Paho MQTT C Client Library: MQTTClient.h File Reference

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Data Structures | Macros | Typedefs | Enumerations | Functions
MQTTClient.h File Reference
`#include "MQTTExportDeclarations.h"`
`#include "MQTTProperties.h"`
`#include "MQTTReasonCodes.h"`
`#include "MQTTSubscribeOpts.h"`
`#include "MQTTClientPersistence.h"`

Go to the source code of this file.

## Data Structures
struct | MQTTClient_init_options
struct | MQTTClient_message
struct | MQTTClient_createOptions
struct | MQTTClient_willOptions
struct | MQTTClient_SSLOptions
struct | MQTTClient_nameValue
struct | MQTTClient_connectOptions
struct | MQTTResponse

## Macros
#define | MQTTCLIENT_SUCCESS 0
#define | MQTTCLIENT_FAILURE -1
#define | MQTTCLIENT_DISCONNECTED -3
#define | MQTTCLIENT_MAX_MESSAGES_INFLIGHT -4
#define | MQTTCLIENT_BAD_UTF8_STRING -5
#define | MQTTCLIENT_NULL_PARAMETER -6
#define | MQTTCLIENT_TOPICNAME_TRUNCATED -7
#define | MQTTCLIENT_BAD_STRUCTURE -8
#define | MQTTCLIENT_BAD_QOS -9
#define | MQTTCLIENT_SSL_NOT_SUPPORTED -10
#define | MQTTCLIENT_BAD_MQTT_VERSION -11
#define | MQTTCLIENT_BAD_PROTOCOL -14
#define | MQTTCLIENT_BAD_MQTT_OPTION -15
#define | MQTTCLIENT_WRONG_MQTT_VERSION -16
#define | MQTTCLIENT_0_LEN_WILL_TOPIC -17
#define | MQTTVERSION_DEFAULT 0
#define | MQTTVERSION_3_1 3
#define | MQTTVERSION_3_1_1 4
#define | MQTTVERSION_5 5
#define | MQTT_BAD_SUBSCRIBE 0x80
#define | MQTTClient_init_options_initializer { {'M', 'Q', 'T', 'G'}, 0, 0 }
#define | MQTTClient_message_initializer { {'M', 'Q', 'T', 'M'}, 1, 0, NULL, 0, 0, 0, 0, MQTTProperties_initializer }
#define | MQTTClient_createOptions_initializer { {'M', 'Q', 'C', 'O'}, 0, MQTTVERSION_DEFAULT }
#define | MQTTClient_willOptions_initializer { {'M', 'Q', 'T', 'W'}, 1, NULL, NULL, 0, 0, {0, NULL} }
#define | MQTT_SSL_VERSION_DEFAULT 0
#define | MQTT_SSL_VERSION_TLS_1_0 1
#define | MQTT_SSL_VERSION_TLS_1_1 2
#define | MQTT_SSL_VERSION_TLS_1_2 3
#define | MQTTClient_SSLOptions_initializer { {'M', 'Q', 'T', 'S'}, 5, NULL, NULL, NULL, NULL, NULL, 1, MQTT_SSL_VERSION_DEFAULT, 0, NULL, NULL, NULL, NULL, NULL, 0, NULL, 0 }
#define | MQTTClient_connectOptions_initializer
#define | MQTTClient_connectOptions_initializer5
#define | MQTTClient_connectOptions_initializer_ws
#define | MQTTClient_connectOptions_initializer5_ws
#define | MQTTResponse_initializer {1, MQTTREASONCODE_SUCCESS, 0, NULL, NULL}

## Typedefs
typedef void * | MQTTClient
typedef int | MQTTClient_deliveryToken
typedef int | MQTTClient_token
typedef int | MQTTClient_messageArrived(void *context, char *topicName, int topicLen, MQTTClient_message *message)
typedef void | MQTTClient_deliveryComplete(void *context, MQTTClient_deliveryToken dt)
typedef void | MQTTClient_connectionLost(void *context, char *cause)
typedef void | MQTTClient_disconnected(void *context, MQTTProperties *properties, enum MQTTReasonCodes reasonCode)
typedef void | MQTTClient_published(void *context, int dt, int packet_type, MQTTProperties *properties, enum MQTTReasonCodes reasonCode)
typedef struct MQTTResponse | MQTTResponse
typedef void | MQTTClient_traceCallback(enum MQTTCLIENT_TRACE_LEVELS level, char *message)

## Enumerations
enum | MQTTCLIENT_TRACE_LEVELS { MQTTCLIENT_TRACE_MAXIMUM = 1 , MQTTCLIENT_TRACE_MEDIUM , MQTTCLIENT_TRACE_MINIMUM , MQTTCLIENT_TRACE_PROTOCOL , MQTTCLIENT_TRACE_ERROR , MQTTCLIENT_TRACE_SEVERE , MQTTCLIENT_TRACE_FATAL }

## Functions
void | MQTTClient_global_init (MQTTClient_init_options *inits)
int | MQTTClient_setCallbacks (MQTTClient handle, void *context, MQTTClient_connectionLost *cl, MQTTClient_messageArrived *ma, MQTTClient_deliveryComplete *dc)
int | MQTTClient_setDisconnected (MQTTClient handle, void *context, MQTTClient_disconnected *co)
int | MQTTClient_setPublished (MQTTClient handle, void *context, MQTTClient_published *co)
int | MQTTClient_create (MQTTClient *handle, const char *serverURI, const char *clientId, int persistence_type, void *persistence_context)
int | MQTTClient_createWithOptions (MQTTClient *handle, const char *serverURI, const char *clientId, int persistence_type, void *persistence_context, MQTTClient_createOptions *options)
MQTTClient_nameValue * | MQTTClient_getVersionInfo (void)
int | MQTTClient_connect (MQTTClient handle, MQTTClient_connectOptions *options)
void | MQTTResponse_free (MQTTResponse response)
MQTTResponse | MQTTClient_connect5 (MQTTClient handle, MQTTClient_connectOptions *options, MQTTProperties *connectProperties, MQTTProperties *willProperties)
int | MQTTClient_disconnect (MQTTClient handle, int timeout)
int | MQTTClient_disconnect5 (MQTTClient handle, int timeout, enum MQTTReasonCodes reason, MQTTProperties *props)
int | MQTTClient_isConnected (MQTTClient handle)
int | MQTTClient_subscribe (MQTTClient handle, const char *topic, int qos)
MQTTResponse | MQTTClient_subscribe5 (MQTTClient handle, const char *topic, int qos, MQTTSubscribe_options *opts, MQTTProperties *props)
int | MQTTClient_subscribeMany (MQTTClient handle, int count, char *const *topic, int *qos)
MQTTResponse | MQTTClient_subscribeMany5 (MQTTClient handle, int count, char *const *topic, int *qos, MQTTSubscribe_options *opts, MQTTProperties *props)
int | MQTTClient_unsubscribe (MQTTClient handle, const char *topic)
MQTTResponse | MQTTClient_unsubscribe5 (MQTTClient handle, const char *topic, MQTTProperties *props)
int | MQTTClient_unsubscribeMany (MQTTClient handle, int count, char *const *topic)
MQTTResponse | MQTTClient_unsubscribeMany5 (MQTTClient handle, int count, char *const *topic, MQTTProperties *props)
int | MQTTClient_publish (MQTTClient handle, const char *topicName, int payloadlen, const void *payload, int qos, int retained, MQTTClient_deliveryToken *dt)
MQTTResponse | MQTTClient_publish5 (MQTTClient handle, const char *topicName, int payloadlen, const void *payload, int qos, int retained, MQTTProperties *properties, MQTTClient_deliveryToken *dt)
int | MQTTClient_publishMessage (MQTTClient handle, const char *topicName, MQTTClient_message *msg, MQTTClient_deliveryToken *dt)
MQTTResponse | MQTTClient_publishMessage5 (MQTTClient handle, const char *topicName, MQTTClient_message *msg, MQTTClient_deliveryToken *dt)
int | MQTTClient_waitForCompletion (MQTTClient handle, MQTTClient_deliveryToken dt, unsigned long timeout)
int | MQTTClient_getPendingDeliveryTokens (MQTTClient handle, MQTTClient_deliveryToken **tokens)
void | MQTTClient_yield (void)
int | MQTTClient_receive (MQTTClient handle, char **topicName, int *topicLen, MQTTClient_message **message, unsigned long timeout)
void | MQTTClient_freeMessage (MQTTClient_message **msg)
void | MQTTClient_free (void *ptr)
void * | MQTTClient_malloc (size_t size)
void | MQTTClient_destroy (MQTTClient *handle)
void | MQTTClient_setTraceLevel (enum MQTTCLIENT_TRACE_LEVELS level)
void | MQTTClient_setTraceCallback (MQTTClient_traceCallback *callback)
int | MQTTClient_setCommandTimeout (MQTTClient handle, unsigned long milliSeconds)
const char * | MQTTClient_strerror (int code)

## Macro Definition Documentation

## ◆ MQTTCLIENT_SUCCESS

#define MQTTCLIENT_SUCCESS 0

Return code: No error. Indicates successful completion of an MQTT client operation.

## ◆ MQTTCLIENT_FAILURE

#define MQTTCLIENT_FAILURE -1

Return code: A generic error code indicating the failure of an MQTT client operation.

## ◆ MQTTCLIENT_DISCONNECTED

#define MQTTCLIENT_DISCONNECTED -3

Return code: The client is disconnected.

## ◆ MQTTCLIENT_MAX_MESSAGES_INFLIGHT

#define MQTTCLIENT_MAX_MESSAGES_INFLIGHT -4

Return code: The maximum number of messages allowed to be simultaneously in-flight has been reached.

## ◆ MQTTCLIENT_BAD_UTF8_STRING

#define MQTTCLIENT_BAD_UTF8_STRING -5

Return code: An invalid UTF-8 string has been detected.

## ◆ MQTTCLIENT_NULL_PARAMETER

#define MQTTCLIENT_NULL_PARAMETER -6

Return code: A NULL parameter has been supplied when this is invalid.

## ◆ MQTTCLIENT_TOPICNAME_TRUNCATED

#define MQTTCLIENT_TOPICNAME_TRUNCATED -7

Return code: The topic has been truncated (the topic string includes embedded NULL characters). String functions will not access the full topic. Use the topic length value to access the full topic.

## ◆ MQTTCLIENT_BAD_STRUCTURE

#define MQTTCLIENT_BAD_STRUCTURE -8

Return code: A structure parameter does not have the correct eyecatcher and version number.

## ◆ MQTTCLIENT_BAD_QOS

#define MQTTCLIENT_BAD_QOS -9

Return code: A QoS value that falls outside of the acceptable range (0,1,2)

## ◆ MQTTCLIENT_SSL_NOT_SUPPORTED

#define MQTTCLIENT_SSL_NOT_SUPPORTED -10

Return code: Attempting SSL connection using non-SSL version of library

## ◆ MQTTCLIENT_BAD_MQTT_VERSION

#define MQTTCLIENT_BAD_MQTT_VERSION -11

Return code: unrecognized MQTT version

## ◆ MQTTCLIENT_BAD_PROTOCOL

#define MQTTCLIENT_BAD_PROTOCOL -14

Return code: protocol prefix in serverURI should be:

- tcp:// or mqtt:// - Insecure TCP
- ssl:// or tls:// or mqtts:// - Encrypted SSL/TLS
- ws:// - Insecure websockets
- wss:// - Secure web sockets The TLS enabled prefixes (ssl, tls, mqtts, wss) are only valid if a TLS version of the library is linked with.

## ◆ MQTTCLIENT_BAD_MQTT_OPTION

#define MQTTCLIENT_BAD_MQTT_OPTION -15

Return code: option not applicable to the requested version of MQTT

## ◆ MQTTCLIENT_WRONG_MQTT_VERSION

#define MQTTCLIENT_WRONG_MQTT_VERSION -16

Return code: call not applicable to the requested version of MQTT

## ◆ MQTTCLIENT_0_LEN_WILL_TOPIC

#define MQTTCLIENT_0_LEN_WILL_TOPIC -17

Return code: 0 length will topic on connect

## ◆ MQTTVERSION_DEFAULT

#define MQTTVERSION_DEFAULT 0

Default MQTT version to connect with. Use 3.1.1 then fall back to 3.1

## ◆ MQTTVERSION_3_1

#define MQTTVERSION_3_1 3

MQTT version to connect with: 3.1

## ◆ MQTTVERSION_3_1_1

#define MQTTVERSION_3_1_1 4

MQTT version to connect with: 3.1.1

## ◆ MQTTVERSION_5

#define MQTTVERSION_5 5

MQTT version to connect with: 5

## ◆ MQTT_BAD_SUBSCRIBE

#define MQTT_BAD_SUBSCRIBE 0x80

Bad return code from subscribe, as defined in the 3.1.1 specification

## ◆ MQTTClient_init_options_initializer

#define MQTTClient_init_options_initializer { {'M', 'Q', 'T', 'G'}, 0, 0 }

## ◆ MQTTClient_message_initializer

#define MQTTClient_message_initializer { {'M', 'Q', 'T', 'M'}, 1, 0, NULL, 0, 0, 0, 0, MQTTProperties_initializer }

## ◆ MQTTClient_createOptions_initializer

#define MQTTClient_createOptions_initializer { {'M', 'Q', 'C', 'O'}, 0, MQTTVERSION_DEFAULT }

## ◆ MQTTClient_willOptions_initializer

#define MQTTClient_willOptions_initializer { {'M', 'Q', 'T', 'W'}, 1, NULL, NULL, 0, 0, {0, NULL} }

## ◆ MQTT_SSL_VERSION_DEFAULT

#define MQTT_SSL_VERSION_DEFAULT 0

## ◆ MQTT_SSL_VERSION_TLS_1_0

#define MQTT_SSL_VERSION_TLS_1_0 1

## ◆ MQTT_SSL_VERSION_TLS_1_1

#define MQTT_SSL_VERSION_TLS_1_1 2

## ◆ MQTT_SSL_VERSION_TLS_1_2

#define MQTT_SSL_VERSION_TLS_1_2 3

## ◆ MQTTClient_SSLOptions_initializer

#define MQTTClient_SSLOptions_initializer { {'M', 'Q', 'T', 'S'}, 5, NULL, NULL, NULL, NULL, NULL, 1, MQTT_SSL_VERSION_DEFAULT, 0, NULL, NULL, NULL, NULL, NULL, 0, NULL, 0 }

## ◆ MQTTClient_connectOptions_initializer

#define MQTTClient_connectOptions_initializer

Value:
{ {'M', 'Q', 'T', 'C'}, 8, 60, 1, 1, NULL, NULL, NULL, 30, 0, NULL,\
0, NULL, MQTTVERSION_DEFAULT, {NULL, 0, 0}, {0, NULL}, -1, 0, NULL, NULL, NULL}
MQTTVERSION_DEFAULT
#define MQTTVERSION_DEFAULT
Definition MQTTClient.h:213

Initializer for connect options for MQTT 3.1.1 non-WebSocket connections

## ◆ MQTTClient_connectOptions_initializer5

#define MQTTClient_connectOptions_initializer5

Value:
{ {'M', 'Q', 'T', 'C'}, 8, 60, 0, 1, NULL, NULL, NULL, 30, 0, NULL,\
0, NULL, MQTTVERSION_5, {NULL, 0, 0}, {0, NULL}, -1, 1, NULL, NULL, NULL}
MQTTVERSION_5
#define MQTTVERSION_5
Definition MQTTClient.h:225

Initializer for connect options for MQTT 5.0 non-WebSocket connections

## ◆ MQTTClient_connectOptions_initializer_ws

#define MQTTClient_connectOptions_initializer_ws

Value:
{ {'M', 'Q', 'T', 'C'}, 8, 45, 1, 1, NULL, NULL, NULL, 30, 0, NULL,\
0, NULL, MQTTVERSION_DEFAULT, {NULL, 0, 0}, {0, NULL}, -1, 0, NULL, NULL, NULL}

Initializer for connect options for MQTT 3.1.1 WebSockets connections. The keepalive interval is set to 45 seconds to avoid webserver 60 second inactivity timeouts.

## ◆ MQTTClient_connectOptions_initializer5_ws

#define MQTTClient_connectOptions_initializer5_ws

Value:
{ {'M', 'Q', 'T', 'C'}, 8, 45, 0, 1, NULL, NULL, NULL, 30, 0, NULL,\
0, NULL, MQTTVERSION_5, {NULL, 0, 0}, {0, NULL}, -1, 1, NULL, NULL, NULL}

Initializer for connect options for MQTT 5.0 WebSockets connections. The keepalive interval is set to 45 seconds to avoid webserver 60 second inactivity timeouts.

## ◆ MQTTResponse_initializer

#define MQTTResponse_initializer {1, MQTTREASONCODE_SUCCESS, 0, NULL, NULL}

## Typedef Documentation

## ◆ MQTTClient

typedef void* MQTTClient

A handle representing an MQTT client. A valid client handle is available following a successful call to MQTTClient_create().

## ◆ MQTTClient_deliveryToken

typedef int MQTTClient_deliveryToken

A value representing an MQTT message. A delivery token is returned to the client application when a message is published. The token can then be used to check that the message was successfully delivered to its destination (see MQTTClient_publish(), MQTTClient_publishMessage(), MQTTClient_deliveryComplete(), MQTTClient_waitForCompletion() and MQTTClient_getPendingDeliveryTokens()).

## ◆ MQTTClient_token

typedef int MQTTClient_token

## ◆ MQTTClient_messageArrived

typedef int MQTTClient_messageArrived(void *context, char *topicName, int topicLen, MQTTClient_message *message)

This is a callback function. The client application must provide an implementation of this function to enable asynchronous receipt of messages. The function is registered with the client library by passing it as an argument to MQTTClient_setCallbacks(). It is called by the client library when a new message that matches a client subscription has been received from the server. This function is executed on a separate thread to the one on which the client application is running.

Parameters

  context | A pointer to the context value originally passed to MQTTClient_setCallbacks(), which contains any application-specific context.
  topicName | The topic associated with the received message.
  topicLen | The length of the topic if there are one more NULL characters embedded in topicName, otherwise topicLen is 0. If topicLen is 0, the value returned by strlen(topicName) can be trusted. If topicLen is greater than 0, the full topic name can be retrieved by accessing topicName as a byte array of length topicLen.
  message | The MQTTClient_message structure for the received message. This structure contains the message payload and attributes.

Returns
  This function must return 0 or 1 indicating whether or not the message has been safely received by the client application.
  Returning 1 indicates that the message has been successfully handled. To free the message storage, MQTTClient_freeMessage must be called. To free the topic name storage, MQTTClient_free must be called.
  Returning 0 indicates that there was a problem. In this case, the client library will reinvoke MQTTClient_messageArrived() to attempt to deliver the message to the application again. Do not free the message and topic storage when returning 0, otherwise the redelivery will fail.

## ◆ MQTTClient_deliveryComplete

typedef void MQTTClient_deliveryComplete(void *context, MQTTClient_deliveryToken dt)

This is a callback function. The client application must provide an implementation of this function to enable asynchronous notification of delivery of messages. The function is registered with the client library by passing it as an argument to MQTTClient_setCallbacks(). It is called by the client library after the client application has published a message to the server. It indicates that the necessary handshaking and acknowledgements for the requested quality of service (see MQTTClient_message.qos) have been completed. This function is executed on a separate thread to the one on which the client application is running. Note: MQTTClient_deliveryComplete() is not called when messages are published at QoS0.

Parameters

  context | A pointer to the context value originally passed to MQTTClient_setCallbacks(), which contains any application-specific context.
  dt | The MQTTClient_deliveryToken associated with the published message. Applications can check that all messages have been correctly published by matching the delivery tokens returned from calls to MQTTClient_publish() and MQTTClient_publishMessage() with the tokens passed to this callback.

## ◆ MQTTClient_connectionLost

typedef void MQTTClient_connectionLost(void *context, char *cause)

This is a callback function. The client application must provide an implementation of this function to enable asynchronous notification of the loss of connection to the server. The function is registered with the client library by passing it as an argument to MQTTClient_setCallbacks(). It is called by the client library if the client loses its connection to the server. The client application must take appropriate action, such as trying to reconnect or reporting the problem. This function is executed on a separate thread to the one on which the client application is running.

Parameters

  context | A pointer to the context value originally passed to MQTTClient_setCallbacks(), which contains any application-specific context.
  cause | The reason for the disconnection. Currently, cause is always set to NULL.

## ◆ MQTTClient_disconnected

typedef void MQTTClient_disconnected(void *context, MQTTProperties *properties, enum MQTTReasonCodes reasonCode)

This is a callback function, which will be called when the a disconnect packet is received from the server. This applies to MQTT V5 and above only.

Parameters

  context | A pointer to the context value originally passed to MQTTClient_setDisconnected(), which contains any application-specific context.
  properties | The MQTT V5 properties received with the disconnect, if any.
  reasonCode | The MQTT V5 reason code received with the disconnect. Currently, cause is always set to NULL.

## ◆ MQTTClient_published

typedef void MQTTClient_published(void *context, int dt, int packet_type, MQTTProperties *properties, enum MQTTReasonCodes reasonCode)

This is a callback function, the MQTT V5 version of MQTTClient_deliveryComplete(). The client application must provide an implementation of this function to enable asynchronous notification of the completed delivery of messages. It is called by the client library after the client application has published a message to the server. It indicates that the necessary handshaking and acknowledgements for the requested quality of service (see MQTTClient_message.qos) have been completed. This function is executed on a separate thread to the one on which the client application is running. Note: It is not called when messages are published at QoS0.

Parameters

  context | A pointer to the context value originally passed to MQTTClient_setCallbacks(), which contains any application-specific context.
  dt | The MQTTClient_deliveryToken associated with the published message. Applications can check that all messages have been correctly published by matching the delivery tokens returned from calls to MQTTClient_publish() and MQTTClient_publishMessage() with the tokens passed to this callback.
  packet_type | the last received packet type for this completion. For QoS 1 always PUBACK. For QoS 2 could be PUBREC or PUBCOMP.
  properties | the MQTT V5 properties returned with the last packet from the server
  reasonCode | the reason code returned from the server

## ◆ MQTTResponse

typedef struct MQTTResponse MQTTResponse

MQTT version 5.0 response information

## ◆ MQTTClient_traceCallback

typedef void MQTTClient_traceCallback(enum MQTTCLIENT_TRACE_LEVELS level, char *message)

This is a callback function prototype which must be implemented if you want to receive trace information. Do not invoke any other Paho API calls in this callback function - unpredictable behavior may result.

Parameters

  level | the trace level of the message returned
  message | the trace message. This is a pointer to a static buffer which will be overwritten on each call. You must copy the data if you want to keep it for later.

## Enumeration Type Documentation

## ◆ MQTTCLIENT_TRACE_LEVELS

enum MQTTCLIENT_TRACE_LEVELS

Enumerator
MQTTCLIENT_TRACE_MAXIMUM |
MQTTCLIENT_TRACE_MEDIUM |
MQTTCLIENT_TRACE_MINIMUM |
MQTTCLIENT_TRACE_PROTOCOL |
MQTTCLIENT_TRACE_ERROR |
MQTTCLIENT_TRACE_SEVERE |
MQTTCLIENT_TRACE_FATAL |

## Function Documentation

## ◆ MQTTClient_global_init()

void MQTTClient_global_init | ( | MQTTClient_init_options * | inits | ) |
| extern

Global init of mqtt library. Call once on program start to set global behaviour. do_openssl_init - if mqtt library should initialize OpenSSL (1) or rely on the caller to do it before using the library (0)

## ◆ MQTTClient_setCallbacks()

int MQTTClient_setCallbacks | ( | MQTTClient | handle,
|  | void * | context,
|  | MQTTClient_connectionLost * | cl,
|  | MQTTClient_messageArrived * | ma,
|  | MQTTClient_deliveryComplete * | dc )
| extern

This function sets the callback functions for a specific client. If your client application doesn't use a particular callback, set the relevant parameter to NULL (except for message arrived, which must be given). Calling MQTTClient_setCallbacks() puts the client into multi-threaded mode. Any necessary message acknowledgements and status communications are handled in the background without any intervention from the client application. See Asynchronous vs synchronous client applications for more information.

Note: The MQTT client must be disconnected when this function is called.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  context | A pointer to any application-specific context. The the context pointer is passed to each of the callback functions to provide access to the context information in the callback.
  cl | A pointer to an MQTTClient_connectionLost() callback function. You can set this to NULL if your application doesn't handle disconnections.
  ma | A pointer to an MQTTClient_messageArrived() callback function. This callback function must be set when you call MQTTClient_setCallbacks(), as otherwise there would be nowhere to deliver any incoming messages.
  dc | A pointer to an MQTTClient_deliveryComplete() callback function. You can set this to NULL if your application publishes synchronously or if you do not want to check for successful delivery.

Returns
  MQTTCLIENT_SUCCESS if the callbacks were correctly set, MQTTCLIENT_FAILURE if an error occurred.

## ◆ MQTTClient_setDisconnected()

int MQTTClient_setDisconnected | ( | MQTTClient | handle,
|  | void * | context,
|  | MQTTClient_disconnected * | co )
| extern

Sets the MQTTClient_disconnected() callback function for a client. This will be called if a disconnect packet is received from the server. Only valid for MQTT V5 and above.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  context | A pointer to any application-specific context. The the context pointer is passed to each of the callback functions to provide access to the context information in the callback.
  co | A pointer to an MQTTClient_disconnected() callback function. NULL removes the callback setting.

Returns
  MQTTCLIENT_SUCCESS if the callbacks were correctly set, MQTTCLIENT_FAILURE if an error occurred.

## ◆ MQTTClient_setPublished()

int MQTTClient_setPublished | ( | MQTTClient | handle,
|  | void * | context,
|  | MQTTClient_published * | co )
| extern

## ◆ MQTTClient_create()

int MQTTClient_create | ( | MQTTClient * | handle,
|  | const char * | serverURI,
|  | const char * | clientId,
|  | int | persistence_type,
|  | void * | persistence_context )
| extern

This function creates an MQTT client ready for connection to the specified server and using the specified persistent storage (see MQTTClient_persistence). See also MQTTClient_destroy().

Parameters

  handle | A pointer to an MQTTClient handle. The handle is populated with a valid client reference following a successful return from this function.
  serverURI | A null-terminated string specifying the server to which the client will connect. It takes the form protocol://host:port. Currently, protocol must be: tcp:// or mqtt:// - Insecure TCP ssl:// or mqtts:// - Encrypted SSL/TLS ws:// - Insecure websockets wss:// - Secure web sockets The TLS enabled prefixes (ssl, mqtts, wss) are only valid if a TLS version of the library is linked with. For host, you can specify either an IP address or a host name. For instance, to connect to a server running on the local machines with the default MQTT port, specify tcp://localhost:1883.
  clientId | The client identifier passed to the server when the client connects to it. It is a null-terminated UTF-8 encoded string.
  persistence_type | The type of persistence to be used by the client: MQTTCLIENT_PERSISTENCE_NONE: Use in-memory persistence. If the device or system on which the client is running fails or is switched off, the current state of any in-flight messages is lost and some messages may not be delivered even at QoS1 and QoS2. MQTTCLIENT_PERSISTENCE_DEFAULT: Use the default (file system-based) persistence mechanism. Status about in-flight messages is held in persistent storage and provides some protection against message loss in the case of unexpected failure. MQTTCLIENT_PERSISTENCE_USER: Use an application-specific persistence implementation. Using this type of persistence gives control of the persistence mechanism to the application. The application has to implement the MQTTClient_persistence interface.
  persistence_context | If the application uses MQTTCLIENT_PERSISTENCE_NONE persistence, this argument is unused and should be set to NULL. For MQTTCLIENT_PERSISTENCE_DEFAULT persistence, it should be set to the location of the persistence directory (if set to NULL, the persistence directory used is the working directory). Applications that use MQTTCLIENT_PERSISTENCE_USER persistence set this argument to point to a valid MQTTClient_persistence structure.

Returns
  MQTTCLIENT_SUCCESS if the client is successfully created, otherwise an error code is returned.

## ◆ MQTTClient_createWithOptions()

int MQTTClient_createWithOptions | ( | MQTTClient * | handle,
|  | const char * | serverURI,
|  | const char * | clientId,
|  | int | persistence_type,
|  | void * | persistence_context,
|  | MQTTClient_createOptions * | options )
| extern

A version of :MQTTClient_create() with additional options. This function creates an MQTT client ready for connection to the specified server and using the specified persistent storage (see MQTTClient_persistence). See also MQTTClient_destroy().

Parameters

  handle | A pointer to an MQTTClient handle. The handle is populated with a valid client reference following a successful return from this function.
  serverURI | A null-terminated string specifying the server to which the client will connect. It takes the form protocol://host:port. Currently, protocol must be tcp or ssl. For host, you can specify either an IP address or a host name. For instance, to connect to a server running on the local machines with the default MQTT port, specify tcp://localhost:1883.
  clientId | The client identifier passed to the server when the client connects to it. It is a null-terminated UTF-8 encoded string.
  persistence_type | The type of persistence to be used by the client: MQTTCLIENT_PERSISTENCE_NONE: Use in-memory persistence. If the device or system on which the client is running fails or is switched off, the current state of any in-flight messages is lost and some messages may not be delivered even at QoS1 and QoS2. MQTTCLIENT_PERSISTENCE_DEFAULT: Use the default (file system-based) persistence mechanism. Status about in-flight messages is held in persistent storage and provides some protection against message loss in the case of unexpected failure. MQTTCLIENT_PERSISTENCE_USER: Use an application-specific persistence implementation. Using this type of persistence gives control of the persistence mechanism to the application. The application has to implement the MQTTClient_persistence interface.
  persistence_context | If the application uses MQTTCLIENT_PERSISTENCE_NONE persistence, this argument is unused and should be set to NULL. For MQTTCLIENT_PERSISTENCE_DEFAULT persistence, it should be set to the location of the persistence directory (if set to NULL, the persistence directory used is the working directory). Applications that use MQTTCLIENT_PERSISTENCE_USER persistence set this argument to point to a valid MQTTClient_persistence structure.
  options | additional options for the create.

Returns
  MQTTCLIENT_SUCCESS if the client is successfully created, otherwise an error code is returned.

## ◆ MQTTClient_getVersionInfo()

MQTTClient_nameValue * MQTTClient_getVersionInfo | ( | void |  | ) |
| extern

This function returns version information about the library. no trace information will be returned.

Returns
  an array of strings describing the library. The last entry is a NULL pointer.

## ◆ MQTTClient_connect()

int MQTTClient_connect | ( | MQTTClient | handle,
|  | MQTTClient_connectOptions * | options )
| extern

This function attempts to connect a previously-created client (see MQTTClient_create()) to an MQTT server using the specified options. If you want to enable asynchronous message and status notifications, you must call MQTTClient_setCallbacks() prior to MQTTClient_connect().

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  options | A pointer to a valid MQTTClient_connectOptions structure.

Returns
  MQTTCLIENT_SUCCESS if the client successfully connects to the server. An error code is returned if the client was unable to connect to the server. Error codes greater than 0 are returned by the MQTT protocol:
  1: Connection refused: Unacceptable protocol version
  2: Connection refused: Identifier rejected
  3: Connection refused: Server unavailable
  4: Connection refused: Bad user name or password
  5: Connection refused: Not authorized
  6-255: Reserved for future use

## ◆ MQTTResponse_free()

void MQTTResponse_free | ( | MQTTResponse | response | ) |
| extern

Frees the storage associated with the MQTT response.

Parameters

  response | the response structure to be freed

## ◆ MQTTClient_connect5()

MQTTResponse MQTTClient_connect5 | ( | MQTTClient | handle,
|  | MQTTClient_connectOptions * | options,
|  | MQTTProperties * | connectProperties,
|  | MQTTProperties * | willProperties )
| extern

Attempts to connect a previously-created client (see MQTTClient_create()) to an MQTT server using MQTT version 5.0 and the specified options. If you want to enable asynchronous message and status notifications, you must call MQTTClient_setCallbacks() prior to MQTTClient_connect().

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  options | A pointer to a valid MQTTClient_connectOptions structure.
  connectProperties | the MQTT 5.0 connect properties to use
  willProperties | the MQTT 5.0 properties to set on the will message

Returns
  the MQTT 5.0 response information: error codes and properties.

## ◆ MQTTClient_disconnect()

int MQTTClient_disconnect | ( | MQTTClient | handle,
|  | int | timeout )
| extern

This function attempts to disconnect the client from the MQTT server. In order to allow the client time to complete handling of messages that are in-flight when this function is called, a timeout period is specified. When the timeout period has expired, the client disconnects even if there are still outstanding message acknowledgements. The next time the client connects to the same server, any QoS 1 or 2 messages which have not completed will be retried depending on the cleansession settings for both the previous and the new connection (see MQTTClient_connectOptions.cleansession and MQTTClient_connect()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  timeout | The client delays disconnection for up to this time (in milliseconds) in order to allow in-flight message transfers to complete.

Returns
  MQTTCLIENT_SUCCESS if the client successfully disconnects from the server. An error code is returned if the client was unable to disconnect from the server

## ◆ MQTTClient_disconnect5()

int MQTTClient_disconnect5 | ( | MQTTClient | handle,
|  | int | timeout,
|  | enum MQTTReasonCodes | reason,
|  | MQTTProperties * | props )
| extern

## ◆ MQTTClient_isConnected()

int MQTTClient_isConnected | ( | MQTTClient | handle | ) |
| extern

This function allows the client application to test whether or not a client is currently connected to the MQTT server.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().

Returns
  Boolean true if the client is connected, otherwise false.

## ◆ MQTTClient_subscribe()

int MQTTClient_subscribe | ( | MQTTClient | handle,
|  | const char * | topic,
|  | int | qos )
| extern

This function attempts to subscribe a client to a single topic, which may contain wildcards (see Subscription wildcards). This call also specifies the Quality of service requested for the subscription (see also MQTTClient_subscribeMany()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topic | The subscription topic, which may include wildcards.
  qos | The requested quality of service for the subscription.

Returns
  MQTTCLIENT_SUCCESS if the subscription request is successful. An error code is returned if there was a problem registering the subscription.

## ◆ MQTTClient_subscribe5()

MQTTResponse MQTTClient_subscribe5 | ( | MQTTClient | handle,
|  | const char * | topic,
|  | int | qos,
|  | MQTTSubscribe_options * | opts,
|  | MQTTProperties * | props )
| extern

This function attempts to subscribe an MQTT version 5.0 client to a single topic, which may contain wildcards (see Subscription wildcards). This call also specifies the Quality of service requested for the subscription (see also MQTTClient_subscribeMany()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topic | The subscription topic, which may include wildcards.
  qos | The requested quality of service for the subscription.
  opts | the MQTT 5.0 subscribe options to be used
  props | the MQTT 5.0 properties to be used

Returns
  the MQTT 5.0 response information: error codes and properties.

## ◆ MQTTClient_subscribeMany()

int MQTTClient_subscribeMany | ( | MQTTClient | handle,
|  | int | count,
|  | char *const * | topic,
|  | int * | qos )
| extern

This function attempts to subscribe a client to a list of topics, which may contain wildcards (see Subscription wildcards). This call also specifies the Quality of service requested for each topic (see also MQTTClient_subscribe()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  count | The number of topics for which the client is requesting subscriptions.
  topic | An array (of length count) of pointers to topics, each of which may include wildcards.
  qos | An array (of length count) of Quality of service values. qos[n] is the requested QoS for topic[n].

Returns
  MQTTCLIENT_SUCCESS if the subscription request is successful. An error code is returned if there was a problem registering the subscriptions.

## ◆ MQTTClient_subscribeMany5()

MQTTResponse MQTTClient_subscribeMany5 | ( | MQTTClient | handle,
|  | int | count,
|  | char *const * | topic,
|  | int * | qos,
|  | MQTTSubscribe_options * | opts,
|  | MQTTProperties * | props )
| extern

This function attempts to subscribe an MQTT version 5.0 client to a list of topics, which may contain wildcards (see Subscription wildcards). This call also specifies the Quality of service requested for each topic (see also MQTTClient_subscribe()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  count | The number of topics for which the client is requesting subscriptions.
  topic | An array (of length count) of pointers to topics, each of which may include wildcards.
  qos | An array (of length count) of Quality of service values. qos[n] is the requested QoS for topic[n].
  opts | the MQTT 5.0 subscribe options to be used
  props | the MQTT 5.0 properties to be used

Returns
  the MQTT 5.0 response information: error codes and properties.

## ◆ MQTTClient_unsubscribe()

int MQTTClient_unsubscribe | ( | MQTTClient | handle,
|  | const char * | topic )
| extern

This function attempts to remove an existing subscription made by the specified client.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topic | The topic for the subscription to be removed, which may include wildcards (see Subscription wildcards).

Returns
  MQTTCLIENT_SUCCESS if the subscription is removed. An error code is returned if there was a problem removing the subscription.

## ◆ MQTTClient_unsubscribe5()

MQTTResponse MQTTClient_unsubscribe5 | ( | MQTTClient | handle,
|  | const char * | topic,
|  | MQTTProperties * | props )
| extern

This function attempts to remove an existing subscription made by the specified client using MQTT 5.0.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topic | The topic for the subscription to be removed, which may include wildcards (see Subscription wildcards).
  props | the MQTT 5.0 properties to be used

Returns
  the MQTT 5.0 response information: error codes and properties.

## ◆ MQTTClient_unsubscribeMany()

int MQTTClient_unsubscribeMany | ( | MQTTClient | handle,
|  | int | count,
|  | char *const * | topic )
| extern

This function attempts to remove existing subscriptions to a list of topics made by the specified client.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  count | The number subscriptions to be removed.
  topic | An array (of length count) of pointers to the topics of the subscriptions to be removed, each of which may include wildcards.

Returns
  MQTTCLIENT_SUCCESS if the subscriptions are removed. An error code is returned if there was a problem removing the subscriptions.

## ◆ MQTTClient_unsubscribeMany5()

MQTTResponse MQTTClient_unsubscribeMany5 | ( | MQTTClient | handle,
|  | int | count,
|  | char *const * | topic,
|  | MQTTProperties * | props )
| extern

This function attempts to remove existing subscriptions to a list of topics made by the specified client using MQTT version 5.0.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  count | The number subscriptions to be removed.
  topic | An array (of length count) of pointers to the topics of the subscriptions to be removed, each of which may include wildcards.
  props | the MQTT 5.0 properties to be used

Returns
  the MQTT 5.0 response information: error codes and properties.

## ◆ MQTTClient_publish()

int MQTTClient_publish | ( | MQTTClient | handle,
|  | const char * | topicName,
|  | int | payloadlen,
|  | const void * | payload,
|  | int | qos,
|  | int | retained,
|  | MQTTClient_deliveryToken * | dt )
| extern

This function attempts to publish a message to a given topic (see also MQTTClient_publishMessage()). An MQTTClient_deliveryToken is issued when this function returns successfully. If the client application needs to test for succesful delivery of QoS1 and QoS2 messages, this can be done either asynchronously or synchronously (see Asynchronous vs synchronous client applications, MQTTClient_waitForCompletion and MQTTClient_deliveryComplete()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topicName | The topic associated with this message.
  payloadlen | The length of the payload in bytes.
  payload | A pointer to the byte array payload of the message.
  qos | The Quality of service of the message.
  retained | The retained flag for the message.
  dt | A pointer to an MQTTClient_deliveryToken. This is populated with a token representing the message when the function returns successfully. If your application does not use delivery tokens, set this argument to NULL.

Returns
  MQTTCLIENT_SUCCESS if the message is accepted for publication. An error code is returned if there was a problem accepting the message.

## ◆ MQTTClient_publish5()

MQTTResponse MQTTClient_publish5 | ( | MQTTClient | handle,
|  | const char * | topicName,
|  | int | payloadlen,
|  | const void * | payload,
|  | int | qos,
|  | int | retained,
|  | MQTTProperties * | properties,
|  | MQTTClient_deliveryToken * | dt )
| extern

Attempts to publish a message to a given topic using MQTT version 5.0 (see also MQTTClient_publishMessage5()). An MQTTClient_deliveryToken is issued when this function returns successfully. If the client application needs to test for succesful delivery of QoS1 and QoS2 messages, this can be done either asynchronously or synchronously (see Asynchronous vs synchronous client applications, MQTTClient_waitForCompletion and MQTTClient_deliveryComplete()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topicName | The topic associated with this message.
  payloadlen | The length of the payload in bytes.
  payload | A pointer to the byte array payload of the message.
  qos | The Quality of service of the message.
  retained | The retained flag for the message.
  properties | the MQTT 5.0 properties to be used
  dt | A pointer to an MQTTClient_deliveryToken. This is populated with a token representing the message when the function returns successfully. If your application does not use delivery tokens, set this argument to NULL.

Returns
  the MQTT 5.0 response information: error codes and properties.

## ◆ MQTTClient_publishMessage()

int MQTTClient_publishMessage | ( | MQTTClient | handle,
|  | const char * | topicName,
|  | MQTTClient_message * | msg,
|  | MQTTClient_deliveryToken * | dt )
| extern

This function attempts to publish a message to a given topic (see also MQTTClient_publish()). An MQTTClient_deliveryToken is issued when this function returns successfully. If the client application needs to test for succesful delivery of QoS1 and QoS2 messages, this can be done either asynchronously or synchronously (see Asynchronous vs synchronous client applications, MQTTClient_waitForCompletion and MQTTClient_deliveryComplete()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topicName | The topic associated with this message.
  msg | A pointer to a valid MQTTClient_message structure containing the payload and attributes of the message to be published.
  dt | A pointer to an MQTTClient_deliveryToken. This is populated with a token representing the message when the function returns successfully. If your application does not use delivery tokens, set this argument to NULL.

Returns
  MQTTCLIENT_SUCCESS if the message is accepted for publication. An error code is returned if there was a problem accepting the message.

## ◆ MQTTClient_publishMessage5()

MQTTResponse MQTTClient_publishMessage5 | ( | MQTTClient | handle,
|  | const char * | topicName,
|  | MQTTClient_message * | msg,
|  | MQTTClient_deliveryToken * | dt )
| extern

Attempts to publish a message to the given topic using MQTT version 5.0 (see also MQTTClient_publish5()). An MQTTClient_deliveryToken is issued when this function returns successfully. If the client application needs to test for succesful delivery of QoS1 and QoS2 messages, this can be done either asynchronously or synchronously (see Asynchronous vs synchronous client applications, MQTTClient_waitForCompletion and MQTTClient_deliveryComplete()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topicName | The topic associated with this message.
  msg | A pointer to a valid MQTTClient_message structure containing the payload and attributes of the message to be published.
  dt | A pointer to an MQTTClient_deliveryToken. This is populated with a token representing the message when the function returns successfully. If your application does not use delivery tokens, set this argument to NULL.

Returns
  the MQTT 5.0 response information: error codes and properties.

## ◆ MQTTClient_waitForCompletion()

int MQTTClient_waitForCompletion | ( | MQTTClient | handle,
|  | MQTTClient_deliveryToken | dt,
|  | unsigned long | timeout )
| extern

This function is called by the client application to synchronize execution of the main thread with completed publication of a message. When called, MQTTClient_waitForCompletion() blocks execution until the message has been successful delivered or the specified timeout has expired. See Asynchronous vs synchronous client applications.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  dt | The MQTTClient_deliveryToken that represents the message being tested for successful delivery. Delivery tokens are issued by the publishing functions MQTTClient_publish() and MQTTClient_publishMessage().
  timeout | The maximum time to wait in milliseconds.

Returns
  MQTTCLIENT_SUCCESS if the message was successfully delivered. An error code is returned if the timeout expires or there was a problem checking the token.

## ◆ MQTTClient_getPendingDeliveryTokens()

int MQTTClient_getPendingDeliveryTokens | ( | MQTTClient | handle,
|  | MQTTClient_deliveryToken ** | tokens )
| extern

This function sets a pointer to an array of delivery tokens for messages that are currently in-flight (pending completion).

Important note: The memory used to hold the array of tokens is malloc()'d in this function. The client application is responsible for freeing this memory when it is no longer required.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  tokens | The address of a pointer to an MQTTClient_deliveryToken. When the function returns successfully, the pointer is set to point to an array of tokens representing messages pending completion. The last member of the array is set to -1 to indicate there are no more tokens. If no tokens are pending, the pointer is set to NULL.

Returns
  MQTTCLIENT_SUCCESS if the function returns successfully. An error code is returned if there was a problem obtaining the list of pending tokens.

## ◆ MQTTClient_yield()

void MQTTClient_yield | ( | void |  | ) |
| extern

When implementing a single-threaded client, call this function periodically to allow processing of message retries and to send MQTT keepalive pings. If the application is calling MQTTClient_receive() regularly, then it is not necessary to call this function.

## ◆ MQTTClient_receive()

int MQTTClient_receive | ( | MQTTClient | handle,
|  | char ** | topicName,
|  | int * | topicLen,
|  | MQTTClient_message ** | message,
|  | unsigned long | timeout )
| extern

This function performs a synchronous receive of incoming messages. It should be used only when the client application has not set callback methods to support asynchronous receipt of messages (see Asynchronous vs synchronous client applications and MQTTClient_setCallbacks()). Using this function allows a single-threaded client subscriber application to be written. When called, this function blocks until the next message arrives or the specified timeout expires (see also MQTTClient_yield()).

Important note: The application must free() the memory allocated to the topic and the message when processing is complete (see MQTTClient_freeMessage()).

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  topicName | The address of a pointer to a topic. This function allocates the memory for the topic and returns it to the application by setting topicName to point to the topic.
  topicLen | The length of the topic. If the return code from this function is MQTTCLIENT_TOPICNAME_TRUNCATED, the topic contains embedded NULL characters and the full topic should be retrieved by using topicLen.
  message | The address of a pointer to the received message. This function allocates the memory for the message and returns it to the application by setting message to point to the received message. The pointer is set to NULL if the timeout expires.
  timeout | The length of time to wait for a message in milliseconds.

Returns
  MQTTCLIENT_SUCCESS or MQTTCLIENT_TOPICNAME_TRUNCATED if a message is received. MQTTCLIENT_SUCCESS can also indicate that the timeout expired, in which case message is NULL. An error code is returned if there was a problem trying to receive a message.

## ◆ MQTTClient_freeMessage()

void MQTTClient_freeMessage | ( | MQTTClient_message ** | msg | ) |
| extern

This function frees memory allocated to an MQTT message, including the additional memory allocated to the message payload. The client application calls this function when the message has been fully processed. Important note: This function does not free the memory allocated to a message topic string. It is the responsibility of the client application to free this memory using the MQTTClient_free() library function.

Parameters

  msg | The address of a pointer to the MQTTClient_message structure to be freed.

## ◆ MQTTClient_free()

void MQTTClient_free | ( | void * | ptr | ) |
| extern

This function frees memory allocated by the MQTT C client library, especially the topic name. This is needed on Windows when the client libary and application program have been compiled with different versions of the C compiler. It is thus good policy to always use this function when freeing any MQTT C client- allocated memory.

Parameters

  ptr | The pointer to the client library storage to be freed.

## ◆ MQTTClient_malloc()

void * MQTTClient_malloc | ( | size_t | size | ) |
| extern

This function is used to allocate memory to be used or freed by the MQTT C client library, especially the data in user persistence. This is needed on Windows when the client library and application program have been compiled with different versions of the C compiler.

Parameters

  size | The size of the memory to be allocated.

## ◆ MQTTClient_destroy()

void MQTTClient_destroy | ( | MQTTClient * | handle | ) |
| extern

This function frees the memory allocated to an MQTT client (see MQTTClient_create()). It should be called when the client is no longer required.

Parameters

  handle | A pointer to the handle referring to the MQTTClient structure to be freed.

## ◆ MQTTClient_setTraceLevel()

void MQTTClient_setTraceLevel | ( | enum MQTTCLIENT_TRACE_LEVELS | level | ) |
| extern

This function sets the level of trace information which will be returned in the trace callback.

Parameters

  level | the trace level required

## ◆ MQTTClient_setTraceCallback()

void MQTTClient_setTraceCallback | ( | MQTTClient_traceCallback * | callback | ) |
| extern

This function sets the trace callback if needed. If set to NULL, no trace information will be returned. The default trace level is MQTTASYNC_TRACE_MINIMUM.

Parameters

  callback | a pointer to the function which will handle the trace information

## ◆ MQTTClient_setCommandTimeout()

int MQTTClient_setCommandTimeout | ( | MQTTClient | handle,
|  | unsigned long | milliSeconds )
| extern

Sets the timeout value for un/subscribe commands when waiting for the un/suback response from the server. Values less than 5000 are not allowed.

Parameters

  handle | A valid client handle from a successful call to MQTTClient_create().
  milliSeconds | the maximum number of milliseconds to wait

Returns
  MQTTCLIENT_SUCCESS or MQTTCLIENT_FAILURE

## ◆ MQTTClient_strerror()

const char * MQTTClient_strerror | ( | int | code | ) |
| extern

Returns a pointer to the string representation of the error or NULL.

Do not free after use. Returns NULL if the error code is unknown.