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 with signals.Notify
from before echo goes off, and reads the line in a goroutine. When one
arrives it puts the terminal settings back, stops catching, and sends
the tool the same signal again, so the tool is still ended by it (130
for SIGINT in a shell). A signal the tool was started with set to be
ignored stays ignored. A test sends SIGINT at the prompt on a
pseudo-terminal.

Unchanged: the Windows prompt, which uses term.ReadPassword.

Model: opus-5-5

README.md

@@ -65,12 +65,10 @@ 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, and `cli/ssh`, `cli/age`
+  `cli/options` holds the flags every command shares, `cli/signals` catches
-  and `cli/mnemonic` are the command groups.
+  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.
 - `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/signals/signals.go

@@ -1,9 +1,5 @@
-// Package signals catches SIGINT, SIGTERM and SIGHUP, the signals that
+// Package signals catches the signals that end the tool, for the
-// end the tool, for the commands that clean up before they end and for
+// commands that clean up before they end.
-// 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 (
@@ -15,8 +11,8 @@ 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 SIGHUP or SIGINT if the tool was
+// stops catching them. It leaves out any of the three the tool was
-// started with it set to be ignored, as nohup does with SIGHUP, because
+// started with 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) {
@@ -41,8 +37,8 @@ func Notify(c chan<- os.Signal) {
 	}
 }
 
-// caught returns SIGINT, SIGTERM and SIGHUP, less any that
+// caught returns those of SIGINT, SIGTERM and SIGHUP that the tool was
-// signal.Ignored reports as ignored.
+// not started with set to be ignored.
 func caught() []os.Signal {
 	endings := []os.Signal{syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP}
 	kept := make([]os.Signal, 0, len(endings))

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/signals"
+	"sneak.berlin/go/keyfunc/internal/cli/signals"
 )
 
 // readWithoutEcho reads one line from the terminal on standard input
@@ -21,9 +21,8 @@ import (
 // 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
+// catches them. One that arrives puts the terminal back as it was and
-// the terminal back as it was and then ends the tool, as it would have
+// then ends the tool, as it would have ended it if it were not caught.
-// ended it if it were not caught.
 func readWithoutEcho() (string, error) {
 	fd := int(os.Stdin.Fd())
 
@@ -49,6 +48,11 @@ 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
@@ -64,26 +68,12 @@ func readWithoutEcho() (string, error) {
 		close(read)
 	}()
 
-	var ending os.Signal
-
 	select {
 	case <-read:
-	case ending = <-received:
+	case ending := <-received:
-	}
+		restore()
-
-	// 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)
 	}