core_mqtt_state.h File Reference

Function to keep state of MQTT PUBLISH packet deliveries. More...

#include "core_mqtt.h"

Go to the source code of this file.

Macros
#define	MQTT_STATE_CURSOR_INITIALIZER   ( ( size_t ) 0 )
	Initializer value for an MQTTStateCursor_t, indicating a search should start at the beginning of a state record array.

Typedefs
typedef size_t	MQTTStateCursor_t
	Cursor for iterating through state records.

Functions
uint16_t	MQTT_PublishToResend (const MQTTContext_t *pMqttContext, MQTTStateCursor_t *pCursor)
	Get the packet ID of next pending publish to be resent.

Detailed Description

Function to keep state of MQTT PUBLISH packet deliveries.

Function Documentation

MQTT_PublishToResend()

uint16_t MQTT_PublishToResend	(	const MQTTContext_t *	pMqttContext,
		MQTTStateCursor_t *	pCursor
	)

Get the packet ID of next pending publish to be resent.

This function will need to be called to get the packet for which a publish need to be sent when a session is reestablished. Calling this function repeatedly until packet id is 0 will give all the packets for which a publish need to be resent in the correct order.

Parameters

[in]	pMqttContext	Initialized MQTT context.
[in,out]	pCursor	Index at which to start searching.

Example

// For this example assume this function returns an outgoing unacknowledged
// QoS 1 or 2 publish from its packet identifier.
MQTTPublishInfo_t * getPublish( uint16_t packetID );
 
// Variables used in this example.
MQTTStatus_t status;
MQTTStateCursor_t cursor = MQTT_STATE_CURSOR_INITIALIZER;
bool sessionPresent;
uint16_t packetID;
MQTTPublishInfo_t * pResendPublish = NULL;
MQTTConnectInfo_t connectInfo = { 0 };
 
// This is assumed to have been initialized before the call to MQTT_Connect().
MQTTContext_t * pContext;
 
// Set clean session to false to attempt session resumption.
connectInfo.cleanSession = false;
connectInfo.pClientIdentifier = "someClientID";
connectInfo.clientIdentifierLength = strlen( connectInfo.pClientIdentifier );
connectInfo.keepAliveSeconds = 60;
// Optional connect parameters are not relevant to this example.
 
// Create an MQTT connection. Use 100 milliseconds as a timeout.
status = MQTT_Connect( pContext, &connectInfo, NULL, 100, &sessionPresent );
 
if( status == MQTTSuccess )
{
     if( sessionPresent )
     {
         // Loop while packet ID is nonzero.
         while( ( packetID = MQTT_PublishToResend( pContext, &cursor ) ) != 0 )
         {
             // Assume this function will succeed.
             pResendPublish = getPublish( packetID );
             // Set DUP flag.
             pResendPublish->dup = true;
             status = MQTT_Publish( pContext, pResendPublish, packetID );
 
             if( status != MQTTSuccess )
             {
                 // Application can decide how to handle a failure.
             }
         }
     }
     else
     {
         // The broker did not resume a session, so we can clean up the
         // list of outgoing publishes.
     }
}