Put the terminal back when a signal ends the mnemonic prompt (closes #91)

A SIGINT, SIGTERM or SIGHUP at the mnemonic prompt killed the tool
with echo still off. The prompt now catches them from before echo goes
off and reads the line in a goroutine. Once the line is read or a
signal arrives, it puts the terminal settings back and stops catching;
if a signal has arrived by then, it sends the tool the same signal
again, so the tool is still ended by it (130 for SIGINT in a shell).
A test sends SIGINT at the prompt on a pseudo-terminal.

The signals package moves from internal/cli to internal/signals, since
the mnemonic prompt now uses it as well.

Untested: a signal that comes just as the line is read.

Model: opus-5-5

README.md

@@ -65,10 +65,12 @@ calls into `internal/`. The packages there are:
   and decrypts with it.
 - `internal/childmnemonic` derives a child mnemonic from the main one using
   BIP-85's own mnemonic application.
+- `internal/signals` catches SIGINT, SIGTERM and SIGHUP for the commands that
+  clean up before they end, and for the mnemonic prompt, which puts the terminal
+  back before the signal ends the tool.
 - `internal/cli` builds the cobra command tree and runs it. Under it,
-  `cli/options` holds the flags every command shares, `cli/signals` catches
-  SIGINT, SIGTERM and SIGHUP for the commands that clean up before they end, and
-  `cli/ssh`, `cli/age` and `cli/mnemonic` are the command groups.
+  `cli/options` holds the flags every command shares, and `cli/ssh`, `cli/age`
+  and `cli/mnemonic` are the command groups.
 - `internal/bip39` is a copy of `github.com/tyler-smith/go-bip39` v1.1.0,
   trimmed to what keyfunc uses.
 
@@ -116,7 +118,11 @@ order; the first one found wins:
 2. Environment variable `KEYFUNC_MNEMONIC_COMMAND`: the same, as a shell command
    held in the environment.
 3. Environment variable `KEYFUNC_MNEMONIC`: the mnemonic itself.
-4. A prompt on the terminal with echo turned off.
+4. A prompt on the terminal with echo turned off. The mnemonic is what is typed
+   up to Enter, and echo is turned back on once it is read. Ctrl-D with nothing
+   typed ends the prompt at once and leaves the mnemonic empty, so the tool
+   refuses it and exits with status 1. After text has been typed, Ctrl-D has to
+   be pressed twice to end the prompt, and the text typed is the mnemonic.
 
 If none of these is available and standard input is not a terminal, the tool
 refuses and exits with status 1. A mnemonic that is empty, does not have 12, 15,
@@ -324,10 +330,11 @@ passes through `ssh`'s own exit status.
 
 SIGINT, SIGTERM and SIGHUP end any command at once, at the mnemonic prompt too,
 with the status a shell gives a program killed by that signal (130 for SIGINT).
-While `age encrypt -o` or `age decrypt -o` is writing a new file or replacing a
-regular one, the signal makes it remove the unfinished file, leave a file
-already at the named path as it was, and exit with status 1. That holds for a
-signal that has reached `keyfunc` when its input ends; a later one leaves the
+At the prompt the terminal's settings are put back as they were first, so echo
+is on again. While `age encrypt -o` or `age decrypt -o` is writing a new file or
+replacing a regular one, the signal makes it remove the unfinished file, leave a
+file already at the named path as it was, and exit with status 1. That holds for
+a signal that has reached `keyfunc` when its input ends; a later one leaves the
 whole file in place. Ctrl-C on a pipeline ends the input at the same moment, and
 on Linux `keyfunc` sees the signal first, though no system promises that. A
 named pipe or a device at the `-o` path, or a path that is the same file as

go.mod

@@ -6,9 +6,11 @@ require (
 	filippo.io/age v1.3.2
 	github.com/btcsuite/btcd v0.25.0
 	github.com/btcsuite/btcd/btcutil v1.2.0
+	github.com/creack/pty v1.1.25-0.20260601142114-9246436fffe8 // v1.1.24's Open can return another pty's terminal
 	github.com/spf13/cobra v1.10.2
 	github.com/stretchr/testify v1.12.1
 	golang.org/x/crypto v0.57.0
+	golang.org/x/sys v0.48.0
 	golang.org/x/term v0.46.0
 	sneak.berlin/go/secret v0.0.0-20261007105610-ef0ae90768c8
 )
@@ -22,5 +24,4 @@ require (
 	github.com/kcalvinalvin/anet v0.0.0-20251112173137-d8ddc1f6dbee // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
 	go.yaml.in/yaml/v3 v3.0.5 // indirect
-	golang.org/x/sys v0.48.0 // indirect
 )

go.sum

@@ -13,6 +13,8 @@ github.com/btcsuite/btcd/btcutil v1.2.0/go.mod h1:/Taflm113pYjUpbWKKQEfa6XOtI/+W
 github.com/btcsuite/btcd/chaincfg/chainhash v1.2.0 h1:yMIg99+4aBvqfl/HzJRKfxTX9rGfikoI9uvFzterhc8=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.2.0/go.mod h1:Y72Ren9gfhlEvnwnT78BGcSNO2UMphTKLn9AorF+5rg=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
+github.com/creack/pty v1.1.25-0.20260601142114-9246436fffe8 h1:CY3gjC7naqYGLMiywvj3suPfa1i0p/QEr7o8ujxL/2M=
+github.com/creack/pty v1.1.25-0.20260601142114-9246436fffe8/go.mod h1:08sCNb52WyoAwi2QDyzUCTgcvVFhUzewun7wtTfvcwE=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0 h1:NMZiJj8QnKe1LgsbDayM4UoHwbvwDRwnI3hwNaAHRnc=

internal/cli/age/age.go

@@ -16,8 +16,8 @@ import (
 	"github.com/spf13/cobra"
 	"sneak.berlin/go/keyfunc/internal/agekey"
 	"sneak.berlin/go/keyfunc/internal/cli/options"
-	"sneak.berlin/go/keyfunc/internal/cli/signals"
 	"sneak.berlin/go/keyfunc/internal/derive"
+	"sneak.berlin/go/keyfunc/internal/signals"
 )
 
 // ErrInterrupted is returned when SIGINT, SIGTERM or SIGHUP has been

internal/cli/cli.go

@@ -87,6 +87,9 @@ func init() {
 // still runs, and "age encrypt -o" and "age decrypt -o" while they
 // write a new file to rename over the named one, so the unfinished file
 // is removed.
+//
+// At the mnemonic prompt the signal is caught only to put the terminal
+// back, and then ends the tool as above.
 func Main() int {
 	err := Root().Execute()
 	if err == nil {

internal/cli/prompt_test.go

@@ -0,0 +1,133 @@
+package cli_test
+
+import (
+	"bufio"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+	"syscall"
+	"testing"
+	"time"
+
+	"github.com/creack/pty"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/term"
+	"sneak.berlin/go/keyfunc/internal/mnemonic"
+)
+
+// TestEndOfInputAtThePromptEndsTheTool starts "age pub" and, at the
+// prompt, types Ctrl-D. The tool has to end with status 1, say that the
+// mnemonic is empty, and leave the terminal set as it found it, so with
+// echo on again.
+//
+// pty.Open returns the two ends of a new terminal: tty is the end the
+// tool uses as its terminal, and ptmx the end the test reads what the
+// terminal shows from and types into.
+func TestEndOfInputAtThePromptEndsTheTool(t *testing.T) {
+	t.Setenv(mnemonic.Variable, "")
+	t.Setenv(mnemonic.CommandVariable, "")
+
+	ptmx, tty, err := pty.Open()
+	require.NoError(t, err)
+
+	defer func() { _ = ptmx.Close() }()
+	defer func() { _ = tty.Close() }()
+
+	before, err := term.GetState(int(tty.Fd()))
+	require.NoError(t, err)
+
+	command, terminal := prompted(t, ptmx, tty)
+
+	_, err = ptmx.WriteString("\x04") // Ctrl-D
+	require.NoError(t, err)
+
+	waitForTool(t, "Ctrl-D at the prompt", command)
+	require.Equal(t, failedStatus, command.ProcessState.ExitCode())
+
+	after, err := term.GetState(int(tty.Fd()))
+	require.NoError(t, err)
+	require.Equal(t, before, after, "the terminal settings were not restored")
+
+	// With the tool ended and this end closed too, ptmx gives what is
+	// left on the terminal and then an error.
+	require.NoError(t, tty.Close())
+
+	said, _ := io.ReadAll(terminal)
+	require.Contains(t, string(said), mnemonic.ErrEmpty.Error())
+}
+
+// TestASignalAtThePromptPutsTheTerminalBack starts "age pub" and, at
+// the prompt, once the tool has turned echo off, sends it SIGINT. The
+// tool has to be ended by SIGINT, which a shell reports as status 130,
+// and leave the terminal set as it found it, so with echo on again.
+func TestASignalAtThePromptPutsTheTerminalBack(t *testing.T) {
+	t.Setenv(mnemonic.Variable, "")
+	t.Setenv(mnemonic.CommandVariable, "")
+
+	ptmx, tty, err := pty.Open()
+	require.NoError(t, err)
+
+	defer func() { _ = ptmx.Close() }()
+	defer func() { _ = tty.Close() }()
+
+	before, err := term.GetState(int(tty.Fd()))
+	require.NoError(t, err)
+
+	command, _ := prompted(t, ptmx, tty)
+
+	// The prompt is shown just before echo is turned off, and the
+	// signal has to come while it is off.
+	require.Eventually(t, func() bool {
+		now, err := term.GetState(int(tty.Fd()))
+
+		return err == nil && !assert.ObjectsAreEqual(before, now)
+	}, 5*time.Second, 5*time.Millisecond, "the tool did not turn echo off")
+
+	require.NoError(t, command.Process.Signal(syscall.SIGINT))
+	waitForTool(t, "SIGINT at the prompt", command)
+
+	status, ok := command.ProcessState.Sys().(syscall.WaitStatus)
+	require.True(t, ok)
+	require.True(t, status.Signaled(), "the tool was not ended by the signal")
+	require.Equal(t, syscall.SIGINT, status.Signal())
+
+	after, err := term.GetState(int(tty.Fd()))
+	require.NoError(t, err)
+	require.Equal(t, before, after, "the terminal settings were not restored")
+}
+
+// prompted starts "age pub" as a subprocess, for a test that has set no
+// mnemonic, with the terminal's tty end on all three streams, and
+// returns once the tool has shown the prompt. The reader returned reads
+// what the terminal shows from its ptmx end. Reading ptmx stops at a
+// deadline, so a prompt that never comes fails the test instead of
+// hanging it.
+func prompted(t *testing.T, ptmx, tty *os.File) (*exec.Cmd, *bufio.Reader) {
+	t.Helper()
+
+	require.NoError(t, ptmx.SetReadDeadline(time.Now().Add(10*time.Second)))
+
+	//nolint:gosec // this test's own binary as the tool
+	command := exec.CommandContext(t.Context(), os.Args[0], "age", "pub")
+
+	command.Env = append(os.Environ(), runAsTool+"=1")
+	command.Stdin = tty
+	command.Stdout = tty
+	command.Stderr = tty
+
+	require.NoError(t, command.Start())
+
+	var shown string
+
+	terminal := bufio.NewReader(ptmx)
+	for !strings.HasSuffix(shown, "mnemonic: ") {
+		char, err := terminal.ReadByte()
+		require.NoError(t, err, "the tool did not prompt: %q", shown)
+
+		shown += string(char)
+	}
+
+	return command, terminal
+}

internal/cli/ssh/install.go

@@ -15,8 +15,8 @@ import (
 	"time"
 
 	"github.com/spf13/cobra"
-	"sneak.berlin/go/keyfunc/internal/cli/signals"
 	"sneak.berlin/go/keyfunc/internal/mnemonic"
+	"sneak.berlin/go/keyfunc/internal/signals"
 )
 
 // Where the key goes on the host and what the file it arrives in is

internal/cli/ssh/to.go

@@ -10,8 +10,8 @@ import (
 	"syscall"
 
 	"github.com/spf13/cobra"
-	"sneak.berlin/go/keyfunc/internal/cli/signals"
 	"sneak.berlin/go/keyfunc/internal/mnemonic"
+	"sneak.berlin/go/keyfunc/internal/signals"
 )
 
 // StatusError says the tool should end with the status ssh ended with.

internal/mnemonic/mnemonic.go

@@ -136,7 +136,7 @@ func ask() (string, error) {
 
 	fmt.Fprint(os.Stderr, "mnemonic: ")
 
-	typed, err := term.ReadPassword(fd)
+	typed, err := readWithoutEcho()
 
 	fmt.Fprintln(os.Stderr)
 
@@ -144,7 +144,7 @@ func ask() (string, error) {
 		return "", fmt.Errorf("reading the mnemonic: %w", err)
 	}
 
-	return checked(string(typed))
+	return checked(typed)
 }
 
 // checked joins the words with single spaces, whatever whitespace

internal/mnemonic/prompt_notunix.go

@@ -0,0 +1,18 @@
+//go:build !aix && !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !solaris && !zos
+
+package mnemonic
+
+import (
+	"os"
+
+	"golang.org/x/term"
+)
+
+// readWithoutEcho reads one line from the terminal on standard input
+// with echo turned off, through term.ReadPassword, on the systems
+// prompt_unix.go is not built for, such as Windows.
+func readWithoutEcho() (string, error) {
+	typed, err := term.ReadPassword(int(os.Stdin.Fd()))
+
+	return string(typed), err
+}

internal/mnemonic/prompt_unix.go

@@ -0,0 +1,111 @@
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos
+
+package mnemonic
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/signal"
+
+	"golang.org/x/sys/unix"
+	"sneak.berlin/go/keyfunc/internal/signals"
+)
+
+// readWithoutEcho reads one line from the terminal on standard input
+// with echo turned off. The line ends at a newline or at the end of
+// input (Ctrl-D). The terminal is set as term.ReadPassword sets it;
+// ReadPassword itself is not used here because it never sees the end
+// of input and goes on waiting.
+//
+// Meanwhile SIGINT, SIGTERM and SIGHUP are caught, as signals.Notify
+// catches them. One that has arrived by the time the line is read puts
+// the terminal back as it was and then ends the tool, as it would have
+// ended it if it were not caught.
+func readWithoutEcho() (string, error) {
+	fd := int(os.Stdin.Fd())
+
+	settings, err := unix.IoctlGetTermios(fd, ioctlReadTermios)
+	if err != nil {
+		return "", fmt.Errorf("reading the terminal settings: %w", err)
+	}
+
+	// Caught from before echo is turned off, so that no signal can end
+	// the tool with echo off.
+	received := make(chan os.Signal, 1)
+	signals.Notify(received)
+
+	defer signal.Stop(received)
+
+	hidden := *settings
+	hidden.Lflag &^= unix.ECHO
+	hidden.Lflag |= unix.ICANON | unix.ISIG
+	hidden.Iflag |= unix.ICRNL
+
+	err = unix.IoctlSetTermios(fd, ioctlWriteTermios, &hidden)
+	if err != nil {
+		return "", fmt.Errorf("turning echo off: %w", err)
+	}
+
+	var (
+		typed  string
+		failed error
+	)
+
+	read := make(chan struct{})
+
+	go func() {
+		// With ICANON set, a read from the terminal returns at most one
+		// line, so the buffer takes nothing past the newline.
+		typed, failed = bufio.NewReader(os.Stdin).ReadString('\n')
+
+		close(read)
+	}()
+
+	var ending os.Signal
+
+	select {
+	case <-read:
+	case ending = <-received:
+	}
+
+	// The terminal is put back while the signals are still caught, so
+	// that none can end the tool with echo off. Stop returns only once
+	// every signal the tool has received has been handed over, so one
+	// that came as the line was read is in received by then.
+	_ = unix.IoctlSetTermios(fd, ioctlWriteTermios, settings)
+
+	signal.Stop(received)
+
+	if len(received) > 0 {
+		ending = <-received
+	}
+
+	if ending != nil {
+		return "", endBy(ending)
+	}
+
+	if errors.Is(failed, io.EOF) {
+		return typed, nil
+	}
+
+	return typed, failed
+}
+
+// endBy sends the tool the signal again, now that nothing catches it,
+// so that it ends the tool, and waits for that. It returns only if the
+// signal could not be sent.
+func endBy(ending os.Signal) error {
+	tool, err := os.FindProcess(os.Getpid())
+	if err == nil {
+		err = tool.Signal(ending)
+	}
+
+	if err != nil {
+		return fmt.Errorf("ending the tool by %s: %w", ending, err)
+	}
+
+	select {}
+}

internal/mnemonic/termios_bsd.go

@@ -0,0 +1,12 @@
+//go:build darwin || dragonfly || freebsd || netbsd || openbsd
+
+package mnemonic
+
+import "golang.org/x/sys/unix"
+
+// The requests that read and set the terminal settings, as
+// golang.org/x/term names them.
+const (
+	ioctlReadTermios  = unix.TIOCGETA
+	ioctlWriteTermios = unix.TIOCSETA
+)

internal/mnemonic/termios_other.go

@@ -0,0 +1,12 @@
+//go:build aix || linux || solaris || zos
+
+package mnemonic
+
+import "golang.org/x/sys/unix"
+
+// The requests that read and set the terminal settings, as
+// golang.org/x/term names them.
+const (
+	ioctlReadTermios  = unix.TCGETS
+	ioctlWriteTermios = unix.TCSETS
+)

internal/signals/signals.go

@@ -1,5 +1,9 @@
-// Package signals catches the signals that end the tool, for the
-// commands that clean up before they end.
+// Package signals catches SIGINT, SIGTERM and SIGHUP, the signals that
+// end the tool, for the commands that clean up before they end and for
+// the mnemonic prompt, which puts the terminal back before the signal
+// ends the tool. Go keeps an inherited ignore only for SIGHUP and
+// SIGINT, so a SIGTERM the tool was started with set to be ignored is
+// not left ignored.
 package signals
 
 import (
@@ -11,8 +15,8 @@ import (
 
 // Context is signal.NotifyContext for SIGINT, SIGTERM and SIGHUP: the
 // context it returns is cancelled when one of them arrives, and stop
-// stops catching them. It leaves out any of the three the tool was
-// started with set to be ignored, as nohup does with SIGHUP, because
+// stops catching them. It leaves out SIGHUP or SIGINT if the tool was
+// started with it set to be ignored, as nohup does with SIGHUP, because
 // catching a signal turns an ignored one back on and would end a run
 // that was meant to survive it.
 func Context(parent context.Context) (context.Context, context.CancelFunc) {
@@ -37,8 +41,8 @@ func Notify(c chan<- os.Signal) {
 	}
 }
 
-// caught returns those of SIGINT, SIGTERM and SIGHUP that the tool was
-// not started with set to be ignored.
+// caught returns SIGINT, SIGTERM and SIGHUP, less any that
+// signal.Ignored reports as ignored.
 func caught() []os.Signal {
 	endings := []os.Signal{syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP}
 	kept := make([]os.Signal, 0, len(endings))