MQTTAsync.h - Man Page

struct MQTTAsync_init_options
struct MQTTAsync_message
struct MQTTAsync_connectData
struct MQTTAsync_failureData
struct MQTTAsync_failureData5
struct MQTTAsync_successData
struct MQTTAsync_successData5
struct MQTTAsync_responseOptions
struct MQTTAsync_createOptions
struct MQTTAsync_willOptions
struct MQTTAsync_SSLOptions
struct MQTTAsync_nameValue
struct MQTTAsync_connectOptions
struct MQTTAsync_disconnectOptions

#define MQTTASYNC_SUCCESS   0
#define MQTTASYNC_FAILURE   -1
#define MQTTASYNC_PERSISTENCE_ERROR   -2
#define MQTTASYNC_DISCONNECTED   -3
#define MQTTASYNC_MAX_MESSAGES_INFLIGHT   -4
#define MQTTASYNC_BAD_UTF8_STRING   -5
#define MQTTASYNC_NULL_PARAMETER   -6
#define MQTTASYNC_TOPICNAME_TRUNCATED   -7
#define MQTTASYNC_BAD_STRUCTURE   -8
#define MQTTASYNC_BAD_QOS   -9
#define MQTTASYNC_NO_MORE_MSGIDS   -10
#define MQTTASYNC_OPERATION_INCOMPLETE   -11
#define MQTTASYNC_MAX_BUFFERED_MESSAGES   -12
#define MQTTASYNC_SSL_NOT_SUPPORTED   -13
#define MQTTASYNC_BAD_PROTOCOL   -14
#define MQTTASYNC_BAD_MQTT_OPTION   -15
#define MQTTASYNC_WRONG_MQTT_VERSION   -16
#define MQTTASYNC_0_LEN_WILL_TOPIC   -17
#define MQTTASYNC_COMMAND_IGNORED   -18
#define MQTTASYNC_MAX_BUFFERED   -19
#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 MQTTAsync_init_options_initializer   { {'M', 'Q', 'T', 'G'}, 0, 0 }
#define MQTTAsync_message_initializer   { {'M', 'Q', 'T', 'M'}, 1, 0, NULL, 0, 0, 0, 0, MQTTProperties_initializer }
#define MQTTAsync_connectData_initializer   {{'M', 'Q', 'C', 'D'}, 0, NULL, {0, NULL}}
#define MQTTAsync_failureData5_initializer   {{'M', 'Q', 'F', 'D'}, 0, 0, MQTTREASONCODE_SUCCESS, MQTTProperties_initializer, 0, NULL, 0}
#define MQTTAsync_successData5_initializer   {{'M', 'Q', 'S', 'D'}, 0, 0, MQTTREASONCODE_SUCCESS, MQTTProperties_initializer, {.sub={0,0}}}
#define MQTTAsync_responseOptions_initializer   { {'M', 'Q', 'T', 'R'}, 1, NULL, NULL, 0, 0, NULL, NULL, MQTTProperties_initializer, MQTTSubscribe_options_initializer, 0, NULL}
#define MQTTAsync_callOptions_initializer   MQTTAsync_responseOptions_initializer
#define MQTTAsync_createOptions_initializer   { {'M', 'Q', 'C', 'O'}, 2, 0, 100, MQTTVERSION_DEFAULT, 0, 0, 1, 1}
#define MQTTAsync_createOptions_initializer5   { {'M', 'Q', 'C', 'O'}, 2, 0, 100, MQTTVERSION_5, 0, 0, 1, 1}
#define MQTTAsync_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 MQTTAsync_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 MQTTAsync_connectOptions_initializer
#define MQTTAsync_connectOptions_initializer5
#define MQTTAsync_connectOptions_initializer_ws
#define MQTTAsync_connectOptions_initializer5_ws
#define MQTTAsync_disconnectOptions_initializer
#define MQTTAsync_disconnectOptions_initializer5
#define MQTTASYNC_TRUE   1

typedef void * MQTTAsync
typedef int MQTTAsync_token
typedef int MQTTAsync_messageArrived(void *context, char *topicName, int topicLen, MQTTAsync_message *message)
typedef void MQTTAsync_deliveryComplete(void *context, MQTTAsync_token token)
typedef void MQTTAsync_connectionLost(void *context, char *cause)
typedef void MQTTAsync_connected(void *context, char *cause)
typedef void MQTTAsync_disconnected(void *context, MQTTProperties *properties, enum MQTTReasonCodes reasonCode)
typedef int MQTTAsync_updateConnectOptions(void *context, MQTTAsync_connectData *data)
typedef void MQTTAsync_onSuccess(void *context, MQTTAsync_successData *response)
typedef void MQTTAsync_onSuccess5(void *context, MQTTAsync_successData5 *response)
typedef void MQTTAsync_onFailure(void *context, MQTTAsync_failureData *response)
typedef void MQTTAsync_onFailure5(void *context, MQTTAsync_failureData5 *response)
typedef struct MQTTAsync_responseOptions MQTTAsync_responseOptions
typedef struct MQTTAsync_responseOptions MQTTAsync_callOptions
typedef void MQTTAsync_traceCallback(enum MQTTASYNC_TRACE_LEVELS level, char *message)

enum MQTTASYNC_TRACE_LEVELS { MQTTASYNC_TRACE_MAXIMUM = 1, MQTTASYNC_TRACE_MEDIUM, MQTTASYNC_TRACE_MINIMUM, MQTTASYNC_TRACE_PROTOCOL, MQTTASYNC_TRACE_ERROR, MQTTASYNC_TRACE_SEVERE, MQTTASYNC_TRACE_FATAL }

void MQTTAsync_global_init (MQTTAsync_init_options *inits)
int MQTTAsync_setDisconnected (MQTTAsync handle, void *context, MQTTAsync_disconnected *co)
int MQTTAsync_setUpdateConnectOptions (MQTTAsync handle, void *context, MQTTAsync_updateConnectOptions *co)
int MQTTAsync_setBeforePersistenceWrite (MQTTAsync handle, void *context, MQTTPersistence_beforeWrite *co)
int MQTTAsync_setAfterPersistenceRead (MQTTAsync handle, void *context, MQTTPersistence_afterRead *co)
int MQTTAsync_setCallbacks (MQTTAsync handle, void *context, MQTTAsync_connectionLost *cl, MQTTAsync_messageArrived *ma, MQTTAsync_deliveryComplete *dc)
int MQTTAsync_setConnectionLostCallback (MQTTAsync handle, void *context, MQTTAsync_connectionLost *cl)
int MQTTAsync_setMessageArrivedCallback (MQTTAsync handle, void *context, MQTTAsync_messageArrived *ma)
int MQTTAsync_setDeliveryCompleteCallback (MQTTAsync handle, void *context, MQTTAsync_deliveryComplete *dc)
int MQTTAsync_setConnected (MQTTAsync handle, void *context, MQTTAsync_connected *co)
int MQTTAsync_reconnect (MQTTAsync handle)
int MQTTAsync_create (MQTTAsync *handle, const char *serverURI, const char *clientId, int persistence_type, void *persistence_context)
int MQTTAsync_createWithOptions (MQTTAsync *handle, const char *serverURI, const char *clientId, int persistence_type, void *persistence_context, MQTTAsync_createOptions *options)
int MQTTAsync_connect (MQTTAsync handle, const MQTTAsync_connectOptions *options)
int MQTTAsync_disconnect (MQTTAsync handle, const MQTTAsync_disconnectOptions *options)
int MQTTAsync_isConnected (MQTTAsync handle)
int MQTTAsync_subscribe (MQTTAsync handle, const char *topic, int qos, MQTTAsync_responseOptions *response)
int MQTTAsync_subscribeMany (MQTTAsync handle, int count, char *const *topic, const int *qos, MQTTAsync_responseOptions *response)
int MQTTAsync_unsubscribe (MQTTAsync handle, const char *topic, MQTTAsync_responseOptions *response)
int MQTTAsync_unsubscribeMany (MQTTAsync handle, int count, char *const *topic, MQTTAsync_responseOptions *response)
int MQTTAsync_send (MQTTAsync handle, const char *destinationName, int payloadlen, const void *payload, int qos, int retained, MQTTAsync_responseOptions *response)
int MQTTAsync_sendMessage (MQTTAsync handle, const char *destinationName, const MQTTAsync_message *msg, MQTTAsync_responseOptions *response)
int MQTTAsync_getPendingTokens (MQTTAsync handle, MQTTAsync_token **tokens)
int MQTTAsync_isComplete (MQTTAsync handle, MQTTAsync_token token)
int MQTTAsync_waitForCompletion (MQTTAsync handle, MQTTAsync_token token, unsigned long timeout)
void MQTTAsync_freeMessage (MQTTAsync_message **msg)
void MQTTAsync_free (void *ptr)
void * MQTTAsync_malloc (size_t size)
void MQTTAsync_destroy (MQTTAsync *handle)
void MQTTAsync_setTraceLevel (enum MQTTASYNC_TRACE_LEVELS level)
void MQTTAsync_setTraceCallback (MQTTAsync_traceCallback *callback)
MQTTAsync_nameValue * MQTTAsync_getVersionInfo (void)
const char * MQTTAsync_strerror (int code)

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

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

Return code: The client is disconnected.

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

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

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

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.

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

Return code: A qos parameter is not 0, 1 or 2

Return code: All 65535 MQTT msgids are being used

Return code: the request is being discarded when not complete

Return code: no more messages can be buffered

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

Return code: protocol prefix in serverURI should 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 the TLS version of the library is linked with.

Return code: don't use options for another version of MQTT

Return code: call not applicable to the client's version of MQTT

Return code: 0 length will topic

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

MQTT version to connect with: 3.1

MQTT version to connect with: 3.1.1

MQTT version to connect with: 5

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

Value:

{ {'M', 'Q', 'T', 'C'}, 8, 60, 1, 65535, NULL, NULL, NULL, 30, 0,\
NULL, NULL, NULL, NULL, 0, NULL, MQTTVERSION_DEFAULT, 0, 1, 60, {0, NULL}, 0, NULL, NULL, NULL, NULL, NULL, NULL, NULL}

Initializer for connect options for MQTT 3.1.1 non-WebSocket connections

Value:

{ {'M', 'Q', 'T', 'C'}, 8, 60, 0, 65535, NULL, NULL, NULL, 30, 0,\
NULL, NULL, NULL, NULL, 0, NULL, MQTTVERSION_5, 0, 1, 60, {0, NULL}, 1, NULL, NULL, NULL, NULL, NULL, NULL, NULL}

Initializer for connect options for MQTT 5.0 non-WebSocket connections

Value:

{ {'M', 'Q', 'T', 'C'}, 8, 45, 1, 65535, NULL, NULL, NULL, 30, 0,\
NULL, NULL, NULL, NULL, 0, NULL, MQTTVERSION_DEFAULT, 0, 1, 60, {0, NULL}, 0, NULL, NULL, NULL, NULL, 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.

Value:

{ {'M', 'Q', 'T', 'C'}, 8, 45, 0, 65535, NULL, NULL, NULL, 30, 0,\
NULL, NULL, NULL, NULL, 0, NULL, MQTTVERSION_5, 0, 1, 60, {0, NULL}, 1, NULL, NULL, NULL, NULL, 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.

Value:

        { {'M', 'Q', 'T', 'D'}, 0, 0, NULL, NULL, NULL,\
        MQTTProperties_initializer, MQTTREASONCODE_SUCCESS, NULL, NULL }

Value:

        { {'M', 'Q', 'T', 'D'}, 1, 0, NULL, NULL, NULL,\
        MQTTProperties_initializer, MQTTREASONCODE_SUCCESS, NULL, NULL }

Tests whether a request corresponding to a token is complete.

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
token An MQTTAsync_token associated with a request.

Returns

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

A value representing an MQTT message. A 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 MQTTAsync_publish(), MQTTAsync_publishMessage(), MQTTAsync_deliveryComplete(), and MQTTAsync_getPendingTokens()).

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 MQTTAsync_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.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

context A pointer to the context value originally passed to MQTTAsync_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 MQTTAsync_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, MQTTAsync_freeMessage must be called. To free the topic name storage, MQTTAsync_free must be called.
Returning 0 indicates that there was a problem. In this case, the client library will reinvoke MQTTAsync_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.

This is a callback function. The client application must provide an implementation of this function to enable asynchronous notification of delivery of messages to the server. The function is registered with the client library by passing it as an argument to MQTTAsync_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 MQTTAsync_message.qos) have been completed. This function is executed on a separate thread to the one on which the client application is running.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

context A pointer to the context value originally passed to MQTTAsync_setCallbacks(), which contains any application-specific context.
token The MQTTAsync_token associated with the published message. Applications can check that all messages have been correctly published by matching the tokens returned from calls to MQTTAsync_send() and MQTTAsync_sendMessage() with the tokens passed to this callback.

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 MQTTAsync_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.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

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

This is a callback function, which will be called when the client library successfully connects. This is superfluous when the connection is made in response to a MQTTAsync_connect call, because the onSuccess callback can be used. It is intended for use when automatic reconnect is enabled, so that when a reconnection attempt succeeds in the background, the application is notified and can take any required actions.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

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

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

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

context A pointer to the context value originally passed to MQTTAsync_setCallbacks(), which contains any application-specific context.
properties the properties in the disconnect packet.
properties the reason code from the disconnect packet Currently, cause is always set to NULL.

This is a callback function which will allow the client application to update the connection data.

Parameters

data The connection data which can be modified by the application.

Returns

Return a non-zero value to update the connect data, zero to keep the same data.

This is a callback function. The client application must provide an implementation of this function to enable asynchronous notification of the successful completion of an API call. The function is registered with the client library by passing it as an argument in MQTTAsync_responseOptions.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

context A pointer to the context value originally passed to MQTTAsync_responseOptions, which contains any application-specific context.
response Any success data associated with the API completion.

This is a callback function, the MQTT V5 version of MQTTAsync_onSuccess. The client application must provide an implementation of this function to enable asynchronous notification of the successful completion of an API call. The function is registered with the client library by passing it as an argument in MQTTAsync_responseOptions.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

context A pointer to the context value originally passed to MQTTAsync_responseOptions, which contains any application-specific context.
response Any success data associated with the API completion.

This is a callback function. The client application must provide an implementation of this function to enable asynchronous notification of the unsuccessful completion of an API call. The function is registered with the client library by passing it as an argument in MQTTAsync_responseOptions.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

context A pointer to the context value originally passed to MQTTAsync_responseOptions, which contains any application-specific context.
response Failure data associated with the API completion.

This is a callback function, the MQTT V5 version of MQTTAsync_onFailure. The application must provide an implementation of this function to enable asynchronous notification of the unsuccessful completion of an API call. The function is registered with the client library by passing it as an argument in MQTTAsync_responseOptions.

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

context A pointer to the context value originally passed to MQTTAsync_responseOptions, which contains any application-specific context.
response Failure data associated with the API completion.

Structure to define call options. For MQTT 5.0 there is input data as well as that describing the response method. So there is now also a synonym MQTTAsync_callOptions to better reflect the use. This responseOptions name is kept for backward compatibility.

A synonym for responseOptions to better reflect its usage since MQTT 5.0

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.

Enumerator

MQTTASYNC_TRACE_MAXIMUM

MQTTASYNC_TRACE_MEDIUM

MQTTASYNC_TRACE_MINIMUM

MQTTASYNC_TRACE_PROTOCOL

MQTTASYNC_TRACE_ERROR

MQTTASYNC_TRACE_SEVERE

MQTTASYNC_TRACE_FATAL

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

Sets the MQTTAsync_disconnected() callback function for a client.

Parameters

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

Note: Neither MQTTAsync_create() nor MQTTAsync_destroy() should be called within this callback.

Parameters

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 MQTTAsync_connected() callback function. NULL removes the callback setting.

Returns

MQTTASYNC_SUCCESS if the callbacks were correctly set, MQTTASYNC_FAILURE if an error occurred.

Sets the MQTTAsync_updateConnectOptions() callback function for a client.

Parameters

handle A valid client handle from a successful call to MQTTAsync_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 MQTTAsync_updateConnectOptions() callback function. NULL removes the callback setting.

Sets the MQTTPersistence_beforeWrite() callback function for a client.

Parameters

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

Sets the MQTTPersistence_afterRead() callback function for a client.

Parameters

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

This function sets the global callback functions for a specific client. If your client application doesn't use a particular callback, set the relevant parameter to NULL. Any necessary message acknowledgements and status communications are handled in the background without any intervention from the client application. If you do not set a messageArrived callback function, you will not be notified of the receipt of any messages as a result of a subscription.

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

Parameters

handle A valid client handle from a successful call to MQTTAsync_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 MQTTAsync_connectionLost() callback function. You can set this to NULL if your application doesn't handle disconnections.
ma A pointer to an MQTTAsync_messageArrived() callback function. If this callback is not set, an error will be returned. You must set this callback because otherwise there would be no way to deliver any incoming messages.
dc A pointer to an MQTTAsync_deliveryComplete() callback function. You can set this to NULL if you do not want to check for successful delivery.

Returns

MQTTASYNC_SUCCESS if the callbacks were correctly set, MQTTASYNC_FAILURE if an error occurred.

This function sets the callback function for a connection lost event for a specific client. Any necessary message acknowledgements and status communications are handled in the background without any intervention from the client application.

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

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
context A pointer to any application-specific context. The the context pointer is passed the callback functions to provide access to the context information in the callback.
cl A pointer to an MQTTAsync_connectionLost() callback function. You can set this to NULL if your application doesn't handle disconnections.

Returns

MQTTASYNC_SUCCESS if the callbacks were correctly set, MQTTASYNC_FAILURE if an error occurred.

This function sets the callback function for a message arrived event for a specific client. Any necessary message acknowledgements and status communications are handled in the background without any intervention from the client application. If you do not set a messageArrived callback function, you will not be notified of the receipt of any messages as a result of a subscription.

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

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
context A pointer to any application-specific context. The the context pointer is passed to the callback functions to provide access to the context information in the callback.
ma A pointer to an MQTTAsync_messageArrived() callback function. You can set this to NULL if your application doesn't handle receipt of messages.

Returns

MQTTASYNC_SUCCESS if the callbacks were correctly set, MQTTASYNC_FAILURE if an error occurred.

This function sets the callback function for a delivery complete event for a specific client. Any necessary message acknowledgements and status communications are handled in the background without any intervention from the client application.

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

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
context A pointer to any application-specific context. The the context pointer is passed to the callback functions to provide access to the context information in the callback.
dc A pointer to an MQTTAsync_deliveryComplete() callback function. You can set this to NULL if you do not want to check for successful delivery.

Returns

MQTTASYNC_SUCCESS if the callbacks were correctly set, MQTTASYNC_FAILURE if an error occurred.

Sets the MQTTAsync_connected() callback function for a client.

Parameters

handle A valid client handle from a successful call to MQTTAsync_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 MQTTAsync_connected() callback function. NULL removes the callback setting.

Returns

MQTTASYNC_SUCCESS if the callbacks were correctly set, MQTTASYNC_FAILURE if an error occurred.

Reconnects a client with the previously used connect options. Connect must have previously been called for this to work.

Parameters

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

Returns

MQTTASYNC_SUCCESS if the callbacks were correctly set, MQTTASYNC_FAILURE if an error occurred.

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

Parameters

handle A pointer to an MQTTAsync 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 where 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

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

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

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
options A pointer to a valid MQTTAsync_connectOptions structure.

Returns

MQTTASYNC_SUCCESS if the client connect request was accepted. If the client was unable to connect to the server, an error code is returned via the onFailure callback, if set. 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

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 MQTTAsync_connectOptions.cleansession and MQTTAsync_connect()).

Parameters

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

Returns

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

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 MQTTAsync_create().

Returns

Boolean true if the client is connected, otherwise false.

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 MQTTAsync_subscribeMany()).

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
topic The subscription topic, which may include wildcards.
qos The requested quality of service for the subscription.
response A pointer to a response options structure. Used to set callback functions.

Returns

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

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 MQTTAsync_subscribe()).

Parameters

handle A valid client handle from a successful call to MQTTAsync_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].
response A pointer to a response options structure. Used to set callback functions.

Returns

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

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

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
topic The topic for the subscription to be removed, which may include wildcards (see Subscription wildcards).
response A pointer to a response options structure. Used to set callback functions.

Returns

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

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 MQTTAsync_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.
response A pointer to a response options structure. Used to set callback functions.

Returns

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

This function attempts to publish a message to a given topic (see also MQTTAsync_sendMessage()). An MQTTAsync_token is issued when this function returns successfully if the QoS is greater than 0. If the client application needs to test for successful delivery of messages, a callback should be set (see MQTTAsync_onSuccess() and MQTTAsync_deliveryComplete()).

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
destinationName 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.
response A pointer to an MQTTAsync_responseOptions structure. Used to set callback functions. This is optional and can be set to NULL.

Returns

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

This function attempts to publish a message to a given topic (see also MQTTAsync_publish()). An MQTTAsync_token is issued when this function returns successfully if the QoS is greater than 0. If the client application needs to test for successful delivery of messages, a callback should be set (see MQTTAsync_onSuccess() and MQTTAsync_deliveryComplete()).

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
destinationName The topic associated with this message.
msg A pointer to a valid MQTTAsync_message structure containing the payload and attributes of the message to be published.
response A pointer to an MQTTAsync_responseOptions structure. Used to set callback functions.

Returns

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

This function sets a pointer to an array of 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 MQTTAsync_create().
tokens The address of a pointer to an MQTTAsync_token. 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

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

Waits for a request corresponding to a token to complete. This only works for messages with QoS greater than 0. A QoS 0 message has no MQTT token. This function will always return MQTTASYNC_SUCCESS for a QoS 0 message.

Parameters

handle A valid client handle from a successful call to MQTTAsync_create().
token An MQTTAsync_token associated with a request.
timeout the maximum time to wait for completion, in milliseconds

Returns

MQTTASYNC_SUCCESS if the request has been completed in the time allocated, MQTTASYNC_FAILURE or MQTTASYNC_DISCONNECTED if not.

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 MQTTAsync_free() library function.

Parameters

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

This function frees memory allocated by the MQTT C client library, especially the topic name. This is needed on Windows when the client library 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.

This function is used to allocate memory to be used or freed by the MQTT C client library, especially the data in the MQTTPersistence_afterRead and MQTTPersistence_beforeWrite callbacks. 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.

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

Parameters

handle A pointer to the handle referring to the MQTTAsync structure to be freed.

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

Parameters

level the trace level required

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

This function returns version information about the library. no trace information will be returned. The default trace level is MQTTASYNC_TRACE_MINIMUM

Returns

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

Returns a pointer to a string representation of the error code, or NULL. Do not free after use. Returns NULL if the error code is unknown.

Parameters

code the MQTTASYNC_ return code.

Returns

a static string representation of the error code.