MQTTSubscribe_options - Man Page

char struct_id [4]
int struct_version
unsigned char noLocal
unsigned char retainAsPublished
unsigned char retainHandling

The eyecatcher for this structure. Must be MQSO.

The version number of this structure. Must be 0.

To not receive our own publications, set to 1. 0 is the original MQTT behaviour - all messages matching the subscription are received.

To keep the retain flag as on the original publish message, set to 1. If 0, defaults to the original MQTT behaviour where the retain flag is only set on publications sent by a broker if in response to a subscribe request.

0 - send retained messages at the time of the subscribe (original MQTT behaviour) 1 - send retained messages on subscribe only if the subscription is new 2 - do not send retained messages at all