Prototype atomic install recovery (T-103)

core/installer/layout.go

@@ -0,0 +1,110 @@
+package installer
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+var (
+	ErrUnsafeInstallLayout = errors.New("unsafe install directory layout")
+	ErrStagingMissing      = errors.New("staging directory is missing")
+	ErrBackupExists        = errors.New("backup directory already exists")
+)
+
+type appLayout struct {
+	root              string
+	current           string
+	staging           string
+	backup            string
+	transaction       string
+	transactionBackup string
+}
+
+type directoryState struct {
+	current bool
+	staging bool
+	backup  bool
+}
+
+func inspectAppLayout(root string) (appLayout, error) {
+	if root == "" {
+		return appLayout{}, fmt.Errorf("%w: empty root", ErrUnsafeInstallLayout)
+	}
+	absolute, err := filepath.Abs(root)
+	if err != nil {
+		return appLayout{}, fmt.Errorf("%w: %v", ErrUnsafeInstallLayout, err)
+	}
+	info, err := os.Lstat(absolute)
+	if err != nil {
+		return appLayout{}, fmt.Errorf("%w: root: %v", ErrUnsafeInstallLayout, err)
+	}
+	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
+		return appLayout{}, fmt.Errorf("%w: root is not a real directory", ErrUnsafeInstallLayout)
+	}
+	transaction, transactionBackup := transactionPaths(absolute)
+	return appLayout{
+		root:              absolute,
+		current:           filepath.Join(absolute, "current"),
+		staging:           filepath.Join(absolute, "staging"),
+		backup:            filepath.Join(absolute, "backup"),
+		transaction:       transaction,
+		transactionBackup: transactionBackup,
+	}, nil
+}
+
+func inspectDirectories(layout appLayout) (directoryState, error) {
+	current, err := inspectManagedDirectory(layout.current)
+	if err != nil {
+		return directoryState{}, err
+	}
+	staging, err := inspectManagedDirectory(layout.staging)
+	if err != nil {
+		return directoryState{}, err
+	}
+	backup, err := inspectManagedDirectory(layout.backup)
+	if err != nil {
+		return directoryState{}, err
+	}
+	return directoryState{
+		current: current,
+		staging: staging,
+		backup:  backup,
+	}, nil
+}
+
+func inspectManagedDirectory(path string) (bool, error) {
+	info, err := os.Lstat(path)
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	if err != nil {
+		return false, fmt.Errorf("%w: inspect %s: %v", ErrUnsafeInstallLayout, path, err)
+	}
+	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
+		return false, fmt.Errorf("%w: %s is not a real directory", ErrUnsafeInstallLayout, path)
+	}
+	return true, nil
+}
+
+func removeManagedDirectory(layout appLayout, target string) error {
+	if filepath.Dir(target) != layout.root {
+		return fmt.Errorf("%w: refuse removal outside app root", ErrUnsafeInstallLayout)
+	}
+	base := filepath.Base(target)
+	if base != "current" && base != "staging" && base != "backup" {
+		return fmt.Errorf("%w: refuse removal of %s", ErrUnsafeInstallLayout, base)
+	}
+	exists, err := inspectManagedDirectory(target)
+	if err != nil {
+		return err
+	}
+	if !exists {
+		return nil
+	}
+	if err := os.RemoveAll(target); err != nil {
+		return fmt.Errorf("remove managed directory %s: %w", base, err)
+	}
+	return nil
+}