Paho MQTT C Client Library
Data Fields
MQTTClient_message Struct Reference

#include <MQTTClient.h>

Data Fields

char struct_id [4]
int struct_version
int payloadlen
void * payload
int qos
int retained
int dup
int msgid
MQTTProperties properties

Detailed Description

A structure representing the payload and attributes of an MQTT message. The message topic is not part of this structure (see MQTTClient_publishMessage(), MQTTClient_publish(), MQTTClient_receive(), MQTTClient_freeMessage() and MQTTClient_messageArrived()).

Field Documentation

◆ struct_id

char struct_id[4]

The eyecatcher for this structure. must be MQTM.

◆ struct_version

int struct_version

The version number of this structure. Must be 0 or 1 0 indicates no message properties

◆ payloadlen

int payloadlen

The length of the MQTT message payload in bytes.

◆ payload

void* payload

A pointer to the payload of the MQTT message.

◆ qos

int qos

The quality of service (QoS) assigned to the message. There are three levels of QoS:

Fire and forget - the message may not be delivered
At least once - the message will be delivered, but may be delivered more than once in some circumstances.
Once and one only - the message will be delivered exactly once.

◆ retained

int 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.

◆ dup

int 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.

◆ msgid

int msgid

The message identifier is normally reserved for internal use by the MQTT client and server.

◆ properties

MQTTProperties properties

The MQTT V5 properties associated with the message.

The documentation for this struct was generated from the following file: