Fix: skip BOM in JSON files (pin_mapping and config)

based on #2387

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);
 };

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;
 

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);

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();
+    }
+}