banger/internal/daemon/open_close_test.go

package daemon

import (
	"errors"
	"io"
	"log/slog"
	"sync/atomic"
	"testing"

	"banger/internal/model"
	"banger/internal/vmdns"
)

// TestCloseOnPartiallyInitialisedDaemon pins the contract that Open's
// error-path defer relies on: Close must be safe to call when a
// startup step failed before every subsystem was set up. If this
// breaks, `defer d.Close() on err != nil` in Open() starts panicking
// on zero-valued fields.
func TestCloseOnPartiallyInitialisedDaemon(t *testing.T) {
	cases := []struct {
		name   string
		build  func(t *testing.T) *Daemon
		verify func(t *testing.T, d *Daemon)
	}{
		{
			name: "only store + closing channel (early failure)",
			build: func(t *testing.T) *Daemon {
				return &Daemon{
					store:   openDaemonStore(t),
					closing: make(chan struct{}),
					logger:  slog.New(slog.NewTextHandler(io.Discard, nil)),
				}
			},
			verify: func(t *testing.T, d *Daemon) {
				// closing channel should have been closed.
				select {
				case <-d.closing:
				default:
					t.Error("closing channel not closed by Close")
				}
			},
		},
		{
			name: "with vmDNS listener (fail after startVMDNS)",
			build: func(t *testing.T) *Daemon {
				server, err := vmdns.New("127.0.0.1:0", nil)
				if err != nil {
					t.Fatalf("vmdns.New: %v", err)
				}
				return &Daemon{
					store:   openDaemonStore(t),
					closing: make(chan struct{}),
					vmDNS:   server,
					logger:  slog.New(slog.NewTextHandler(io.Discard, nil)),
				}
			},
			verify: func(t *testing.T, d *Daemon) {
				if d.vmDNS != nil {
					t.Error("vmDNS not cleared by Close")
				}
			},
		},
	}
	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			d := tc.build(t)
			if err := d.Close(); err != nil {
				t.Fatalf("Close returned error: %v", err)
			}
			tc.verify(t, d)

			// Second Close must be a no-op (sync.Once) — must not
			// panic on channel or re-close.
			if err := d.Close(); err != nil {
				t.Fatalf("second Close error: %v", err)
			}
		})
	}
}

// TestCloseIdempotentUnderConcurrency catches regressions of the
// sync.Once guard that makes repeated Close calls safe. The open-
// failure defer relies on this: if the user cancels before Open
// returns and also calls Close afterwards, both paths must survive.
func TestCloseIdempotentUnderConcurrency(t *testing.T) {
	d := &Daemon{
		store:   openDaemonStore(t),
		closing: make(chan struct{}),
		logger:  slog.New(slog.NewTextHandler(io.Discard, nil)),
		config:  model.DaemonConfig{BridgeName: ""},
	}

	var count atomic.Int32
	done := make(chan struct{})
	for i := 0; i < 5; i++ {
		go func() {
			if err := d.Close(); err != nil {
				t.Errorf("Close error: %v", err)
			}
			count.Add(1)
			if count.Load() == 5 {
				close(done)
			}
		}()
	}
	<-done

	// Channel must be closed exactly once (sync.Once covers the
	// inner close(d.closing)). Reading from a closed channel is
	// non-blocking; panicking here would mean the channel wasn't
	// closed or was double-closed (close panics are uncatchable).
	select {
	case <-d.closing:
	default:
		t.Fatal("closing channel not closed after concurrent Close calls")
	}
}

// TestOpenFailureRunsCloseCleanup is a structural check: confirms
// the deferred rollback in Open actually fires. Can't easily run
// Open() end-to-end (hits paths.Resolve + sudo), but we can simulate
// the pattern by threading a named-return err through the same
// defer and asserting Close runs.
func TestOpenFailureRunsCloseCleanup(t *testing.T) {
	closed := false
	fakeClose := func() { closed = true }

	runOpen := func() (err error) {
		defer func() {
			if err != nil {
				fakeClose()
			}
		}()
		err = errors.New("simulated late-stage startup failure")
		return err
	}

	if err := runOpen(); err == nil {
		t.Fatal("expected simulated error")
	}
	if !closed {
		t.Fatal("deferred cleanup did not fire on err != nil")
	}
}