Initial commit: Go driver for the Lian Li Galahad II LCD

Streams H.264 to the Galahad II LCD via USB (gousb) with:
- ffmpeg CLI transcoding (no fragile FFmpeg C-ABI bindings)
- pure-Go Annex-B access-unit splitting
- framerate pacing with graceful shutdown and USB reconnect
- TOML config, cobra CLI, structured slog logging, unit tests

internal/service/service.go

@@ -0,0 +1,34 @@
+// Package service manages the galahad2lcd systemd unit.
+package service
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+)
+
+// Service represents the installed systemd unit.
+type Service struct {
+	name string
+	// runCmd is the command constructor; overridable for tests.
+	runCmd func(ctx context.Context, name string, arg ...string) *exec.Cmd
+}
+
+// New returns a Service wrapper for the given unit name.
+func New(name string) *Service {
+	return &Service{name: name, runCmd: exec.CommandContext}
+}
+
+// Restart tells systemd to restart the service. It fails early when the
+// caller lacks privileges.
+func (s *Service) Restart(ctx context.Context) error {
+	cmd := s.runCmd(ctx, "systemctl", "restart", s.name)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		if len(out) > 0 {
+			return fmt.Errorf("systemctl restart %s: %w (%s)", s.name, err, string(out))
+		}
+		return fmt.Errorf("systemctl restart %s: %w", s.name, err)
+	}
+	return nil
+}

internal/service/service_test.go

@@ -0,0 +1,59 @@
+package service
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// fakeSystemctl installs a fake systemctl on PATH and returns the path to its
+// directory.
+func fakeSystemctl(t *testing.T, script string) string {
+	t.Helper()
+	dir := t.TempDir()
+	path := filepath.Join(dir, "systemctl")
+	if err := os.WriteFile(path, []byte("#!/bin/sh\n"+script), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("PATH", dir+string(os.PathListSeparator)+os.Getenv("PATH"))
+	return path
+}
+
+func TestRestartSuccess(t *testing.T) {
+	fakeSystemctl(t, "exit 0\n")
+	if err := New("galahad2lcd").Restart(context.Background()); err != nil {
+		t.Fatalf("Restart error = %v", err)
+	}
+}
+
+func TestRestartFailure(t *testing.T) {
+	fakeSystemctl(t, "echo 'permission denied' >&2; exit 1\n")
+	err := New("galahad2lcd").Restart(context.Background())
+	if err == nil {
+		t.Fatal("Restart returned nil error, want failure")
+	}
+}
+
+func TestRestartCancellation(t *testing.T) {
+	fakeSystemctl(t, "sleep 5\n")
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	err := New("galahad2lcd").Restart(ctx)
+	if err == nil {
+		t.Fatal("Restart returned nil error for cancelled context")
+	}
+}
+
+// Ensure the default constructor wires up the real exec.CommandContext.
+func TestNewDefaultRunCmd(t *testing.T) {
+	s := New("x")
+	if s.runCmd == nil {
+		t.Fatal("runCmd not initialised")
+	}
+	cmd := s.runCmd(context.Background(), "true")
+	if cmd == nil {
+		t.Fatal("runCmd returned nil command")
+	}
+}