Extracted the class Latch

also fixed a buffer overrun and reduced the code size

src/ArduinoJson/Json/Latch.hpp

@@ -0,0 +1,54 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Polyfills/assert.hpp>
+
+namespace ARDUINOJSON_NAMESPACE {
+
+template <typename TReader>
+class Latch {
+ public:
+  Latch(TReader reader) : _reader(reader), _loaded(false) {
+#ifdef ARDUINOJSON_DEBUG
+    _ended = false;
+#endif
+  }
+
+  void clear() {
+    _loaded = false;
+  }
+
+  int last() const {
+    return _current;
+  }
+
+  FORCE_INLINE char current() {
+    if (!_loaded) {
+      load();
+    }
+    return _current;
+  }
+
+ private:
+  void load() {
+    ARDUINOJSON_ASSERT(!_ended);
+    int c = _reader.read();
+#ifdef ARDUINOJSON_DEBUG
+    if (c <= 0) _ended = true;
+#endif
+    _current = static_cast<char>(c > 0 ? c : 0);
+    _loaded = true;
+  }
+
+  TReader _reader;
+  char _current;
+  bool _loaded;
+#ifdef ARDUINOJSON_DEBUG
+  bool _ended;
+#endif
+};
+
+}  // namespace ARDUINOJSON_NAMESPACE