$args =
{
 message_type => MQTT_CONNECT,
 client_id => 'mosquitto_sub_3926',
 connect_reserved_flag => 1,
 user_name => 'guest', user_name_flag => 1,
 password => 'passw0rd', password_flag => 1,
 dup => 1,
}

18 31 00 06  4d 51 49 73    64 70 03 c3  00 3c 00 12
6d 6f 73 71  75 69 74 74    6f 5f 73 75  62 5f 33 39
32 36 00 05  67 75 65 73    74 00 08 70  61 73 73 77
30 72 64

Connect/at-most-once,dup MQIsdp/3/mosquitto_sub_3926 user=guest pass=passw0rd