coreMQTT v1.1.2
MQTT 3.1.1 Client Library
core_mqtt.c File Reference

Implements the user-facing functions in core_mqtt.h. More...

#include <string.h>
#include <assert.h>
#include "core_mqtt.h"
#include "core_mqtt_state.h"

Functions

static int32_t sendPacket (MQTTContext_t *pContext, const uint8_t *pBufferToSend, size_t bytesToSend)
 Sends provided buffer to network using transport send. More...
 
static uint32_t calculateElapsedTime (uint32_t later, uint32_t start)
 Calculate the interval between two millisecond timestamps, including when the later value has overflowed. More...
 
static MQTTPubAckType_t getAckFromPacketType (uint8_t packetType)
 Convert a byte indicating a publish ack type to an MQTTPubAckType_t. More...
 
static int32_t recvExact (const MQTTContext_t *pContext, size_t bytesToRecv)
 Receive bytes into the network buffer. More...
 
static MQTTStatus_t discardPacket (const MQTTContext_t *pContext, size_t remainingLength, uint32_t timeoutMs)
 Discard a packet from the transport interface. More...
 
static MQTTStatus_t receivePacket (const MQTTContext_t *pContext, MQTTPacketInfo_t incomingPacket, uint32_t remainingTimeMs)
 Receive a packet from the transport interface. More...
 
static uint8_t getAckTypeToSend (MQTTPublishState_t state)
 Get the correct ack type to send. More...
 
static MQTTStatus_t sendPublishAcks (MQTTContext_t *pContext, uint16_t packetId, MQTTPublishState_t publishState)
 Send acks for received QoS 1/2 publishes. More...
 
static MQTTStatus_t handleKeepAlive (MQTTContext_t *pContext)
 Send a keep alive PINGREQ if the keep alive interval has elapsed. More...
 
static MQTTStatus_t handleIncomingPublish (MQTTContext_t *pContext, MQTTPacketInfo_t *pIncomingPacket)
 Handle received MQTT PUBLISH packet. More...
 
static MQTTStatus_t handlePublishAcks (MQTTContext_t *pContext, MQTTPacketInfo_t *pIncomingPacket)
 Handle received MQTT publish acks. More...
 
static MQTTStatus_t handleIncomingAck (MQTTContext_t *pContext, MQTTPacketInfo_t *pIncomingPacket, bool manageKeepAlive)
 Handle received MQTT ack. More...
 
static MQTTStatus_t receiveSingleIteration (MQTTContext_t *pContext, uint32_t remainingTimeMs, bool manageKeepAlive)
 Run a single iteration of the receive loop. More...
 
static MQTTStatus_t validateSubscribeUnsubscribeParams (const MQTTContext_t *pContext, const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, uint16_t packetId)
 Validates parameters of MQTT_Subscribe or MQTT_Unsubscribe. More...
 
static MQTTStatus_t sendPublish (MQTTContext_t *pContext, const MQTTPublishInfo_t *pPublishInfo, size_t headerSize)
 Send serialized publish packet using transport send. More...
 
static MQTTStatus_t receiveConnack (const MQTTContext_t *pContext, uint32_t timeoutMs, bool cleanSession, MQTTPacketInfo_t *pIncomingPacket, bool *pSessionPresent)
 Receives a CONNACK MQTT packet. More...
 
static MQTTStatus_t handleSessionResumption (MQTTContext_t *pContext, bool sessionPresent)
 Resends pending acks for a re-established MQTT session, or clears existing state records for a clean session. More...
 
static MQTTStatus_t serializePublish (const MQTTContext_t *pContext, const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId, size_t *const pHeaderSize)
 Serializes a PUBLISH message. More...
 
static MQTTStatus_t validatePublishParams (const MQTTContext_t *pContext, const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId)
 Function to validate MQTT_Publish parameters. More...
 
static bool matchEndWildcardsSpecialCases (const char *pTopicFilter, uint16_t topicFilterLength, uint16_t filterIndex)
 Performs matching for special cases when a topic filter ends with a wildcard character. More...
 
static bool matchWildcards (const char *pTopicName, uint16_t topicNameLength, const char *pTopicFilter, uint16_t topicFilterLength, uint16_t *pNameIndex, uint16_t *pFilterIndex, bool *pMatch)
 Attempt to match topic name with a topic filter starting with a wildcard. More...
 
static bool matchTopicFilter (const char *pTopicName, uint16_t topicNameLength, const char *pTopicFilter, uint16_t topicFilterLength)
 Match a topic name and topic filter allowing the use of wildcards. More...
 
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. More...
 
MQTTStatus_t MQTT_Connect (MQTTContext_t *pContext, const MQTTConnectInfo_t *pConnectInfo, const MQTTPublishInfo_t *pWillInfo, uint32_t timeoutMs, bool *pSessionPresent)
 Establish an MQTT session. More...
 
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. More...
 
MQTTStatus_t MQTT_Publish (MQTTContext_t *pContext, const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId)
 Publishes a message to the given topic name. More...
 
MQTTStatus_t MQTT_Ping (MQTTContext_t *pContext)
 Sends an MQTT PINGREQ to broker. More...
 
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. More...
 
MQTTStatus_t MQTT_Disconnect (MQTTContext_t *pContext)
 Disconnect an MQTT session. More...
 
MQTTStatus_t MQTT_ProcessLoop (MQTTContext_t *pContext, uint32_t timeoutMs)
 Loop to receive packets from the transport interface. Handles keep alive. More...
 
MQTTStatus_t MQTT_ReceiveLoop (MQTTContext_t *pContext, uint32_t timeoutMs)
 Loop to receive packets from the transport interface. Does not handle keep alive. More...
 
uint16_t MQTT_GetPacketId (MQTTContext_t *pContext)
 Get a packet ID that is valid according to the MQTT 3.1.1 spec. More...
 
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. More...
 
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. More...
 
const char * MQTT_Status_strerror (MQTTStatus_t status)
 Error code to string conversion for MQTT statuses. More...
 

Detailed Description

Implements the user-facing functions in core_mqtt.h.

Function Documentation

◆ sendPacket()

static int32_t sendPacket ( MQTTContext_t pContext,
const uint8_t *  pBufferToSend,
size_t  bytesToSend 
)
static

Sends provided buffer to network using transport send.

param[in] pContext Initialized MQTT context.

param[in] pBufferToSend Buffer to be sent to network.

param[in] bytesToSend Number of bytes to be sent.

Note
This operation may call the transport send function repeatedly to send bytes over the network until either:
  1. The requested number of bytes bytesToSend have been sent. OR
  2. No byte cannot be sent over the network for the MQTT_SEND_RETRY_TIMEOUT_MS duration. OR
  3. There is an error in sending data over the network.
Returns
Total number of bytes sent, or negative value on network error.

◆ calculateElapsedTime()

static uint32_t calculateElapsedTime ( uint32_t  later,
uint32_t  start 
)
static

Calculate the interval between two millisecond timestamps, including when the later value has overflowed.

Note
In C, the operands are promoted to signed integers in subtraction. Using this function avoids the need to cast the result of subtractions back to uint32_t.
Parameters
[in]laterThe later time stamp, in milliseconds.
[in]startThe earlier time stamp, in milliseconds.
Returns
later - start.

◆ getAckFromPacketType()

static MQTTPubAckType_t getAckFromPacketType ( uint8_t  packetType)
static

Convert a byte indicating a publish ack type to an MQTTPubAckType_t.

Parameters
[in]packetTypeFirst byte of fixed header.
Returns
Type of ack.

◆ recvExact()

static int32_t recvExact ( const MQTTContext_t pContext,
size_t  bytesToRecv 
)
static

Receive bytes into the network buffer.

Parameters
[in]pContextInitialized MQTT Context.
[in]bytesToRecvNumber of bytes to receive.
Note
This operation calls the transport receive function repeatedly to read bytes from the network until either:
  1. The requested number of bytes bytesToRecv are read. OR
  2. No data is received from the network for MQTT_RECV_POLLING_TIMEOUT_MS duration.
                OR
    
  3. There is an error in reading from the network.
Returns
Number of bytes received, or negative number on network error.

◆ discardPacket()

static MQTTStatus_t discardPacket ( const MQTTContext_t pContext,
size_t  remainingLength,
uint32_t  timeoutMs 
)
static

Discard a packet from the transport interface.

Parameters
[in]pContextMQTT Connection context.
[in]remainingLengthRemaining length of the packet to dump.
[in]timeoutMsTime remaining to discard the packet.
Returns
MQTTRecvFailed or MQTTNoDataAvailable.

◆ receivePacket()

static MQTTStatus_t receivePacket ( const MQTTContext_t pContext,
MQTTPacketInfo_t  incomingPacket,
uint32_t  remainingTimeMs 
)
static

Receive a packet from the transport interface.

Parameters
[in]pContextMQTT Connection context.
[in]incomingPacketpacket struct with remaining length.
[in]remainingTimeMsTime remaining to receive the packet.
Returns
MQTTSuccess or MQTTRecvFailed.

◆ getAckTypeToSend()

static uint8_t getAckTypeToSend ( MQTTPublishState_t  state)
static

Get the correct ack type to send.

Parameters
[in]stateCurrent state of publish.
Returns
Packet Type byte of PUBACK, PUBREC, PUBREL, or PUBCOMP if one of those should be sent, else 0.

◆ sendPublishAcks()

static MQTTStatus_t sendPublishAcks ( MQTTContext_t pContext,
uint16_t  packetId,
MQTTPublishState_t  publishState 
)
static

Send acks for received QoS 1/2 publishes.

Parameters
[in]pContextMQTT Connection context.
[in]packetIdpacket ID of original PUBLISH.
[in]publishStateCurrent publish state in record.
Returns
MQTTSuccess, MQTTIllegalState or MQTTSendFailed.

◆ handleKeepAlive()

static MQTTStatus_t handleKeepAlive ( MQTTContext_t pContext)
static

Send a keep alive PINGREQ if the keep alive interval has elapsed.

Parameters
[in]pContextInitialized MQTT Context.
Returns
MQTTKeepAliveTimeout if a PINGRESP is not received in time, MQTTSendFailed if the PINGREQ cannot be sent, or MQTTSuccess.

◆ handleIncomingPublish()

static MQTTStatus_t handleIncomingPublish ( MQTTContext_t pContext,
MQTTPacketInfo_t pIncomingPacket 
)
static

Handle received MQTT PUBLISH packet.

Parameters
[in]pContextMQTT Connection context.
[in]pIncomingPacketIncoming packet.
Returns
MQTTSuccess, MQTTIllegalState or deserialization error.

◆ handlePublishAcks()

static MQTTStatus_t handlePublishAcks ( MQTTContext_t pContext,
MQTTPacketInfo_t pIncomingPacket 
)
static

Handle received MQTT publish acks.

Parameters
[in]pContextMQTT Connection context.
[in]pIncomingPacketIncoming packet.
Returns
MQTTSuccess, MQTTIllegalState, or deserialization error.

◆ handleIncomingAck()

static MQTTStatus_t handleIncomingAck ( MQTTContext_t pContext,
MQTTPacketInfo_t pIncomingPacket,
bool  manageKeepAlive 
)
static

Handle received MQTT ack.

Parameters
[in]pContextMQTT Connection context.
[in]pIncomingPacketIncoming packet.
[in]manageKeepAliveFlag indicating if PINGRESPs should not be given to the application
Returns
MQTTSuccess, MQTTIllegalState, or deserialization error.

◆ receiveSingleIteration()

static MQTTStatus_t receiveSingleIteration ( MQTTContext_t pContext,
uint32_t  remainingTimeMs,
bool  manageKeepAlive 
)
static

Run a single iteration of the receive loop.

Parameters
[in]pContextMQTT Connection context.
[in]remainingTimeMsRemaining time for the loop in milliseconds.
[in]manageKeepAliveFlag indicating if keep alive should be handled.
Returns
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; MQTTSuccess on success.

◆ validateSubscribeUnsubscribeParams()

static MQTTStatus_t validateSubscribeUnsubscribeParams ( const MQTTContext_t pContext,
const MQTTSubscribeInfo_t pSubscriptionList,
size_t  subscriptionCount,
uint16_t  packetId 
)
static

Validates parameters of MQTT_Subscribe or MQTT_Unsubscribe.

Parameters
[in]pContextInitialized MQTT context.
[in]pSubscriptionListList of MQTT subscription info.
[in]subscriptionCountThe number of elements in pSubscriptionList.
[in]packetIdPacket identifier.
Returns
MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

◆ sendPublish()

static MQTTStatus_t sendPublish ( MQTTContext_t pContext,
const MQTTPublishInfo_t pPublishInfo,
size_t  headerSize 
)
static

Send serialized publish packet using transport send.

param[in] pContext Initialized MQTT context.

param[in] pPublishInfo MQTT PUBLISH packet parameters.

param[in] headerSize Header size of the PUBLISH packet.

Returns
MQTTSendFailed if transport write failed; MQTTSuccess otherwise.

◆ receiveConnack()

static MQTTStatus_t receiveConnack ( const MQTTContext_t pContext,
uint32_t  timeoutMs,
bool  cleanSession,
MQTTPacketInfo_t pIncomingPacket,
bool *  pSessionPresent 
)
static

Receives a CONNACK MQTT packet.

Parameters
[in]pContextInitialized MQTT context.
[in]timeoutMsTimeout for waiting for CONNACK packet.
[in]cleanSessionClean session flag set by application.
[out]pIncomingPacketList of MQTT subscription info.
[out]pSessionPresentWhether a previous session was present. Only relevant if not establishing a clean session.
Returns
MQTTBadResponse if a bad response is received; MQTTNoDataAvailable if no data available for transport recv;

MQTTRecvFailed if transport recv failed;

MQTTSuccess otherwise.

◆ handleSessionResumption()

static MQTTStatus_t handleSessionResumption ( MQTTContext_t pContext,
bool  sessionPresent 
)
static

Resends pending acks for a re-established MQTT session, or clears existing state records for a clean session.

Parameters
[in]pContextInitialized MQTT context.
[in]sessionPresentSession present flag received from the MQTT broker.
Returns
MQTTSendFailed if transport send during resend failed; MQTTSuccess otherwise.

◆ serializePublish()

static MQTTStatus_t serializePublish ( const MQTTContext_t pContext,
const MQTTPublishInfo_t pPublishInfo,
uint16_t  packetId,
size_t *const  pHeaderSize 
)
static

Serializes a PUBLISH message.

param[in] pContext Initialized MQTT context.

param[in] pPublishInfo MQTT PUBLISH packet parameters.

param[in] packetId Packet Id of the publish packet.

param[out] pHeaderSize Size of the serialized PUBLISH header.

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

◆ validatePublishParams()

static MQTTStatus_t validatePublishParams ( const MQTTContext_t pContext,
const MQTTPublishInfo_t pPublishInfo,
uint16_t  packetId 
)
static

Function to validate MQTT_Publish parameters.

param[in] pContext Initialized MQTT context.

param[in] pPublishInfo MQTT PUBLISH packet parameters.

param[in] packetId Packet Id for the MQTT PUBLISH packet.

Returns
MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

◆ matchEndWildcardsSpecialCases()

static bool matchEndWildcardsSpecialCases ( const char *  pTopicFilter,
uint16_t  topicFilterLength,
uint16_t  filterIndex 
)
static

Performs matching for special cases when a topic filter ends with a wildcard character.

When the topic name has been consumed but there are remaining characters to to match in topic filter, this function handles the following 2 cases:

  • When the topic filter ends with "/+" or "/#" characters, but the topic name only ends with '/'.
  • When the topic filter ends with "/#" characters, but the topic name ends at the parent level.
Note
This function ASSUMES that the topic name been consumed in linear matching with the topic filer, but the topic filter has remaining characters to be matched.
Parameters
[in]pTopicFilterThe topic filter containing the wildcard.
[in]topicFilterLengthLength of the topic filter being examined.
[in]filterIndexIndex of the topic filter being examined.
Returns
Returns whether the topic filter and the topic name match.

◆ matchWildcards()

static bool matchWildcards ( const char *  pTopicName,
uint16_t  topicNameLength,
const char *  pTopicFilter,
uint16_t  topicFilterLength,
uint16_t *  pNameIndex,
uint16_t *  pFilterIndex,
bool *  pMatch 
)
static

Attempt to match topic name with a topic filter starting with a wildcard.

If the topic filter starts with a '+' (single-level) wildcard, the function advances the pNameIndex by a level in the topic name. If the topic filter starts with a '#' (multi-level) wildcard, the function concludes that both the topic name and topic filter match.

Parameters
[in]pTopicNameThe topic name to match.
[in]topicNameLengthLength of the topic name.
[in]pTopicFilterThe topic filter to match.
[in]topicFilterLengthLength of the topic filter.
[in,out]pNameIndexCurrent index in the topic name being examined. It is advanced by one level for + wildcards.
[in,out]pFilterIndexCurrent index in the topic filter being examined. It is advanced to position of '/' level separator for '+' wildcard.
[out]pMatchWhether the topic filter and topic name match.
Returns
true if the caller of this function should exit; false if the caller should continue parsing the topics.

◆ matchTopicFilter()

static bool matchTopicFilter ( const char *  pTopicName,
uint16_t  topicNameLength,
const char *  pTopicFilter,
uint16_t  topicFilterLength 
)
static

Match a topic name and topic filter allowing the use of wildcards.

Parameters
[in]pTopicNameThe topic name to check.
[in]topicNameLengthLength of the topic name.
[in]pTopicFilterThe topic filter to check.
[in]topicFilterLengthLength of topic filter.
Returns
true if the topic name and topic filter match; false otherwise.

◆ 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 a 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_RETRY_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]pContextThe context to initialize.
[in]pTransportInterfaceThe transport interface to use with the context.
[in]getTimeFunctionThe time utility function to use with the context.
[in]userCallbackThe user callback to use with the context to notify about incoming packet events.
[in]pNetworkBufferNetwork buffer provided for the context.
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;
MQTTFixedBuffer_t fixedBuffer;
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.
}
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.
Definition: core_mqtt.c:1693
@ MQTTSuccess
Definition: core_mqtt_serializer.h:98
struct NetworkContext NetworkContext_t
The NetworkContext is an incomplete type. An implementation of this interface must define struct Netw...
Definition: transport_interface.h:189
A struct representing an MQTT connection.
Definition: core_mqtt.h:169
Struct to hold deserialized packet information for an MQTTEventCallback_t callback.
Definition: core_mqtt.h:233
Buffer passed to MQTT library.
Definition: core_mqtt_serializer.h:130
size_t size
Size of buffer.
Definition: core_mqtt_serializer.h:132
uint8_t * pBuffer
Pointer to buffer.
Definition: core_mqtt_serializer.h:131
MQTT incoming packet parameters.
Definition: core_mqtt_serializer.h:251
The transport layer interface.
Definition: transport_interface.h:252
TransportSend_t send
Definition: transport_interface.h:254
TransportRecv_t recv
Definition: transport_interface.h:253
NetworkContext_t * pNetworkContext
Definition: transport_interface.h:255

◆ 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:

  1. If timeoutMs is greater than 0: MQTTContext_t.getTime is used to ensure that the function does not wait more than timeoutMs for CONNACK.
  2. 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_RETRY_TIMEOUT_MS timeout configurations MUST be set to 0.
Parameters
[in]pContextInitialized MQTT context.
[in]pConnectInfoMQTT CONNECT packet information.
[in]pWillInfoLast Will and Testament. Pass NULL if Last Will and Testament is not used.
[in]timeoutMsMaximum 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]pSessionPresentWhether a previous session was present. 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:
  1. 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.
  2. 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.
}
MQTTStatus_t MQTT_Connect(MQTTContext_t *pContext, const MQTTConnectInfo_t *pConnectInfo, const MQTTPublishInfo_t *pWillInfo, uint32_t timeoutMs, bool *pSessionPresent)
Establish an MQTT session.
Definition: core_mqtt.c:1752
MQTTStatus_t
Return codes from MQTT functions.
Definition: core_mqtt_serializer.h:97
@ MQTTQoS0
Definition: core_mqtt_serializer.h:117
MQTT CONNECT packet parameters.
Definition: core_mqtt_serializer.h:140
const char * pClientIdentifier
MQTT client identifier. Must be unique per client.
Definition: core_mqtt_serializer.h:154
const char * pUserName
MQTT user name. Set to NULL if not used.
Definition: core_mqtt_serializer.h:164
bool cleanSession
Whether to establish a new, clean session or resume a previous session.
Definition: core_mqtt_serializer.h:144
uint16_t userNameLength
Length of MQTT user name. Set to 0 if not used.
Definition: core_mqtt_serializer.h:169
uint16_t keepAliveSeconds
MQTT keep alive period.
Definition: core_mqtt_serializer.h:149
uint16_t clientIdentifierLength
Length of the client identifier.
Definition: core_mqtt_serializer.h:159
uint16_t passwordLength
Length of MQTT password. Set to 0 if not used.
Definition: core_mqtt_serializer.h:179
const char * pPassword
MQTT password. Set to NULL if not used.
Definition: core_mqtt_serializer.h:174
MQTT PUBLISH packet parameters.
Definition: core_mqtt_serializer.h:209
MQTTQoS_t qos
Quality of Service for message.
Definition: core_mqtt_serializer.h:213
uint16_t topicNameLength
Length of topic name.
Definition: core_mqtt_serializer.h:233
size_t payloadLength
Message payload length.
Definition: core_mqtt_serializer.h:243
const char * pTopicName
Topic name on which the message is published.
Definition: core_mqtt_serializer.h:228
const void * pPayload
Message payload.
Definition: core_mqtt_serializer.h:238

◆ 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]pContextInitialized MQTT context.
[in]pSubscriptionListList of MQTT subscription info.
[in]subscriptionCountThe number of elements in pSubscriptionList.
[in]packetIdPacket 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.
}
uint16_t MQTT_GetPacketId(MQTTContext_t *pContext)
Get a packet ID that is valid according to the MQTT 3.1.1 spec.
Definition: core_mqtt.c:2272
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.
Definition: core_mqtt.c:1849
MQTT SUBSCRIBE packet parameters.
Definition: core_mqtt_serializer.h:187
MQTTQoS_t qos
Quality of Service for subscription.
Definition: core_mqtt_serializer.h:191
uint16_t topicFilterLength
Length of subscription topic filter.
Definition: core_mqtt_serializer.h:201
const char * pTopicFilter
Topic filter to subscribe to.
Definition: core_mqtt_serializer.h:196

◆ 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]pContextInitialized MQTT context.
[in]pPublishInfoMQTT PUBLISH packet parameters.
[in]packetIdpacket 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.
}
MQTTStatus_t MQTT_Publish(MQTTContext_t *pContext, const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId)
Publishes a message to the given topic name.
Definition: core_mqtt.c:1909
@ MQTTQoS1
Definition: core_mqtt_serializer.h:118

◆ MQTT_Ping()

MQTTStatus_t MQTT_Ping ( MQTTContext_t pContext)

Sends an MQTT PINGREQ to broker.

Parameters
[in]pContextInitialized 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]pContextInitialized MQTT context.
[in]pSubscriptionListList of MQTT subscription info.
[in]subscriptionCountThe number of elements in pSubscriptionList.
[in]packetIdpacket 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.
}
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.
Definition: core_mqtt.c:2044

◆ MQTT_Disconnect()

MQTTStatus_t MQTT_Disconnect ( MQTTContext_t pContext)

Disconnect an MQTT session.

Parameters
[in]pContextInitialized 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,
uint32_t  timeoutMs 
)

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

Note
Passing a timeout value of 0 will run the loop for a single iteration.
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]pContextInitialized and connected MQTT context.
[in]timeoutMsMinimum time in milliseconds that the receive loop will run, unless an error occurs.
Note
Calling this function blocks the calling context for a time period that depends on the passed timeoutMs, the configuration macros, MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_RETRY_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; MQTTSuccess on success.

Example

// Variables used in this example.
MQTTStatus_t status;
uint32_t timeoutMs = 100;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
while( true )
{
status = MQTT_ProcessLoop( pContext, timeoutMs );
if( status != MQTTSuccess )
{
// Determine the error. It's possible we might need to disconnect
// the underlying transport connection.
}
else
{
// Other application functions.
}
}
MQTTStatus_t MQTT_ProcessLoop(MQTTContext_t *pContext, uint32_t timeoutMs)
Loop to receive packets from the transport interface. Handles keep alive.
Definition: core_mqtt.c:2160

◆ MQTT_ReceiveLoop()

MQTTStatus_t MQTT_ReceiveLoop ( MQTTContext_t pContext,
uint32_t  timeoutMs 
)

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

Note
Passing a timeout value of 0 will run the loop for a single iteration. If a dummy MQTTGetCurrentTimeFunc_t was passed to MQTT_Init, then the timeout value passed to the API MUST be 0, and the MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_RETRY_TIMEOUT_MS timeout configurations MUST be set to 0.
Parameters
[in]pContextInitialized and connected MQTT context.
[in]timeoutMsMinimum time in milliseconds that the receive loop will run, unless an error occurs.
Note
Calling this function blocks the calling context for a time period that depends on the passed timeoutMs, the configuration macros, MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_RETRY_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; MQTTSuccess on success.

Example

// Variables used in this example.
MQTTStatus_t status;
uint32_t timeoutMs = 100;
uint32_t keepAliveMs = 60 * 1000;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
while( true )
{
status = MQTT_ReceiveLoop( pContext, timeoutMs );
if( status != MQTTSuccess )
{
// 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->lastPacketTime ) > keepAliveMs )
{
status = MQTT_Ping( pContext );
}
// Other application functions.
}
}
MQTTStatus_t MQTT_ReceiveLoop(MQTTContext_t *pContext, uint32_t timeoutMs)
Loop to receive packets from the transport interface. Does not handle keep alive.
Definition: core_mqtt.c:2217
MQTTStatus_t MQTT_Ping(MQTTContext_t *pContext)
Sends an MQTT PINGREQ to broker.
Definition: core_mqtt.c:1983
MQTTGetCurrentTimeFunc_t getTime
Function used to get millisecond timestamps.
Definition: core_mqtt.h:203
uint32_t lastPacketTime
Timestamp of the last packet sent by the library.
Definition: core_mqtt.h:213

◆ 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]pContextInitialized 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]pTopicNameThe topic name to check.
[in]topicNameLengthLength of the topic name.
[in]pTopicFilterThe topic filter to check.
[in]topicFilterLengthLength of topic filter.
[out]pIsMatchThis is filled with the whether there exists a match or not.
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:

Example

// Variables used in this example.
const char * pTopic = "topic/match/1";
const char * pFilter = "topic/#";
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.
}
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 ...
Definition: core_mqtt.c:2297

◆ 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]pSubackPacketThe SUBACK packet whose payload is to be parsed.
[out]pPayloadStartThis is populated with the starting address of the payload (or return codes for topic filters) in the SUBACK packet.
[out]pPayloadSizeThis 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:

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
)
{
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 ] )
{
"Requested QoS %u, but granted QoS %u for %s",
pSubscribes[ i ].qos, pCodes[ i ], pSubscribes[ i ].pTopicFilter
) );
}
}
}
}
// Handle other packet types.
}
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 ...
Definition: core_mqtt.c:2366
#define LogWarn(message)
Macro that is called in the MQTT library for logging "Warning" level messages.
Definition: core_mqtt_config_defaults.h:213
#define MQTT_PACKET_TYPE_SUBACK
SUBACK (server-to-client).
Definition: core_mqtt_serializer.h:71
@ MQTTSubAckFailure
Failure.
Definition: core_mqtt.h:150
uint8_t type
Type of incoming MQTT packet.
Definition: core_mqtt_serializer.h:255

◆ MQTT_Status_strerror()

const char * MQTT_Status_strerror ( MQTTStatus_t  status)

Error code to string conversion for MQTT statuses.

Parameters
[in]statusThe status to convert to a string.
Returns
The string representation of the status.