From 12f6fbc00534cc18805e8f1eb5c4d071fca36300 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Frank=20M=C3=B6hle?=
 <91616163+softhack007@users.noreply.github.com>
Date: Sun, 5 Apr 2026 22:11:00 +0200
Subject: [PATCH] robustness: Rewind file pointer before writing initial data

if the presets.json file initially contains ``{}`` (valid JSON, could be created by user edit), we need to first rewind the file. Otherwise the result would be ``{}{"0":{}}`` (ivalid JSON)
---
 wled00/file.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/wled00/file.cpp b/wled00/file.cpp
index dcc2d57c4..5a169d645 100644
--- a/wled00/file.cpp
+++ b/wled00/file.cpp
@@ -188,6 +188,7 @@ static bool appendObjectToFile(const char* key, const JsonDocument* content, uin
   if (f.size() < 3) {
     char init[10];
     strcpy_P(init, PSTR("{\"0\":{}}"));
+    f.seek(0, SeekSet);           // rewind to ensure we overwrite from the start, instead of appending
     f.print(init);
   }