Ask before removing a secret, version, vault or unlocker (closes #39)

secret rm, secret version rm, secret vault remove and secret unlocker
remove ask [y/N] on a terminal, naming what they remove, and go ahead
only on y or yes. Without --force, a command whose stdin is not a
terminal fails at once. --force, now also on rm and version rm,
removes without asking; it replaces the old refusals to remove a vault
with secrets or the last unlocker without --force. The checks run and
the question is asked before the state directory lock is taken; under
the lock the checks run again, and nothing is removed if they would
ask a different question.

Model: opus-5-5

internal/cli/confirm.go

@@ -0,0 +1,108 @@
+package cli
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"git.eeqj.de/sneak/secret/internal/vault"
+	"github.com/spf13/cobra"
+	"golang.org/x/term"
+)
+
+// Sentinel errors for asking the user to confirm a removal
+var (
+	errNoTerminal = errors.New("stdin is not a terminal, so there is " +
+		"nobody to ask for confirmation; pass --force to remove without asking")
+	errNotConfirmed       = errors.New("cancelled; nothing was removed")
+	errChangedWhileAsking = errors.New("what was to be removed changed " +
+		"while waiting for the answer; nothing was removed")
+)
+
+// askThenLock asks the user to confirm a removal, unless force is set, and
+// then takes the state directory lock and returns the function that
+// releases it. find makes the command's checks, keeps what it found for
+// the caller to remove, and returns the question that names it. find runs
+// before the question, which is asked without the lock so that no other
+// command waits while the user answers, and runs again once the lock is
+// taken. That run is the last, so the caller removes what find found under
+// the lock. If its question then differs from the one the user answered,
+// something changed in between, and askThenLock fails.
+func (cli *Instance) askThenLock(
+	cmd *cobra.Command, force bool, find func() (string, error),
+) (func(), error) {
+	asked := ""
+
+	if !force {
+		question, err := find()
+		if err != nil {
+			return nil, err
+		}
+
+		err = cli.confirm(cmd, question)
+		if err != nil {
+			return nil, err
+		}
+
+		asked = question
+	}
+
+	release, err := vault.LockStateDir(cli.fs, cli.stateDir)
+	if err != nil {
+		return nil, err
+	}
+
+	question, err := find()
+	if err == nil && !force && question != asked {
+		err = errChangedWhileAsking
+	}
+
+	if err != nil {
+		release()
+
+		return nil, err
+	}
+
+	return release, nil
+}
+
+// confirm asks question and returns nil only when the user answers y or
+// yes; any other answer, a bare Enter included, cancels. When stdin is not
+// a terminal it asks nothing and fails at once: nobody is there to answer,
+// and waiting for an answer would hang a script. Stdin decides, not
+// stdout, because the answer is read from stdin: `secret rm foo | tee log`
+// still asks. The question goes to stderr.
+func (cli *Instance) confirm(cmd *cobra.Command, question string) error {
+	answers := cli.terminal
+	if answers == nil {
+		answers = cmd.InOrStdin()
+
+		if !isTerminal(answers) {
+			return errNoTerminal
+		}
+	}
+
+	_, _ = fmt.Fprintf(cmd.ErrOrStderr(), "%s [y/N] ", question)
+
+	answer, err := bufio.NewReader(answers).ReadString('\n')
+	if err != nil && !errors.Is(err, io.EOF) {
+		return fmt.Errorf("failed to read the answer: %w", err)
+	}
+
+	switch strings.ToLower(strings.TrimSpace(answer)) {
+	case "y", "yes":
+		return nil
+	default:
+		return errNotConfirmed
+	}
+}
+
+// isTerminal reports whether r is a terminal.
+func isTerminal(r io.Reader) bool {
+	file, ok := r.(*os.File)
+
+	return ok && term.IsTerminal(int(file.Fd()))
+}