coreMQTT v2.0.0
MQTT 3.1.1 Client Library
core_mqtt_serializer.h File Reference

User-facing functions for serializing and deserializing MQTT 3.1.1 packets. This header should be included for building a lighter weight MQTT client than the managed CSDK MQTT library API in core_mqtt.h, by using the serializer and de-serializer functions exposed in this file's API. More...

#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>
#include "core_mqtt_config.h"
#include "core_mqtt_config_defaults.h"
#include "transport_interface.h"

Go to the source code of this file.

Data Structures

struct  MQTTFixedBuffer_t
 Buffer passed to MQTT library. More...
 
struct  MQTTConnectInfo_t
 MQTT CONNECT packet parameters. More...
 
struct  MQTTSubscribeInfo_t
 MQTT SUBSCRIBE packet parameters. More...
 
struct  MQTTPublishInfo_t
 MQTT PUBLISH packet parameters. More...
 
struct  MQTTPacketInfo_t
 MQTT incoming packet parameters. More...
 

Macros

#define MQTT_PACKET_TYPE_CONNECT   ( ( uint8_t ) 0x10U )
 CONNECT (client-to-server).
 
#define MQTT_PACKET_TYPE_CONNACK   ( ( uint8_t ) 0x20U )
 CONNACK (server-to-client).
 
#define MQTT_PACKET_TYPE_PUBLISH   ( ( uint8_t ) 0x30U )
 PUBLISH (bidirectional).
 
#define MQTT_PACKET_TYPE_PUBACK   ( ( uint8_t ) 0x40U )
 PUBACK (bidirectional).
 
#define MQTT_PACKET_TYPE_PUBREC   ( ( uint8_t ) 0x50U )
 PUBREC (bidirectional).
 
#define MQTT_PACKET_TYPE_PUBREL   ( ( uint8_t ) 0x62U )
 PUBREL (bidirectional).
 
#define MQTT_PACKET_TYPE_PUBCOMP   ( ( uint8_t ) 0x70U )
 PUBCOMP (bidirectional).
 
#define MQTT_PACKET_TYPE_SUBSCRIBE   ( ( uint8_t ) 0x82U )
 SUBSCRIBE (client-to-server).
 
#define MQTT_PACKET_TYPE_SUBACK   ( ( uint8_t ) 0x90U )
 SUBACK (server-to-client).
 
#define MQTT_PACKET_TYPE_UNSUBSCRIBE   ( ( uint8_t ) 0xA2U )
 UNSUBSCRIBE (client-to-server).
 
#define MQTT_PACKET_TYPE_UNSUBACK   ( ( uint8_t ) 0xB0U )
 UNSUBACK (server-to-client).
 
#define MQTT_PACKET_TYPE_PINGREQ   ( ( uint8_t ) 0xC0U )
 PINGREQ (client-to-server).
 
#define MQTT_PACKET_TYPE_PINGRESP   ( ( uint8_t ) 0xD0U )
 PINGRESP (server-to-client).
 
#define MQTT_PACKET_TYPE_DISCONNECT   ( ( uint8_t ) 0xE0U )
 DISCONNECT (client-to-server).
 
#define MQTT_PUBLISH_ACK_PACKET_SIZE   ( 4UL )
 The size of MQTT PUBACK, PUBREC, PUBREL, and PUBCOMP packets, per MQTT spec.
 

Enumerations

enum  MQTTStatus_t {
  MQTTSuccess = 0 , MQTTBadParameter , MQTTNoMemory , MQTTSendFailed ,
  MQTTRecvFailed , MQTTBadResponse , MQTTServerRefused , MQTTNoDataAvailable ,
  MQTTIllegalState , MQTTStateCollision , MQTTKeepAliveTimeout , MQTTNeedMoreBytes
}
 Return codes from MQTT functions. More...
 
enum  MQTTQoS_t { MQTTQoS0 = 0 , MQTTQoS1 = 1 , MQTTQoS2 = 2 }
 MQTT Quality of Service values. More...
 

Functions

MQTTStatus_t MQTT_GetConnectPacketSize (const MQTTConnectInfo_t *pConnectInfo, const MQTTPublishInfo_t *pWillInfo, size_t *pRemainingLength, size_t *pPacketSize)
 Get the size and Remaining Length of an MQTT CONNECT packet. More...
 
MQTTStatus_t MQTT_SerializeConnect (const MQTTConnectInfo_t *pConnectInfo, const MQTTPublishInfo_t *pWillInfo, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
 Serialize an MQTT CONNECT packet in the given fixed buffer pFixedBuffer. More...
 
MQTTStatus_t MQTT_GetSubscribePacketSize (const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, size_t *pRemainingLength, size_t *pPacketSize)
 Get packet size and Remaining Length of an MQTT SUBSCRIBE packet. More...
 
MQTTStatus_t MQTT_SerializeSubscribe (const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
 Serialize an MQTT SUBSCRIBE packet in the given buffer. More...
 
MQTTStatus_t MQTT_GetUnsubscribePacketSize (const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, size_t *pRemainingLength, size_t *pPacketSize)
 Get packet size and Remaining Length of an MQTT UNSUBSCRIBE packet. More...
 
MQTTStatus_t MQTT_SerializeUnsubscribe (const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
 Serialize an MQTT UNSUBSCRIBE packet in the given buffer. More...
 
MQTTStatus_t MQTT_GetPublishPacketSize (const MQTTPublishInfo_t *pPublishInfo, size_t *pRemainingLength, size_t *pPacketSize)
 Get the packet size and remaining length of an MQTT PUBLISH packet. More...
 
MQTTStatus_t MQTT_SerializePublish (const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
 Serialize an MQTT PUBLISH packet in the given buffer. More...
 
MQTTStatus_t MQTT_SerializePublishHeaderWithoutTopic (const MQTTPublishInfo_t *pPublishInfo, size_t remainingLength, uint8_t *pBuffer, size_t *headerSize)
 Serialize an MQTT PUBLISH packet header without the topic string in the given buffer. This function will add the topic string length to the provided buffer. This helps reduce an unnecessary copy of the topic string into the buffer. More...
 
MQTTStatus_t MQTT_SerializePublishHeader (const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer, size_t *pHeaderSize)
 Serialize an MQTT PUBLISH packet header in the given buffer. More...
 
MQTTStatus_t MQTT_SerializeAck (const MQTTFixedBuffer_t *pFixedBuffer, uint8_t packetType, uint16_t packetId)
 Serialize an MQTT PUBACK, PUBREC, PUBREL, or PUBCOMP into the given buffer. More...
 
MQTTStatus_t MQTT_GetDisconnectPacketSize (size_t *pPacketSize)
 Get the size of an MQTT DISCONNECT packet. More...
 
MQTTStatus_t MQTT_SerializeDisconnect (const MQTTFixedBuffer_t *pFixedBuffer)
 Serialize an MQTT DISCONNECT packet into the given buffer. More...
 
MQTTStatus_t MQTT_GetPingreqPacketSize (size_t *pPacketSize)
 Get the size of an MQTT PINGREQ packet. More...
 
MQTTStatus_t MQTT_SerializePingreq (const MQTTFixedBuffer_t *pFixedBuffer)
 Serialize an MQTT PINGREQ packet into the given buffer. More...
 
MQTTStatus_t MQTT_DeserializePublish (const MQTTPacketInfo_t *pIncomingPacket, uint16_t *pPacketId, MQTTPublishInfo_t *pPublishInfo)
 Deserialize an MQTT PUBLISH packet. More...
 
MQTTStatus_t MQTT_DeserializeAck (const MQTTPacketInfo_t *pIncomingPacket, uint16_t *pPacketId, bool *pSessionPresent)
 Deserialize an MQTT CONNACK, SUBACK, UNSUBACK, PUBACK, PUBREC, PUBREL, PUBCOMP, or PINGRESP. More...
 
MQTTStatus_t MQTT_GetIncomingPacketTypeAndLength (TransportRecv_t readFunc, NetworkContext_t *pNetworkContext, MQTTPacketInfo_t *pIncomingPacket)
 Extract the MQTT packet type and length from incoming packet. More...
 
MQTTStatus_t MQTT_ProcessIncomingPacketTypeAndLength (const uint8_t *pBuffer, const size_t *pIndex, MQTTPacketInfo_t *pIncomingPacket)
 Extract the MQTT packet type and length from incoming packet. More...
 

Detailed Description

User-facing functions for serializing and deserializing MQTT 3.1.1 packets. This header should be included for building a lighter weight MQTT client than the managed CSDK MQTT library API in core_mqtt.h, by using the serializer and de-serializer functions exposed in this file's API.

Function Documentation

◆ MQTT_GetConnectPacketSize()

MQTTStatus_t MQTT_GetConnectPacketSize ( const MQTTConnectInfo_t pConnectInfo,
const MQTTPublishInfo_t pWillInfo,
size_t *  pRemainingLength,
size_t *  pPacketSize 
)

Get the size and Remaining Length of an MQTT CONNECT packet.

This function must be called before MQTT_SerializeConnect in order to get the size of the MQTT CONNECT packet that is generated from MQTTConnectInfo_t and optional MQTTPublishInfo_t. The size of the MQTTFixedBuffer_t supplied to MQTT_SerializeConnect must be at least pPacketSize. The provided pConnectInfo and pWillInfo are valid for serialization with MQTT_SerializeConnect only if this function returns MQTTSuccess. The remaining length returned in pRemainingLength and the packet size returned in pPacketSize are valid only if this function returns MQTTSuccess.

Parameters
[in]pConnectInfoMQTT CONNECT packet parameters.
[in]pWillInfoLast Will and Testament. Pass NULL if not used.
[out]pRemainingLengthThe Remaining Length of the MQTT CONNECT packet.
[out]pPacketSizeThe total size of the MQTT CONNECT packet.
Returns
MQTTBadParameter if the packet would exceed the size allowed by the MQTT spec; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTConnectInfo_t connectInfo = { 0 };
MQTTPublishInfo_t willInfo = { 0 };
size_t remainingLength = 0, packetSize = 0;
// Initialize the connection info, the details are out of scope for this example.
initializeConnectInfo( &connectInfo );
// Initialize the optional will info, the details are out of scope for this example.
initializeWillInfo( &willInfo );
// Get the size requirement for the connect packet.
&connectInfo, &willInfo, &remainingLength, &packetSize
);
if( status == MQTTSuccess )
{
// The application should allocate or use a static #MQTTFixedBuffer_t
// of size >= packetSize to serialize the connect request.
}
MQTTStatus_t MQTT_GetConnectPacketSize(const MQTTConnectInfo_t *pConnectInfo, const MQTTPublishInfo_t *pWillInfo, size_t *pRemainingLength, size_t *pPacketSize)
Get the size and Remaining Length of an MQTT CONNECT packet.
Definition: core_mqtt_serializer.c:1692
MQTTStatus_t
Return codes from MQTT functions.
Definition: core_mqtt_serializer.h:97
@ MQTTSuccess
Definition: core_mqtt_serializer.h:98
MQTT CONNECT packet parameters.
Definition: core_mqtt_serializer.h:143
MQTT PUBLISH packet parameters.
Definition: core_mqtt_serializer.h:212

◆ MQTT_SerializeConnect()

MQTTStatus_t MQTT_SerializeConnect ( const MQTTConnectInfo_t pConnectInfo,
const MQTTPublishInfo_t pWillInfo,
size_t  remainingLength,
const MQTTFixedBuffer_t pFixedBuffer 
)

Serialize an MQTT CONNECT packet in the given fixed buffer pFixedBuffer.

MQTT_GetConnectPacketSize should be called with pConnectInfo and pWillInfo before invoking this function to get the size of the required MQTTFixedBuffer_t and remainingLength. The remainingLength must be the same as returned by MQTT_GetConnectPacketSize. The MQTTFixedBuffer_t must be at least as large as the size returned by MQTT_GetConnectPacketSize.

Parameters
[in]pConnectInfoMQTT CONNECT packet parameters.
[in]pWillInfoLast Will and Testament. Pass NULL if not used.
[in]remainingLengthRemaining Length provided by MQTT_GetConnectPacketSize.
[out]pFixedBufferBuffer for packet serialization.
Returns
MQTTNoMemory if pFixedBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTConnectInfo_t connectInfo = { 0 };
MQTTPublishInfo_t willInfo = { 0 };
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
size_t remainingLength = 0, packetSize = 0;
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// Assume connectInfo and willInfo are initialized. Get the size requirement for
// the connect packet.
&connectInfo, &willInfo, &remainingLength, &packetSize
);
assert( status == MQTTSuccess );
assert( packetSize <= BUFFER_SIZE );
// Serialize the connect packet into the fixed buffer.
status = MQTT_SerializeConnect( &connectInfo, &willInfo, remainingLength, &fixedBuffer );
if( status == MQTTSuccess )
{
// The connect packet can now be sent to the broker.
}
MQTTStatus_t MQTT_SerializeConnect(const MQTTConnectInfo_t *pConnectInfo, const MQTTPublishInfo_t *pWillInfo, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
Serialize an MQTT CONNECT packet in the given fixed buffer pFixedBuffer.
Definition: core_mqtt_serializer.c:1792
Buffer passed to MQTT library.
Definition: core_mqtt_serializer.h:133
size_t size
Size of buffer.
Definition: core_mqtt_serializer.h:135
uint8_t * pBuffer
Pointer to buffer.
Definition: core_mqtt_serializer.h:134

◆ MQTT_GetSubscribePacketSize()

MQTTStatus_t MQTT_GetSubscribePacketSize ( const MQTTSubscribeInfo_t pSubscriptionList,
size_t  subscriptionCount,
size_t *  pRemainingLength,
size_t *  pPacketSize 
)

Get packet size and Remaining Length of an MQTT SUBSCRIBE packet.

This function must be called before MQTT_SerializeSubscribe in order to get the size of the MQTT SUBSCRIBE packet that is generated from the list of MQTTSubscribeInfo_t. The size of the MQTTFixedBuffer_t supplied to MQTT_SerializeSubscribe must be at least pPacketSize. The provided pSubscriptionList is valid for serialization with MQTT_SerializeSubscribe only if this function returns MQTTSuccess. The remaining length returned in pRemainingLength and the packet size returned in pPacketSize are valid only if this function returns MQTTSuccess.

Parameters
[in]pSubscriptionListList of MQTT subscription info.
[in]subscriptionCountThe number of elements in pSubscriptionList.
[out]pRemainingLengthThe Remaining Length of the MQTT SUBSCRIBE packet.
[out]pPacketSizeThe total size of the MQTT SUBSCRIBE packet.
Returns
MQTTBadParameter if the packet would exceed the size allowed by the MQTT spec; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t subscriptionList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
size_t remainingLength = 0, packetSize = 0;
// 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 ] );
}
// Get the size requirement for the subscribe packet.
&subscriptionList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, &remainingLength, &packetSize
);
if( status == MQTTSuccess )
{
// The application should allocate or use a static #MQTTFixedBuffer_t
// of size >= packetSize to serialize the subscribe request.
}
MQTTStatus_t MQTT_GetSubscribePacketSize(const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, size_t *pRemainingLength, size_t *pPacketSize)
Get packet size and Remaining Length of an MQTT SUBSCRIBE packet.
Definition: core_mqtt_serializer.c:1850
@ MQTTQoS0
Definition: core_mqtt_serializer.h:120
MQTT SUBSCRIBE packet parameters.
Definition: core_mqtt_serializer.h:190
MQTTQoS_t qos
Quality of Service for subscription.
Definition: core_mqtt_serializer.h:194
uint16_t topicFilterLength
Length of subscription topic filter.
Definition: core_mqtt_serializer.h:204
const char * pTopicFilter
Topic filter to subscribe to.
Definition: core_mqtt_serializer.h:199

◆ MQTT_SerializeSubscribe()

MQTTStatus_t MQTT_SerializeSubscribe ( const MQTTSubscribeInfo_t pSubscriptionList,
size_t  subscriptionCount,
uint16_t  packetId,
size_t  remainingLength,
const MQTTFixedBuffer_t pFixedBuffer 
)

Serialize an MQTT SUBSCRIBE packet in the given buffer.

MQTT_GetSubscribePacketSize should be called with pSubscriptionList before invoking this function to get the size of the required MQTTFixedBuffer_t and remainingLength. The remainingLength must be the same as returned by MQTT_GetSubscribePacketSize. The MQTTFixedBuffer_t must be at least as large as the size returned by MQTT_GetSubscribePacketSize.

Parameters
[in]pSubscriptionListList of MQTT subscription info.
[in]subscriptionCountThe number of elements in pSubscriptionList.
[in]packetIdpacket ID generated by MQTT_GetPacketId.
[in]remainingLengthRemaining Length provided by MQTT_GetSubscribePacketSize.
[out]pFixedBufferBuffer for packet serialization.
Returns
MQTTNoMemory if pFixedBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t subscriptionList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
size_t remainingLength = 0, packetSize = 0;
uint16_t packetId;
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// Function to return a valid, unused packet identifier. The details are out of
// scope for this example.
packetId = getNewPacketId();
// Assume subscriptionList has been initialized. Get the subscribe packet size.
&subscriptionList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, &remainingLength, &packetSize
);
assert( status == MQTTSuccess );
assert( packetSize <= BUFFER_SIZE );
// Serialize the subscribe packet into the fixed buffer.
&subscriptionList[ 0 ],
NUMBER_OF_SUBSCRIPTIONS,
packetId,
remainingLength,
&fixedBuffer
);
if( status == MQTTSuccess )
{
// The subscribe packet can now be sent to the broker.
}
MQTTStatus_t MQTT_SerializeSubscribe(const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
Serialize an MQTT SUBSCRIBE packet in the given buffer.
Definition: core_mqtt_serializer.c:1934

◆ MQTT_GetUnsubscribePacketSize()

MQTTStatus_t MQTT_GetUnsubscribePacketSize ( const MQTTSubscribeInfo_t pSubscriptionList,
size_t  subscriptionCount,
size_t *  pRemainingLength,
size_t *  pPacketSize 
)

Get packet size and Remaining Length of an MQTT UNSUBSCRIBE packet.

This function must be called before MQTT_SerializeUnsubscribe in order to get the size of the MQTT UNSUBSCRIBE packet that is generated from the list of MQTTSubscribeInfo_t. The size of the MQTTFixedBuffer_t supplied to MQTT_SerializeUnsubscribe must be at least pPacketSize. The provided pSubscriptionList is valid for serialization with MQTT_SerializeUnsubscribe only if this function returns MQTTSuccess. The remaining length returned in pRemainingLength and the packet size returned in pPacketSize are valid only if this function returns MQTTSuccess.

Parameters
[in]pSubscriptionListList of MQTT subscription info.
[in]subscriptionCountThe number of elements in pSubscriptionList.
[out]pRemainingLengthThe Remaining Length of the MQTT UNSUBSCRIBE packet.
[out]pPacketSizeThe total size of the MQTT UNSUBSCRIBE packet.
Returns
MQTTBadParameter if the packet would exceed the size allowed by the MQTT spec; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t subscriptionList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
size_t remainingLength = 0, packetSize = 0;
// Initialize the subscribe info. The details are out of scope for this example.
initializeSubscribeInfo( &subscriptionList[ 0 ] );
// Get the size requirement for the unsubscribe packet.
&subscriptionList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, &remainingLength, &packetSize
);
if( status == MQTTSuccess )
{
// The application should allocate or use a static #MQTTFixedBuffer_t
// of size >= packetSize to serialize the unsubscribe request.
}
MQTTStatus_t MQTT_GetUnsubscribePacketSize(const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, size_t *pRemainingLength, size_t *pPacketSize)
Get packet size and Remaining Length of an MQTT UNSUBSCRIBE packet.
Definition: core_mqtt_serializer.c:1980

◆ MQTT_SerializeUnsubscribe()

MQTTStatus_t MQTT_SerializeUnsubscribe ( const MQTTSubscribeInfo_t pSubscriptionList,
size_t  subscriptionCount,
uint16_t  packetId,
size_t  remainingLength,
const MQTTFixedBuffer_t pFixedBuffer 
)

Serialize an MQTT UNSUBSCRIBE packet in the given buffer.

MQTT_GetUnsubscribePacketSize should be called with pSubscriptionList before invoking this function to get the size of the required MQTTFixedBuffer_t and remainingLength. The remainingLength must be the same as returned by MQTT_GetUnsubscribePacketSize. The MQTTFixedBuffer_t must be at least as large as the size returned by MQTT_GetUnsubscribePacketSize.

Parameters
[in]pSubscriptionListList of MQTT subscription info.
[in]subscriptionCountThe number of elements in pSubscriptionList.
[in]packetIdpacket ID generated by MQTT_GetPacketId.
[in]remainingLengthRemaining Length provided by MQTT_GetUnsubscribePacketSize.
[out]pFixedBufferBuffer for packet serialization.
Returns
MQTTNoMemory if pFixedBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t subscriptionList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
size_t remainingLength = 0, packetSize = 0;
uint16_t packetId;
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// Function to return a valid, unused packet identifier. The details are out of
// scope for this example.
packetId = getNewPacketId();
// Assume subscriptionList has been initialized. Get the unsubscribe packet size.
&subscriptionList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, &remainingLength, &packetSize
);
assert( status == MQTTSuccess );
assert( packetSize <= BUFFER_SIZE );
// Serialize the unsubscribe packet into the fixed buffer.
&subscriptionList[ 0 ],
NUMBER_OF_SUBSCRIPTIONS,
packetId,
remainingLength,
&fixedBuffer
);
if( status == MQTTSuccess )
{
// The unsubscribe packet can now be sent to the broker.
}
MQTTStatus_t MQTT_SerializeUnsubscribe(const MQTTSubscribeInfo_t *pSubscriptionList, size_t subscriptionCount, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
Serialize an MQTT UNSUBSCRIBE packet in the given buffer.
Definition: core_mqtt_serializer.c:2018

◆ MQTT_GetPublishPacketSize()

MQTTStatus_t MQTT_GetPublishPacketSize ( const MQTTPublishInfo_t pPublishInfo,
size_t *  pRemainingLength,
size_t *  pPacketSize 
)

Get the packet size and remaining length of an MQTT PUBLISH packet.

This function must be called before MQTT_SerializePublish in order to get the size of the MQTT PUBLISH packet that is generated from MQTTPublishInfo_t. The size of the MQTTFixedBuffer_t supplied to MQTT_SerializePublish must be at least pPacketSize. The provided pPublishInfo is valid for serialization with MQTT_SerializePublish only if this function returns MQTTSuccess. The remaining length returned in pRemainingLength and the packet size returned in pPacketSize are valid only if this function returns MQTTSuccess.

Parameters
[in]pPublishInfoMQTT PUBLISH packet parameters.
[out]pRemainingLengthThe Remaining Length of the MQTT PUBLISH packet.
[out]pPacketSizeThe total size of the MQTT PUBLISH packet.
Returns
MQTTBadParameter if the packet would exceed the size allowed by the MQTT spec or if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTPublishInfo_t publishInfo = { 0 };
size_t remainingLength = 0, packetSize = 0;
// Initialize the publish info.
publishInfo.qos = MQTTQoS0;
publishInfo.pTopicName = "/some/topic/name";
publishInfo.topicNameLength = strlen( publishInfo.pTopicName );
publishInfo.pPayload = "Hello World!";
publishInfo.payloadLength = strlen( "Hello World!" );
// Get the size requirement for the publish packet.
&publishInfo, &remainingLength, &packetSize
);
if( status == MQTTSuccess )
{
// The application should allocate or use a static #MQTTFixedBuffer_t
// of size >= packetSize to serialize the publish.
}
MQTTStatus_t MQTT_GetPublishPacketSize(const MQTTPublishInfo_t *pPublishInfo, size_t *pRemainingLength, size_t *pPacketSize)
Get the packet size and remaining length of an MQTT PUBLISH packet.
Definition: core_mqtt_serializer.c:2059
MQTTQoS_t qos
Quality of Service for message.
Definition: core_mqtt_serializer.h:216
uint16_t topicNameLength
Length of topic name.
Definition: core_mqtt_serializer.h:236
size_t payloadLength
Message payload length.
Definition: core_mqtt_serializer.h:246
const char * pTopicName
Topic name on which the message is published.
Definition: core_mqtt_serializer.h:231
const void * pPayload
Message payload.
Definition: core_mqtt_serializer.h:241

◆ MQTT_SerializePublish()

MQTTStatus_t MQTT_SerializePublish ( const MQTTPublishInfo_t pPublishInfo,
uint16_t  packetId,
size_t  remainingLength,
const MQTTFixedBuffer_t pFixedBuffer 
)

Serialize an MQTT PUBLISH packet in the given buffer.

This function will serialize complete MQTT PUBLISH packet into the given buffer. If the PUBLISH payload can be sent separately, consider using MQTT_SerializePublishHeader, which will serialize only the PUBLISH header into the buffer.

MQTT_GetPublishPacketSize should be called with pPublishInfo before invoking this function to get the size of the required MQTTFixedBuffer_t and remainingLength. The remainingLength must be the same as returned by MQTT_GetPublishPacketSize. The MQTTFixedBuffer_t must be at least as large as the size returned by MQTT_GetPublishPacketSize.

Parameters
[in]pPublishInfoMQTT PUBLISH packet parameters.
[in]packetIdpacket ID generated by MQTT_GetPacketId.
[in]remainingLengthRemaining Length provided by MQTT_GetPublishPacketSize.
[out]pFixedBufferBuffer for packet serialization.
Returns
MQTTNoMemory if pFixedBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTPublishInfo_t publishInfo = { 0 };
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
size_t remainingLength = 0, packetSize = 0;
uint16_t packetId;
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// A packet identifier is unused for QoS 0 publishes. Otherwise, a valid, unused packet
// identifier must be used.
packetId = 0;
// Assume publishInfo has been initialized. Get publish packet size.
&publishInfo, &remainingLength, &packetSize
);
assert( status == MQTTSuccess );
assert( packetSize <= BUFFER_SIZE );
// Serialize the publish packet into the fixed buffer.
&publishInfo,
packetId,
remainingLength,
&fixedBuffer
);
if( status == MQTTSuccess )
{
// The publish packet can now be sent to the broker.
}
MQTTStatus_t MQTT_SerializePublish(const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer)
Serialize an MQTT PUBLISH packet in the given buffer.
Definition: core_mqtt_serializer.c:2100

◆ MQTT_SerializePublishHeaderWithoutTopic()

MQTTStatus_t MQTT_SerializePublishHeaderWithoutTopic ( const MQTTPublishInfo_t pPublishInfo,
size_t  remainingLength,
uint8_t *  pBuffer,
size_t *  headerSize 
)

Serialize an MQTT PUBLISH packet header without the topic string in the given buffer. This function will add the topic string length to the provided buffer. This helps reduce an unnecessary copy of the topic string into the buffer.

Parameters
[in]pPublishInfoMQTT PUBLISH packet parameters.
[in]remainingLengthRemaining Length provided by MQTT_GetPublishPacketSize.
[out]pBufferBuffer for packet serialization.
[out]headerSizeSize of the serialized MQTT PUBLISH header.
Returns
MQTTSuccess if the serialization is successful. Otherwise, MQTTBadParameter.

◆ MQTT_SerializePublishHeader()

MQTTStatus_t MQTT_SerializePublishHeader ( const MQTTPublishInfo_t pPublishInfo,
uint16_t  packetId,
size_t  remainingLength,
const MQTTFixedBuffer_t pFixedBuffer,
size_t *  pHeaderSize 
)

Serialize an MQTT PUBLISH packet header in the given buffer.

This function serializes PUBLISH header in to the given buffer. The payload for PUBLISH will not be copied over to the buffer. This will help reduce the memory needed for the buffer and avoid an unwanted copy operation of the PUBLISH payload into the buffer. If the payload also would need to be part of the serialized buffer, consider using MQTT_SerializePublish.

MQTT_GetPublishPacketSize should be called with pPublishInfo before invoking this function to get the size of the required MQTTFixedBuffer_t and remainingLength. The remainingLength must be the same as returned by MQTT_GetPublishPacketSize. The MQTTFixedBuffer_t must be at least as large as the size returned by MQTT_GetPublishPacketSize.

Parameters
[in]pPublishInfoMQTT PUBLISH packet parameters.
[in]packetIdpacket ID generated by MQTT_GetPacketId.
[in]remainingLengthRemaining Length provided by MQTT_GetPublishPacketSize.
[out]pFixedBufferBuffer for packet serialization.
[out]pHeaderSizeSize of the serialized MQTT PUBLISH header.
Returns
MQTTNoMemory if pFixedBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTPublishInfo_t publishInfo = { 0 };
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
size_t remainingLength = 0, packetSize = 0, headerSize = 0;
uint16_t packetId;
int32_t bytesSent;
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// A packet identifier is unused for QoS 0 publishes. Otherwise, a valid, unused packet
// identifier must be used.
packetId = 0;
// Assume publishInfo has been initialized. Get the publish packet size.
&publishInfo, &remainingLength, &packetSize
);
assert( status == MQTTSuccess );
// The payload will not be serialized, so the the fixed buffer does not need to hold it.
assert( ( packetSize - publishInfo.payloadLength ) <= BUFFER_SIZE );
// Serialize the publish packet header into the fixed buffer.
&publishInfo,
packetId,
remainingLength,
&fixedBuffer,
&headerSize
);
if( status == MQTTSuccess )
{
// The publish header and payload can now be sent to the broker.
// mqttSocket here is a socket descriptor created and connected to the MQTT
// broker outside of this function.
bytesSent = send( mqttSocket, ( void * ) fixedBuffer.pBuffer, headerSize, 0 );
assert( bytesSent == headerSize );
bytesSent = send( mqttSocket, publishInfo.pPayload, publishInfo.payloadLength, 0 );
assert( bytesSent == publishInfo.payloadLength );
}
MQTTStatus_t MQTT_SerializePublishHeader(const MQTTPublishInfo_t *pPublishInfo, uint16_t packetId, size_t remainingLength, const MQTTFixedBuffer_t *pFixedBuffer, size_t *pHeaderSize)
Serialize an MQTT PUBLISH packet header in the given buffer.
Definition: core_mqtt_serializer.c:2185

◆ MQTT_SerializeAck()

MQTTStatus_t MQTT_SerializeAck ( const MQTTFixedBuffer_t pFixedBuffer,
uint8_t  packetType,
uint16_t  packetId 
)

Serialize an MQTT PUBACK, PUBREC, PUBREL, or PUBCOMP into the given buffer.

Parameters
[out]pFixedBufferBuffer for packet serialization.
[in]packetTypeByte of the corresponding packet fixed header per the MQTT spec.
[in]packetIdPacket ID of the publish.
Returns
MQTTBadParameter, MQTTNoMemory, or MQTTSuccess.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
uint16_t packetId;
uint8_t packetType;
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// The fixed buffer must be large enough to hold 4 bytes.
assert( BUFFER_SIZE >= MQTT_PUBLISH_ACK_PACKET_SIZE );
// The packet ID must be the same as the original publish packet.
packetId = publishPacketId;
// The byte representing a packet of type ACK. This function accepts PUBACK, PUBREC, PUBREL, or PUBCOMP.
// Serialize the publish acknowledgment into the fixed buffer.
status = MQTT_SerializeAck( &fixedBuffer, packetType, packetId );
if( status == MQTTSuccess )
{
// The publish acknowledgment can now be sent to the broker.
}
MQTTStatus_t MQTT_SerializeAck(const MQTTFixedBuffer_t *pFixedBuffer, uint8_t packetType, uint16_t packetId)
Serialize an MQTT PUBACK, PUBREC, PUBREL, or PUBCOMP into the given buffer.
Definition: core_mqtt_serializer.c:2268
#define MQTT_PUBLISH_ACK_PACKET_SIZE
The size of MQTT PUBACK, PUBREC, PUBREL, and PUBCOMP packets, per MQTT spec.
Definition: core_mqtt_serializer.h:83
#define MQTT_PACKET_TYPE_PUBACK
PUBACK (bidirectional).
Definition: core_mqtt_serializer.h:66

◆ MQTT_GetDisconnectPacketSize()

MQTTStatus_t MQTT_GetDisconnectPacketSize ( size_t *  pPacketSize)

Get the size of an MQTT DISCONNECT packet.

Parameters
[out]pPacketSizeThe size of the MQTT DISCONNECT packet.
Returns
MQTTSuccess, or MQTTBadParameter if pPacketSize is NULL.

Example

// Variables used in this example.
MQTTStatus_t status;
size_t packetSize = 0;
// Get the size requirement for the disconnect packet.
status = MQTT_GetDisconnectPacketSize( &packetSize );
assert( status == MQTTSuccess );
assert( packetSize == 2 );
// The application should allocate or use a static #MQTTFixedBuffer_t of
// size >= 2 to serialize the disconnect packet.
MQTTStatus_t MQTT_GetDisconnectPacketSize(size_t *pPacketSize)
Get the size of an MQTT DISCONNECT packet.
Definition: core_mqtt_serializer.c:2323

◆ MQTT_SerializeDisconnect()

MQTTStatus_t MQTT_SerializeDisconnect ( const MQTTFixedBuffer_t pFixedBuffer)

Serialize an MQTT DISCONNECT packet into the given buffer.

The input MQTTFixedBuffer_t.size must be at least as large as the size returned by MQTT_GetDisconnectPacketSize.

Parameters
[out]pFixedBufferBuffer for packet serialization.
Returns
MQTTNoMemory if pFixedBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// Get the disconnect packet size.
status = MQTT_GetDisconnectPacketSize( &packetSize );
assert( status == MQTTSuccess );
assert( packetSize <= BUFFER_SIZE );
// Serialize the disconnect into the fixed buffer.
status = MQTT_SerializeDisconnect( &fixedBuffer );
if( status == MQTTSuccess )
{
// The disconnect packet can now be sent to the broker.
}
MQTTStatus_t MQTT_SerializeDisconnect(const MQTTFixedBuffer_t *pFixedBuffer)
Serialize an MQTT DISCONNECT packet into the given buffer.
Definition: core_mqtt_serializer.c:2343

◆ MQTT_GetPingreqPacketSize()

MQTTStatus_t MQTT_GetPingreqPacketSize ( size_t *  pPacketSize)

Get the size of an MQTT PINGREQ packet.

Parameters
[out]pPacketSizeThe size of the MQTT PINGREQ packet.
Returns
MQTTSuccess or MQTTBadParameter if pPacketSize is NULL.

Example

// Variables used in this example.
MQTTStatus_t status;
size_t packetSize = 0;
// Get the size requirement for the ping request packet.
status = MQTT_GetPingreqPacketSize( &packetSize );
assert( status == MQTTSuccess );
assert( packetSize == 2 );
// The application should allocate or use a static #MQTTFixedBuffer_t of
// size >= 2 to serialize the ping request.
MQTTStatus_t MQTT_GetPingreqPacketSize(size_t *pPacketSize)
Get the size of an MQTT PINGREQ packet.
Definition: core_mqtt_serializer.c:2386

◆ MQTT_SerializePingreq()

MQTTStatus_t MQTT_SerializePingreq ( const MQTTFixedBuffer_t pFixedBuffer)

Serialize an MQTT PINGREQ packet into the given buffer.

The input MQTTFixedBuffer_t.size must be at least as large as the size returned by MQTT_GetPingreqPacketSize.

Parameters
[out]pFixedBufferBuffer for packet serialization.
Returns
MQTTNoMemory if pFixedBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ BUFFER_SIZE ];
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = BUFFER_SIZE;
// Get the ping request packet size.
status = MQTT_GetPingreqPacketSize( &packetSize );
assert( status == MQTTSuccess );
assert( packetSize <= BUFFER_SIZE );
// Serialize the ping request into the fixed buffer.
status = MQTT_SerializePingreq( &fixedBuffer );
if( status == MQTTSuccess )
{
// The ping request can now be sent to the broker.
}
MQTTStatus_t MQTT_SerializePingreq(const MQTTFixedBuffer_t *pFixedBuffer)
Serialize an MQTT PINGREQ packet into the given buffer.
Definition: core_mqtt_serializer.c:2406

◆ MQTT_DeserializePublish()

MQTTStatus_t MQTT_DeserializePublish ( const MQTTPacketInfo_t pIncomingPacket,
uint16_t *  pPacketId,
MQTTPublishInfo_t pPublishInfo 
)

Deserialize an MQTT PUBLISH packet.

Parameters
[in]pIncomingPacketMQTTPacketInfo_t containing the buffer.
[out]pPacketIdThe packet ID obtained from the buffer.
[out]pPublishInfoStruct containing information about the publish.
Returns
MQTTBadParameter, MQTTBadResponse, or MQTTSuccess.

Example

// TransportRecv_t function for reading from the network.
int32_t socket_recv(
NetworkContext_t * pNetworkContext,
void * pBuffer,
size_t bytesToRecv
);
// Some context to be used with the above transport receive function.
NetworkContext_t networkContext;
// Other variables used in this example.
MQTTStatus_t status;
MQTTPacketInfo_t incomingPacket;
MQTTPublishInfo_t publishInfo = { 0 };
uint16_t packetId;
int32_t bytesRecvd;
// A buffer to hold remaining data of the incoming packet.
uint8_t buffer[ BUFFER_SIZE ];
// Populate all fields of the incoming packet.
socket_recv,
&networkContext,
&incomingPacket
);
assert( status == MQTTSuccess );
assert( incomingPacket.remainingLength <= BUFFER_SIZE );
bytesRecvd = socket_recv(
&networkContext,
( void * ) buffer,
incomingPacket.remainingLength
);
incomingPacket.pRemainingData = buffer;
// Deserialize the publish information if the incoming packet is a publish.
if( ( incomingPacket.type & 0xF0 ) == MQTT_PACKET_TYPE_PUBLISH )
{
status = MQTT_DeserializePublish( &incomingPacket, &packetId, &publishInfo );
if( status == MQTTSuccess )
{
// The deserialized publish information can now be used from `publishInfo`.
}
}
MQTTStatus_t MQTT_DeserializePublish(const MQTTPacketInfo_t *pIncomingPacket, uint16_t *pPacketId, MQTTPublishInfo_t *pPublishInfo)
Deserialize an MQTT PUBLISH packet.
Definition: core_mqtt_serializer.c:2449
MQTTStatus_t MQTT_GetIncomingPacketTypeAndLength(TransportRecv_t readFunc, NetworkContext_t *pNetworkContext, MQTTPacketInfo_t *pIncomingPacket)
Extract the MQTT packet type and length from incoming packet.
Definition: core_mqtt_serializer.c:2563
#define MQTT_PACKET_TYPE_PUBLISH
PUBLISH (bidirectional).
Definition: core_mqtt_serializer.h:65
struct NetworkContext NetworkContext_t
The NetworkContext is an incomplete type. An implementation of this interface must define struct Netw...
Definition: transport_interface.h:189
MQTT incoming packet parameters.
Definition: core_mqtt_serializer.h:254
size_t remainingLength
Length of remaining serialized data.
Definition: core_mqtt_serializer.h:268
uint8_t type
Type of incoming MQTT packet.
Definition: core_mqtt_serializer.h:258
uint8_t * pRemainingData
Remaining serialized data in the MQTT packet.
Definition: core_mqtt_serializer.h:263

◆ MQTT_DeserializeAck()

MQTTStatus_t MQTT_DeserializeAck ( const MQTTPacketInfo_t pIncomingPacket,
uint16_t *  pPacketId,
bool *  pSessionPresent 
)

Deserialize an MQTT CONNACK, SUBACK, UNSUBACK, PUBACK, PUBREC, PUBREL, PUBCOMP, or PINGRESP.

Parameters
[in]pIncomingPacketMQTTPacketInfo_t containing the buffer.
[out]pPacketIdThe packet ID of obtained from the buffer. Not used in CONNACK or PINGRESP.
[out]pSessionPresentBoolean flag from a CONNACK indicating present session.
Returns
MQTTBadParameter, MQTTBadResponse, MQTTServerRefused, or MQTTSuccess.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTPacketInfo_t incomingPacket;
// Used for SUBACK, UNSUBACK, PUBACK, PUBREC, PUBREL, and PUBCOMP.
uint16_t packetId;
// Used for CONNACK.
bool sessionPresent;
// Receive an incoming packet and populate all fields. The details are out of scope
// for this example.
receiveIncomingPacket( &incomingPacket );
// Deserialize ack information if the incoming packet is not a publish.
if( ( incomingPacket.type & 0xF0 ) != MQTT_PACKET_TYPE_PUBLISH )
{
status = MQTT_DeserializeAck( &incomingPacket, &packetId, &sessionPresent );
if( status == MQTTSuccess )
{
// The packet ID or session present flag information is available. For
// ping response packets, the only information is the status code.
}
}
MQTTStatus_t MQTT_DeserializeAck(const MQTTPacketInfo_t *pIncomingPacket, uint16_t *pPacketId, bool *pSessionPresent)
Deserialize an MQTT CONNACK, SUBACK, UNSUBACK, PUBACK, PUBREC, PUBREL, PUBCOMP, or PINGRESP.
Definition: core_mqtt_serializer.c:2486

◆ MQTT_GetIncomingPacketTypeAndLength()

MQTTStatus_t MQTT_GetIncomingPacketTypeAndLength ( TransportRecv_t  readFunc,
NetworkContext_t pNetworkContext,
MQTTPacketInfo_t pIncomingPacket 
)

Extract the MQTT packet type and length from incoming packet.

This function must be called for every incoming packet to retrieve the MQTTPacketInfo_t.type and MQTTPacketInfo_t.remainingLength. A MQTTPacketInfo_t is not valid until this routine has been invoked.

Parameters
[in]readFuncTransport layer read function pointer.
[in]pNetworkContextThe network context pointer provided by the application.
[out]pIncomingPacketPointer to MQTTPacketInfo_t structure. This is where type, remaining length and packet identifier are stored.
Returns
MQTTSuccess on successful extraction of type and length, MQTTBadParameter if pIncomingPacket is invalid, MQTTRecvFailed on transport receive failure, MQTTBadResponse if an invalid packet is read, and MQTTNoDataAvailable if there is nothing to read.

Example

// TransportRecv_t function for reading from the network.
int32_t socket_recv(
NetworkContext_t * pNetworkContext,
void * pBuffer,
size_t bytesToRecv
);
// Some context to be used with above transport receive function.
NetworkContext_t networkContext;
// Struct to hold the incoming packet information.
MQTTPacketInfo_t incomingPacket;
int32_t bytesRecvd;
// Buffer to hold the remaining data of the incoming packet.
uint8_t buffer[ BUFFER_SIZE ];
// Loop until data is available to be received.
do{
socket_recv,
&networkContext,
&incomingPacket
);
} while( status == MQTTNoDataAvailable );
assert( status == MQTTSuccess );
// Receive the rest of the incoming packet.
assert( incomingPacket.remainingLength <= BUFFER_SIZE );
bytesRecvd = socket_recv(
&networkContext,
( void * ) buffer,
incomingPacket.remainingLength
);
// Set the remaining data field.
incomingPacket.pRemainingData = buffer;
@ MQTTNoDataAvailable
Definition: core_mqtt_serializer.h:105

◆ MQTT_ProcessIncomingPacketTypeAndLength()

MQTTStatus_t MQTT_ProcessIncomingPacketTypeAndLength ( const uint8_t *  pBuffer,
const size_t *  pIndex,
MQTTPacketInfo_t pIncomingPacket 
)

Extract the MQTT packet type and length from incoming packet.

This function must be called for every incoming packet to retrieve the MQTTPacketInfo_t.type and MQTTPacketInfo_t.remainingLength. A MQTTPacketInfo_t is not valid until this routine has been invoked.

Parameters
[in]pBufferThe buffer holding the raw data to be processed
[in]pIndexPointer to the index within the buffer to marking the end of raw data available.
[out]pIncomingPacketStructure used to hold the fields of the incoming packet.
Returns
MQTTSuccess on successful extraction of type and length, MQTTBadParameter if pIncomingPacket is invalid, MQTTBadResponse if an invalid packet is read, and MQTTNoDataAvailable if there is nothing to read.