ThothII/tools/tht/internal/lifecycle/lock.go

// Package lifecycle coordinates installation-wide mutating operations.
package lifecycle

import (
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"

	"github.com/aritmolab/thothii/tools/tht/internal/config"
)

var (
	ErrLocked                  = errors.New("another lifecycle operation is already running for this installation")
	ErrOwnership               = errors.New("lifecycle lock ownership changed; refusing to remove it")
	ErrTransactionInactive     = errors.New("lifecycle transaction capability is not active")
	ErrTransactionInstallation = errors.New("lifecycle transaction capability belongs to another installation")
)

const lockFileName = "lifecycle.lock.owner.json"

type owner struct {
	Token     string    `json:"token"`
	PID       int       `json:"pid"`
	CreatedAt time.Time `json:"created_at"`
}

// Lock is an exclusively-created owner file scoped to one installation descriptor.
type Lock struct {
	path     string
	token    string
	mu       sync.Mutex
	released bool
}

// Transaction is an opaque, installation-bound capability for work that must run while a
// lifecycle lock remains owned. Its fields are deliberately private so callers can obtain one
// only through AcquireTransaction.
type Transaction struct {
	lock             *Lock
	controlDirectory string
}

// Acquire obtains the shared lock used by backup, restore, Pi lifecycle and product updates.
func Acquire(installation config.Installation) (*Lock, error) {
	directory := installation.ControlDirectory()
	if err := os.MkdirAll(directory, 0o700); err != nil {
		return nil, fmt.Errorf("create lifecycle control directory: %w", err)
	}
	info, err := os.Lstat(directory)
	if err != nil || !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {
		return nil, errors.New("lifecycle control directory is not a regular directory")
	}
	if err := os.Chmod(directory, 0o700); err != nil {
		return nil, fmt.Errorf("protect lifecycle control directory: %w", err)
	}

	tokenBytes := make([]byte, 16)
	if _, err := rand.Read(tokenBytes); err != nil {
		return nil, fmt.Errorf("create lifecycle lock owner: %w", err)
	}
	token := hex.EncodeToString(tokenBytes)
	path := filepath.Join(directory, lockFileName)
	file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
	if errors.Is(err, os.ErrExist) {
		return nil, ErrLocked
	}
	if err != nil {
		return nil, fmt.Errorf("acquire lifecycle lock: %w", err)
	}
	value := owner{Token: token, PID: os.Getpid(), CreatedAt: time.Now().UTC()}
	encodeErr := json.NewEncoder(file).Encode(value)
	if encodeErr == nil {
		encodeErr = file.Sync()
	}
	closeErr := file.Close()
	if encodeErr != nil || closeErr != nil {
		_ = os.Remove(path)
		return nil, fmt.Errorf("persist lifecycle lock owner: %w", errors.Join(encodeErr, closeErr))
	}
	return &Lock{path: path, token: token}, nil
}

// AcquireTransaction obtains a lifecycle lock and returns the capability required by callers
// that perform nested work inside the same non-reentrant transaction.
func AcquireTransaction(installation config.Installation) (*Transaction, error) {
	lock, err := Acquire(installation)
	if err != nil {
		return nil, err
	}
	return &Transaction{
		lock:             lock,
		controlDirectory: filepath.Clean(installation.ControlDirectory()),
	}, nil
}

// Verify refuses a nil, released, replaced, or foreign-installation capability before a nested
// lifecycle operation can begin.
func (transaction *Transaction) Verify(installation config.Installation) error {
	if transaction == nil || transaction.lock == nil {
		return ErrTransactionInactive
	}
	if transaction.controlDirectory != filepath.Clean(installation.ControlDirectory()) {
		return ErrTransactionInstallation
	}
	return transaction.lock.verifyHeld()
}

// Release relinquishes the lifecycle lock associated with this transaction capability.
func (transaction *Transaction) Release() error {
	if transaction == nil || transaction.lock == nil {
		return nil
	}
	return transaction.lock.Release()
}

// Path returns the installation-private owner-file path for diagnostics and tests.
func (lock *Lock) Path() string {
	if lock == nil {
		return ""
	}
	return lock.path
}

// Release removes only the owner file created by this Lock.
func (lock *Lock) Release() error {
	if lock == nil {
		return nil
	}
	lock.mu.Lock()
	defer lock.mu.Unlock()
	if lock.released {
		return nil
	}
	contents, err := os.ReadFile(lock.path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return ErrOwnership
		}
		return fmt.Errorf("read lifecycle lock owner: %w", err)
	}
	var current owner
	if json.Unmarshal(contents, &current) != nil || current.Token == "" || current.Token != lock.token {
		return ErrOwnership
	}
	if err := os.Remove(lock.path); err != nil {
		return fmt.Errorf("release lifecycle lock: %w", err)
	}
	lock.released = true
	return nil
}

func (lock *Lock) verifyHeld() error {
	if lock == nil {
		return ErrTransactionInactive
	}
	lock.mu.Lock()
	defer lock.mu.Unlock()
	if lock.released {
		return ErrTransactionInactive
	}
	contents, err := os.ReadFile(lock.path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return ErrOwnership
		}
		return fmt.Errorf("read lifecycle lock owner: %w", err)
	}
	var current owner
	if json.Unmarshal(contents, &current) != nil || current.Token == "" || current.Token != lock.token {
		return ErrOwnership
	}
	return nil
}