|  | MQTT C Client Libraries Internals
    | 
A structure representing the payload and attributes of an MQTT message. More...
#include <MQTTAsync.h>

| Data Fields | |
| char | struct_id [4] | 
| The eyecatcher for this structure.  More... | |
| int | struct_version | 
| The version number of this structure.  More... | |
| int | payloadlen | 
| The length of the MQTT message payload in bytes. | |
| void * | payload | 
| A pointer to the payload of the MQTT message. | |
| int | qos | 
| The quality of service (QoS) assigned to the message.  More... | |
| int | retained | 
| The retained flag serves two purposes depending on whether the message it is associated with is being published or received.  More... | |
| int | dup | 
| The dup flag indicates whether or not this message is a duplicate.  More... | |
| int | msgid | 
| The message identifier is reserved for internal use by the MQTT client and server.  More... | |
| MQTTProperties | properties | 
| The MQTT V5 properties associated with the message. | |
A structure representing the payload and attributes of an MQTT message.
The message topic is not part of this structure (see MQTTAsync_publishMessage(), MQTTAsync_publish(), MQTTAsync_receive(), MQTTAsync_freeMessage() and MQTTAsync_messageArrived()).
| int MQTTAsync_message::dup | 
The dup flag indicates whether or not this message is a duplicate.
It is only meaningful when receiving QoS1 messages. When true, the client application should take appropriate action to deal with the duplicate message. This is an output parameter only.
| int MQTTAsync_message::msgid | 
The message identifier is reserved for internal use by the MQTT client and server.
It is an output parameter only - writing to it will serve no purpose. It contains the MQTT message id of an incoming publish message.
| int MQTTAsync_message::qos | 
The quality of service (QoS) assigned to the message.
There are three levels of QoS:
| int MQTTAsync_message::retained | 
The retained flag serves two purposes depending on whether the message it is associated with is being published or received.
retained = true
 For messages being published, a true setting indicates that the MQTT server should retain a copy of the message. The message will then be transmitted to new subscribers to a topic that matches the message topic. For subscribers registering a new subscription, the flag being true indicates that the received message is not a new one, but one that has been retained by the MQTT server.
retained = false 
 For publishers, this indicates that this message should not be retained by the MQTT server. For subscribers, a false setting indicates this is a normal message, received as a result of it being published to the server. 
| char MQTTAsync_message::struct_id[4] | 
The eyecatcher for this structure.
must be MQTM.
| int MQTTAsync_message::struct_version | 
The version number of this structure.
Must be 0 or 1. 0 indicates no message properties
 1.8.17
 1.8.17