use espMqttClient, qos2 fixed

lib/espMqttClient/src/Packets/String.cpp

@@ -0,0 +1,26 @@
+/*
+Copyright (c) 2022 Bert Melis. All rights reserved.
+
+This work is licensed under the terms of the MIT license.  
+For a copy, see <https://opensource.org/licenses/MIT> or
+the LICENSE file.
+*/
+
+#include "String.h"
+
+namespace espMqttClientInternals {
+
+size_t encodeString(const char* source, uint8_t* dest) {
+  size_t length = strlen(source);
+  if (length > 65535) {
+    emc_log_e("String length error");
+    return 0;
+  }
+
+  dest[0] = static_cast<uint16_t>(length) >> 8;
+  dest[1] = static_cast<uint16_t>(length) & 0xFF;
+  memcpy(&dest[2], source, length);
+  return 2 + length;
+}
+
+}  // namespace espMqttClientInternals