feat: backend native executor implement

internal/systemd/systemctl.go

@@ -0,0 +1,134 @@
+package systemd
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+const (
+	loadStateProperty   = "LoadState"
+	activeStateProperty = "ActiveState"
+	subStateProperty    = "SubState"
+	loadedState         = "loaded"
+	notFoundState       = "not-found"
+)
+
+// Systemctl invokes one exact systemctl executable directly, never through a shell.
+type Systemctl struct {
+	executable string
+}
+
+// NewSystemctl requires the absolute executable path supplied by local daemon configuration.
+func NewSystemctl(executable string) (*Systemctl, error) {
+	if !filepath.IsAbs(executable) {
+		return nil, errors.New("systemctl executable path must be absolute")
+	}
+	return &Systemctl{executable: executable}, nil
+}
+
+func (s *Systemctl) Inspect(ctx context.Context, unitName string) (Unit, error) {
+	if err := validateUnitName(unitName); err != nil {
+		return Unit{}, err
+	}
+	command := exec.CommandContext(ctx, s.executable,
+		"show",
+		"--no-pager",
+		"--property="+loadStateProperty,
+		"--property="+activeStateProperty,
+		"--property="+subStateProperty,
+		"--",
+		unitName,
+	)
+	output, err := command.CombinedOutput()
+	if err != nil {
+		return Unit{}, commandError("inspect systemd unit "+unitName, output, err)
+	}
+	unit, err := parseUnitProperties(unitName, output)
+	if err != nil {
+		return Unit{}, err
+	}
+	if unit.LoadState == notFoundState {
+		return Unit{}, fmt.Errorf("inspect systemd unit %s: %w", unitName, ErrUnitNotFound)
+	}
+	if unit.LoadState != loadedState {
+		return Unit{}, fmt.Errorf("systemd unit %s has unsupported load state %q", unitName, unit.LoadState)
+	}
+	return unit, nil
+}
+
+func (s *Systemctl) Start(ctx context.Context, unitName string) error {
+	return s.changeState(ctx, "start", unitName)
+}
+
+func (s *Systemctl) Stop(ctx context.Context, unitName string) error {
+	return s.changeState(ctx, "stop", unitName)
+}
+
+func (s *Systemctl) changeState(ctx context.Context, action, unitName string) error {
+	if err := validateUnitName(unitName); err != nil {
+		return err
+	}
+	output, err := exec.CommandContext(ctx, s.executable, action, "--", unitName).CombinedOutput()
+	if err != nil {
+		return commandError(action+" systemd unit "+unitName, output, err)
+	}
+	return nil
+}
+
+func parseUnitProperties(unitName string, output []byte) (Unit, error) {
+	values := make(map[string]string, 3)
+	scanner := bufio.NewScanner(bytes.NewReader(output))
+	for scanner.Scan() {
+		line := scanner.Text()
+		key, value, found := strings.Cut(line, "=")
+		if !found {
+			return Unit{}, fmt.Errorf("decode systemd unit %s property line %q", unitName, line)
+		}
+		switch key {
+		case loadStateProperty, activeStateProperty, subStateProperty:
+			if _, duplicate := values[key]; duplicate {
+				return Unit{}, fmt.Errorf("decode systemd unit %s duplicate property %s", unitName, key)
+			}
+			values[key] = value
+		default:
+			return Unit{}, fmt.Errorf("decode systemd unit %s unexpected property %q", unitName, key)
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return Unit{}, fmt.Errorf("decode systemd unit %s properties: %w", unitName, err)
+	}
+	for _, key := range []string{loadStateProperty, activeStateProperty, subStateProperty} {
+		if _, found := values[key]; !found {
+			return Unit{}, fmt.Errorf("decode systemd unit %s missing property %s", unitName, key)
+		}
+	}
+	return Unit{
+		Name:        unitName,
+		LoadState:   values[loadStateProperty],
+		ActiveState: values[activeStateProperty],
+		SubState:    values[subStateProperty],
+	}, nil
+}
+
+func validateUnitName(unitName string) error {
+	if unitName == "" || strings.TrimSpace(unitName) != unitName {
+		return errors.New("exact systemd unit name is required")
+	}
+	return nil
+}
+
+func commandError(action string, output []byte, err error) error {
+	detail := strings.TrimSpace(string(output))
+	if detail == "" {
+		return fmt.Errorf("%s: %w", action, err)
+	}
+	return fmt.Errorf("%s: %w: %s", action, err, detail)
+}
+
+var _ Manager = (*Systemctl)(nil)