Add structured logging and better error handling

main.go

@@ -3,7 +3,8 @@ package main
 import (
 	"context"
 	"errors"
-	"log"
+	"fmt"
+	"log/slog"
 	"net/http"
 	"os"
 	"os/signal"
@@ -15,6 +16,7 @@ import (
 	"ddc/internal/config"
 	"ddc/internal/history"
 	"ddc/internal/jobs"
+	"ddc/internal/logging"
 	"ddc/internal/preferences"
 	"ddc/internal/server"
 )
@@ -22,45 +24,41 @@ import (
 const (
 	settingsFileName = ".settings.json"
 	historyFileName  = ".history.json"
+	shutdownTimeout  = 10 * time.Second
 )
 
 func main() {
 	settings, err := config.Load()
 	if err != nil {
-		log.Fatalf("configuration error: %v", err)
+		logging.Fatal("configuration error", err)
+	}
+	if err := logging.Setup(settings.LogLevel, settings.LogFormat); err != nil {
+		logging.Fatal("logging configuration error", err)
 	}
 
-	if err := os.MkdirAll(settings.DownloadDir, 0o755); err != nil {
-		log.Fatalf("download directory error: %v", err)
-	}
-	resolvedDownloadDir, err := filepath.EvalSymlinks(settings.DownloadDir)
-	if err != nil {
-		log.Fatalf("download directory error: %v", err)
-	}
-	settings.DownloadDir = resolvedDownloadDir
-	if err := ensureWritable(settings.DownloadDir); err != nil {
-		log.Fatalf("download directory %s is not writable by uid %d gid %d: %v", settings.DownloadDir, os.Getuid(), os.Getgid(), err)
+	if err := prepareDownloadDir(&settings); err != nil {
+		logging.Fatal("download directory error", err, "path", settings.DownloadDir)
 	}
 
 	store, err := preferences.Open(filepath.Join(settings.DownloadDir, settingsFileName), settings.Defaults)
 	if err != nil {
-		log.Fatalf("settings error: %v", err)
+		logging.Fatal("could not load settings", err)
 	}
-
 	historyStore, err := history.Open(filepath.Join(settings.DownloadDir, historyFileName))
 	if err != nil {
-		log.Fatalf("history error: %v", err)
+		logging.Fatal("could not load history", err)
 	}
 
 	manager := jobs.NewManager(settings, store, historyStore)
 	if err := manager.RestoreExisting(); err != nil {
-		log.Printf("could not restore existing downloads: %v", err)
+		slog.Error("could not restore existing downloads", "error", err)
 	}
 
 	sessions := auth.NewSessionStore(settings.SessionTTL)
 	httpServer := &http.Server{
 		Addr:              settings.ListenAddr,
 		Handler:           server.New(settings, sessions, manager),
+		ErrorLog:          slog.NewLogLogger(slog.Default().Handler(), slog.LevelWarn),
 		ReadHeaderTimeout: 10 * time.Second,
 		ReadTimeout:       30 * time.Second,
 		WriteTimeout:      60 * time.Second,
@@ -71,20 +69,41 @@ func main() {
 	defer stopListening()
 
 	go func() {
-		log.Printf("listening on %s", settings.ListenAddr)
+		slog.Info("server started",
+			"listen", settings.ListenAddr,
+			"download_dir", settings.DownloadDir,
+			"library_roots", settings.LibraryRoots,
+			"log_level", settings.LogLevel,
+		)
 		if err := httpServer.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
-			log.Fatalf("server error: %v", err)
+			logging.Fatal("server stopped unexpectedly", err)
 		}
 	}()
 
 	<-shutdownSignal.Done()
-	log.Printf("shutting down")
-	shutdownContext, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	slog.Info("shutting down, saving download progress")
+	shutdownContext, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
 	defer cancel()
 	manager.Shutdown(shutdownContext)
 	if err := httpServer.Shutdown(shutdownContext); err != nil {
-		log.Printf("shutdown error: %v", err)
+		slog.Error("shutdown did not finish cleanly", "error", err)
 	}
+	slog.Info("stopped")
+}
+
+func prepareDownloadDir(settings *config.Settings) error {
+	if err := os.MkdirAll(settings.DownloadDir, 0o755); err != nil {
+		return err
+	}
+	resolved, err := filepath.EvalSymlinks(settings.DownloadDir)
+	if err != nil {
+		return err
+	}
+	settings.DownloadDir = resolved
+	if err := ensureWritable(resolved); err != nil {
+		return fmt.Errorf("not writable by uid %d gid %d: %w", os.Getuid(), os.Getgid(), err)
+	}
+	return nil
 }
 
 func ensureWritable(directory string) error {