MQTT_SUB_OPT_NO_LOCAL = 0x04
MQTT_SUB_OPT_RETAIN_AS_PUBLISHED = 0x08
MQTT_SUB_OPT_SEND_RETAIN_ALWAYS = 0x00
MQTT_SUB_OPT_SEND_RETAIN_NEW = 0x10
MQTT_SUB_OPT_SEND_RETAIN_NEVER = 0x20