Added fuzzer

fuzzing/fuzzer.cpp

@@ -0,0 +1,23 @@
+#include <ArduinoJson.h>
+
+class memstream : public std::istream {
+  struct membuf : std::streambuf {
+    membuf(const uint8_t *p, size_t l) {
+      setg((char *)p, (char *)p, (char *)p + l);
+    }
+  };
+  membuf _buffer;
+
+ public:
+  memstream(const uint8_t *p, size_t l)
+      : std::istream(&_buffer), _buffer(p, l) {
+    rdbuf(&_buffer);
+  }
+};
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  DynamicJsonBuffer jsonBuffer;
+  memstream json(data, size);
+  jsonBuffer.parse(json);
+  return 0;
+}