/*******************************************************************************
* Copyright (c) 2009, 2014 IBM Corp.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* and Eclipse Distribution License v1.0 which accompany this distribution.
*
* The Eclipse Public License is available at
* http://www.eclipse.org/legal/epl-v10.html
* 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
*******************************************************************************/
/********************************************************************/
/**
* @cond MQTTAsync_main
* @mainpage Asynchronous MQTT client library for C
*
* © Copyright IBM Corp. 2009, 2014
*
* @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.
*
* Using the client
* Applications that use the client library typically use a similar structure:
*
* - Create a client object
* - Set the options to connect to an MQTT server
* - Set up callback functions
* - Connect the client to an MQTT server
* - Subscribe to any topics the client needs to receive
* - Repeat until finished:
*
* - Publish any messages the client needs to
* - Handle any incoming messages
*
* - Disconnect the client
* - Free any memory being used by the client
*
* Some simple examples are shown here:
*
* - @ref publish
* - @ref subscribe
*
* Additional information about important concepts is provided here:
*
* - @ref async
* - @ref wildcard
* - @ref qos
* - @ref tracing
*
* @endcond
*/
/// @cond EXCLUDE
#if defined(__cplusplus)
extern "C" {
#endif
#if !defined(MQTTASYNC_H)
#define MQTTASYNC_H
#if defined(WIN32) || defined(WIN64)
#define DLLImport __declspec(dllimport)
#define DLLExport __declspec(dllexport)
#else
#define DLLImport extern
#define DLLExport __attribute__ ((visibility ("default")))
#endif
#include
/// @endcond
#if !defined(NO_PERSISTENCE)
#include "MQTTClientPersistence.h"
#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
/**
* 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
/**
* Bad return code from subscribe, as defined in the 3.1.1 specification
*/
#define MQTT_BAD_SUBSCRIBE 0x80
/**
* 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 */
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:
*
* - QoS0
* - Fire and forget - the message may not be delivered
* - QoS1
* - At least once - the message will be delivered, but may be
* delivered more than once in some circumstances.
* - QoS2
* - Once and one only - the message will be delivered exactly once.
*
*/
int qos;
/**
* The retained flag serves two purposes depending on whether the message
* it is associated with is being published or received.
*
* retained = true
* 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.
*
* retained = false
* For publishers, this ndicates 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.
*/
int dup;
/** The message identifier is normally reserved for internal use by the
* MQTT client and server.
*/
int msgid;
} MQTTAsync_message;
#define MQTTAsync_message_initializer { {'M', 'Q', 'T', 'M'}, 0, 0, NULL, 0, 0, 0, 0 }
/**
* 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.
* @param context A pointer to the context 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 topicName, otherwise topicLen
* is 0. If topicLen is 0, the value returned by strlen(topicName)
* can be trusted. If topicLen is greater than 0, the full topic name
* can be retrieved by accessing topicName as a byte array of length
* topicLen.
* @param message The MQTTAsync_message structure for the received message.
* This structure contains the message payload and attributes.
* @return This function must return a boolean value indicating whether or not
* the message has been safely received by the client application. Returning
* true indicates that the message has been successfully handled.
* Returning false 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.
*/
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.
* @param context A pointer to the context 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.
* @param context A pointer to the context value originally passed to
* MQTTAsync_setCallbacks(), which contains any application-specific context.
* @param cause The reason for the disconnection.
* Currently, cause is always set to NULL.
*/
typedef void MQTTAsync_connectionLost(void* context, char* cause);
/** 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. */
char* message;
} MQTTAsync_failureData;
/** 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. */
int qos;
/** For subscribeMany, 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;
char* destinationName;
} pub;
/* For connect, the server connected to, MQTT version used, and sessionPresent flag */
struct
{
char* serverURI;
int MQTTVersion;
int sessionPresent;
} connect;
} alt;
} MQTTAsync_successData;
/**
* 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.
* @param context A pointer to the context 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 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.
* @param context A pointer to the context value originally passed to
* ::MQTTAsync_responseOptions, which contains any application-specific context.
* @param response Any failure data associated with the API completion.
*/
typedef void MQTTAsync_onFailure(void* context, MQTTAsync_failureData* response);
typedef struct
{
/** The eyecatcher for this structure. Must be MQTR */
char struct_id[4];
/** The version number of this structure. Must be 0 */
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 context pointer is passed to success or failure callback functions to
* provide access to the context information in the callback.
*/
void* context;
MQTTAsync_token token; /* output */
} MQTTAsync_responseOptions;
#define MQTTAsync_responseOptions_initializer { {'M', 'Q', 'T', 'R'}, 0, NULL, NULL, 0, 0 }
/**
* This function sets the global callback functions for a specific client.
* If your client application doesn't use a particular callback, set the
* relevant parameter to NULL. Any necessary message acknowledgements and
* status communications are handled in the background without any intervention
* from the client application. If you do not set a messageArrived callback
* function, you will not be notified of the receipt of any messages as a
* result of a subscription.
*
* Note: The MQTT client must be disconnected when this function is
* called.
* @param handle A valid client handle from a successful call to
* MQTTAsync_create().
* @param context A pointer to any application-specific context. The
* the context pointer is passed to each of the callback functions to
* provide access to the context information in the callback.
* @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. You can set this to NULL if your application doesn't handle
* receipt of 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.
*/
DLLExport int MQTTAsync_setCallbacks(MQTTAsync handle, void* context, MQTTAsync_connectionLost* cl,
MQTTAsync_messageArrived* ma, MQTTAsync_deliveryComplete* dc);
/**
* 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 protocol://host:port.
* protocol must be tcp or ssl. For host, 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
* tcp://localhost:1883.
* @param clientId The client identifier passed to the server when the
* client connects to it. It is a null-terminated UTF-8 encoded string.
* ClientIDs must be no longer than 23 characters according to the MQTT
* specification.
* @param persistence_type The type of persistence to be used by the client:
*
* ::MQTTCLIENT_PERSISTENCE_NONE: Use in-memory persistence. If the device or
* system on which the client is running fails or is switched off, the current
* state of any in-flight messages is lost and some messages may not be
* delivered even at QoS1 and QoS2.
*
* ::MQTTCLIENT_PERSISTENCE_DEFAULT: Use the default (file system-based)
* persistence mechanism. Status about in-flight messages is held in persistent
* storage and provides some protection against message loss in the case of
* unexpected failure.
*
* ::MQTTCLIENT_PERSISTENCE_USER: Use an application-specific persistence
* implementation. Using this type of persistence gives control of the
* persistence mechanism to the application. The application has to implement
* the MQTTClient_persistence interface.
* @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.
*/
DLLExport int MQTTAsync_create(MQTTAsync* handle, const char* serverURI, const char* clientId,
int persistence_type, void* persistence_context);
/**
* 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. */
const char struct_id[4];
/** The version number of this structure. Must be 0 */
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;
} MQTTAsync_willOptions;
#define MQTTAsync_willOptions_initializer { {'M', 'Q', 'T', 'W'}, 0, NULL, NULL, 0, 0 }
/**
* 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 */
const char struct_id[4];
/** The version number of this structure. Must be 0 */
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;
} MQTTAsync_SSLOptions;
#define MQTTAsync_SSLOptions_initializer { {'M', 'Q', 'T', 'S'}, 0, NULL, NULL, NULL, NULL, NULL, 1 }
/**
* MQTTAsync_connectOptions defines several settings that control the way the
* client connects to an MQTT server. Default values are set in
* MQTTAsync_connectOptions_initializer.
*/
typedef struct
{
/** The eyecatcher for this structure. must be MQTC. */
const char struct_id[4];
/** The version number of this structure. Must be 0, 1 or 2.
* 0 signifies no SSL options and no serverURIs
* 1 signifies no serverURIs
* 2 signifies no MQTTVersion
*/
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
*/
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 context 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 protocol://host:port.
* protocol must be tcp or ssl. For host, 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
* tcp://localhost:1883.
*/
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;
} MQTTAsync_connectOptions;
#define MQTTAsync_connectOptions_initializer { {'M', 'Q', 'T', 'C'}, 3, 60, 1, 10, NULL, NULL, NULL, 30, 0, NULL, NULL, NULL, NULL, 0, NULL, 0}
/**
* 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:
* 1: Connection refused: Unacceptable protocol version
* 2: Connection refused: Identifier rejected
* 3: Connection refused: Server unavailable
* 4: Connection refused: Bad user name or password
* 5: Connection refused: Not authorized
* 6-255: Reserved for future use
*/
DLLExport int MQTTAsync_connect(MQTTAsync handle, const MQTTAsync_connectOptions* options);
typedef struct
{
/** The eyecatcher for this structure. Must be MQTD. */
const char struct_id[4];
/** The version number of this structure. Must be 0 or 1. 0 signifies no SSL options */
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 context pointer is passed to success or failure callback functions to
* provide access to the context information in the callback.
*/
void* context;
} MQTTAsync_disconnectOptions;
#define MQTTAsync_disconnectOptions_initializer { {'M', 'Q', 'T', 'D'}, 0, 0, NULL, 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
*/
DLLExport 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.
*/
DLLExport 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.
*/
DLLExport 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 count) of pointers to
* topics, each of which may include wildcards.
* @param qos An array (of length count) 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.
*/
DLLExport int MQTTAsync_subscribeMany(MQTTAsync handle, int count, char* const* topic, 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.
*/
DLLExport 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 count) 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.
*/
DLLExport 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 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.
*/
DLLExport int MQTTAsync_send(MQTTAsync handle, const char* destinationName, int payloadlen, 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 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.
*/
DLLExport 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).
*
* Important note: The memory used to hold the array of tokens is
* malloc()'d in this function. The client application is responsible for
* freeing this memory when it is no longer required.
* @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.
*/
DLLExport int MQTTAsync_getPendingTokens(MQTTAsync handle, MQTTAsync_token **tokens);
#define MQTTASYNC_TRUE 1
DLLExport int MQTTAsync_isComplete(MQTTAsync handle, MQTTAsync_token dt);
DLLExport int MQTTAsync_waitForCompletion(MQTTAsync handle, MQTTAsync_token dt, 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. Important
* note: This function does not free the memory allocated to a message
* topic string. It is the responsibility of the client application to free
* this memory using the MQTTAsync_free() library function.
* @param msg The address of a pointer to the ::MQTTAsync_message structure
* to be freed.
*/
DLLExport 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 libary and application
* program have been compiled with different versions of the C compiler. It is
* thus good policy to always use this function when freeing any MQTT C client-
* allocated memory.
* @param ptr The pointer to the client library storage to be freed.
*/
DLLExport void MQTTAsync_free(void* ptr);
/**
* 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.
*/
DLLExport 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
*/
DLLExport 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.
* @param level the trace level of the message returned
* @param meesage 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
*/
DLLExport void MQTTAsync_setTraceCallback(MQTTAsync_traceCallback* callback);
typedef struct
{
const char* name;
const char* value;
} MQTTAsync_nameValue;
/**
* 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.
*/
DLLExport MQTTAsync_nameValue* MQTTAsync_getVersionInfo();
/**
* @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.
* 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()).
*
* @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:
*
* - 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.
* - 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.
*
* 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:
*
* QoS0, At most once: 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.
*
* QoS1, At least once: 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.
*
* QoS2, Exactly once: 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"
#define ADDRESS "tcp://localhost:1883"
#define CLIENTID "ExampleClientPub"
#define TOPIC "MQTT Examples"
#define PAYLOAD "Hello World!"
#define QOS 1
#define TIMEOUT 10000L
volatile MQTTAsync_token deliveredtoken;
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 onDisconnect(void* context, MQTTAsync_successData* response)
{
printf("Successful disconnection\n");
finished = 1;
}
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.context = client;
if ((rc = MQTTAsync_disconnect(client, &opts)) != MQTTASYNC_SUCCESS)
{
printf("Failed to start sendMessage, return code %d\n", rc);
exit(-1);
}
}
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.context = client;
pubmsg.payload = PAYLOAD;
pubmsg.payloadlen = strlen(PAYLOAD);
pubmsg.qos = QOS;
pubmsg.retained = 0;
deliveredtoken = 0;
if ((rc = MQTTAsync_sendMessage(client, TOPIC, &pubmsg, &opts)) != MQTTASYNC_SUCCESS)
{
printf("Failed to start sendMessage, return code %d\n", rc);
exit(-1);
}
}
int main(int argc, char* argv[])
{
MQTTAsync client;
MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
MQTTAsync_token token;
int rc;
MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
MQTTAsync_setCallbacks(client, NULL, connlost, NULL, NULL);
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(-1);
}
printf("Waiting for publication of %s\n"
"on topic %s for client with ClientID: %s\n",
PAYLOAD, TOPIC, CLIENTID);
while (!finished)
#if defined(WIN32) || defined(WIN64)
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"
#define ADDRESS "tcp://localhost:1883"
#define CLIENTID "ExampleClientSub"
#define TOPIC "MQTT Examples"
#define PAYLOAD "Hello World!"
#define QOS 1
#define TIMEOUT 10000L
volatile MQTTAsync_token deliveredtoken;
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");
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)
{
int i;
char* payloadptr;
printf("Message arrived\n");
printf(" topic: %s\n", topicName);
printf(" message: ");
payloadptr = message->payload;
for(i=0; ipayloadlen; i++)
{
putchar(*payloadptr++);
}
putchar('\n');
MQTTAsync_freeMessage(&message);
MQTTAsync_free(topicName);
return 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 ? response->code : 0);
finished = 1;
}
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");
printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
"Press Q to quit\n\n", TOPIC, CLIENTID, QOS);
opts.onSuccess = onSubscribe;
opts.onFailure = onSubscribeFailure;
opts.context = client;
deliveredtoken = 0;
if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS)
{
printf("Failed to start subscribe, return code %d\n", rc);
exit(-1);
}
}
int main(int argc, char* argv[])
{
MQTTAsync client;
MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
MQTTAsync_disconnectOptions disc_opts = MQTTAsync_disconnectOptions_initializer;
MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
MQTTAsync_token token;
int rc;
int ch;
MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
MQTTAsync_setCallbacks(client, NULL, connlost, msgarrvd, NULL);
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(-1);
}
while (!subscribed)
#if defined(WIN32) || defined(WIN64)
Sleep(100);
#else
usleep(10000L);
#endif
if (finished)
goto exit;
do
{
ch = getchar();
} while (ch!='Q' && ch != 'q');
disc_opts.onSuccess = onDisconnect;
if ((rc = MQTTAsync_disconnect(client, &disc_opts)) != MQTTASYNC_SUCCESS)
{
printf("Failed to start disconnect, return code %d\n", rc);
exit(-1);
}
while (!disc_finished)
#if defined(WIN32) || defined(WIN64)
Sleep(100);
#else
usleep(10000L);
#endif
exit:
MQTTAsync_destroy(&client);
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
*/
#endif
#ifdef __cplusplus
}
#endif