feat: Allow users to set json log output

cmd/tusd/cli/flags.go

@@ -65,6 +65,7 @@ var Flags struct {
 	PprofMutexProfileRate            int
 	BehindProxy                      bool
 	VerboseOutput                    bool
+	LogFormat                        string
 	S3TransferAcceleration           bool
 	TLSCertFile                      string
 	TLSKeyFile                       string
@@ -178,6 +179,7 @@ func ParseFlags() {
 		f.BoolVar(&Flags.ShowGreeting, "show-greeting", true, "Show the greeting message")
 		f.BoolVar(&Flags.ShowVersion, "version", false, "Print tusd version information")
 		f.BoolVar(&Flags.VerboseOutput, "verbose", true, "Enable verbose logging output")
+		f.StringVar(&Flags.LogFormat, "log-format", "text", "Logging format (txt or json)")
 	})
 
 	fs.AddGroup("Timeout options", func(f *flag.FlagSet) {

cmd/tusd/cli/log.go

@@ -16,22 +16,38 @@ func SetupStructuredLogger() {
 		level = slog.LevelDebug
 	}
 
-	slogger := slog.New(
-		slog.NewTextHandler(logWriter{stdout}, &slog.HandlerOptions{
+	replaceAttrFunc := func(groups []string, a slog.Attr) slog.Attr {
+		// Remove time attribute, because that is handled by the logger
+		if a.Key == slog.TimeKey {
+			return slog.Attr{}
+		}
+		// Rename `msg` to `event`
+		if a.Key == slog.MessageKey {
+			a.Key = "event"
+		}
+		return a
+	}
+
+	var handler slog.Handler
+	switch Flags.LogFormat {
+	case "json":
+		handler = slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
 			Level: level,
-			ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
-				// Remove time attribute, because that is handled by the logger
-				if a.Key == slog.TimeKey {
-					return slog.Attr{}
-				}
-				// Rename `msg` to `event`
-				if a.Key == slog.MessageKey {
-					a.Key = "event"
-				}
-				return a
-			},
-		}))
-	slog.SetDefault(slogger)
+		})
+	default:
+		handler = slog.NewTextHandler(logWriter{log.New(os.Stdout, "", log.LstdFlags|log.Lmicroseconds)}, &slog.HandlerOptions{
+			Level:       level,
+			ReplaceAttr: replaceAttrFunc,
+		})
+	}
+
+	slog.SetDefault(slog.New(handler))
+
+	if Flags.LogFormat == "json" {
+		// stdout and stderr helpers need to be overwritten to use slog
+		stdout = log.Default()
+		stderr = log.Default()
+	}
 }
 
 // logWriter is an io.Writer that forwards all input to the given log.Logger,