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
+  `cli/options` holds the flags every command shares, and `cli/ssh`, `cli/age`
-  SIGINT, SIGTERM and SIGHUP for the commands that clean up before they end, and
+  and `cli/mnemonic` are the command groups.
-  `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.
 

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/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/prompt_unix.go

@@ -11,7 +11,7 @@ import (
 	"os/signal"
 
 	"golang.org/x/sys/unix"
-	"sneak.berlin/go/keyfunc/internal/cli/signals"
+	"sneak.berlin/go/keyfunc/internal/signals"
 )
 
 // readWithoutEcho reads one line from the terminal on standard input
@@ -21,8 +21,9 @@ import (
 // of input and goes on waiting.
 //
 // Meanwhile SIGINT, SIGTERM and SIGHUP are caught, as signals.Notify
-// catches them. One that arrives puts the terminal back as it was and
+// catches them. One that has arrived by the time the line is read puts
-// then ends the tool, as it would have ended it if it were not caught.
+// 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())
 
@@ -48,11 +49,6 @@ func readWithoutEcho() (string, error) {
 		return "", fmt.Errorf("turning echo off: %w", err)
 	}
 
-	restore := func() {
-		_ = unix.IoctlSetTermios(fd, ioctlWriteTermios, settings)
-	}
-	defer restore()
-
 	var (
 		typed  string
 		failed error
@@ -68,12 +64,26 @@ func readWithoutEcho() (string, error) {
 		close(read)
 	}()
 
+	var ending os.Signal
+
 	select {
 	case <-read:
-	case ending := <-received:
+	case ending = <-received:
-		restore()
+	}
-		signal.Stop(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)
 	}
 

internal/signals/signals.go

@@ -1,5 +1,9 @@
-// Package signals catches the signals that end the tool, for the
+// Package signals catches SIGINT, SIGTERM and SIGHUP, the signals that
-// commands that clean up before they end.
+// 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
+// stops catching them. It leaves out SIGHUP or SIGINT if the tool was
-// started with set to be ignored, as nohup does with SIGHUP, because
+// 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
+// caught returns SIGINT, SIGTERM and SIGHUP, less any that
-// not started with set to be ignored.
+// 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))