feat: OpenRC and runit init backends behind an Init interface

Extract init-neutral unit resolution into service/, add initsys.Init with systemd, openrc and runit backends, selected by 'init:' config or autodetect. OpenRC and runit are root only; rootless units run as system services as that user. Add docs and generated examples for all three.

initsys/initsys.go

@@ -0,0 +1,77 @@
+// Package initsys selects the init system backend that installs and controls
+// unitdore services.
+package initsys
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/warkanum/unitdore/config"
+	"github.com/warkanum/unitdore/openrc"
+	"github.com/warkanum/unitdore/runit"
+	"github.com/warkanum/unitdore/systemd"
+)
+
+// Backend names.
+const (
+	Systemd = "systemd"
+	OpenRC  = "openrc"
+	Runit   = "runit"
+)
+
+// Init is implemented by every init system backend. u.User selects the scope;
+// backends that cannot do per-user managers run user units as system services.
+type Init interface {
+	Name() string
+	ServiceName(u config.Unit, prefix, suffix string) string
+	UnitPath(u config.Unit, prefix, suffix string) (string, error)
+	Generate(u config.Unit, prefix, suffix string) (string, error)
+	Install(u config.Unit, prefix, suffix string) error
+	Uninstall(u config.Unit, prefix, suffix string) error
+	Enable(u config.Unit, prefix, suffix string) error
+	Disable(u config.Unit, prefix, suffix string) error
+	Start(u config.Unit, prefix, suffix string) error
+	Stop(u config.Unit, prefix, suffix string) error
+	// Status returns active | inactive | failed | activating | deactivating | unknown.
+	Status(u config.Unit, prefix, suffix string) string
+	IsInstalled(u config.Unit, prefix, suffix string) bool
+	// SupportsLinger reports whether user units need systemd-style linger.
+	SupportsLinger() bool
+}
+
+// New returns the backend named in cfg.Init, or the detected one.
+func New(cfg *config.Config) (Init, error) {
+	name := cfg.Init
+	if name == "" {
+		name = Detect("/")
+	}
+	switch name {
+	case Systemd:
+		return systemd.Backend{}, nil
+	case OpenRC:
+		return openrc.Backend{}, nil
+	case Runit:
+		return runit.Backend{ServiceDir: cfg.ServiceDir}, nil
+	default:
+		return nil, fmt.Errorf("unknown init %q (want systemd, openrc or runit)", name)
+	}
+}
+
+// Detect guesses the running init system below root. Falls back to systemd.
+func Detect(root string) string {
+	has := func(p string) bool {
+		_, err := os.Stat(filepath.Join(root, p))
+		return err == nil
+	}
+	switch {
+	case has("run/systemd/system"):
+		return Systemd
+	case has("run/openrc"), has("sbin/openrc-run"):
+		return OpenRC
+	case has("run/runit"), has("etc/runit"):
+		return Runit
+	default:
+		return Systemd
+	}
+}

initsys/initsys_test.go

@@ -0,0 +1,52 @@
+package initsys
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/warkanum/unitdore/config"
+)
+
+func TestDetect(t *testing.T) {
+	tests := []struct {
+		name  string
+		paths []string
+		want  string
+	}{
+		{"systemd", []string{"run/systemd/system"}, Systemd},
+		{"openrc", []string{"run/openrc"}, OpenRC},
+		{"openrc binary", []string{"sbin/openrc-run"}, OpenRC},
+		{"runit", []string{"etc/runit"}, Runit},
+		{"systemd wins", []string{"run/systemd/system", "etc/runit"}, Systemd},
+		{"fallback", nil, Systemd},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			root := t.TempDir()
+			for _, p := range tt.paths {
+				if err := os.MkdirAll(filepath.Dir(filepath.Join(root, p)), 0755); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(filepath.Join(root, p), nil, 0644); err != nil {
+					t.Fatal(err)
+				}
+			}
+			if got := Detect(root); got != tt.want {
+				t.Errorf("Detect() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestNew(t *testing.T) {
+	for _, name := range []string{Systemd, OpenRC, Runit} {
+		ini, err := New(&config.Config{Init: name})
+		if err != nil || ini.Name() != name {
+			t.Errorf("New(%q) = %v, %v", name, ini, err)
+		}
+	}
+	if _, err := New(&config.Config{Init: "sysv"}); err == nil {
+		t.Error("New() should reject an unknown init")
+	}
+}