MQTTAsync.h

/*******************************************************************************
 * Copyright (c) 2009, 2024 IBM Corp., Ian Craggs and others
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v2.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 *
 * The Eclipse Public License is available at
 *    https://www.eclipse.org/legal/epl-2.0/
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Ian Craggs - initial API and implementation
 *    Ian Craggs, Allan Stockdill-Mander - SSL connections
 *    Ian Craggs - multiple server connection support
 *    Ian Craggs - MQTT 3.1.1 support
 *    Ian Craggs - fix for bug 444103 - success/failure callbacks not invoked
 *    Ian Craggs - automatic reconnect and offline buffering (send while disconnected)
 *    Ian Craggs - binary will message
 *    Ian Craggs - binary password
 *    Ian Craggs - remove const on eyecatchers #168
 *    Ian Craggs - MQTT 5.0
 *******************************************************************************/

/********************************************************************/

/**
 * @cond MQTTAsync_main
 * @mainpage Asynchronous MQTT client library for C (MQTTAsync)
 *
 * © Copyright 2009, 2023 IBM Corp., Ian Craggs and others
 *
 * @brief An Asynchronous MQTT client library for C.
 *
 * An MQTT client application connects to MQTT-capable servers.
 * A typical client is responsible for collecting information from a telemetry
 * device and publishing the information to the server. It can also subscribe
 * to topics, receive messages, and use this information to control the
 * telemetry device.
 *
 * MQTT clients implement the published MQTT v3 protocol. You can write your own
 * API to the MQTT protocol using the programming language and platform of your
 * choice. This can be time-consuming and error-prone.
 *
 * To simplify writing MQTT client applications, this library encapsulates
 * the MQTT v3 protocol for you. Using this library enables a fully functional
 * MQTT client application to be written in a few lines of code.
 * The information presented here documents the API provided
 * by the Asynchronous MQTT Client library for C.
 *
 * <b>Using the client</b><br>
 * Applications that use the client library typically use a similar structure:
 * <ul>
 * <li>Create a client object</li>
 * <li>Set the options to connect to an MQTT server</li>
 * <li>Set up callback functions</li>
 * <li>Connect the client to an MQTT server</li>
 * <li>Subscribe to any topics the client needs to receive</li>
 * <li>Repeat until finished:</li>
 *     <ul>
 *     <li>Publish any messages the client needs to</li>
 *     <li>Handle any incoming messages</li>
 *     </ul>
 * <li>Disconnect the client</li>
 * <li>Free any memory being used by the client</li>
 * </ul>
 * Some simple examples are shown here:
 * <ul>
 * <li>@ref publish</li>
 * <li>@ref subscribe</li>
 * </ul>
 * Additional information about important concepts is provided here:
 * <ul>
 * <li>@ref async</li>
 * <li>@ref wildcard</li>
 * <li>@ref qos</li>
 * <li>@ref tracing</li>
 * <li>@ref auto_reconnect</li>
 * <li>@ref offline_publish</li>
 * </ul>
 * @endcond
 */

/*
/// @cond EXCLUDE
*/
#if !defined(MQTTASYNC_H)
#define MQTTASYNC_H

#if defined(__cplusplus)
 extern "C" {
#endif

#include <stdio.h>
/*
/// @endcond
*/

#include "MQTTExportDeclarations.h"

#include "MQTTProperties.h"
#include "MQTTReasonCodes.h"
#include "MQTTSubscribeOpts.h"
#if !defined(NO_PERSISTENCE)
#include "MQTTClientPersistence.h"
#else
#define MQTTCLIENT_PERSISTENCE_NONE 1
#endif

/**
 * Return code: No error. Indicates successful completion of an MQTT client
 * operation.
 */
#define MQTTASYNC_SUCCESS 0
/**
 * Return code: A generic error code indicating the failure of an MQTT client
 * operation.
 */
#define MQTTASYNC_FAILURE -1

/* error code -2 is MQTTAsync_PERSISTENCE_ERROR */

#define MQTTASYNC_PERSISTENCE_ERROR -2

/**
 * Return code: The client is disconnected.
 */
#define MQTTASYNC_DISCONNECTED -3
/**
 * Return code: The maximum number of messages allowed to be simultaneously
 * in-flight has been reached.
 */
#define MQTTASYNC_MAX_MESSAGES_INFLIGHT -4
/**
 * Return code: An invalid UTF-8 string has been detected.
 */
#define MQTTASYNC_BAD_UTF8_STRING -5
/**
 * Return code: A NULL parameter has been supplied when this is invalid.
 */
#define MQTTASYNC_NULL_PARAMETER -6
/**
 * 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.
 */
#define MQTTASYNC_TOPICNAME_TRUNCATED -7
/**
 * Return code: A structure parameter does not have the correct eyecatcher
 * and version number.
 */
#define MQTTASYNC_BAD_STRUCTURE -8
/**
 * Return code: A qos parameter is not 0, 1 or 2
 */
#define MQTTASYNC_BAD_QOS -9
/**
 * Return code: All 65535 MQTT msgids are being used
 */
#define MQTTASYNC_NO_MORE_MSGIDS -10
/**
 * Return code: the request is being discarded when not complete
 */
#define MQTTASYNC_OPERATION_INCOMPLETE -11
/**
 * Return code: no more messages can be buffered
 */
#define MQTTASYNC_MAX_BUFFERED_MESSAGES -12
/**
 * Return code: Attempting SSL connection using non-SSL version of library
 */
#define MQTTASYNC_SSL_NOT_SUPPORTED -13
/**
 * Return code: protocol prefix in serverURI should be:
 * @li @em tcp:// or @em mqtt:// - Insecure TCP
 * @li @em ssl:// or @em mqtts:// - Encrypted SSL/TLS
 * @li @em ws:// - Insecure websockets
 * @li @em wss:// - Secure web sockets
 *
 * The TLS enabled prefixes (ssl, mqtts, wss) are only valid if the TLS
 * version of the library is linked with.
 */
#define MQTTASYNC_BAD_PROTOCOL -14
/**
 * Return code: don't use options for another version of MQTT
 */
#define MQTTASYNC_BAD_MQTT_OPTION -15
/**
 * Return code: call not applicable to the client's version of MQTT
 */
#define MQTTASYNC_WRONG_MQTT_VERSION -16
/**
 *  Return code: 0 length will topic
 */
#define MQTTASYNC_0_LEN_WILL_TOPIC -17
/*
 * Return code: connect or disconnect command ignored because there is already a connect or disconnect
 * command at the head of the list waiting to be processed. Use the onSuccess/onFailure callbacks to wait
 * for the previous connect or disconnect command to be complete.
 */
#define MQTTASYNC_COMMAND_IGNORED -18
 /*
  * Return code: maxBufferedMessages in the connect options must be >= 0
  */
 #define MQTTASYNC_MAX_BUFFERED -19

/**
 * Default MQTT version to connect with.  Use 3.1.1 then fall back to 3.1
 */
#define MQTTVERSION_DEFAULT 0
/**
 * MQTT version to connect with: 3.1
 */
#define MQTTVERSION_3_1 3
/**
 * MQTT version to connect with: 3.1.1
 */
#define MQTTVERSION_3_1_1 4
/**
 * MQTT version to connect with: 5
 */
#define MQTTVERSION_5 5
/**
 * Bad return code from subscribe, as defined in the 3.1.1 specification
 */
#define MQTT_BAD_SUBSCRIBE 0x80


/**
 *  Initialization options
 */
typedef struct
{
	/** The eyecatcher for this structure.  Must be MQTG. */
	char struct_id[4];
	/** The version number of this structure.  Must be 0 */
	int struct_version;
	/** 1 = we do openssl init, 0 = leave it to the application */
	int do_openssl_init;
} MQTTAsync_init_options;

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

/**
 * 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)
 */
LIBMQTT_API void MQTTAsync_global_init(MQTTAsync_init_options* inits);

/**
 * A handle representing an MQTT client. A valid client handle is available
 * following a successful call to MQTTAsync_create().
 */
typedef void* MQTTAsync;
/**
 * 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()).
 */
typedef int MQTTAsync_token;

/**
 * A structure representing the payload and attributes of an MQTT message. The
 * message topic is not part of this structure (see MQTTAsync_publishMessage(),
 * MQTTAsync_publish(), MQTTAsync_receive(), MQTTAsync_freeMessage()
 * and MQTTAsync_messageArrived()).
 */
typedef struct
{
	/** The eyecatcher for this structure.  must be MQTM. */
	char struct_id[4];
	/** The version number of this structure.  Must be 0 or 1.
	 *  0 indicates no message properties */
	int struct_version;
	/** The length of the MQTT message payload in bytes. */
	int payloadlen;
	/** A pointer to the payload of the MQTT message. */
	void* payload;
	/**
     * The quality of service (QoS) assigned to the message.
     * There are three levels of QoS:
     * <DL>
     * <DT><B>QoS0</B></DT>
     * <DD>Fire and forget - the message may not be delivered</DD>
     * <DT><B>QoS1</B></DT>
     * <DD>At least once - the message will be delivered, but may be
     * delivered more than once in some circumstances.</DD>
     * <DT><B>QoS2</B></DT>
     * <DD>Once and one only - the message will be delivered exactly once.</DD>
     * </DL>
     */
	int qos;
	/**
     * The retained flag serves two purposes depending on whether the message
     * it is associated with is being published or received.
     *
     * <b>retained = true</b><br>
     * For messages being published, a true setting indicates that the MQTT
     * server should retain a copy of the message. The message will then be
     * transmitted to new subscribers to a topic that matches the message topic.
     * For subscribers registering a new subscription, the flag being true
     * indicates that the received message is not a new one, but one that has
     * been retained by the MQTT server.
     *
     * <b>retained = false</b> <br>
     * For publishers, this indicates that this message should not be retained
     * by the MQTT server. For subscribers, a false setting indicates this is
     * a normal message, received as a result of it being published to the
     * server.
     */
	int retained;
	/**
      * The dup flag indicates whether or not this message is a duplicate.
      * It is only meaningful when receiving QoS1 messages. When true, the
      * client application should take appropriate action to deal with the
      * duplicate message.  This is an output parameter only.
      */
	int dup;
	/** The message identifier is reserved for internal use by the
      * MQTT client and server.  It is an output parameter only - writing
      * to it will serve no purpose.  It contains the MQTT message id of
      * an incoming publish message.
      */
	int msgid;
	/**
	 * The MQTT V5 properties associated with the message.
	 */
	MQTTProperties properties;
} MQTTAsync_message;

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

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * MQTTAsync_setCallbacks(), which contains any application-specific context.
 * @param topicName The topic associated with the received message.
 * @param topicLen The length of the topic if there are one
 * more NULL characters embedded in <i>topicName</i>, otherwise <i>topicLen</i>
 * is 0. If <i>topicLen</i> is 0, the value returned by <i>strlen(topicName)</i>
 * can be trusted. If <i>topicLen</i> is greater than 0, the full topic name
 * can be retrieved by accessing <i>topicName</i> as a byte array of length
 * <i>topicLen</i>.
 * @param message The MQTTAsync_message structure for the received message.
 * This structure contains the message payload and attributes.
 * @return This function must return 0 or 1 indicating whether or not
 * the message has been safely received by the client application. <br>
 * 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.<br>
 * 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.
 */
typedef int MQTTAsync_messageArrived(void* context, char* topicName, int topicLen, MQTTAsync_message* message);

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * MQTTAsync_setCallbacks(), which contains any application-specific context.
 * @param 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.
 */
typedef void MQTTAsync_deliveryComplete(void* context, MQTTAsync_token token);

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * MQTTAsync_setCallbacks(), which contains any application-specific context.
 * @param cause The reason for the disconnection.
 * Currently, <i>cause</i> is always set to NULL.
 */
typedef void MQTTAsync_connectionLost(void* context, char* cause);


/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * MQTTAsync_setCallbacks(), which contains any application-specific context.
 * @param cause The reason for the disconnection.
 * Currently, <i>cause</i> is always set to NULL.
 */
typedef void MQTTAsync_connected(void* context, char* cause);

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * MQTTAsync_setCallbacks(), which contains any application-specific context.
 * @param properties the properties in the disconnect packet.
 * @param properties the reason code from the disconnect packet
 * Currently, <i>cause</i> is always set to NULL.
 */
typedef void MQTTAsync_disconnected(void* context, MQTTProperties* properties,
		enum MQTTReasonCodes reasonCode);

/**
 * Sets the MQTTAsync_disconnected() callback function for a client.
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to each of the callback functions to
 * provide access to the context information in the callback.
 * @param co A pointer to an MQTTAsync_connected() callback
 * function.  NULL removes the callback setting.
 * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
 * ::MQTTASYNC_FAILURE if an error occurred.
 */
LIBMQTT_API int MQTTAsync_setDisconnected(MQTTAsync handle, void* context, MQTTAsync_disconnected* co);

/** The connect options that can be updated before an automatic reconnect. */
typedef struct
{
	/** The eyecatcher for this structure.  Will be MQCD. */
	char struct_id[4];
	/** The version number of this structure.  Will be 0 */
	int struct_version;
	/**
	 * MQTT servers that support the MQTT v3.1 protocol provide authentication
	 * and authorisation by user name and password. This is the user name parameter.
	 * Set data to NULL to remove.  To change, allocate new
	 * storage with ::MQTTAsync_allocate - this will then be free later by the library.
	 */
	const char* username;
	/**
	 * The password parameter of the MQTT authentication.
	 * Set data to NULL to remove.  To change, allocate new
	 * storage with ::MQTTAsync_allocate - this will then be free later by the library.
	 */
	struct {
		int len;           /**< binary password length */
		const void* data;  /**< binary password data */
	} binarypwd;
} MQTTAsync_connectData;

#define MQTTAsync_connectData_initializer {{'M', 'Q', 'C', 'D'}, 0, NULL, {0, NULL}}

/**
 * This is a callback function which will allow the client application to update the
 * connection data.
 * @param data The connection data which can be modified by the application.
 * @return Return a non-zero value to update the connect data, zero to keep the same data.
 */
typedef int MQTTAsync_updateConnectOptions(void* context, MQTTAsync_connectData* data);

/**
 * Sets the MQTTAsync_updateConnectOptions() callback function for a client.
 * @param handle A valid client handle from a successful call to MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to each of the callback functions to
 * provide access to the context information in the callback.
 * @param co A pointer to an MQTTAsync_updateConnectOptions() callback
 * function.  NULL removes the callback setting.
 */
LIBMQTT_API int MQTTAsync_setUpdateConnectOptions(MQTTAsync handle, void* context, MQTTAsync_updateConnectOptions* co);

#if !defined(NO_PERSISTENCE)
/**
 * Sets the MQTTPersistence_beforeWrite() callback function for a client.
 * @param handle A valid client handle from a successful call to MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to the callback function to
 * provide access to the context information in the callback.
 * @param co A pointer to an MQTTPersistence_beforeWrite() callback
 * function.  NULL removes the callback setting.
 */
LIBMQTT_API int MQTTAsync_setBeforePersistenceWrite(MQTTAsync handle, void* context, MQTTPersistence_beforeWrite* co);


/**
 * Sets the MQTTPersistence_afterRead() callback function for a client.
 * @param handle A valid client handle from a successful call to MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to the callback function to
 * provide access to the context information in the callback.
 * @param co A pointer to an MQTTPersistence_beforeWrite() callback
 * function.  NULL removes the callback setting.
 */
LIBMQTT_API int MQTTAsync_setAfterPersistenceRead(MQTTAsync handle, void* context, MQTTPersistence_afterRead* co);
#endif

/** The data returned on completion of an unsuccessful API call in the response callback onFailure. */
typedef struct
{
	/** A token identifying the failed request. */
	MQTTAsync_token token;
	/** A numeric code identifying the error. */
	int code;
	/** Optional text explaining the error. Can be NULL. */
	const char *message;
} MQTTAsync_failureData;


/** The data returned on completion of an unsuccessful API call in the response callback onFailure. */
typedef struct
{
	/** The eyecatcher for this structure.  Will be MQFD. */
	char struct_id[4];
	/** The version number of this structure.  Will be 0 */
	int struct_version;
	/** A token identifying the failed request. */
	MQTTAsync_token token;
	/** The MQTT reason code returned. */
	enum MQTTReasonCodes reasonCode;
	/** The MQTT properties on the ack, if any. */
	MQTTProperties properties;
	/** A numeric code identifying the MQTT client library error. */
	int code;
	/** Optional further text explaining the error. Can be NULL. */
	const char *message;
	/** Packet type on which the failure occurred - used for publish QoS 1/2 exchanges*/
	int packet_type;
} MQTTAsync_failureData5;

#define MQTTAsync_failureData5_initializer {{'M', 'Q', 'F', 'D'}, 0, 0, MQTTREASONCODE_SUCCESS, MQTTProperties_initializer, 0, NULL, 0}

/** The data returned on completion of a successful API call in the response callback onSuccess. */
typedef struct
{
	/** A token identifying the successful request. Can be used to refer to the request later. */
	MQTTAsync_token token;
	/** A union of the different values that can be returned for subscribe, unsubscribe and publish. */
	union
	{
		/** For subscribe, the granted QoS of the subscription returned by the server.
		 * Also for subscribeMany, if only 1 subscription was requested. */
		int qos;
		/** For subscribeMany, if more than one subscription was requested,
		 * the list of granted QoSs of the subscriptions returned by the server. */
		int* qosList;
		/** For publish, the message being sent to the server. */
		struct
		{
			MQTTAsync_message message; /**< the message being sent to the server */
			char* destinationName;     /**< the topic destination for the message */
		} pub;
		/* For connect, the server connected to, MQTT version used, and sessionPresent flag */
		struct
		{
			char* serverURI; /**< the connection string of the server */
			int MQTTVersion; /**< the version of MQTT being used */
			int sessionPresent; /**< the session present flag returned from the server */
		} connect;
	} alt;
} MQTTAsync_successData;


/** The data returned on completion of a successful API call in the response callback onSuccess. */
typedef struct
{
	char struct_id[4];    	/**< The eyecatcher for this structure.  Will be MQSD. */
	int struct_version;  	/**< The version number of this structure.  Will be 0 */
	/** A token identifying the successful request. Can be used to refer to the request later. */
	MQTTAsync_token token;
	enum MQTTReasonCodes reasonCode;  	/**< MQTT V5 reason code returned */
	MQTTProperties properties;  	        /**< MQTT V5 properties returned, if any */
	/** A union of the different values that can be returned for subscribe, unsubscribe and publish. */
	union
	{
		/** For subscribeMany, the list of reasonCodes returned by the server. */
		struct
		{
			int reasonCodeCount; /**< the number of reason codes in the reasonCodes array */
			enum MQTTReasonCodes* reasonCodes; /**< an array of reasonCodes */
		} sub;
		/** For publish, the message being sent to the server. */
		struct
		{
			MQTTAsync_message message; /**< the message being sent to the server */
			char* destinationName;     /**< the topic destination for the message */
		} pub;
		/* For connect, the server connected to, MQTT version used, and sessionPresent flag */
		struct
		{
			char* serverURI;  /**< the connection string of the server */
			int MQTTVersion;  /**< the version of MQTT being used */
			int sessionPresent;  /**< the session present flag returned from the server */
		} connect;
		/** For unsubscribeMany, the list of reasonCodes returned by the server. */
		struct
		{
			int reasonCodeCount; /**< the number of reason codes in the reasonCodes array */
			enum MQTTReasonCodes* reasonCodes; /**< an array of reasonCodes */
		} unsub;
	} alt;
} MQTTAsync_successData5;

#define MQTTAsync_successData5_initializer {{'M', 'Q', 'S', 'D'}, 0, 0, MQTTREASONCODE_SUCCESS, MQTTProperties_initializer, {.sub={0,0}}}

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * ::MQTTAsync_responseOptions, which contains any application-specific context.
 * @param response Any success data associated with the API completion.
 */
typedef void MQTTAsync_onSuccess(void* context, MQTTAsync_successData* response);

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * ::MQTTAsync_responseOptions, which contains any application-specific context.
 * @param response Any success data associated with the API completion.
 */
typedef void MQTTAsync_onSuccess5(void* context, MQTTAsync_successData5* response);

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * ::MQTTAsync_responseOptions, which contains any application-specific context.
 * @param response Failure data associated with the API completion.
 */
typedef void MQTTAsync_onFailure(void* context,  MQTTAsync_failureData* response);

/**
 * 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.
 *
 * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
 * called within this callback.
 * @param context A pointer to the <i>context</i> value originally passed to
 * ::MQTTAsync_responseOptions, which contains any application-specific context.
 * @param response Failure data associated with the API completion.
 */
typedef void MQTTAsync_onFailure5(void* context,  MQTTAsync_failureData5* response);

/** 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.
 */
typedef struct MQTTAsync_responseOptions
{
	/** The eyecatcher for this structure.  Must be MQTR */
	char struct_id[4];
	/** The version number of this structure.  Must be 0 or 1
	 *   if 0, no MQTTV5 options */
	int struct_version;
	/**
    * A pointer to a callback function to be called if the API call successfully
    * completes.  Can be set to NULL, in which case no indication of successful
    * completion will be received.
    */
	MQTTAsync_onSuccess* onSuccess;
	/**
    * A pointer to a callback function to be called if the API call fails.
    * Can be set to NULL, in which case no indication of unsuccessful
    * completion will be received.
    */
	MQTTAsync_onFailure* onFailure;
	/**
    * A pointer to any application-specific context. The
    * the <i>context</i> pointer is passed to success or failure callback functions to
    * provide access to the context information in the callback.
    */
	void* context;
	/**
    * A token is returned from the call.  It can be used to track
    * the state of this request, both in the callbacks and in future calls
    * such as ::MQTTAsync_waitForCompletion. This is output only - any
    * change by the application will be ignored.
    */
	MQTTAsync_token token;
	/**
    * A pointer to a callback function to be called if the API call successfully
    * completes.  Can be set to NULL, in which case no indication of successful
    * completion will be received.
    */
	MQTTAsync_onSuccess5* onSuccess5;
	/**
    * A pointer to a callback function to be called if the API call successfully
    * completes.  Can be set to NULL, in which case no indication of successful
    * completion will be received.
    */
	MQTTAsync_onFailure5* onFailure5;
	/**
	 * MQTT V5 input properties
	 */
	MQTTProperties properties;
	/*
	 * MQTT V5 subscribe options, when used with subscribe only.
	 */
	MQTTSubscribe_options subscribeOptions;
	/*
	 * MQTT V5 subscribe option count, when used with subscribeMany only.
	 * The number of entries in the subscribe_options_list array.
	 */
	int subscribeOptionsCount;
	/*
	 * MQTT V5 subscribe option array, when used with subscribeMany only.
	 */
	MQTTSubscribe_options* subscribeOptionsList;
} MQTTAsync_responseOptions;

#define MQTTAsync_responseOptions_initializer { {'M', 'Q', 'T', 'R'}, 1, NULL, NULL, 0, 0, NULL, NULL, MQTTProperties_initializer, MQTTSubscribe_options_initializer, 0, NULL}

/** A synonym for responseOptions to better reflect its usage since MQTT 5.0 */
typedef struct MQTTAsync_responseOptions MQTTAsync_callOptions;
#define MQTTAsync_callOptions_initializer MQTTAsync_responseOptions_initializer

/**
 * 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.
 *
 * <b>Note:</b> The MQTT client must be disconnected when this function is
 * called.
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to each of the callback functions to
 * provide access to the context information in the callback.
 * @param cl A pointer to an MQTTAsync_connectionLost() callback
 * function. You can set this to NULL if your application doesn't handle
 * disconnections.
 * @param 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.
 * @param 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.
 * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
 * ::MQTTASYNC_FAILURE if an error occurred.
 */
LIBMQTT_API int MQTTAsync_setCallbacks(MQTTAsync handle, void* context, MQTTAsync_connectionLost* cl,
									 MQTTAsync_messageArrived* ma, MQTTAsync_deliveryComplete* dc);

/**
 * 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.
 *
 * <b>Note:</b> The MQTT client must be disconnected when this function is
 * called.
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed the callback functions to provide
 * access to the context information in the callback.
 * @param cl A pointer to an MQTTAsync_connectionLost() callback
 * function. You can set this to NULL if your application doesn't handle
 * disconnections.
 * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
 * ::MQTTASYNC_FAILURE if an error occurred.
 */

LIBMQTT_API int MQTTAsync_setConnectionLostCallback(MQTTAsync handle, void* context,
												  MQTTAsync_connectionLost* cl);

/**
 * 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.
 *
 * <b>Note:</b> The MQTT client must be disconnected when this function is
 * called.
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to the callback functions to provide
 * access to the context information in the callback.
 * @param ma A pointer to an MQTTAsync_messageArrived() callback
 * function.  You can set this to NULL if your application doesn't handle
 * receipt of messages.
 * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
 * ::MQTTASYNC_FAILURE if an error occurred.
 */
LIBMQTT_API int MQTTAsync_setMessageArrivedCallback(MQTTAsync handle, void* context,
												  MQTTAsync_messageArrived* ma);

/**
 * 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.
 *
 * <b>Note:</b> The MQTT client must be disconnected when this function is
 * called.
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to the callback functions to provide
 * access to the context information in the callback.
 * @param 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.
 * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
 * ::MQTTASYNC_FAILURE if an error occurred.
 */
LIBMQTT_API int MQTTAsync_setDeliveryCompleteCallback(MQTTAsync handle, void* context,
													MQTTAsync_deliveryComplete* dc);

/**
 * Sets the MQTTAsync_connected() callback function for a client.
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @param context A pointer to any application-specific context. The
 * the <i>context</i> pointer is passed to each of the callback functions to
 * provide access to the context information in the callback.
 * @param co A pointer to an MQTTAsync_connected() callback
 * function.  NULL removes the callback setting.
 * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
 * ::MQTTASYNC_FAILURE if an error occurred.
 */
LIBMQTT_API int MQTTAsync_setConnected(MQTTAsync handle, void* context, MQTTAsync_connected* co);


/**
 * Reconnects a client with the previously used connect options.  Connect
 * must have previously been called for this to work.
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
 * ::MQTTASYNC_FAILURE if an error occurred.
 */
LIBMQTT_API int MQTTAsync_reconnect(MQTTAsync handle);


/**
 * 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().
 * @param handle A pointer to an ::MQTTAsync handle. The handle is
 * populated with a valid client reference following a successful return from
 * this function.
 * @param serverURI A null-terminated string specifying the server to
 * which the client will connect. It takes the form
 * <i>protocol://host:port</i> where <i>protocol</i> must be:
 * <br>
 * @em tcp:// or @em mqtt:// - Insecure TCP
 * <br>
 * @em ssl:// or @em mqtts:// - Encrypted SSL/TLS
 * <br>
 * @em ws:// - Insecure websockets
 * <br>
 * @em wss:// - Secure web sockets
 * <br>
 * The TLS enabled prefixes (ssl, mqtts, wss) are only valid if a TLS
 * version of the library is linked with.
 * For <i>host</i>, 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 <i>tcp://localhost:1883</i>.
 * @param clientId The client identifier passed to the server when the
 * client connects to it. It is a null-terminated UTF-8 encoded string.
 * @param persistence_type The type of persistence to be used by the client:
 * <br>
 * ::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.
 * <br>
 * ::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.
 * <br>
 * ::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.
 * @param 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.
 * @return ::MQTTASYNC_SUCCESS if the client is successfully created, otherwise
 * an error code is returned.
 */
LIBMQTT_API int MQTTAsync_create(MQTTAsync* handle, const char* serverURI, const char* clientId,
		int persistence_type, void* persistence_context);

/** Options for the ::MQTTAsync_createWithOptions call */
typedef struct
{
	/** The eyecatcher for this structure.  must be MQCO. */
	char struct_id[4];
	/** The version number of this structure.  Must be 0, 1, 2 or 3
	 * 0 means no MQTTVersion
	 * 1 means no allowDisconnectedSendAtAnyTime, deleteOldestMessages, restoreMessages
	 * 2 means no persistQoS0
	 */
	int struct_version;
	/** Whether to allow messages to be sent when the client library is not connected. */
	int sendWhileDisconnected;
	/** The maximum number of messages allowed to be buffered. This is intended to be used to
	 * limit the number of messages queued while the client is not connected. It also applies
	 * when the client is connected, however, so has to be greater than 0. */
	int maxBufferedMessages;
	/** Whether the MQTT version is 3.1, 3.1.1, or 5.  To use V5, this must be set.
	 *  MQTT V5 has to be chosen here, because during the create call the message persistence
	 *  is initialized, and we want to know whether the format of any persisted messages
	 *  is appropriate for the MQTT version we are going to connect with.  Selecting 3.1 or
	 *  3.1.1 and attempting to read 5.0 persisted messages will result in an error on create.  */
	int MQTTVersion;
	/**
	 * Allow sending of messages while disconnected before a first successful connect.
	 */
	int allowDisconnectedSendAtAnyTime;
	/*
	 * When the maximum number of buffered messages is reached, delete the oldest rather than the newest.
	 */
	int deleteOldestMessages;
	/*
	 * Restore messages from persistence on create - or clear it.
	 */
	int restoreMessages;
	/*
	 * Persist QoS0 publish commands - an option to not persist them.
	 */
	int persistQoS0;
} MQTTAsync_createOptions;

#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}


LIBMQTT_API int MQTTAsync_createWithOptions(MQTTAsync* handle, const char* serverURI, const char* clientId,
		int persistence_type, void* persistence_context, MQTTAsync_createOptions* options);

/**
 * MQTTAsync_willOptions defines the MQTT "Last Will and Testament" (LWT) settings for
 * the client. In the event that a client unexpectedly loses its connection to
 * the server, the server publishes the LWT message to the LWT topic on
 * behalf of the client. This allows other clients (subscribed to the LWT topic)
 * to be made aware that the client has disconnected. To enable the LWT
 * function for a specific client, a valid pointer to an MQTTAsync_willOptions
 * structure is passed in the MQTTAsync_connectOptions structure used in the
 * MQTTAsync_connect() call that connects the client to the server. The pointer
 * to MQTTAsync_willOptions can be set to NULL if the LWT function is not
 * required.
 */
typedef struct
{
	/** The eyecatcher for this structure.  must be MQTW. */
	char struct_id[4];
	/** The version number of this structure.  Must be 0 or 1
	    0 indicates no binary will message support
	 */
	int struct_version;
	/** The LWT topic to which the LWT message will be published. */
	const char* topicName;
	/** The LWT payload. */
	const char* message;
	/**
      * The retained flag for the LWT message (see MQTTAsync_message.retained).
      */
	int retained;
	/**
      * The quality of service setting for the LWT message (see
      * MQTTAsync_message.qos and @ref qos).
      */
	int qos;
	/** The LWT payload in binary form. This is only checked and used if the message option is NULL */
	struct
	{
  	int len;            /**< binary payload length */
		const void* data;  /**< binary payload data */
	} payload;
} MQTTAsync_willOptions;

#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

/**
* MQTTAsync_sslProperties defines the settings to establish an SSL/TLS connection using the
* OpenSSL library. It covers the following scenarios:
* - Server authentication: The client needs the digital certificate of the server. It is included
*   in a store containting trusted material (also known as "trust store").
* - Mutual authentication: Both client and server are authenticated during the SSL handshake. In
*   addition to the digital certificate of the server in a trust store, the client will need its own
*   digital certificate and the private key used to sign its digital certificate stored in a "key store".
* - Anonymous connection: Both client and server do not get authenticated and no credentials are needed
*   to establish an SSL connection. Note that this scenario is not fully secure since it is subject to
*   man-in-the-middle attacks.
*/
typedef struct
{
	/** The eyecatcher for this structure.  Must be MQTS */
	char struct_id[4];

	/** The version number of this structure. Must be [0-6].
	 * 0 means no sslVersion
	 * 1 means no verify, CApath
	 * 2 means no ssl_error_context, ssl_error_cb
	 * 3 means no ssl_psk_cb, ssl_psk_context, disableDefaultTrustStore
	 * 4 means no protos, protos_len
   * 5 means no providerName
	 */
	int struct_version;

	/** The file in PEM format containing the public digital certificates trusted by the client. */
	const char* trustStore;

	/** The file in PEM format containing the public certificate chain of the client. It may also include
	* the client's private key.
	*/
	const char* keyStore;

	/** If not included in the sslKeyStore, this setting points to the file in PEM format containing
	* the client's private key.
	*/
	const char* privateKey;

	/** The password to load the client's privateKey if encrypted. */
	const char* privateKeyPassword;

	/**
	* The list of cipher suites that the client will present to the server during the SSL handshake. For a
	* full explanation of the cipher list format, please see the OpenSSL on-line documentation:
	* http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT
	* If this setting is ommitted, its default value will be "ALL", that is, all the cipher suites -excluding
	* those offering no encryption- will be considered.
	* This setting can be used to set an SSL anonymous connection ("aNULL" string value, for instance).
	*/
	const char* enabledCipherSuites;

    /** True/False option to enable verification of the server certificate **/
    int enableServerCertAuth;

    /** The SSL/TLS version to use. Specify one of MQTT_SSL_VERSION_DEFAULT (0),
    * MQTT_SSL_VERSION_TLS_1_0 (1), MQTT_SSL_VERSION_TLS_1_1 (2) or MQTT_SSL_VERSION_TLS_1_2 (3).
    * Only used if struct_version is >= 1.
    */
    int sslVersion;

    /**
     * Whether to carry out post-connect checks, including that a certificate
     * matches the given host name.
     * Exists only if struct_version >= 2
     */
    int verify;

    /**
     * From the OpenSSL documentation:
     * If CApath is not NULL, it points to a directory containing CA certificates in PEM format.
     * Exists only if struct_version >= 2
	 */
	const char* CApath;

    /**
     * Callback function for OpenSSL error handler ERR_print_errors_cb
     * Exists only if struct_version >= 3
     */
    int (*ssl_error_cb) (const char *str, size_t len, void *u);

    /**
     * Application-specific contex for OpenSSL error handler ERR_print_errors_cb
     * Exists only if struct_version >= 3
     */
    void* ssl_error_context;

	/**
	 * Callback function for setting TLS-PSK options. Parameters correspond to that of
	 * SSL_CTX_set_psk_client_callback, except for u which is the pointer ssl_psk_context.
	 * Exists only if struct_version >= 4
	 */
	unsigned int (*ssl_psk_cb) (const char *hint, char *identity, unsigned int max_identity_len, unsigned char *psk, unsigned int max_psk_len, void *u);

	/**
	 * Application-specific contex for ssl_psk_cb
	 * Exists only if struct_version >= 4
	 */
	void* ssl_psk_context;

	/**
	 * Don't load default SSL CA. Should be used together with PSK to make sure
	 * regular servers with certificate in place is not accepted.
	 * Exists only if struct_version >= 4
	 */
	int disableDefaultTrustStore;

	/**
	 * The protocol-lists must be in wire-format, which is defined as a vector of non-empty, 8-bit length-prefixed, byte strings.
	 * The length-prefix byte is not included in the length. Each string is limited to 255 bytes. A byte-string length of 0 is invalid.
	 * A truncated byte-string is invalid.
	 * Check documentation for SSL_CTX_set_alpn_protos
	 * Exists only if struct_version >= 5
	 */
	const unsigned char *protos;

	/**
	 * The length of the vector protos vector
	 * Exists only if struct_version >= 5
	 */
	unsigned int protos_len;

	/** OpenSSL provider to used, NULL if disabled. */
	const char* providerName;

} MQTTAsync_SSLOptions;

#define MQTTAsync_SSLOptions_initializer { {'M', 'Q', 'T', 'S'}, 6, NULL, NULL, NULL, NULL, NULL, 1, MQTT_SSL_VERSION_DEFAULT, 0, NULL, NULL, NULL, NULL, NULL, 0, NULL, 0, NULL }

/** Utility structure where name/value pairs are needed */
typedef struct
{
	const char* name; /**< name string */
	const char* value; /**< value string */
} MQTTAsync_nameValue;

/**
 * MQTTAsync_connectOptions defines several settings that control the way the
 * client connects to an MQTT server.
 *
 * Suitable default values are set in the following initializers:
 * - MQTTAsync_connectOptions_initializer: for MQTT 3.1.1 non-WebSockets
 * - MQTTAsync_connectOptions_initializer5: for MQTT 5.0 non-WebSockets
 * - MQTTAsync_connectOptions_initializer_ws: for MQTT 3.1.1 WebSockets
 * - MQTTAsync_connectOptions_initializer5_ws: for MQTT 5.0 WebSockets
 */
typedef struct
{
	/** The eyecatcher for this structure.  must be MQTC. */
	char struct_id[4];
	/** The version number of this structure.  Must be 0, 1, 2, 3 4 5 6, 7 or 8.
	  * 0 signifies no SSL options and no serverURIs
	  * 1 signifies no serverURIs
      * 2 signifies no MQTTVersion
      * 3 signifies no automatic reconnect options
      * 4 signifies no binary password option (just string)
      * 5 signifies no MQTTV5 properties
      * 6 signifies no HTTP headers option
      * 7 signifies no HTTP proxy and HTTPS proxy options
	  */
	int struct_version;
	/** The "keep alive" interval, measured in seconds, defines the maximum time
      * that should pass without communication between the client and the server
      * The client will ensure that at least one message travels across the
      * network within each keep alive period.  In the absence of a data-related
	  * message during the time period, the client sends a very small MQTT
      * "ping" message, which the server will acknowledge. The keep alive
      * interval enables the client to detect when the server is no longer
	  * available without having to wait for the long TCP/IP timeout.
	  * Set to 0 if you do not want any keep alive processing.
	  */
	int keepAliveInterval;
	/**
      * This is a boolean value. The cleansession setting controls the behaviour
      * of both the client and the server at connection and disconnection time.
      * The client and server both maintain session state information. This
      * information is used to ensure "at least once" and "exactly once"
      * delivery, and "exactly once" receipt of messages. Session state also
      * includes subscriptions created by an MQTT client. You can choose to
      * maintain or discard state information between sessions.
      *
      * When cleansession is true, the state information is discarded at
      * connect and disconnect. Setting cleansession to false keeps the state
      * information. When you connect an MQTT client application with
      * MQTTAsync_connect(), the client identifies the connection using the
      * client identifier and the address of the server. The server checks
      * whether session information for this client
      * has been saved from a previous connection to the server. If a previous
      * session still exists, and cleansession=true, then the previous session
      * information at the client and server is cleared. If cleansession=false,
      * the previous session is resumed. If no previous session exists, a new
      * session is started.
	  */
	int cleansession;
	/**
      * This controls how many messages can be in-flight simultaneously.
	  */
	int maxInflight;
	/**
      * This is a pointer to an MQTTAsync_willOptions structure. If your
      * application does not make use of the Last Will and Testament feature,
      * set this pointer to NULL.
      */
	MQTTAsync_willOptions* will;
	/**
      * MQTT servers that support the MQTT v3.1 protocol provide authentication
      * and authorisation by user name and password. This is the user name
      * parameter.
      */
	const char* username;
	/**
      * MQTT servers that support the MQTT v3.1 protocol provide authentication
      * and authorisation by user name and password. This is the password
      * parameter.
      */
	const char* password;
	/**
      * The time interval in seconds to allow a connect to complete.
      */
	int connectTimeout;
	/**
	 * The time interval in seconds after which unacknowledged publish requests are
	 * retried during a TCP session.  With MQTT 3.1.1 and later, retries are
	 * not required except on reconnect.  0 turns off in-session retries, and is the
	 * recommended setting.  Adding retries to an already overloaded network only
	 * exacerbates the problem.
	 */
	int retryInterval;
	/**
      * This is a pointer to an MQTTAsync_SSLOptions structure. If your
      * application does not make use of SSL, set this pointer to NULL.
      */
	MQTTAsync_SSLOptions* ssl;
	/**
      * A pointer to a callback function to be called if the connect successfully
      * completes.  Can be set to NULL, in which case no indication of successful
      * completion will be received.
      */
	MQTTAsync_onSuccess* onSuccess;
	/**
      * A pointer to a callback function to be called if the connect fails.
      * Can be set to NULL, in which case no indication of unsuccessful
      * completion will be received.
      */
	MQTTAsync_onFailure* onFailure;
	/**
	  * A pointer to any application-specific context. The
      * the <i>context</i> pointer is passed to success or failure callback functions to
      * provide access to the context information in the callback.
      */
	void* context;
	/**
	  * The number of entries in the serverURIs array.
	  */
	int serverURIcount;
	/**
	  * An array of null-terminated strings specifying the servers to
      * which the client will connect. Each string takes the form <i>protocol://host:port</i>.
      * <i>protocol</i> must be <i>tcp</i>, <i>ssl</i>, <i>ws</i> or <i>wss</i>.
      * The TLS enabled prefixes (ssl, wss) are only valid if a TLS version of the library
      * is linked with.
      * For <i>host</i>, you can
      * specify either an IP address or a domain name. For instance, to connect to
      * a server running on the local machines with the default MQTT port, specify
      * <i>tcp://localhost:1883</i>.
      */
	char* const* serverURIs;
	/**
      * Sets the version of MQTT to be used on the connect.
      * MQTTVERSION_DEFAULT (0) = default: start with 3.1.1, and if that fails, fall back to 3.1
      * MQTTVERSION_3_1 (3) = only try version 3.1
      * MQTTVERSION_3_1_1 (4) = only try version 3.1.1
	  */
	int MQTTVersion;
	/**
	  * Reconnect automatically in the case of a connection being lost. 0=false, 1=true
	  */
	int automaticReconnect;
	/**
	  * The minimum automatic reconnect retry interval in seconds. Doubled on each failed retry.
	  */
	int minRetryInterval;
	/**
	  * The maximum automatic reconnect retry interval in seconds. The doubling stops here on failed retries.
	  */
	int maxRetryInterval;
	/**
	 * Optional binary password.  Only checked and used if the password option is NULL
	 */
	struct {
		int len;            /**< binary password length */
		const void* data;  /**< binary password data */
	} binarypwd;
	/*
	 * MQTT V5 clean start flag.  Only clears state at the beginning of the session.
	 */
	int cleanstart;
	/**
	 * MQTT V5 properties for connect
	 */
	MQTTProperties *connectProperties;
	/**
	 * MQTT V5 properties for the will message in the connect
	 */
	MQTTProperties *willProperties;
	/**
      * A pointer to a callback function to be called if the connect successfully
      * completes.  Can be set to NULL, in which case no indication of successful
      * completion will be received.
      */
	MQTTAsync_onSuccess5* onSuccess5;
	/**
      * A pointer to a callback function to be called if the connect fails.
      * Can be set to NULL, in which case no indication of unsuccessful
      * completion will be received.
      */
	MQTTAsync_onFailure5* onFailure5;
	/**
	 * HTTP headers for websockets
	 */
	const MQTTAsync_nameValue* httpHeaders;
	/**
	 * HTTP proxy
	 */
	const char* httpProxy;
	/**
	 * HTTPS proxy
	 */
	const char* httpsProxy;
} MQTTAsync_connectOptions;

/** Initializer for connect options for MQTT 3.1.1 non-WebSocket connections */
#define MQTTAsync_connectOptions_initializer { {'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 5.0 non-WebSocket connections */
#define MQTTAsync_connectOptions_initializer5 { {'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 3.1.1 WebSockets connections.
  * The keepalive interval is set to 45 seconds to avoid webserver 60 second inactivity timeouts.
  */
#define MQTTAsync_connectOptions_initializer_ws { {'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 5.0 WebSockets connections.
  * The keepalive interval is set to 45 seconds to avoid webserver 60 second inactivity timeouts.
  */
#define MQTTAsync_connectOptions_initializer5_ws { {'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}


/**
  * 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().
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param options A pointer to a valid MQTTAsync_connectOptions
  * structure.
  * @return ::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:<br><br>
  * <b>1</b>: Connection refused: Unacceptable protocol version<br>
  * <b>2</b>: Connection refused: Identifier rejected<br>
  * <b>3</b>: Connection refused: Server unavailable<br>
  * <b>4</b>: Connection refused: Bad user name or password<br>
  * <b>5</b>: Connection refused: Not authorized<br>
  * <b>6-255</b>: Reserved for future use<br>
  */
LIBMQTT_API int MQTTAsync_connect(MQTTAsync handle, const MQTTAsync_connectOptions* options);

/** Options for the ::MQTTAsync_disconnect call */
typedef struct
{
	/** The eyecatcher for this structure. Must be MQTD. */
	char struct_id[4];
	/** The version number of this structure.  Must be 0 or 1.  0 signifies no V5 properties */
	int struct_version;
	/**
      * The client delays disconnection for up to this time (in
      * milliseconds) in order to allow in-flight message transfers to complete.
      */
	int timeout;
	/**
    * A pointer to a callback function to be called if the disconnect successfully
    * completes.  Can be set to NULL, in which case no indication of successful
    * completion will be received.
    */
	MQTTAsync_onSuccess* onSuccess;
	/**
    * A pointer to a callback function to be called if the disconnect fails.
    * Can be set to NULL, in which case no indication of unsuccessful
    * completion will be received.
    */
	MQTTAsync_onFailure* onFailure;
	/**
	* A pointer to any application-specific context. The
    * the <i>context</i> pointer is passed to success or failure callback functions to
    * provide access to the context information in the callback.
    */
	void* context;
	/**
	 * MQTT V5 input properties
	 */
	MQTTProperties properties;
	/**
	 * Reason code for MQTTV5 disconnect
	 */
	enum MQTTReasonCodes reasonCode;
	/**
    * A pointer to a callback function to be called if the disconnect successfully
    * completes.  Can be set to NULL, in which case no indication of successful
    * completion will be received.
    */
	MQTTAsync_onSuccess5* onSuccess5;
	/**
    * A pointer to a callback function to be called if the disconnect fails.
    * Can be set to NULL, in which case no indication of unsuccessful
    * completion will be received.
    */
	MQTTAsync_onFailure5* onFailure5;
} MQTTAsync_disconnectOptions;

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

#define MQTTAsync_disconnectOptions_initializer5 { {'M', 'Q', 'T', 'D'}, 1, 0, NULL, NULL, NULL,\
	MQTTProperties_initializer, MQTTREASONCODE_SUCCESS, NULL, NULL }

/**
  * 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()).
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param options The client delays disconnection for up to this time (in
  * milliseconds) in order to allow in-flight message transfers to complete.
  * @return ::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
  */
LIBMQTT_API int MQTTAsync_disconnect(MQTTAsync handle, const MQTTAsync_disconnectOptions* options);


/**
  * This function allows the client application to test whether or not a
  * client is currently connected to the MQTT server.
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @return Boolean true if the client is connected, otherwise false.
  */
LIBMQTT_API int MQTTAsync_isConnected(MQTTAsync handle);


/**
  * This function attempts to subscribe a client to a single topic, which may
  * contain wildcards (see @ref wildcard). This call also specifies the
  * @ref qos requested for the subscription
  * (see also MQTTAsync_subscribeMany()).
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param topic The subscription topic, which may include wildcards.
  * @param qos The requested quality of service for the subscription.
  * @param response A pointer to a response options structure. Used to set callback functions.
  * @return ::MQTTASYNC_SUCCESS if the subscription request is successful.
  * An error code is returned if there was a problem registering the
  * subscription.
  */
LIBMQTT_API int MQTTAsync_subscribe(MQTTAsync handle, const char* topic, int qos, MQTTAsync_responseOptions* response);


/**
  * This function attempts to subscribe a client to a list of topics, which may
  * contain wildcards (see @ref wildcard). This call also specifies the
  * @ref qos requested for each topic (see also MQTTAsync_subscribe()).
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param count The number of topics for which the client is requesting
  * subscriptions.
  * @param topic An array (of length <i>count</i>) of pointers to
  * topics, each of which may include wildcards.
  * @param qos An array (of length <i>count</i>) of @ref qos
  * values. qos[n] is the requested QoS for topic[n].
  * @param response A pointer to a response options structure. Used to set callback functions.
  * @return ::MQTTASYNC_SUCCESS if the subscription request is successful.
  * An error code is returned if there was a problem registering the
  * subscriptions.
  */
LIBMQTT_API int MQTTAsync_subscribeMany(MQTTAsync handle, int count, char* const* topic, const int* qos, MQTTAsync_responseOptions* response);

/**
  * This function attempts to remove an existing subscription made by the
  * specified client.
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param topic The topic for the subscription to be removed, which may
  * include wildcards (see @ref wildcard).
  * @param response A pointer to a response options structure. Used to set callback functions.
  * @return ::MQTTASYNC_SUCCESS if the subscription is removed.
  * An error code is returned if there was a problem removing the
  * subscription.
  */
LIBMQTT_API int MQTTAsync_unsubscribe(MQTTAsync handle, const char* topic, MQTTAsync_responseOptions* response);

/**
  * This function attempts to remove existing subscriptions to a list of topics
  * made by the specified client.
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param count The number subscriptions to be removed.
  * @param topic An array (of length <i>count</i>) of pointers to the topics of
  * the subscriptions to be removed, each of which may include wildcards.
  * @param response A pointer to a response options structure. Used to set callback functions.
  * @return ::MQTTASYNC_SUCCESS if the subscriptions are removed.
  * An error code is returned if there was a problem removing the subscriptions.
  */
LIBMQTT_API int MQTTAsync_unsubscribeMany(MQTTAsync handle, int count, char* const* topic, MQTTAsync_responseOptions* response);


/**
  * 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()).
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param destinationName The topic associated with this message.
  * @param payloadlen The length of the payload in bytes.
  * @param payload A pointer to the byte array payload of the message.
  * @param qos The @ref qos of the message.
  * @param retained The retained flag for the message.
  * @param response A pointer to an ::MQTTAsync_responseOptions structure. Used to set callback functions.
  * This is optional and can be set to NULL.
  * @return ::MQTTASYNC_SUCCESS if the message is accepted for publication.
  * An error code is returned if there was a problem accepting the message.
  */
LIBMQTT_API int MQTTAsync_send(MQTTAsync handle, const char* destinationName, int payloadlen, const void* payload, int qos,
		int retained, MQTTAsync_responseOptions* response);

/**
  * 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()).
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param destinationName The topic associated with this message.
  * @param msg A pointer to a valid MQTTAsync_message structure containing
  * the payload and attributes of the message to be published.
  * @param response A pointer to an ::MQTTAsync_responseOptions structure. Used to set callback functions.
  * @return ::MQTTASYNC_SUCCESS if the message is accepted for publication.
  * An error code is returned if there was a problem accepting the message.
  */
LIBMQTT_API int MQTTAsync_sendMessage(MQTTAsync handle, const char* destinationName, const MQTTAsync_message* msg, MQTTAsync_responseOptions* response);


/**
  * This function sets a pointer to an array of tokens for
  * messages that are currently in-flight (pending completion).
  *
  * <b>Important note:</b> 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.
  * @param handle A valid client handle from a successful call to
  * MQTTAsync_create().
  * @param 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.
  * @return ::MQTTASYNC_SUCCESS if the function returns successfully.
  * An error code is returned if there was a problem obtaining the list of
  * pending tokens.
  */
LIBMQTT_API int MQTTAsync_getPendingTokens(MQTTAsync handle, MQTTAsync_token **tokens);

/**
 * Tests whether a request corresponding to a token is complete.
 *
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @param token An ::MQTTAsync_token associated with a request.
 * @return 1 if the request has been completed, 0 if not.
 */
#define MQTTASYNC_TRUE 1
LIBMQTT_API int MQTTAsync_isComplete(MQTTAsync handle, MQTTAsync_token token);


/**
 * 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.
 *
 * @param handle A valid client handle from a successful call to
 * MQTTAsync_create().
 * @param token An ::MQTTAsync_token associated with a request.
 * @param timeout the maximum time to wait for completion, in milliseconds
 * @return ::MQTTASYNC_SUCCESS if the request has been completed in the time allocated,
 *  ::MQTTASYNC_FAILURE or ::MQTTASYNC_DISCONNECTED if not.
 */
LIBMQTT_API int MQTTAsync_waitForCompletion(MQTTAsync handle, MQTTAsync_token token, unsigned long timeout);


/**
  * 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. <b>Important
  * note:</b> 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.
  * @param msg The address of a pointer to the ::MQTTAsync_message structure
  * to be freed.
  */
LIBMQTT_API void MQTTAsync_freeMessage(MQTTAsync_message** msg);

/**
  * 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.
  * @param ptr The pointer to the client library storage to be freed.
  */
LIBMQTT_API void MQTTAsync_free(void* ptr);

/**
  * 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.
  * @param size The size of the memory to be allocated.
  */
LIBMQTT_API void* MQTTAsync_malloc(size_t size);

/**
  * This function frees the memory allocated to an MQTT client (see
  * MQTTAsync_create()). It should be called when the client is no longer
  * required.
  * @param handle A pointer to the handle referring to the ::MQTTAsync
  * structure to be freed.
  */
LIBMQTT_API void MQTTAsync_destroy(MQTTAsync* handle);



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,
};


/**
  * This function sets the level of trace information which will be
  * returned in the trace callback.
  * @param level the trace level required
  */
LIBMQTT_API void MQTTAsync_setTraceLevel(enum MQTTASYNC_TRACE_LEVELS level);


/**
  * 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.
  * @param level the trace level of the message returned
  * @param 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.
  */
typedef void MQTTAsync_traceCallback(enum MQTTASYNC_TRACE_LEVELS level, char* message);

/**
  * 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.
  * @param callback a pointer to the function which will handle the trace information
  */
LIBMQTT_API void MQTTAsync_setTraceCallback(MQTTAsync_traceCallback* callback);

/**
  * This function returns version information about the library.
  * no trace information will be returned.  The default trace level is
  * MQTTASYNC_TRACE_MINIMUM
  * @return an array of strings describing the library.  The last entry is a NULL pointer.
  */
LIBMQTT_API MQTTAsync_nameValue* MQTTAsync_getVersionInfo(void);

/**
 * 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.
 * @param code the MQTTASYNC_ return code.
 * @return a static string representation of the error code.
 */
LIBMQTT_API const char* MQTTAsync_strerror(int code);


/*!
  * @cond MQTTAsync_main
  * @page async Threading
  * The client application runs on several threads.
  * Processing of handshaking and maintaining
  * the network connection is performed in the background.
  * This API is thread safe: functions may be called by multiple application
  * threads.
  * Notifications of status and message reception are provided to the client
  * application using callbacks registered with the library by the call to
  * MQTTAsync_setCallbacks() (see MQTTAsync_messageArrived(),
  * MQTTAsync_connectionLost() and MQTTAsync_deliveryComplete()).
  * In addition, some functions allow success and failure callbacks to be set
  * for individual requests, in the ::MQTTAsync_responseOptions structure.  Applications
  * can be written as a chain of callback functions.
  *
  * @page callbacks Callbacks
  * Any function from this API may be used within a callback.  It is not advisable to
  * use ::MQTTAsync_waitForCompletion within a callback, however, as it is the only
  * API call that may take some time to complete, which may cause unpredictable
  * behaviour.  All the other API calls are intended to complete quickly, starting
  * a request in the background, with success or failure notified by other callbacks.
  *
  * If no callbacks are assigned, this will include the message arrived callback.
  * This could be done if the application is a pure publisher, and does
  * not subscribe to any topics.  If however messages are received, and no message
  * arrived callback is set, then those messages will accumulate
  * and take up memory, as there is no place for them to be delivered.
  * A log message will be written to highlight the issue, but it is up
  * to the application to protect against this situation.
  *
  * @page auto_reconnect Automatic Reconnect
  * The ability for the client library to reconnect automatically in the event
  * of a connection failure was added in 1.1.  The connection lost callback
  * allows a flexible response to the loss of a connection, so almost any
  * behaviour can be implemented in that way.  Automatic reconnect does have the
  * advantage of being a little simpler to use.
  *
  * To switch on automatic reconnect, the connect options field
  * automaticReconnect should be set to non-zero.  The minimum and maximum times
  * before the next connection attempt can also be set, the defaults being 1 and
  * 60 seconds.  At each failure to reconnect, the retry interval is doubled until
  * the maximum value is reached, and there it stays until the connection is
  * successfully re-established whereupon it is reset.
  *
  * When a reconnection attempt is successful, the ::MQTTAsync_connected callback
  * function is invoked, if set by calling ::MQTTAsync_setConnected.  This allows
  * the application to take any actions needed, such as amending subscriptions.
  *
  * @page offline_publish Publish While Disconnected
  * This feature was not originally available because with persistence enabled,
  * messages could be stored locally without ever knowing if they could be sent.
  * The client application could have created the client with an erroneous broker
  * address or port for instance.
  *
  * To enable messages to be published when the application is disconnected
  * ::MQTTAsync_createWithOptions must be used instead of ::MQTTAsync_create to
  * create the client object.  The ::MQTTAsync_createOptions field sendWhileDisconnected
  * must be set to non-zero, and the maxBufferedMessages field set as required -
  * the default being 100.
  *
  * ::MQTTAsync_getPendingTokens can be called to return the ids of the messages
  * waiting to be sent, or for which the sending process has not completed.
  *
  * @page wildcard Subscription wildcards
  * Every MQTT message includes a topic that classifies it. MQTT servers use
  * topics to determine which subscribers should receive messages published to
  * the server.
  *
  * Consider the server receiving messages from several environmental sensors.
  * Each sensor publishes its measurement data as a message with an associated
  * topic. Subscribing applications need to know which sensor originally
  * published each received message. A unique topic is thus used to identify
  * each sensor and measurement type. Topics such as SENSOR1TEMP,
  * SENSOR1HUMIDITY, SENSOR2TEMP and so on achieve this but are not very
  * flexible. If additional sensors are added to the system at a later date,
  * subscribing applications must be modified to receive them.
  *
  * To provide more flexibility, MQTT supports a hierarchical topic namespace.
  * This allows application designers to organize topics to simplify their
  * management. Levels in the hierarchy are delimited by the '/' character,
  * such as SENSOR/1/HUMIDITY. Publishers and subscribers use these
  * hierarchical topics as already described.
  *
  * For subscriptions, two wildcard characters are supported:
  * <ul>
  * <li>A '#' character represents a complete sub-tree of the hierarchy and
  * thus must be the last character in a subscription topic string, such as
  * SENSOR/#. This will match any topic starting with SENSOR/, such as
  * SENSOR/1/TEMP and SENSOR/2/HUMIDITY.</li>
  * <li> A '+' character represents a single level of the hierarchy and is
  * used between delimiters. For example, SENSOR/+/TEMP will match
  * SENSOR/1/TEMP and SENSOR/2/TEMP.</li>
  * </ul>
  * Publishers are not allowed to use the wildcard characters in their topic
  * names.
  *
  * Deciding on your topic hierarchy is an important step in your system design.
  *
  * @page qos Quality of service
  * The MQTT protocol provides three qualities of service for delivering
  * messages between clients and servers: "at most once", "at least once" and
  * "exactly once".
  *
  * Quality of service (QoS) is an attribute of an individual message being
  * published. An application sets the QoS for a specific message by setting the
  * MQTTAsync_message.qos field to the required value.
  *
  * A subscribing client can set the maximum quality of service a server uses
  * to send messages that match the client subscriptions. The
  * MQTTAsync_subscribe() and MQTTAsync_subscribeMany() functions set this
  * maximum. The QoS of a message forwarded to a subscriber thus might be
  * different to the QoS given to the message by the original publisher.
  * The lower of the two values is used to forward a message.
  *
  * The three levels are:
  *
  * <b>QoS0, At most once:</b> The message is delivered at most once, or it
  * may not be delivered at all. Its delivery across the network is not
  * acknowledged. The message is not stored. The message could be lost if the
  * client is disconnected, or if the server fails. QoS0 is the fastest mode of
  * transfer. It is sometimes called "fire and forget".
  *
  * The MQTT protocol does not require servers to forward publications at QoS0
  * to a client. If the client is disconnected at the time the server receives
  * the publication, the publication might be discarded, depending on the
  * server implementation.
  *
  * <b>QoS1, At least once:</b> The message is always delivered at least once.
  * It might be delivered multiple times if there is a failure before an
  * acknowledgment is received by the sender. The message must be stored
  * locally at the sender, until the sender receives confirmation that the
  * message has been published by the receiver. The message is stored in case
  * the message must be sent again.
  *
  * <b>QoS2, Exactly once:</b> The message is always delivered exactly once.
  * The message must be stored locally at the sender, until the sender receives
  * confirmation that the message has been published by the receiver. The
  * message is stored in case the message must be sent again. QoS2 is the
  * safest, but slowest mode of transfer. A more sophisticated handshaking
  * and acknowledgement sequence is used than for QoS1 to ensure no duplication
  * of messages occurs.
  * @page publish Publication example
@code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTAsync.h"

#if !defined(_WIN32)
#include <unistd.h>
#else
#include <windows.h>
#endif

#if defined(_WRS_KERNEL)
#include <OsWrapper.h>
#endif

#define ADDRESS     "tcp://mqtt.eclipseprojects.io:1883"
#define CLIENTID    "ExampleClientPub"
#define TOPIC       "MQTT Examples"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

int finished = 0;

void connlost(void *context, char *cause)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
	int rc;

	printf("\nConnection lost\n");
	printf("     cause: %s\n", cause);

	printf("Reconnecting\n");
	conn_opts.keepAliveInterval = 20;
	conn_opts.cleansession = 1;
	if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start connect, return code %d\n", rc);
 		finished = 1;
	}
}

void onDisconnectFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Disconnect failed\n");
	finished = 1;
}

void onDisconnect(void* context, MQTTAsync_successData* response)
{
	printf("Successful disconnection\n");
	finished = 1;
}

void onSendFailure(void* context, MQTTAsync_failureData* response)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_disconnectOptions opts = MQTTAsync_disconnectOptions_initializer;
	int rc;

	printf("Message send failed token %d error code %d\n", response->token, response->code);
	opts.onSuccess = onDisconnect;
	opts.onFailure = onDisconnectFailure;
	opts.context = client;
	if ((rc = MQTTAsync_disconnect(client, &opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start disconnect, return code %d\n", rc);
		exit(EXIT_FAILURE);
	}
}

void onSend(void* context, MQTTAsync_successData* response)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_disconnectOptions opts = MQTTAsync_disconnectOptions_initializer;
	int rc;

	printf("Message with token value %d delivery confirmed\n", response->token);
	opts.onSuccess = onDisconnect;
	opts.onFailure = onDisconnectFailure;
	opts.context = client;
	if ((rc = MQTTAsync_disconnect(client, &opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start disconnect, return code %d\n", rc);
		exit(EXIT_FAILURE);
	}
}


void onConnectFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Connect failed, rc %d\n", response ? response->code : 0);
	finished = 1;
}


void onConnect(void* context, MQTTAsync_successData* response)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
	MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
	int rc;

	printf("Successful connection\n");
	opts.onSuccess = onSend;
	opts.onFailure = onSendFailure;
	opts.context = client;
	pubmsg.payload = PAYLOAD;
	pubmsg.payloadlen = (int)strlen(PAYLOAD);
	pubmsg.qos = QOS;
	pubmsg.retained = 0;
	if ((rc = MQTTAsync_sendMessage(client, TOPIC, &pubmsg, &opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start sendMessage, return code %d\n", rc);
		exit(EXIT_FAILURE);
	}
}

int messageArrived(void* context, char* topicName, int topicLen, MQTTAsync_message* m)
{
	// not expecting any messages
	return 1;
}

int main(int argc, char* argv[])
{
	MQTTAsync client;
	MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
	int rc;

	if ((rc = MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to create client object, return code %d\n", rc);
		exit(EXIT_FAILURE);
	}

	if ((rc = MQTTAsync_setCallbacks(client, NULL, connlost, messageArrived, NULL)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to set callback, return code %d\n", rc);
		exit(EXIT_FAILURE);
	}

	conn_opts.keepAliveInterval = 20;
	conn_opts.cleansession = 1;
	conn_opts.onSuccess = onConnect;
	conn_opts.onFailure = onConnectFailure;
	conn_opts.context = client;
	if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start connect, return code %d\n", rc);
		exit(EXIT_FAILURE);
	}

	printf("Waiting for publication of %s\n"
         "on topic %s for client with ClientID: %s\n",
         PAYLOAD, TOPIC, CLIENTID);
	while (!finished)
		#if defined(_WIN32)
			Sleep(100);
		#else
			usleep(10000L);
		#endif

	MQTTAsync_destroy(&client);
 	return rc;
}

  * @endcode
  * @page subscribe Subscription example
@code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTAsync.h"

#if !defined(_WIN32)
#include <unistd.h>
#else
#include <windows.h>
#endif

#if defined(_WRS_KERNEL)
#include <OsWrapper.h>
#endif

#define ADDRESS     "tcp://mqtt.eclipseprojects.io:1883"
#define CLIENTID    "ExampleClientSub"
#define TOPIC       "MQTT Examples"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

int disc_finished = 0;
int subscribed = 0;
int finished = 0;

void connlost(void *context, char *cause)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
	int rc;

	printf("\nConnection lost\n");
	if (cause)
		printf("     cause: %s\n", cause);

	printf("Reconnecting\n");
	conn_opts.keepAliveInterval = 20;
	conn_opts.cleansession = 1;
	if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start connect, return code %d\n", rc);
		finished = 1;
	}
}


int msgarrvd(void *context, char *topicName, int topicLen, MQTTAsync_message *message)
{
    printf("Message arrived\n");
    printf("     topic: %s\n", topicName);
    printf("   message: %.*s\n", message->payloadlen, (char*)message->payload);
    MQTTAsync_freeMessage(&message);
    MQTTAsync_free(topicName);
    return 1;
}

void onDisconnectFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Disconnect failed, rc %d\n", response->code);
	disc_finished = 1;
}

void onDisconnect(void* context, MQTTAsync_successData* response)
{
	printf("Successful disconnection\n");
	disc_finished = 1;
}

void onSubscribe(void* context, MQTTAsync_successData* response)
{
	printf("Subscribe succeeded\n");
	subscribed = 1;
}

void onSubscribeFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Subscribe failed, rc %d\n", response->code);
	finished = 1;
}


void onConnectFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Connect failed, rc %d\n", response->code);
	finished = 1;
}


void onConnect(void* context, MQTTAsync_successData* response)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
	int rc;

	printf("Successful connection\n");

	printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
           "Press Q<Enter> to quit\n\n", TOPIC, CLIENTID, QOS);
	opts.onSuccess = onSubscribe;
	opts.onFailure = onSubscribeFailure;
	opts.context = client;
	if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start subscribe, return code %d\n", rc);
		finished = 1;
	}
}


int main(int argc, char* argv[])
{
	MQTTAsync client;
	MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
	MQTTAsync_disconnectOptions disc_opts = MQTTAsync_disconnectOptions_initializer;
	int rc;
	int ch;

	if ((rc = MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL))
			!= MQTTASYNC_SUCCESS)
	{
		printf("Failed to create client, return code %d\n", rc);
		rc = EXIT_FAILURE;
		goto exit;
	}

	if ((rc = MQTTAsync_setCallbacks(client, client, connlost, msgarrvd, NULL)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to set callbacks, return code %d\n", rc);
		rc = EXIT_FAILURE;
		goto destroy_exit;
	}

	conn_opts.keepAliveInterval = 20;
	conn_opts.cleansession = 1;
	conn_opts.onSuccess = onConnect;
	conn_opts.onFailure = onConnectFailure;
	conn_opts.context = client;
	if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start connect, return code %d\n", rc);
		rc = EXIT_FAILURE;
		goto destroy_exit;
	}

	while (!subscribed && !finished)
		#if defined(_WIN32)
			Sleep(100);
		#else
			usleep(10000L);
		#endif

	if (finished)
		goto exit;

	do
	{
		ch = getchar();
	} while (ch!='Q' && ch != 'q');

	disc_opts.onSuccess = onDisconnect;
	disc_opts.onFailure = onDisconnectFailure;
	if ((rc = MQTTAsync_disconnect(client, &disc_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start disconnect, return code %d\n", rc);
		rc = EXIT_FAILURE;
		goto destroy_exit;
	}
 	while (!disc_finished)
 	{
		#if defined(_WIN32)
			Sleep(100);
		#else
			usleep(10000L);
		#endif
 	}

destroy_exit:
	MQTTAsync_destroy(&client);
exit:
 	return rc;
}

  * @endcode
* @page tracing Tracing
  *
  * Runtime tracing can be controlled by environment variables or API calls.
  *
  * #### Environment variables
  *
  * Tracing is switched on by setting the MQTT_C_CLIENT_TRACE environment variable.
  * A value of ON, or stdout, prints to stdout, any other value is interpreted as a file name to use.
  *
  * The amount of trace detail is controlled with the MQTT_C_CLIENT_TRACE_LEVEL environment
  * variable - valid values are ERROR, PROTOCOL, MINIMUM, MEDIUM and MAXIMUM
  * (from least to most verbose).
  *
  * The variable MQTT_C_CLIENT_TRACE_MAX_LINES limits the number of lines of trace that are output
  * to a file.  Two files are used at most, when they are full, the last one is overwritten with the
  * new trace entries.  The default size is 1000 lines.
  *
  * #### Trace API calls
  *
  * MQTTAsync_traceCallback() is used to set a callback function which is called whenever trace
  * information is available.  This will be the same information as that printed if the
  * environment variables were used to control the trace.
  *
  * The MQTTAsync_setTraceLevel() calls is used to set the maximum level of trace entries that will be
  * passed to the callback function.  The levels are:
  * 1. ::MQTTASYNC_TRACE_MAXIMUM
  * 2. ::MQTTASYNC_TRACE_MEDIUM
  * 3. ::MQTTASYNC_TRACE_MINIMUM
  * 4. ::MQTTASYNC_TRACE_PROTOCOL
  * 5. ::MQTTASYNC_TRACE_ERROR
  * 6. ::MQTTASYNC_TRACE_SEVERE
  * 7. ::MQTTASYNC_TRACE_FATAL
  *
  * Selecting ::MQTTASYNC_TRACE_MAXIMUM will cause all trace entries at all levels to be returned.
  * Choosing ::MQTTASYNC_TRACE_ERROR will cause ERROR, SEVERE and FATAL trace entries to be returned
  * to the callback function.
  *
  * ### MQTT Packet Tracing
  *
  * A feature that can be very useful is printing the MQTT packets that are sent and received.  To
  * achieve this, use the following environment variable settings:
  * @code
    MQTT_C_CLIENT_TRACE=ON
    MQTT_C_CLIENT_TRACE_LEVEL=PROTOCOL
  * @endcode
  * The output you should see looks like this:
  * @code
    20130528 155936.813 3 stdout-subscriber -> CONNECT cleansession: 1 (0)
    20130528 155936.813 3 stdout-subscriber <- CONNACK rc: 0
    20130528 155936.813 3 stdout-subscriber -> SUBSCRIBE msgid: 1 (0)
    20130528 155936.813 3 stdout-subscriber <- SUBACK msgid: 1
    20130528 155941.818 3 stdout-subscriber -> DISCONNECT (0)
  * @endcode
  * where the fields are:
  * 1. date
  * 2. time
  * 3. socket number
  * 4. client id
  * 5. direction (-> from client to server, <- from server to client)
  * 6. packet details
  *
  * ### Default Level Tracing
  *
  * This is an extract of a default level trace of a call to connect:
  * @code
    19700101 010000.000 (1152206656) (0)> MQTTClient_connect:893
    19700101 010000.000 (1152206656)  (1)> MQTTClient_connectURI:716
    20130528 160447.479 Connecting to serverURI localhost:1883
    20130528 160447.479 (1152206656)   (2)> MQTTProtocol_connect:98
    20130528 160447.479 (1152206656)    (3)> MQTTProtocol_addressPort:48
    20130528 160447.479 (1152206656)    (3)< MQTTProtocol_addressPort:73
    20130528 160447.479 (1152206656)    (3)> Socket_new:599
    20130528 160447.479 New socket 4 for localhost, port 1883
    20130528 160447.479 (1152206656)     (4)> Socket_addSocket:163
    20130528 160447.479 (1152206656)      (5)> Socket_setnonblocking:73
    20130528 160447.479 (1152206656)      (5)< Socket_setnonblocking:78 (0)
    20130528 160447.479 (1152206656)     (4)< Socket_addSocket:176 (0)
    20130528 160447.479 (1152206656)     (4)> Socket_error:95
    20130528 160447.479 (1152206656)     (4)< Socket_error:104 (115)
    20130528 160447.479 Connect pending
    20130528 160447.479 (1152206656)    (3)< Socket_new:683 (115)
    20130528 160447.479 (1152206656)   (2)< MQTTProtocol_connect:131 (115)
  * @endcode
  * where the fields are:
  * 1. date
  * 2. time
  * 3. thread id
  * 4. function nesting level
  * 5. function entry (>) or exit (<)
  * 6. function name : line of source code file
  * 7. return value (if there is one)
  *
  * ### Memory Allocation Tracing
  *
  * Setting the trace level to maximum causes memory allocations and frees to be traced along with
  * the default trace entries, with messages like the following:
  * @code
    20130528 161819.657 Allocating 16 bytes in heap at file /home/icraggs/workspaces/mqrtc/mqttv3c/src/MQTTPacket.c line 177 ptr 0x179f930

    20130528 161819.657 Freeing 16 bytes in heap at file /home/icraggs/workspaces/mqrtc/mqttv3c/src/MQTTPacket.c line 201, heap use now 896 bytes
  * @endcode
  * When the last MQTT client object is destroyed, if the trace is being recorded
  * and all memory allocated by the client library has not been freed, an error message will be
  * written to the trace.  This can help with fixing memory leaks.  The message will look like this:
  * @code
    20130528 163909.208 Some memory not freed at shutdown, possible memory leak
    20130528 163909.208 Heap scan start, total 880 bytes
    20130528 163909.208 Heap element size 32, line 354, file /home/icraggs/workspaces/mqrtc/mqttv3c/src/MQTTPacket.c, ptr 0x260cb00
    20130528 163909.208   Content
    20130528 163909.209 Heap scan end
  * @endcode
  * @endcond
  */

#if defined(__cplusplus)
     }
#endif

#endif