mgsh/input_test.go

package main

// input_test.go — the y/n prompt is the last thing between `init` and a wiped
// server repository, so the terminal handling around it is pinned here.

import (
	"os"
	"strings"
	"sync"
	"testing"
	"time"
)

// fakeTTY stands in for the terminal driver. It models the one detail that made
// the skipped-question bug possible: MIN and TIME are not part of the
// canonical/non-canonical switch, so they survive `stty icanon` and carry over
// into the next prompt.
type fakeTTY struct {
	mu    sync.Mutex
	state map[string]string
	calls [][]string
	ready chan struct{} // signalled once single-key mode is in effect
}

func newFakeTTY() *fakeTTY {
	return &fakeTTY{
		state: map[string]string{"icanon": "on", "echo": "on", "min": "1", "time": "0"},
		ready: make(chan struct{}, 4),
	}
}

func (f *fakeTTY) run(args ...string) (string, error) {
	f.mu.Lock()
	defer f.mu.Unlock()
	f.calls = append(f.calls, args)

	switch {
	case len(args) == 1 && args[0] == "-g":
		return f.serializeLocked(), nil
	case len(args) == 1 && strings.HasPrefix(args[0], "saved:"):
		for _, kv := range strings.Split(strings.TrimPrefix(args[0], "saved:"), ",") {
			if k, v, ok := strings.Cut(kv, "="); ok {
				f.state[k] = v
			}
		}
		return "", nil
	}
	for i := 0; i < len(args); i++ {
		switch a := args[i]; a {
		case "min", "time":
			if i+1 < len(args) {
				f.state[a] = args[i+1]
				i++
			}
		default:
			f.state[strings.TrimPrefix(a, "-")] = boolWord(!strings.HasPrefix(a, "-"))
		}
	}
	if strings.Join(args, " ") == strings.Join(keyModeArgs, " ") {
		f.ready <- struct{}{} // single-key mode is set; the read comes next
	}
	return "", nil
}

func boolWord(on bool) string {
	if on {
		return "on"
	}
	return "off"
}

// serializeLocked renders the settings as one token, the way `stty -g` does.
func (f *fakeTTY) serializeLocked() string {
	return "saved:icanon=" + f.state["icanon"] + ",echo=" + f.state["echo"] +
		",min=" + f.state["min"] + ",time=" + f.state["time"]
}

func (f *fakeTTY) get(k string) string {
	f.mu.Lock()
	defer f.mu.Unlock()
	return f.state[k]
}

func (f *fakeTTY) snapshot() string {
	f.mu.Lock()
	defer f.mu.Unlock()
	return f.serializeLocked()
}

// installFakeTTY points getkey at the fake terminal for the duration of a test.
func installFakeTTY(t *testing.T) *fakeTTY {
	t.Helper()
	f := newFakeTTY()
	oldRun, oldIsTTY, oldStdin := sttyRun, stdinIsTTY, os.Stdin
	sttyRun = f.run
	stdinIsTTY = func() bool { return true }
	t.Cleanup(func() {
		sttyRun, stdinIsTTY, os.Stdin = oldRun, oldIsTTY, oldStdin
	})
	return f
}

// askOnce runs one getkey against the fake terminal, answering with keys once
// the terminal is actually in single-key mode. It reports the MIN in effect at
// the moment of the read — the value the old code got wrong.
func askOnce(t *testing.T, f *fakeTTY, keys string) (key string, ok bool, minAtRead string) {
	t.Helper()
	r, w, err := os.Pipe()
	if err != nil {
		t.Fatal(err)
	}
	os.Stdin = r

	done := make(chan struct{})
	go func() {
		key, ok = getkey("question? ")
		close(done)
	}()

	select {
	case <-f.ready:
	case <-time.After(5 * time.Second):
		t.Fatal("the terminal was never put into single-key mode")
	}
	minAtRead = f.get("min")
	w.WriteString(keys)
	w.Close() // so the drain that follows the keypress sees EOF instead of blocking
	<-done
	r.Close()
	return key, ok, minAtRead
}

// TestEveryQuestionWaitsForAnAnswer is the regression test for the bug where the
// second y/n question of a session was skipped: drainTTY left the terminal at
// "min 0" ("return what is buffered, do not wait"), the restore only named
// icanon and echo, and so the next read returned zero bytes and answered the
// question with its default.
func TestEveryQuestionWaitsForAnAnswer(t *testing.T) {
	f := installFakeTTY(t)

	for i, want := range []string{"y", "n", "y"} {
		key, ok, minAtRead := askOnce(t, f, want)
		if !ok || key != want {
			t.Fatalf("question %d: got (%q, %v), want (%q, true)", i+1, key, ok, want)
		}
		if minAtRead != "1" {
			t.Errorf("question %d read the terminal at min=%s, want min=1 — "+
				"min 0 returns without waiting and answers the question by itself",
				i+1, minAtRead)
		}
	}
}

// TestPromptHandsTheTerminalBackUnchanged: mgsh must not leave the terminal in
// a mode it chose. The old restore named only icanon and echo and left "min 0"
// behind, which outlived mgsh itself and broke the next program's single-key
// reads too.
func TestPromptHandsTheTerminalBackUnchanged(t *testing.T) {
	f := installFakeTTY(t)
	initial := f.snapshot()

	if _, ok, _ := askOnce(t, f, "y"); !ok {
		t.Fatal("getkey did not read the key")
	}
	if got := f.snapshot(); got != initial {
		t.Errorf("terminal left as %s, want it back at %s", got, initial)
	}
}

// TestPromptRestoresFromTheSavedState pins *how* the terminal is restored: from
// the state captured with `stty -g`, not by naming the flags we changed.
func TestPromptRestoresFromTheSavedState(t *testing.T) {
	f := installFakeTTY(t)
	if _, ok, _ := askOnce(t, f, "y"); !ok {
		t.Fatal("getkey did not read the key")
	}

	f.mu.Lock()
	defer f.mu.Unlock()
	if len(f.calls) == 0 {
		t.Fatal("stty was never called")
	}
	if first := f.calls[0]; len(first) != 1 || first[0] != "-g" {
		t.Errorf("first stty call was %v, want [-g]: the state has to be captured "+
			"before it is changed", first)
	}
	last := f.calls[len(f.calls)-1]
	if len(last) != 1 || !strings.HasPrefix(last[0], "saved:") {
		t.Errorf("last stty call was %v, want the saved state played back", last)
	}
}

// TestSingleKeyModeSetsMinExplicitly: MIN and TIME are inherited, so they have
// to be named on the way in. Without that, a terminal left at "min 0" by an
// earlier program (or an earlier mgsh) skips the question.
func TestSingleKeyModeSetsMinExplicitly(t *testing.T) {
	args := strings.Join(keyModeArgs, " ")
	for _, want := range []string{"-icanon", "-echo", "min 1", "time 0"} {
		if !strings.Contains(args, want) {
			t.Errorf("single-key mode is %q, missing %q", args, want)
		}
	}
}

// TestQuestionSkippedByAPoisonedTerminalIsNotAYes: even if the terminal is
// already in the broken state when mgsh starts, the answer must not be the
// default — nobody saw the question, so nobody agreed to anything.
func TestQuestionSkippedByAPoisonedTerminalIsNotAYes(t *testing.T) {
	oldRun, oldIsTTY, oldStdin := sttyRun, stdinIsTTY, os.Stdin
	defer func() { sttyRun, stdinIsTTY, os.Stdin = oldRun, oldIsTTY, oldStdin }()

	sttyRun = func(args ...string) (string, error) { return "", nil }
	stdinIsTTY = func() bool { return true }

	r, w, _ := os.Pipe()
	w.Close() // a terminal that returns nothing at all
	os.Stdin = r
	defer r.Close()

	if key, ok := getkey("question? "); ok {
		t.Fatalf("getkey reported a key %q from a terminal that gave none", key)
	}
	if yesno("destroy everything?", true) {
		t.Error("an unanswerable question was taken as yes")
	}
}