$args =
{
 message_type => MQTT_CONNECT,
 client_id => 'mosquitto_sub_10888',
 will_flag => 1,
 will_qos => MQTT_QOS_AT_LEAST_ONCE,
 will_retain => 1,
 will_topic => 'topic',
 will_message => 'msg',
}

10 2d 00 06  4d 51 49 73    64 70 03 2e  00 3c 00 13
6d 6f 73 71  75 69 74 74    6f 5f 73 75  62 5f 31 30
38 38 38 00  05 74 6f 70    69 63 00 03  6d 73 67

Connect/at-most-once MQIsdp/3/mosquitto_sub_10888 will=topic,"msg",1,at-least-once