From 55c98ef880a900085cc6c0cb9cd59833af3720c9 Mon Sep 17 00:00:00 2001
From: Thomas Basler <thomas@familie-basler.net>
Date: Fri, 1 Nov 2024 22:07:48 +0100
Subject: [PATCH] Fix: skip BOM in JSON files (pin_mapping and config)

based on #2387
---
 include/Utils.h       |  2 ++
 src/Configuration.cpp |  1 +
 src/PinMapping.cpp    |  3 +++
 src/Utils.cpp         | 12 ++++++++++++
 4 files changed, 18 insertions(+)

diff --git a/include/Utils.h b/include/Utils.h
index 759402b1..39994f32 100644
--- a/include/Utils.h
+++ b/include/Utils.h
@@ -2,6 +2,7 @@
 #pragma once
 
 #include <ArduinoJson.h>
+#include <LittleFS.h>
 #include <cstdint>
 
 class Utils {
@@ -12,4 +13,5 @@ public:
     static bool checkJsonAlloc(const JsonDocument& doc, const char* function, const uint16_t line);
     static void removeAllFiles();
     static String generateMd5FromFile(String file);
+    static void skipBom(File& f);
 };
diff --git a/src/Configuration.cpp b/src/Configuration.cpp
index 04bcfa65..10fd92fd 100644
--- a/src/Configuration.cpp
+++ b/src/Configuration.cpp
@@ -159,6 +159,7 @@ bool ConfigurationClass::write()
 bool ConfigurationClass::read()
 {
     File f = LittleFS.open(CONFIG_FILENAME, "r", false);
+    Utils::skipBom(f);
 
     JsonDocument doc;
 
diff --git a/src/PinMapping.cpp b/src/PinMapping.cpp
index bd5ea995..1a721e04 100644
--- a/src/PinMapping.cpp
+++ b/src/PinMapping.cpp
@@ -4,6 +4,7 @@
  */
 #include "PinMapping.h"
 #include "MessageOutput.h"
+#include "Utils.h"
 #include <ArduinoJson.h>
 #include <LittleFS.h>
 #include <string.h>
@@ -199,6 +200,8 @@ bool PinMappingClass::init(const String& deviceMapping)
         return false;
     }
 
+    Utils::skipBom(f);
+
     JsonDocument doc;
     // Deserialize the JSON document
     DeserializationError error = deserializeJson(doc, f);
diff --git a/src/Utils.cpp b/src/Utils.cpp
index e5746079..c567ec11 100644
--- a/src/Utils.cpp
+++ b/src/Utils.cpp
@@ -111,3 +111,15 @@ String Utils::generateMd5FromFile(String file)
 
     return md5.toString();
 }
+
+void Utils::skipBom(File& f)
+{
+    // skip Byte Order Mask (BOM). valid JSON docs always start with '{' or '['.
+    while (f.available() > 0) {
+        int c = f.peek();
+        if (c == '{' || c == '[') {
+            break;
+        }
+        f.read();
+    }
+}