":
use_askpass = allow_askpass
case "never":
allow_askpass = false
}
}
if use_askpass {
slog.Debug("requested to askpass")
} else if (flags & RP_USE_ASKPASS) != 0 {
use_askpass = true
} else if (flags & RP_ALLOW_STDIN) != 0 {
if !isTerminal(os.Stdout.Fd()) {
slog.Debug("stdin is not a tty")
use_askpass = true
}
}
if use_askpass && allow_askpass {
if (flags & RP_ASK_PERMISSION) != 0 {
askpass_hint = "confirm"
}
return SshAskPass(prompt, askpass_hint)
}
// If we want to echo stuff, we read directly from stdin
// using bufio.NewReader.
if (flags & RPP_ECHO_ON) != 0 {
fmt.Printf("%s", prompt)
reader := bufio.NewReader(os.Stdin)
input, err := reader.ReadString('\n')
if err != nil {
return []byte(""), nil
}
return []byte(strings.TrimSpace(input)), nil
}
// Then we are defaulting to TTY prompt
fmt.Printf("%s", prompt)
pin, err := term.ReadPassword(int(syscall.Stdin))
if err != nil {
return []byte{}, nil
}
if (flags & RP_NEWLINE) != 0 {
fmt.Println("")
}
return pin, nil
}
func SshAskPass(prompt, hint string) ([]byte, error) {
var askpass string
var err error
if s, ok := os.LookupEnv("SSH_ASKPASS"); ok {
askpass = s
} else if s, _ := exec.LookPath("ssh-askpass"); s != "" {
askpass = s
} else {
askpass, err = findAskPass()
if err != nil {
return nil, err
}
}
if hint != "" {
os.Setenv("SSH_ASKPASS_PROMPT", hint)
}
out, err := exec.Command(askpass, prompt).Output()
switch hint {
case "confirm":
// TODO: Ugly and needs a rework
var exerr *exec.ExitError
if errors.As(err, &exerr) {
if exerr.ExitCode() != 0 {
return []byte("no"), nil
}
} else {
return []byte("yes"), nil
}
}
if err != nil {
return []byte{}, err
}
return bytes.TrimSpace(out), nil
}
// AskPremission runs SSH_ASKPASS in with SSH_ASKPASS_PROMPT=confirm set as env
// it will expect exit code 0 or !0 and return 'yes' and 'no' respectively.
func AskPermission() (bool, error) {
a, err := ReadPassphrase("Confirm touch", RP_USE_ASKPASS|RP_ASK_PERMISSION)
if err != nil {
return false, err
}
if bytes.Equal(a, []byte("yes")) {
return true, nil
} else if bytes.Equal(a, []byte("no")) {
return false, nil
}
return false, nil
}
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