Add JSON API

test/fuzz.c

@@ -43,5 +43,8 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
   struct mg_str k, v, s = mg_str_n((char *) data, size);
   while (mg_commalist(&s, &k, &v)) k.len = v.len = 0;
 
+  int n;
+  mg_json_get((char *) data, (int) size, "$", &n);
+
   return 0;
 }