Refactor logging to use slog package across the application

- Replaced standard log package with log/slog in httpclient, nginx manager, sync service, updater, and other components for structured logging.
- Introduced environment variable `LOG_LEVEL` to control logging levels (debug, info, warn, error).
- Updated documentation to reflect changes in logging configuration and requirements.
- Added a new logging setup function in the ats_agent internal package to initialize the slog logger.

atsf_agent/internal/sync/service.go

@@ -4,7 +4,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
-	"log"
+	"log/slog"
 	"strings"
 
 	"atsflare-agent/internal/protocol"
@@ -70,13 +70,13 @@ func (s *Service) sync(ctx context.Context, startup bool, target *protocol.Activ
 
 	if target == nil || target.Version == "" || target.Checksum == "" {
 		if !startup {
-			log.Printf("skipping sync because heartbeat returned no active config summary: mode=%s", mode)
+			slog.Debug("skipping sync because heartbeat returned no active config summary", "mode", mode)
 			return nil
 		}
-		log.Printf("sync startup fallback: active config summary unavailable, fetching active config directly")
+		slog.Info("sync startup fallback: active config summary unavailable, fetching active config directly")
 		config, fetchErr := s.client.GetActiveConfig(ctx)
 		if fetchErr != nil {
-			log.Printf("fetch active config failed: mode=%s error=%v", mode, fetchErr)
+			slog.Error("fetch active config failed", "mode", mode, "error", fetchErr)
 			return fetchErr
 		}
 		target = &protocol.ActiveConfigMeta{
@@ -87,33 +87,33 @@ func (s *Service) sync(ctx context.Context, startup bool, target *protocol.Activ
 	}
 
 	if currentChecksum == target.Checksum {
-		log.Printf("local openresty config already up to date: mode=%s version=%s", mode, target.Version)
+		slog.Info("local openresty config already up to date", "mode", mode, "version", target.Version)
 		if startup {
-			log.Printf("ensuring openresty runtime on startup: version=%s", target.Version)
+			slog.Info("ensuring openresty runtime on startup", "version", target.Version)
 			if err = s.nginxManager.EnsureRuntime(ctx, true); err != nil {
 				snapshot.OpenrestyStatus = protocol.OpenrestyStatusUnhealthy
 				snapshot.OpenrestyMessage = err.Error()
 				_ = s.stateStore.Save(snapshot)
 				return err
 			}
-			log.Printf("openresty runtime ensured on startup: version=%s", target.Version)
+			slog.Info("openresty runtime ensured on startup", "version", target.Version)
 			snapshot.OpenrestyStatus = protocol.OpenrestyStatusHealthy
 			snapshot.OpenrestyMessage = ""
 		}
 		snapshot.CurrentVersion = target.Version
 		snapshot.CurrentChecksum = target.Checksum
 		snapshot.LastError = ""
-		log.Printf("sync finished without changes: mode=%s version=%s", mode, target.Version)
+		slog.Info("sync finished without changes", "mode", mode, "version", target.Version)
 		return s.stateStore.Save(snapshot)
 	}
 	if snapshot.CurrentVersion == target.Version && snapshot.CurrentChecksum == target.Checksum && !startup {
-		log.Printf("skipping config fetch because state already records target version/checksum: version=%s checksum=%s", target.Version, target.Checksum)
+		slog.Debug("skipping config fetch because state already records target version/checksum", "version", target.Version, "checksum", target.Checksum)
 		return nil
 	}
 
 	config, err := s.client.GetActiveConfig(ctx)
 	if err != nil {
-		log.Printf("fetch active config failed: mode=%s error=%v", mode, err)
+		slog.Error("fetch active config failed", "mode", mode, "error", err)
 		return err
 	}
 	return s.applyIfNeeded(ctx, mode, startup, snapshot, currentChecksum, target, config)
@@ -121,30 +121,30 @@ func (s *Service) sync(ctx context.Context, startup bool, target *protocol.Activ
 
 func (s *Service) applyIfNeeded(ctx context.Context, mode string, startup bool, snapshot *state.Snapshot, currentChecksum string, target *protocol.ActiveConfigMeta, config *protocol.ActiveConfigResponse) error {
 	if currentChecksum == config.Checksum {
-		log.Printf("local openresty config already up to date: mode=%s version=%s", mode, config.Version)
+		slog.Info("local openresty config already up to date", "mode", mode, "version", config.Version)
 		if startup {
-			log.Printf("ensuring openresty runtime on startup: version=%s", config.Version)
+			slog.Info("ensuring openresty runtime on startup", "version", config.Version)
 			if err := s.nginxManager.EnsureRuntime(ctx, true); err != nil {
 				snapshot.OpenrestyStatus = protocol.OpenrestyStatusUnhealthy
 				snapshot.OpenrestyMessage = err.Error()
 				_ = s.stateStore.Save(snapshot)
 				return err
 			}
-			log.Printf("openresty runtime ensured on startup: version=%s", config.Version)
+			slog.Info("openresty runtime ensured on startup", "version", config.Version)
 			snapshot.OpenrestyStatus = protocol.OpenrestyStatusHealthy
 			snapshot.OpenrestyMessage = ""
 		}
 		snapshot.CurrentVersion = config.Version
 		snapshot.CurrentChecksum = config.Checksum
 		snapshot.LastError = ""
-		log.Printf("sync finished without changes: mode=%s version=%s", mode, config.Version)
+		slog.Info("sync finished without changes", "mode", mode, "version", config.Version)
 		return s.stateStore.Save(snapshot)
 	}
 	if target != nil && (target.Version != config.Version || target.Checksum != config.Checksum) {
-		log.Printf("active config changed between heartbeat and fetch: heartbeat_version=%s heartbeat_checksum=%s fetched_version=%s fetched_checksum=%s", target.Version, target.Checksum, config.Version, config.Checksum)
+		slog.Warn("active config changed between heartbeat and fetch", "heartbeat_version", target.Version, "heartbeat_checksum", target.Checksum, "fetched_version", config.Version, "fetched_checksum", config.Checksum)
 	}
 	if snapshot.CurrentVersion == config.Version && snapshot.CurrentChecksum == config.Checksum && !startup {
-		log.Printf("skipping apply because state already records target version/checksum: version=%s checksum=%s", config.Version, config.Checksum)
+		slog.Debug("skipping apply because state already records target version/checksum", "version", config.Version, "checksum", config.Checksum)
 		return nil
 	}
 	routeConfig := config.RouteConfig
@@ -153,9 +153,9 @@ func (s *Service) applyIfNeeded(ctx context.Context, mode string, startup bool,
 	}
 	mainConfigChecksum := checksumString(config.MainConfig)
 	routeConfigChecksum := checksumString(routeConfig)
-	log.Printf("applying new openresty config: mode=%s from_version=%s to_version=%s old_checksum=%s new_checksum=%s", mode, snapshot.CurrentVersion, config.Version, currentChecksum, config.Checksum)
+	slog.Info("applying new openresty config", "mode", mode, "from_version", snapshot.CurrentVersion, "to_version", config.Version, "old_checksum", currentChecksum, "new_checksum", config.Checksum)
 	if err := s.nginxManager.Apply(ctx, config.MainConfig, routeConfig, config.SupportFiles); err != nil {
-		log.Printf("apply openresty config failed: mode=%s version=%s error=%v", mode, config.Version, err)
+		slog.Error("apply openresty config failed", "mode", mode, "version", config.Version, "error", err)
 		snapshot.LastError = err.Error()
 		snapshot.OpenrestyStatus = protocol.OpenrestyStatusUnhealthy
 		snapshot.OpenrestyMessage = err.Error()
@@ -171,13 +171,13 @@ func (s *Service) applyIfNeeded(ctx context.Context, mode string, startup bool,
 			SupportFileCount:    len(config.SupportFiles),
 		})
 		if reportErr != nil {
-			log.Printf("report failed apply log failed: version=%s error=%v", config.Version, reportErr)
+			slog.Error("report failed apply log failed", "version", config.Version, "error", reportErr)
 			return reportErr
 		}
-		log.Printf("failed apply log reported: version=%s", config.Version)
+		slog.Warn("failed apply log reported", "version", config.Version)
 		return err
 	}
-	log.Printf("openresty config applied successfully: mode=%s version=%s", mode, config.Version)
+	slog.Info("openresty config applied successfully", "mode", mode, "version", config.Version)
 	snapshot.CurrentVersion = config.Version
 	snapshot.CurrentChecksum = config.Checksum
 	snapshot.LastError = ""
@@ -196,10 +196,10 @@ func (s *Service) applyIfNeeded(ctx context.Context, mode string, startup bool,
 		RouteConfigChecksum: routeConfigChecksum,
 		SupportFileCount:    len(config.SupportFiles),
 	}); err != nil {
-		log.Printf("report successful apply log failed: version=%s error=%v", config.Version, err)
+		slog.Error("report successful apply log failed", "version", config.Version, "error", err)
 		return err
 	}
-	log.Printf("successful apply log reported: version=%s", config.Version)
+	slog.Info("successful apply log reported", "version", config.Version)
 	return nil
 }