Fix logging Example : log only first field, when using

[arckadious]

Changes

This PR follows issue #691.

Verification

grpc_logging.UnaryServerInterceptor(InterceptorLogrus(logger),grpc_logging.WithLogOnEvents(grpc_logging.FinishCall)),

My logging interceptor function :

func InterceptorLogrus(l log.FieldLogger) grpc_logging.Logger {
	return grpc_logging.LoggerFunc(func(_ context.Context, lvl grpc_logging.Level, msg string, fields ...any) {
		f := make(map[string]any, len(fields)/2)

		logFields := grpc_logging.Fields(fields)

		i := logFields.Iterator()

		for i.Next() {
			k, v := i.At()
			f[k] = v
		}
		l := l.WithFields(f)

		if _, ok := f["protocol"]; ok {
			l = l.WithField("system", f["protocol"])
		}
		l = l.WithField("span.kind", "server")

		switch lvl {
		case grpc_logging.LevelDebug:
			l.Debug(msg)
		case grpc_logging.LevelInfo:
			l.Info(msg)
		case grpc_logging.LevelWarn:
			l.Warn(msg)
		case grpc_logging.LevelError:
			l.Error(msg)
		default:
			l.Error(fmt.Sprintf("InterceptorLogrus : unknown level %v", lvl), " - logging message : ", msg)
		}
	})
}