$args =
{
 message_type => MQTT_PUBLISH,
 qos => MQTT_QOS_EXACTLY_ONCE,
 topic => 'testing',
 message => 'test',
 message_id => 1,
 retain => 1,
}

35 0f 00 07  74 65 73 74    69 6e 67 00  01 74 65 73
74

Publish/exactly-once,retain testing/1 
  74 65 73 74                                      test