User-facing functions of the MQTT 3.1.1 library. More...

#include "core_mqtt_serializer.h"
#include "transport_interface.h"

Data Structures
struct	MQTTPubAckInfo_t
	An element of the state engine records for QoS 1 or Qos 2 publishes. More...

struct	MQTTContext_t
	A struct representing an MQTT connection. More...

struct	MQTTDeserializedInfo_t
	Struct to hold deserialized packet information for an MQTTEventCallback_t callback. More...

Macros
#define	MQTT_PACKET_ID_INVALID ( ( uint16_t ) 0U )
	Invalid packet identifier.

Typedefs
typedef uint32_t(*	MQTTGetCurrentTimeFunc_t) (void)
	Application provided function to query the time elapsed since a given epoch in milliseconds.

typedef void(*	MQTTEventCallback_t) (struct MQTTContext pContext, struct MQTTPacketInfo pPacketInfo, struct MQTTDeserializedInfo *pDeserializedInfo)
	Application callback for receiving incoming publishes and incoming acks.

Enumerations
enum	MQTTConnectionStatus_t { MQTTNotConnected , MQTTConnected }
	Values indicating if an MQTT connection exists. More...

enum	MQTTPublishState_t { MQTTStateNull = 0 , MQTTPublishSend , MQTTPubAckSend , MQTTPubRecSend , MQTTPubRelSend , MQTTPubCompSend , MQTTPubAckPending , MQTTPubRecPending , MQTTPubRelPending , MQTTPubCompPending , MQTTPublishDone }
	The state of QoS 1 or QoS 2 MQTT publishes, used in the state engine. More...

enum	MQTTPubAckType_t { MQTTPuback , MQTTPubrec , MQTTPubrel , MQTTPubcomp }
	Packet types used in acknowledging QoS 1 or QoS 2 publishes. More...

enum	MQTTSubAckStatus_t { MQTTSubAckSuccessQos0 = 0x00 , MQTTSubAckSuccessQos1 = 0x01 , MQTTSubAckSuccessQos2 = 0x02 , MQTTSubAckFailure = 0x80 }
	The status codes in the SUBACK response to a subscription request. More...

Functions
MQTTStatus_t	MQTT_Init (MQTTContext_t pContext, const TransportInterface_t pTransportInterface, MQTTGetCurrentTimeFunc_t getTimeFunction, MQTTEventCallback_t userCallback, const MQTTFixedBuffer_t *pNetworkBuffer)
	Initialize an MQTT context.

MQTTStatus_t	MQTT_InitStatefulQoS (MQTTContext_t pContext, MQTTPubAckInfo_t pOutgoingPublishRecords, size_t outgoingPublishCount, MQTTPubAckInfo_t *pIncomingPublishRecords, size_t incomingPublishCount)
	Initialize an MQTT context for QoS > 0.

MQTTStatus_t	MQTT_Connect (MQTTContext_t pContext, const MQTTConnectInfo_t pConnectInfo, const MQTTPublishInfo_t pWillInfo, uint32_t timeoutMs, bool pSessionPresent)
	Establish an MQTT session.

MQTTStatus_t	MQTT_Subscribe (MQTTContext_t pContext, const MQTTSubscribeInfo_t pSubscriptionList, size_t subscriptionCount, uint16_t packetId)
	Sends MQTT SUBSCRIBE for the given list of topic filters to the broker.

MQTTStatus_t	MQTT_Publish (MQTTContext_t pContext, const MQTTPublishInfo_t pPublishInfo, uint16_t packetId)
	Publishes a message to the given topic name.

MQTTStatus_t	MQTT_CancelCallback (const MQTTContext_t *pContext, uint16_t packetId)
	Cancels an outgoing publish callback (only for QoS > QoS0) by removing it from the pending ACK list.

MQTTStatus_t	MQTT_Ping (MQTTContext_t *pContext)
	Sends an MQTT PINGREQ to broker.

MQTTStatus_t	MQTT_Unsubscribe (MQTTContext_t pContext, const MQTTSubscribeInfo_t pSubscriptionList, size_t subscriptionCount, uint16_t packetId)
	Sends MQTT UNSUBSCRIBE for the given list of topic filters to the broker.

MQTTStatus_t	MQTT_Disconnect (MQTTContext_t *pContext)
	Disconnect an MQTT session.

MQTTStatus_t	MQTT_ProcessLoop (MQTTContext_t *pContext)
	Loop to receive packets from the transport interface. Handles keep alive.

MQTTStatus_t	MQTT_ReceiveLoop (MQTTContext_t *pContext)
	Loop to receive packets from the transport interface. Does not handle keep alive.

uint16_t	MQTT_GetPacketId (MQTTContext_t *pContext)
	Get a packet ID that is valid according to the MQTT 3.1.1 spec.

MQTTStatus_t	MQTT_MatchTopic (const char pTopicName, const uint16_t topicNameLength, const char pTopicFilter, const uint16_t topicFilterLength, bool *pIsMatch)
	A utility function that determines whether the passed topic filter and topic name match according to the MQTT 3.1.1 protocol specification.

MQTTStatus_t	MQTT_GetSubAckStatusCodes (const MQTTPacketInfo_t pSubackPacket, uint8_t pPayloadStart, size_t pPayloadSize)
	Parses the payload of an MQTT SUBACK packet that contains status codes corresponding to topic filter subscription requests from the original subscribe packet.

const char *	MQTT_Status_strerror (MQTTStatus_t status)
	Error code to string conversion for MQTT statuses.

Detailed Description

User-facing functions of the MQTT 3.1.1 library.

Function Documentation

◆ MQTT_Init()

MQTTStatus_t MQTT_Init	(	MQTTContext_t *	pContext,
		const TransportInterface_t *	pTransportInterface,
		MQTTGetCurrentTimeFunc_t	getTimeFunction,
		MQTTEventCallback_t	userCallback,
		const MQTTFixedBuffer_t *	pNetworkBuffer
	)

Initialize an MQTT context.

This function must be called on an MQTTContext_t before any other function.

Note: The MQTTGetCurrentTimeFunc_t function for querying time must be defined. If there is no time implementation, it is the responsibility of the application to provide a dummy function to always return 0, provide 0 timeouts for all calls to MQTT_Connect, MQTT_ProcessLoop, and MQTT_ReceiveLoop and configure the MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_TIMEOUT_MS configurations to be 0. This will result in loop functions running for a single iteration, and MQTT_Connect relying on MQTT_MAX_CONNACK_RECEIVE_RETRY_COUNT to receive the CONNACK packet.

Parameters

[in]	pContext	The context to initialize.
[in]	pTransportInterface	The transport interface to use with the context.
[in]	getTimeFunction	The time utility function which can return the amount of time (in milliseconds) elapsed since a given epoch. This function will be used to ensure that timeouts in the API calls are met and keep-alive messages are sent on time.
[in]	userCallback	The user callback to use with the context to notify about incoming packet events.
[in]	pNetworkBuffer	Network buffer provided for the context. This buffer will be used to receive incoming messages from the broker. This buffer must remain valid and in scope for the entire lifetime of the `pContext` and must not be used by another context and/or application.

Returns: MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Function for obtaining a timestamp.
uint32_t getTimeStampMs();
// Callback function for receiving packets.
void eventCallback(
     MQTTContext_t * pContext,
     MQTTPacketInfo_t * pPacketInfo,
     MQTTDeserializedInfo_t * pDeserializedInfo
);
// Network send.
int32_t networkSend( NetworkContext_t * pContext, const void * pBuffer, size_t bytes );
// Network receive.
int32_t networkRecv( NetworkContext_t * pContext, void * pBuffer, size_t bytes );
 
MQTTContext_t mqttContext;
TransportInterface_t transport;
MQTTFixedBuffer_t fixedBuffer;
// Create a globally accessible buffer which remains in scope for the entire duration
// of the MQTT context.
uint8_t buffer[ 1024 ];
 
// Clear context.
memset( ( void * ) &mqttContext, 0x00, sizeof( MQTTContext_t ) );
 
// Set transport interface members.
transport.pNetworkContext = &someTransportContext;
transport.send = networkSend;
transport.recv = networkRecv;
 
// Set buffer members.
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = 1024;
 
status = MQTT_Init( &mqttContext, &transport, getTimeStampMs, eventCallback, &fixedBuffer );
 
if( status == MQTTSuccess )
{
     // Do something with mqttContext. The transport and fixedBuffer structs were
     // copied into the context, so the original structs do not need to stay in scope.
     // However, the memory pointed to by the fixedBuffer.pBuffer must remain in scope.
}

◆ MQTT_InitStatefulQoS()

MQTTStatus_t MQTT_InitStatefulQoS	(	MQTTContext_t *	pContext,
		MQTTPubAckInfo_t *	pOutgoingPublishRecords,
		size_t	outgoingPublishCount,
		MQTTPubAckInfo_t *	pIncomingPublishRecords,
		size_t	incomingPublishCount
	)

Initialize an MQTT context for QoS > 0.

This function must be called on an MQTTContext_t after MQTT_Init and before any other function.

Parameters

[in]	pContext	The context to initialize.
[in]	pOutgoingPublishRecords	Pointer to memory which will be used to store state of outgoing publishes.
[in]	outgoingPublishCount	Maximum number of records which can be kept in the memory pointed to by `pOutgoingPublishRecords`.
[in]	pIncomingPublishRecords	Pointer to memory which will be used to store state of incoming publishes.
[in]	incomingPublishCount	Maximum number of records which can be kept in the memory pointed to by `pIncomingPublishRecords`.

Returns: MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Function for obtaining a timestamp.
uint32_t getTimeStampMs();
// Callback function for receiving packets.
void eventCallback(
     MQTTContext_t * pContext,
     MQTTPacketInfo_t * pPacketInfo,
     MQTTDeserializedInfo_t * pDeserializedInfo
);
// Network send.
int32_t networkSend( NetworkContext_t * pContext, const void * pBuffer, size_t bytes );
// Network receive.
int32_t networkRecv( NetworkContext_t * pContext, void * pBuffer, size_t bytes );
 
MQTTContext_t mqttContext;
TransportInterface_t transport;
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ 1024 ];
const size_t outgoingPublishCount = 30;
MQTTPubAckInfo_t outgoingPublishes[ outgoingPublishCount ];
 
// Clear context.
memset( ( void * ) &mqttContext, 0x00, sizeof( MQTTContext_t ) );
 
// Set transport interface members.
transport.pNetworkContext = &someTransportContext;
transport.send = networkSend;
transport.recv = networkRecv;
 
// Set buffer members.
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = 1024;
 
status = MQTT_Init( &mqttContext, &transport, getTimeStampMs, eventCallback, &fixedBuffer );
 
if( status == MQTTSuccess )
{
     // We do not expect any incoming publishes in this example, therefore the incoming
     // publish pointer is NULL and the count is zero.
     status = MQTT_InitStatefulQoS( &mqttContext, outgoingPublishes, outgoingPublishCount, NULL, 0 );
 
     // Now QoS1 and/or QoS2 publishes can be sent with this context.
}

◆ MQTT_Connect()

MQTTStatus_t MQTT_Connect	(	MQTTContext_t *	pContext,
		const MQTTConnectInfo_t *	pConnectInfo,
		const MQTTPublishInfo_t *	pWillInfo,
		uint32_t	timeoutMs,
		bool *	pSessionPresent
	)

Establish an MQTT session.

This function will send MQTT CONNECT packet and receive a CONNACK packet. The send and receive from the network is done through the transport interface.

The maximum time this function waits for a CONNACK is decided in one of the following ways:

If timeoutMs is greater than 0: MQTTContext_t.getTime is used to ensure that the function does not wait more than timeoutMs for CONNACK.
If timeoutMs is 0: The network receive for CONNACK is retried up to the number of times configured by MQTT_MAX_CONNACK_RECEIVE_RETRY_COUNT.

Note: If a dummy MQTTGetCurrentTimeFunc_t was passed to MQTT_Init, then a timeout value of 0 MUST be passed to the API, and the MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_TIMEOUT_MS timeout configurations MUST be set to 0.

Parameters

[in]	pContext	Initialized MQTT context.
[in]	pConnectInfo	MQTT CONNECT packet information.
[in]	pWillInfo	Last Will and Testament. Pass NULL if Last Will and Testament is not used.
[in]	timeoutMs	Maximum time in milliseconds to wait for a CONNACK packet. A zero timeout makes use of the retries for receiving CONNACK as configured with MQTT_MAX_CONNACK_RECEIVE_RETRY_COUNT.
[out]	pSessionPresent	This value will be set to true if a previous session was present; otherwise it will be set to false. It is only relevant if not establishing a clean session.

Returns: MQTTNoMemory if the MQTTContext_t.networkBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSendFailed if transport send failed; MQTTRecvFailed if transport receive failed for CONNACK; MQTTNoDataAvailable if no data available to receive in transport until the timeoutMs for CONNACK; MQTTSuccess otherwise.

Note: This API may spend more time than provided in the timeoutMS parameters in certain conditions as listed below:

Timeouts are incorrectly configured - If the timeoutMS is less than the transport receive timeout and if a CONNACK packet is not received within the transport receive timeout, the API will spend the transport receive timeout (which is more time than the timeoutMs). It is the case of incorrect timeout configuration as the timeoutMs parameter passed to this API must be greater than the transport receive timeout. Please refer to the transport interface documentation for more details about timeout configurations.
Partial CONNACK packet is received right before the expiry of the timeout - It is possible that first two bytes of CONNACK packet (packet type and remaining length) are received right before the expiry of the timeoutMS. In that case, the API makes one more network receive call in an attempt to receive the remaining 2 bytes. In the worst case, it can happen that the remaining 2 bytes are never received and this API will end up spending timeoutMs + transport receive timeout.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTConnectInfo_t connectInfo = { 0 };
MQTTPublishInfo_t willInfo = { 0 };
bool sessionPresent;
// This is assumed to have been initialized before calling this function.
MQTTContext_t * pContext;
 
// True for creating a new session with broker, false if we want to resume an old one.
connectInfo.cleanSession = true;
// Client ID must be unique to broker. This field is required.
connectInfo.pClientIdentifier = "someClientID";
connectInfo.clientIdentifierLength = strlen( connectInfo.pClientIdentifier );
 
// The following fields are optional.
// Value for keep alive.
connectInfo.keepAliveSeconds = 60;
// Optional username and password.
connectInfo.pUserName = "someUserName";
connectInfo.userNameLength = strlen( connectInfo.pUserName );
connectInfo.pPassword = "somePassword";
connectInfo.passwordLength = strlen( connectInfo.pPassword );
 
// The last will and testament is optional, it will be published by the broker
// should this client disconnect without sending a DISCONNECT packet.
willInfo.qos = MQTTQoS0;
willInfo.pTopicName = "/lwt/topic/name";
willInfo.topicNameLength = strlen( willInfo.pTopicName );
willInfo.pPayload = "LWT Message";
willInfo.payloadLength = strlen( "LWT Message" );
 
// Send the connect packet. Use 100 ms as the timeout to wait for the CONNACK packet.
status = MQTT_Connect( pContext, &connectInfo, &willInfo, 100, &sessionPresent );
 
if( status == MQTTSuccess )
{
     // Since we requested a clean session, this must be false
     assert( sessionPresent == false );
 
     // Do something with the connection.
}

◆ MQTT_Subscribe()

MQTTStatus_t MQTT_Subscribe	(	MQTTContext_t *	pContext,
		const MQTTSubscribeInfo_t *	pSubscriptionList,
		size_t	subscriptionCount,
		uint16_t	packetId
	)

Sends MQTT SUBSCRIBE for the given list of topic filters to the broker.

Parameters

[in]	pContext	Initialized MQTT context.
[in]	pSubscriptionList	Array of MQTT subscription info.
[in]	subscriptionCount	The number of elements in @ pSubscriptionList array.
[in]	packetId	Packet ID generated by MQTT_GetPacketId.

Returns: MQTTNoMemory if the MQTTContext_t.networkBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSendFailed if transport write failed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t subscriptionList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
uint16_t packetId;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
// This is assumed to be a list of filters we want to subscribe to.
const char * filters[ NUMBER_OF_SUBSCRIPTIONS ];
 
// Set each subscription.
for( int i = 0; i < NUMBER_OF_SUBSCRIPTIONS; i++ )
{
     subscriptionList[ i ].qos = MQTTQoS0;
     // Each subscription needs a topic filter.
     subscriptionList[ i ].pTopicFilter = filters[ i ];
     subscriptionList[ i ].topicFilterLength = strlen( filters[ i ] );
}
 
// Obtain a new packet id for the subscription.
packetId = MQTT_GetPacketId( pContext );
 
status = MQTT_Subscribe( pContext, &subscriptionList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, packetId );
 
if( status == MQTTSuccess )
{
     // We must now call MQTT_ReceiveLoop() or MQTT_ProcessLoop() to receive the SUBACK.
     // If the broker accepts the subscription we can now receive publishes
     // on the requested topics.
}

◆ MQTT_Publish()

MQTTStatus_t MQTT_Publish	(	MQTTContext_t *	pContext,
		const MQTTPublishInfo_t *	pPublishInfo,
		uint16_t	packetId
	)

Publishes a message to the given topic name.

Parameters

[in]	pContext	Initialized MQTT context.
[in]	pPublishInfo	MQTT PUBLISH packet parameters.
[in]	packetId	packet ID generated by MQTT_GetPacketId.

Returns: MQTTNoMemory if pBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSendFailed if transport write failed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTPublishInfo_t publishInfo;
uint16_t packetId;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
 
// QoS of publish.
publishInfo.qos = MQTTQoS1;
publishInfo.pTopicName = "/some/topic/name";
publishInfo.topicNameLength = strlen( publishInfo.pTopicName );
publishInfo.pPayload = "Hello World!";
publishInfo.payloadLength = strlen( "Hello World!" );
 
// Packet ID is needed for QoS > 0.
packetId = MQTT_GetPacketId( pContext );
 
status = MQTT_Publish( pContext, &publishInfo, packetId );
 
if( status == MQTTSuccess )
{
     // Since the QoS is > 0, we will need to call MQTT_ReceiveLoop()
     // or MQTT_ProcessLoop() to process the publish acknowledgments.
}

◆ MQTT_CancelCallback()

MQTTStatus_t MQTT_CancelCallback	(	const MQTTContext_t *	pContext,
		uint16_t	packetId
	)

Cancels an outgoing publish callback (only for QoS > QoS0) by removing it from the pending ACK list.

Note: This cannot cancel the actual publish as that might have already been sent to the broker. This only removes the details of the given packet ID from the list of unACKed packet. That allows the caller to free any memory associated with the publish payload, topic string etc. Also, after this API call, the user provided callback will not be invoked when the ACK packet is received.

Parameters

[in]	pContext	Initialized MQTT context.
[in]	packetId	packet ID corresponding to the outstanding publish.

Returns: MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

◆ MQTT_Ping()

MQTTStatus_t MQTT_Ping ( MQTTContext_t * pContext )

Sends an MQTT PINGREQ to broker.

Parameters

[in] pContext Initialized and connected MQTT context.

Returns: MQTTNoMemory if pBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSendFailed if transport write failed; MQTTSuccess otherwise.

◆ MQTT_Unsubscribe()

MQTTStatus_t MQTT_Unsubscribe	(	MQTTContext_t *	pContext,
		const MQTTSubscribeInfo_t *	pSubscriptionList,
		size_t	subscriptionCount,
		uint16_t	packetId
	)

Sends MQTT UNSUBSCRIBE for the given list of topic filters to the broker.

Parameters

[in]	pContext	Initialized MQTT context.
[in]	pSubscriptionList	List of MQTT subscription info.
[in]	subscriptionCount	The number of elements in pSubscriptionList.
[in]	packetId	packet ID generated by MQTT_GetPacketId.

Returns: MQTTNoMemory if the MQTTContext_t.networkBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSendFailed if transport write failed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t unsubscribeList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
uint16_t packetId;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
// This is assumed to be a list of filters we want to unsubscribe from.
const char * filters[ NUMBER_OF_SUBSCRIPTIONS ];
 
// Set information for each unsubscribe request.
for( int i = 0; i < NUMBER_OF_SUBSCRIPTIONS; i++ )
{
     unsubscribeList[ i ].pTopicFilter = filters[ i ];
     unsubscribeList[ i ].topicFilterLength = strlen( filters[ i ] );
 
     // The QoS field of MQTT_SubscribeInfo_t is unused for unsubscribing.
}
 
// Obtain a new packet id for the unsubscribe request.
packetId = MQTT_GetPacketId( pContext );
 
status = MQTT_Unsubscribe( pContext, &unsubscribeList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, packetId );
 
if( status == MQTTSuccess )
{
     // We must now call MQTT_ReceiveLoop() or MQTT_ProcessLoop() to receive the UNSUBACK.
     // After this the broker should no longer send publishes for these topics.
}

◆ MQTT_Disconnect()

MQTTStatus_t MQTT_Disconnect ( MQTTContext_t * pContext )

Disconnect an MQTT session.

Parameters

[in] pContext Initialized and connected MQTT context.

Returns: MQTTNoMemory if the MQTTContext_t.networkBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSendFailed if transport send failed; MQTTSuccess otherwise.

◆ MQTT_ProcessLoop()

MQTTStatus_t MQTT_ProcessLoop ( MQTTContext_t * pContext )

Loop to receive packets from the transport interface. Handles keep alive.

Note: If a dummy timer function, MQTTGetCurrentTimeFunc_t, is passed to the library, then the keep-alive mechanism is not supported by the MQTT_ProcessLoop API. In that case, the MQTT_ReceiveLoop API function should be used instead.

Parameters

[in] pContext Initialized and connected MQTT context.

Note: Calling this function blocks the calling context for a time period that depends on the passed the configuration macros, MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_TIMEOUT_MS, and the underlying transport interface implementation timeouts, unless an error occurs. The blocking period also depends on the execution time of the MQTTEventCallback_t callback supplied to the library. It is recommended that the supplied MQTTEventCallback_t callback does not contain blocking operations to prevent potential non-deterministic blocking period of the MQTT_ProcessLoop API call.

Returns: MQTTBadParameter if context is NULL; MQTTRecvFailed if a network error occurs during reception; MQTTSendFailed if a network error occurs while sending an ACK or PINGREQ; MQTTBadResponse if an invalid packet is received; MQTTKeepAliveTimeout if the server has not sent a PINGRESP before MQTT_PINGRESP_TIMEOUT_MS milliseconds; MQTTIllegalState if an incoming QoS 1/2 publish or ack causes an invalid transition for the internal state machine; MQTTNeedMoreBytes if MQTT_ProcessLoop has received incomplete data; it should be called again (probably after a delay); MQTTSuccess on success.

Example

// Variables used in this example.
MQTTStatus_t status;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
 
while( true )
{
     status = MQTT_ProcessLoop( pContext );
 
     if( status != MQTTSuccess && status != MQTTNeedMoreBytes )
     {
         // Determine the error. It's possible we might need to disconnect
         // the underlying transport connection.
     }
     else
     {
         // Other application functions.
     }
}

◆ MQTT_ReceiveLoop()

MQTTStatus_t MQTT_ReceiveLoop ( MQTTContext_t * pContext )

Loop to receive packets from the transport interface. Does not handle keep alive.

Note: If a dummy MQTTGetCurrentTimeFunc_t was passed to MQTT_Init, then the MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_TIMEOUT_MS timeout configurations MUST be set to 0.

Parameters

[in] pContext Initialized and connected MQTT context.

Note: Calling this function blocks the calling context for a time period that depends on the the configuration macros, MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_TIMEOUT_MS, and the underlying transport interface implementation timeouts, unless an error occurs. The blocking period also depends on the execution time of the MQTTEventCallback_t callback supplied to the library. It is recommended that the supplied MQTTEventCallback_t callback does not contain blocking operations to prevent potential non-deterministic blocking period of the MQTT_ReceiveLoop API call.

Returns: MQTTBadParameter if context is NULL; MQTTRecvFailed if a network error occurs during reception; MQTTSendFailed if a network error occurs while sending an ACK or PINGREQ; MQTTBadResponse if an invalid packet is received; MQTTIllegalState if an incoming QoS 1/2 publish or ack causes an invalid transition for the internal state machine; MQTTNeedMoreBytes if MQTT_ReceiveLoop has received incomplete data; it should be called again (probably after a delay); MQTTSuccess on success.

Example

// Variables used in this example.
MQTTStatus_t status;
uint32_t keepAliveMs = 60 * 1000;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
 
while( true )
{
     status = MQTT_ReceiveLoop( pContext );
 
     if( status != MQTTSuccess && status != MQTTNeedMoreBytes )
     {
         // Determine the error. It's possible we might need to disconnect
         // the underlying transport connection.
     }
     else
     {
         // Since this function does not send pings, the application may need
         // to in order to comply with keep alive.
         if( ( pContext->getTime() - pContext->lastPacketTxTime ) > keepAliveMs )
         {
             status = MQTT_Ping( pContext );
         }
 
         // Other application functions.
     }
}

◆ MQTT_GetPacketId()

uint16_t MQTT_GetPacketId ( MQTTContext_t * pContext )

Get a packet ID that is valid according to the MQTT 3.1.1 spec.

Parameters

[in] pContext Initialized MQTT context.

Returns: A non-zero number.

◆ MQTT_MatchTopic()

MQTTStatus_t MQTT_MatchTopic	(	const char *	pTopicName,
		const uint16_t	topicNameLength,
		const char *	pTopicFilter,
		const uint16_t	topicFilterLength,
		bool *	pIsMatch
	)

A utility function that determines whether the passed topic filter and topic name match according to the MQTT 3.1.1 protocol specification.

Parameters

[in]	pTopicName	The topic name to check.
[in]	topicNameLength	Length of the topic name.
[in]	pTopicFilter	The topic filter to check.
[in]	topicFilterLength	Length of topic filter.
[out]	pIsMatch	If the match is performed without any error, that is if the return value is MQTTSuccess, then and only then the value in this parameter is valid and updated. In such a case, if the topic filter and the topic name match, then this value is set to true; otherwise if there is no match then it is set to false.

Note: The API assumes that the passed topic name is valid to meet the requirements of the MQTT 3.1.1 specification. Invalid topic names (for example, containing wildcard characters) should not be passed to the function. Also, the API checks validity of topic filter for wildcard characters ONLY if the passed topic name and topic filter do not have an exact string match.

Returns

Returns one of the following:

MQTTBadParameter, if any of the input parameters is invalid.
MQTTSuccess, if the matching operation was performed.

Example

// Variables used in this example.
const char * pTopic = "topic/match/1";
const char * pFilter = "topic/#";
MQTTStatus_t status = MQTTSuccess;
bool match = false;
 
status = MQTT_MatchTopic( pTopic, strlen( pTopic ), pFilter, strlen( pFilter ), &match );
// Our parameters were valid, so this will return success.
assert( status == MQTTSuccess );
 
// For this specific example, we already know this value is true. This
// check is placed here as an example for use with variable topic names.
if( match )
{
     // Application can decide what to do with the matching topic name.
}

◆ MQTT_GetSubAckStatusCodes()

MQTTStatus_t MQTT_GetSubAckStatusCodes	(	const MQTTPacketInfo_t *	pSubackPacket,
		uint8_t **	pPayloadStart,
		size_t *	pPayloadSize
	)

Parses the payload of an MQTT SUBACK packet that contains status codes corresponding to topic filter subscription requests from the original subscribe packet.

Each return code in the SUBACK packet corresponds to a topic filter in the SUBSCRIBE Packet being acknowledged. The status codes can be one of the following:

0x00 - Success - Maximum QoS 0
0x01 - Success - Maximum QoS 1
0x02 - Success - Maximum QoS 2
0x80 - Failure Refer to MQTTSubAckStatus_t for the status codes.

Parameters

[in]	pSubackPacket	The SUBACK packet whose payload is to be parsed.
[out]	pPayloadStart	This is populated with the starting address of the payload (or return codes for topic filters) in the SUBACK packet.
[out]	pPayloadSize	This is populated with the size of the payload in the SUBACK packet. It represents the number of topic filters whose SUBACK status is present in the packet.

Returns

Returns one of the following:

MQTTBadParameter if the input SUBACK packet is invalid.
MQTTSuccess if parsing the payload was successful.

Example

// Global variable used in this example.
// This is assumed to be the subscription list in the original SUBSCRIBE packet.
MQTTSubscribeInfo_t pSubscribes[ NUMBER_OF_SUBSCRIPTIONS ];
 
// MQTT_GetSubAckStatusCodes is intended to be used from the application
// callback that is called by the library in MQTT_ProcessLoop or MQTT_ReceiveLoop.
void eventCallback(
     MQTTContext_t * pContext,
     MQTTPacketInfo_t * pPacketInfo,
     MQTTDeserializedInfo_t * pDeserializedInfo
)
{
     MQTTStatus_t status = MQTTSuccess;
     uint8_t * pCodes;
     size_t numCodes;
 
     if( pPacketInfo->type == MQTT_PACKET_TYPE_SUBACK )
     {
         status = MQTT_GetSubAckStatusCodes( pPacketInfo, &pCodes, &numCodes );
 
         // Since the pointers to the payload and payload size are not NULL, and
         // we use the packet info struct passed to the app callback (verified
         // to be valid by the library), this function must return success.
         assert( status == MQTTSuccess );
         // The server must send a response code for each topic filter in the
         // original SUBSCRIBE packet.
         assert( numCodes == NUMBER_OF_SUBSCRIPTIONS );
 
         for( int i = 0; i < numCodes; i++ )
         {
             // The only failure code is 0x80 = MQTTSubAckFailure.
             if( pCodes[ i ] == MQTTSubAckFailure )
             {
                 // The subscription failed, we may want to retry the
                 // subscription in pSubscribes[ i ] outside of this callback.
             }
             else
             {
                 // The subscription was granted, but the maximum QoS may be
                 // lower than what was requested. We can verify the granted QoS.
                 if( pSubscribes[ i ].qos != pCodes[ i ] )
                 {
                     LogWarn( (
                         "Requested QoS %u, but granted QoS %u for %s",
                         pSubscribes[ i ].qos, pCodes[ i ], pSubscribes[ i ].pTopicFilter
                     ) );
                 }
             }
         }
     }
     // Handle other packet types.
}

◆ MQTT_Status_strerror()

const char * MQTT_Status_strerror ( MQTTStatus_t status )

Error code to string conversion for MQTT statuses.

Parameters

[in] status The status to convert to a string.

Returns: The string representation of the status.

Data Structures

Macros

Typedefs

Enumerations

Functions

Detailed Description

Function Documentation

◆ MQTT_Init()

◆ MQTT_InitStatefulQoS()

◆ MQTT_Connect()

◆ MQTT_Subscribe()

◆ MQTT_Publish()

◆ MQTT_CancelCallback()

◆ MQTT_Ping()

◆ MQTT_Unsubscribe()

◆ MQTT_Disconnect()

◆ MQTT_ProcessLoop()

◆ MQTT_ReceiveLoop()

◆ MQTT_GetPacketId()

◆ MQTT_MatchTopic()

◆ MQTT_GetSubAckStatusCodes()

◆ MQTT_Status_strerror()