MQTTAsync_message(3)

NAME
MQTTAsync_message

SYNOPSIS

#include <MQTTAsync.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 MQTTAsync_publishMessage(), MQTTAsync_publish(), MQTTAsync_receive(), MQTTAsync_freeMessage() and MQTTAsync_messageArrived()).

Field Documentation

  char struct_id[4]
The eyecatcher for this structure. must be MQTM.

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

  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. There are three levels of QoS:

QoS0
    Fire and forget - the message may not be delivered

QoS1
    At least once - the message will be delivered, but may be delivered more than once in some circumstances.

QoS2
    Once and one only - the message will be delivered exactly once.

  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.

  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. This is an output parameter only.

  int 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.

  MQTTProperties properties
The MQTT V5 properties associated with the message.

Author

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