secret/internal/vault/lock_test.go

package vault_test

import (
	"path/filepath"
	"testing"
	"time"

	"github.com/spf13/afero"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"sneak.berlin/go/secret/internal/secret"
	"sneak.berlin/go/secret/internal/vault"
)

const (
	// lockWait is how long a test waits for the lock before deciding it
	// will never come free.
	lockWait = 10 * time.Second

	// heldWait is how long a test watches a second holder fail to take a
	// lock that is held. Broken exclusion lets it in at once.
	heldWait = 100 * time.Millisecond
)

// lockFilesystem is a filesystem LockStateDir can lock, with a state
// directory on it.
type lockFilesystem struct {
	name     string
	fs       afero.Fs
	stateDir string
}

// lockFilesystems returns the real filesystem, locked with flock, and the
// in-memory one, locked with a mutex.
func lockFilesystems(t *testing.T) []lockFilesystem {
	t.Helper()

	return []lockFilesystem{
		{"memory", afero.NewMemMapFs(), testStateDir},
		{"real", afero.NewOsFs(), t.TempDir()},
	}
}

// lockInBackground starts taking the lock and returns a channel that
// delivers the function releasing it once it has been taken.
func lockInBackground(
	t *testing.T, fs afero.Fs, stateDir string,
) <-chan func() {
	t.Helper()

	taken := make(chan func(), 1)

	go func() {
		release, err := vault.LockStateDir(fs, stateDir)
		if assert.NoError(t, err) {
			taken <- release
		}
	}()

	return taken
}

// TestLockStateDirExcludes checks that while the lock is held a second
// holder, with its own open lock file on the real filesystem, waits, and
// that it gets the lock once the first releases it.
func TestLockStateDirExcludes(t *testing.T) {
	t.Parallel()

	for _, lfs := range lockFilesystems(t) {
		t.Run(lfs.name, func(t *testing.T) {
			t.Parallel()

			release, err := vault.LockStateDir(lfs.fs, lfs.stateDir)
			require.NoError(t, err)

			taken := lockInBackground(t, lfs.fs, lfs.stateDir)

			select {
			case second := <-taken:
				second()
				release()
				t.Fatal("a second holder took the lock while it was held")
			case <-time.After(heldWait):
			}

			release()

			select {
			case second := <-taken:
				second()
			case <-time.After(lockWait):
				t.Fatal("the second holder never got the lock")
			}
		})
	}
}

// TestLockStateDirFreeAfterPanic checks that a holder that panics, and
// releases the lock with defer as every command does, leaves it free.
func TestLockStateDirFreeAfterPanic(t *testing.T) {
	t.Parallel()

	for _, lfs := range lockFilesystems(t) {
		t.Run(lfs.name, func(t *testing.T) {
			t.Parallel()

			assert.Panics(t, func() {
				release, err := vault.LockStateDir(lfs.fs, lfs.stateDir)
				require.NoError(t, err)

				defer release()

				panic("the command failed")
			})

			select {
			case release := <-lockInBackground(t, lfs.fs, lfs.stateDir):
				release()
			case <-time.After(lockWait):
				t.Fatal("the lock was still held after its holder panicked")
			}
		})
	}
}

// TestLockStateDirRemovesLeftoversOnlyAfterKill checks that taking the lock
// deletes a temporary directory a killed command left only when the last
// holder of the lock did not release it. A holder killed while it holds the
// lock leaves the lock file as it is at that moment.
func TestLockStateDirRemovesLeftoversOnlyAfterKill(t *testing.T) {
	t.Parallel()

	for _, lfs := range lockFilesystems(t) {
		t.Run(lfs.name, func(t *testing.T) {
			t.Parallel()

			lockFile := filepath.Join(lfs.stateDir, "lock")
			leftover := filepath.Join(lfs.stateDir, ".tmp-1")

			release, err := vault.LockStateDir(lfs.fs, lfs.stateDir)
			require.NoError(t, err)

			whileHeld, err := afero.ReadFile(lfs.fs, lockFile)
			require.NoError(t, err)
			release()

			require.NoError(t, lfs.fs.MkdirAll(leftover, secret.DirPerms))

			release, err = vault.LockStateDir(lfs.fs, lfs.stateDir)
			require.NoError(t, err)
			release()

			exists, err := afero.DirExists(lfs.fs, leftover)
			require.NoError(t, err)
			assert.True(t, exists, "searched after a holder that finished")

			require.NoError(t, afero.WriteFile(lfs.fs, lockFile, whileHeld,
				secret.FilePerms))

			release, err = vault.LockStateDir(lfs.fs, lfs.stateDir)
			require.NoError(t, err)
			release()

			exists, err = afero.DirExists(lfs.fs, leftover)
			require.NoError(t, err)
			assert.False(t, exists, "not searched after a holder that was killed")
		})
	}
}

// TestLockStateDirRefusesOtherFilesystems checks that a filesystem with no
// lock implementation is refused instead of being used unlocked.
func TestLockStateDirRefusesOtherFilesystems(t *testing.T) {
	t.Parallel()

	fs := afero.NewReadOnlyFs(afero.NewMemMapFs())

	release, err := vault.LockStateDir(fs, testStateDir)
	require.ErrorIs(t, err, vault.ErrNoLockForFilesystem)
	assert.Nil(t, release)
}