/******************************************************************************* * 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 and/or initial documentation * Ian Craggs, Allan Stockdill-Mander - SSL updates * Ian Craggs - multiple server connection support * Ian Craggs - MQTT 3.1.1 support *******************************************************************************/ /** * @cond MQTTClient_internal * @mainpage MQTT Client Library Internals * In the beginning there was one MQTT C client library, MQTTClient, as implemented in MQTTClient.c * This library was designed to be easy to use for applications which didn't mind if some of the calls * blocked for a while. For instance, the MQTTClient_connect call will block until a successful * connection has completed, or a connection has failed, which could be as long as the "connection * timeout" interval, whose default is 30 seconds. * * However in mobile devices and other windowing environments, blocking on the GUI thread is a bad * thing as it causes the user interface to freeze. Hence a new API, MQTTAsync, implemented * in MQTTAsync.c, was devised. There are no blocking calls in this library, so it is well suited * to GUI and mobile environments, at the expense of some extra complexity. * * Both libraries are designed to be sparing in the use of threads. So multiple client objects are * handled by one or two threads, with a select call in Socket_getReadySocket(), used to determine * when a socket has incoming data. * * @endcond * @cond MQTTClient_main * @mainpage MQTT Client library for C * © Copyright IBM Corp. 2009, 2014 * * @brief An MQTT client library in C. * * These pages describe the original more synchronous API which might be * considered easier to use. Some of the calls will block. For the new * totally asynchronous API where no calls block, which is especially suitable * for use in windowed environments, see the * MQTT C Client Asynchronous API Documentation. * * 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 MQTT Client library for C. * * Using the client
* Applications that use the client library typically use a similar structure: * * Some simple examples are shown here: * * Additional information about important concepts is provided here: * * @endcond */ /// @cond EXCLUDE #if defined(__cplusplus) extern "C" { #endif #if !defined(MQTTCLIENT_H) #define MQTTCLIENT_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 MQTTCLIENT_SUCCESS 0 /** * Return code: A generic error code indicating the failure of an MQTT client * operation. */ #define MQTTCLIENT_FAILURE -1 /* error code -2 is MQTTCLIENT_PERSISTENCE_ERROR */ /** * Return code: The client is disconnected. */ #define MQTTCLIENT_DISCONNECTED -3 /** * Return code: The maximum number of messages allowed to be simultaneously * in-flight has been reached. */ #define MQTTCLIENT_MAX_MESSAGES_INFLIGHT -4 /** * Return code: An invalid UTF-8 string has been detected. */ #define MQTTCLIENT_BAD_UTF8_STRING -5 /** * Return code: A NULL parameter has been supplied when this is invalid. */ #define MQTTCLIENT_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 MQTTCLIENT_TOPICNAME_TRUNCATED -7 /** * Return code: A structure parameter does not have the correct eyecatcher * and version number. */ #define MQTTCLIENT_BAD_STRUCTURE -8 /** * Return code: A QoS value that falls outside of the acceptable range (0,1,2) */ #define MQTTCLIENT_BAD_QOS -9 /** * 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 MQTTClient_create(). */ typedef void* MQTTClient; /** * A value representing an MQTT message. A delivery token is returned to the * client application when a message is published. The token can then be used to * check that the message was successfully delivered to its destination (see * MQTTClient_publish(), * MQTTClient_publishMessage(), * MQTTClient_deliveryComplete(), * MQTTClient_waitForCompletion() and * MQTTClient_getPendingDeliveryTokens()). */ typedef int MQTTClient_deliveryToken; typedef int MQTTClient_token; /** * A structure representing the payload and attributes of an MQTT message. The * message topic is not part of this structure (see MQTTClient_publishMessage(), * MQTTClient_publish(), MQTTClient_receive(), MQTTClient_freeMessage() * and MQTTClient_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; } MQTTClient_message; #define MQTTClient_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 MQTTClient_setCallbacks(). It is * called by the client library when a new message that matches a client * subscription has been received from the server. This function is executed on * a separate thread to the one on which the client application is running. * @param context A pointer to the context value originally passed to * MQTTClient_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 MQTTClient_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 MQTTClient_messageArrived() to * attempt to deliver the message to the application again. */ typedef int MQTTClient_messageArrived(void* context, char* topicName, int topicLen, MQTTClient_message* message); /** * This is a callback function. The client application * must provide an implementation of this function to enable asynchronous * notification of delivery of messages. The function is registered with the * client library by passing it as an argument to MQTTClient_setCallbacks(). * It is called by the client library after the client application has * published a message to the server. It indicates that the necessary * handshaking and acknowledgements for the requested quality of service (see * MQTTClient_message.qos) have been completed. This function is executed on a * separate thread to the one on which the client application is running. * Note:MQTTClient_deliveryComplete() is not called when messages are * published at QoS0. * @param context A pointer to the context value originally passed to * MQTTClient_setCallbacks(), which contains any application-specific context. * @param dt The ::MQTTClient_deliveryToken associated with * the published message. Applications can check that all messages have been * correctly published by matching the delivery tokens returned from calls to * MQTTClient_publish() and MQTTClient_publishMessage() with the tokens passed * to this callback. */ typedef void MQTTClient_deliveryComplete(void* context, MQTTClient_deliveryToken dt); /** * This is a callback function. The client application * must provide an implementation of this function to enable asynchronous * notification of the loss of connection to the server. The function is * registered with the client library by passing it as an argument to * MQTTClient_setCallbacks(). It is called by the client library if the client * loses its connection to the server. The client application must take * appropriate action, such as trying to reconnect or reporting the problem. * This function is executed on a separate thread to the one on which the * client application is running. * @param context A pointer to the context value originally passed to * MQTTClient_setCallbacks(), which contains any application-specific context. * @param cause The reason for the disconnection. * Currently, cause is always set to NULL. */ typedef void MQTTClient_connectionLost(void* context, char* cause); /** * This function sets the callback functions for a specific client. * If your client application doesn't use a particular callback, set the * relevant parameter to NULL. Calling MQTTClient_setCallbacks() puts the * client into multi-threaded mode. Any necessary message acknowledgements and * status communications are handled in the background without any intervention * from the client application. See @ref async for more information. * * Note: The MQTT client must be disconnected when this function is * called. * @param handle A valid client handle from a successful call to * MQTTClient_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 MQTTClient_connectionLost() callback * function. You can set this to NULL if your application doesn't handle * disconnections. * @param ma A pointer to an MQTTClient_messageArrived() callback * function. This callback function must be specified when you call * MQTTClient_setCallbacks(). * @param dc A pointer to an MQTTClient_deliveryComplete() callback * function. You can set this to NULL if your application publishes * synchronously or if you do not want to check for successful delivery. * @return ::MQTTCLIENT_SUCCESS if the callbacks were correctly set, * ::MQTTCLIENT_FAILURE if an error occurred. */ DLLExport int MQTTClient_setCallbacks(MQTTClient handle, void* context, MQTTClient_connectionLost* cl, MQTTClient_messageArrived* ma, MQTTClient_deliveryComplete* dc); /** * This function creates an MQTT client ready for connection to the * specified server and using the specified persistent storage (see * MQTTClient_persistence). See also MQTTClient_destroy(). * @param handle A pointer to an ::MQTTClient 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. * Currently, protocol must be tcp. 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 ::MQTTCLIENT_SUCCESS if the client is successfully created, otherwise * an error code is returned. */ DLLExport int MQTTClient_create(MQTTClient* handle, const char* serverURI, const char* clientId, int persistence_type, void* persistence_context); /** * MQTTClient_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 MQTTClient_willOptions * structure is passed in the MQTTClient_connectOptions structure used in the * MQTTClient_connect() call that connects the client to the server. The pointer * to MQTTClient_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 MQTTClient_message.retained). */ int retained; /** * The quality of service setting for the LWT message (see * MQTTClient_message.qos and @ref qos). */ int qos; } MQTTClient_willOptions; #define MQTTClient_willOptions_initializer { {'M', 'Q', 'T', 'W'}, 0, NULL, NULL, 0, 0 } /** * MQTTClient_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; } MQTTClient_SSLOptions; #define MQTTClient_SSLOptions_initializer { {'M', 'Q', 'T', 'S'}, 0, NULL, NULL, NULL, NULL, NULL, 1 } /** * MQTTClient_connectOptions defines several settings that control the way the * client connects to an MQTT server. * * Note: Default values are not defined for members of * MQTTClient_connectOptions so it is good practice to specify all settings. * If the MQTTClient_connectOptions structure is defined as an automatic * variable, all members are set to random values and thus must be set by the * client application. If the MQTTClient_connectOptions structure is defined * as a static variable, initialization (in compliant compilers) sets all * values to 0 (NULL for pointers). A #keepAliveInterval setting of 0 prevents * correct operation of the client and so you must at least set a value * for #keepAliveInterval. */ 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, 2, 3 or 4. * 0 signifies no SSL options and no serverURIs * 1 signifies no serverURIs * 2 signifies no MQTTVersion * 3 signifies no returned values */ 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. */ 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 * MQTTClient_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 is a boolean value that controls how many messages can be in-flight * simultaneously. Setting reliable to true means that a published * message must be completed (acknowledgements received) before another * can be sent. Attempts to publish additional messages receive an * ::MQTTCLIENT_MAX_MESSAGES_INFLIGHT return code. Setting this flag to * false allows up to 10 messages to be in-flight. This can increase * overall throughput in some circumstances. */ int reliable; /** * This is a pointer to an MQTTClient_willOptions structure. If your * application does not make use of the Last Will and Testament feature, * set this pointer to NULL. */ MQTTClient_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 MQTTClient_SSLOptions structure. If your * application does not make use of SSL, set this pointer to NULL. */ MQTTClient_SSLOptions* ssl; /** * The number of entries in the optional serverURIs array. Defaults to 0. */ int serverURIcount; /** * An optional 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 host name. For instance, to connect to * a server running on the local machines with the default MQTT port, specify * tcp://localhost:1883. * If this list is empty (the default), the server URI specified on MQTTClient_create() * is used. */ 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; /** * Returned from the connect when the MQTT version used to connect is 3.1.1 */ struct { const char* serverURI; /**< the serverURI connected to */ int MQTTVersion; /**< the MQTT version used to connect with */ int sessionPresent; /**< if the MQTT version is 3.1.1, the value of sessionPresent returned in the connack */ } returned; } MQTTClient_connectOptions; #define MQTTClient_connectOptions_initializer { {'M', 'Q', 'T', 'C'}, 4, 60, 1, 1, NULL, NULL, NULL, 30, 20, NULL, 0, NULL, 0} /** * MQTTClient_libraryInfo is used to store details relating to the currently used * library such as the version in use, the time it was built and relevant openSSL * options. * There is one static instance of this struct in MQTTClient.c */ typedef struct { const char* name; const char* value; } MQTTClient_nameValue; /** * This function returns version information about the library. * no trace information will be returned. * @return an array of strings describing the library. The last entry is a NULL pointer. */ DLLExport MQTTClient_nameValue* MQTTClient_getVersionInfo(void); /** * This function attempts to connect a previously-created client (see * MQTTClient_create()) to an MQTT server using the specified options. If you * want to enable asynchronous message and status notifications, you must call * MQTTClient_setCallbacks() prior to MQTTClient_connect(). * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param options A pointer to a valid MQTTClient_connectOptions * structure. * @return ::MQTTCLIENT_SUCCESS if the client successfully connects to the * server. An error code is returned if the client was unable to connect to * the server. * Error codes greater than 0 are returned by the MQTT protocol:

* 1: Connection refused: Unacceptable protocol version
* 2: Connection refused: Identifier rejected
* 3: Connection refused: Server unavailable
* 4: Connection refused: Bad user name or password
* 5: Connection refused: Not authorized
* 6-255: Reserved for future use
*/ DLLExport int MQTTClient_connect(MQTTClient handle, MQTTClient_connectOptions* options); /** * This function attempts to disconnect the client from the MQTT * server. In order to allow the client time to complete handling of messages * that are in-flight when this function is called, a timeout period is * specified. When the timeout period has expired, the client disconnects even * if there are still outstanding message acknowledgements. * The next time the client connects to the same server, any QoS 1 or 2 * messages which have not completed will be retried depending on the * cleansession settings for both the previous and the new connection (see * MQTTClient_connectOptions.cleansession and MQTTClient_connect()). * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param timeout The client delays disconnection for up to this time (in * milliseconds) in order to allow in-flight message transfers to complete. * @return ::MQTTCLIENT_SUCCESS if the client successfully disconnects from * the server. An error code is returned if the client was unable to disconnect * from the server */ DLLExport int MQTTClient_disconnect(MQTTClient handle, int timeout); /** * 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 * MQTTClient_create(). * @return Boolean true if the client is connected, otherwise false. */ DLLExport int MQTTClient_isConnected(MQTTClient handle); /* Subscribe is synchronous. QoS list parameter is changed on return to granted QoSs. Returns return code, MQTTCLIENT_SUCCESS == success, non-zero some sort of error (TBD) */ /** * 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 MQTTClient_subscribeMany()). * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param topic The subscription topic, which may include wildcards. * @param qos The requested quality of service for the subscription. * @return ::MQTTCLIENT_SUCCESS if the subscription request is successful. * An error code is returned if there was a problem registering the * subscription. */ DLLExport int MQTTClient_subscribe(MQTTClient handle, const char* topic, int qos); /** * 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 MQTTClient_subscribe()). * @param handle A valid client handle from a successful call to * MQTTClient_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]. * @return ::MQTTCLIENT_SUCCESS if the subscription request is successful. * An error code is returned if there was a problem registering the * subscriptions. */ DLLExport int MQTTClient_subscribeMany(MQTTClient handle, int count, char* const* topic, int* qos); /** * This function attempts to remove an existing subscription made by the * specified client. * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param topic The topic for the subscription to be removed, which may * include wildcards (see @ref wildcard). * @return ::MQTTCLIENT_SUCCESS if the subscription is removed. * An error code is returned if there was a problem removing the * subscription. */ DLLExport int MQTTClient_unsubscribe(MQTTClient handle, const char* topic); /** * 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 * MQTTClient_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. * @return ::MQTTCLIENT_SUCCESS if the subscriptions are removed. * An error code is returned if there was a problem removing the subscriptions. */ DLLExport int MQTTClient_unsubscribeMany(MQTTClient handle, int count, char* const* topic); /** * This function attempts to publish a message to a given topic (see also * MQTTClient_publishMessage()). An ::MQTTClient_deliveryToken is issued when * this function returns successfully. If the client application needs to * test for succesful delivery of QoS1 and QoS2 messages, this can be done * either asynchronously or synchronously (see @ref async, * ::MQTTClient_waitForCompletion and MQTTClient_deliveryComplete()). * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param topicName 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 dt A pointer to an ::MQTTClient_deliveryToken. This is populated * with a token representing the message when the function returns * successfully. If your application does not use delivery tokens, set this * argument to NULL. * @return ::MQTTCLIENT_SUCCESS if the message is accepted for publication. * An error code is returned if there was a problem accepting the message. */ DLLExport int MQTTClient_publish(MQTTClient handle, const char* topicName, int payloadlen, void* payload, int qos, int retained, MQTTClient_deliveryToken* dt); /** * This function attempts to publish a message to a given topic (see also * MQTTClient_publish()). An ::MQTTClient_deliveryToken is issued when * this function returns successfully. If the client application needs to * test for succesful delivery of QoS1 and QoS2 messages, this can be done * either asynchronously or synchronously (see @ref async, * ::MQTTClient_waitForCompletion and MQTTClient_deliveryComplete()). * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param topicName The topic associated with this message. * @param msg A pointer to a valid MQTTClient_message structure containing * the payload and attributes of the message to be published. * @param dt A pointer to an ::MQTTClient_deliveryToken. This is populated * with a token representing the message when the function returns * successfully. If your application does not use delivery tokens, set this * argument to NULL. * @return ::MQTTCLIENT_SUCCESS if the message is accepted for publication. * An error code is returned if there was a problem accepting the message. */ DLLExport int MQTTClient_publishMessage(MQTTClient handle, const char* topicName, MQTTClient_message* msg, MQTTClient_deliveryToken* dt); /** * This function is called by the client application to synchronize execution * of the main thread with completed publication of a message. When called, * MQTTClient_waitForCompletion() blocks execution until the message has been * successful delivered or the specified timeout has expired. See @ref async. * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param dt The ::MQTTClient_deliveryToken that represents the message being * tested for successful delivery. Delivery tokens are issued by the * publishing functions MQTTClient_publish() and MQTTClient_publishMessage(). * @param timeout The maximum time to wait in milliseconds. * @return ::MQTTCLIENT_SUCCESS if the message was successfully delivered. * An error code is returned if the timeout expires or there was a problem * checking the token. */ DLLExport int MQTTClient_waitForCompletion(MQTTClient handle, MQTTClient_deliveryToken dt, unsigned long timeout); /** * This function sets a pointer to an array of delivery tokens for * messages that are currently in-flight (pending completion). * * Important note: The memory used to hold the array of tokens is * malloc()'d in this function. The client application is responsible for * freeing this memory when it is no longer required. * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param tokens The address of a pointer to an ::MQTTClient_deliveryToken. * When the function returns successfully, the pointer is set to point to an * array of tokens representing messages pending completion. The last member of * the array is set to -1 to indicate there are no more tokens. If no tokens * are pending, the pointer is set to NULL. * @return ::MQTTCLIENT_SUCCESS if the function returns successfully. * An error code is returned if there was a problem obtaining the list of * pending tokens. */ DLLExport int MQTTClient_getPendingDeliveryTokens(MQTTClient handle, MQTTClient_deliveryToken **tokens); /** * When implementing a single-threaded client, call this function periodically * to allow processing of message retries and to send MQTT keepalive pings. * If the application is calling MQTTClient_receive() regularly, then it is * not necessary to call this function. */ DLLExport void MQTTClient_yield(void); /** * This function performs a synchronous receive of incoming messages. It should * be used only when the client application has not set callback methods to * support asynchronous receipt of messages (see @ref async and * MQTTClient_setCallbacks()). Using this function allows a single-threaded * client subscriber application to be written. When called, this function * blocks until the next message arrives or the specified timeout expires *(see also MQTTClient_yield()). * * Important note: The application must free() the memory allocated * to the topic and the message when processing is complete (see * MQTTClient_freeMessage()). * @param handle A valid client handle from a successful call to * MQTTClient_create(). * @param topicName The address of a pointer to a topic. This function * allocates the memory for the topic and returns it to the application * by setting topicName to point to the topic. * @param topicLen The length of the topic. If the return code from this * function is ::MQTTCLIENT_TOPICNAME_TRUNCATED, the topic contains embedded * NULL characters and the full topic should be retrieved by using * topicLen. * @param message The address of a pointer to the received message. This * function allocates the memory for the message and returns it to the * application by setting message to point to the received message. * The pointer is set to NULL if the timeout expires. * @param timeout The length of time to wait for a message in milliseconds. * @return ::MQTTCLIENT_SUCCESS or ::MQTTCLIENT_TOPICNAME_TRUNCATED if a * message is received. ::MQTTCLIENT_SUCCESS can also indicate that the * timeout expired, in which case message is NULL. An error code is * returned if there was a problem trying to receive a message. */ DLLExport int MQTTClient_receive(MQTTClient handle, char** topicName, int* topicLen, MQTTClient_message** message, 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 MQTTClient_free() library function. * @param msg The address of a pointer to the ::MQTTClient_message structure * to be freed. */ DLLExport void MQTTClient_freeMessage(MQTTClient_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 MQTTClient_free(void* ptr); /** * This function frees the memory allocated to an MQTT client (see * MQTTClient_create()). It should be called when the client is no longer * required. * @param handle A pointer to the handle referring to the ::MQTTClient * structure to be freed. */ DLLExport void MQTTClient_destroy(MQTTClient* handle); #endif #ifdef __cplusplus } #endif /** * @cond MQTTClient_main * @page async Asynchronous vs synchronous client applications * The client library supports two modes of operation. These are referred to * as synchronous and asynchronous modes. If your application * calls MQTTClient_setCallbacks(), this puts the client into asynchronous * mode, otherwise it operates in synchronous mode. * * In synchronous mode, the client application runs on a single thread. * Messages are published using the MQTTClient_publish() and * MQTTClient_publishMessage() functions. To determine that a QoS1 or QoS2 * (see @ref qos) message has been successfully delivered, the application * must call the MQTTClient_waitForCompletion() function. An example showing * synchronous publication is shown in @ref pubsync. Receiving messages in * synchronous mode uses the MQTTClient_receive() function. Client applicaitons * must call either MQTTClient_receive() or MQTTClient_yield() relatively * frequently in order to allow processing of acknowledgements and the MQTT * "pings" that keep the network connection to the server alive. * * In asynchronous mode, the client application runs on several threads. The * main program calls functions in the client library to publish and subscribe, * just as for the synchronous mode. Processing of handshaking and maintaining * the network connection is performed in the background, however. * Notifications of status and message reception are provided to the client * application using callbacks registered with the library by the call to * MQTTClient_setCallbacks() (see MQTTClient_messageArrived(), * MQTTClient_connectionLost() and MQTTClient_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: * * 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 * MQTTClient_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 * MQTTClient_subscribe() and MQTTClient_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 pubsync Synchronous publication example @code #include "stdio.h" #include "stdlib.h" #include "string.h" #include "MQTTClient.h" #define ADDRESS "tcp://localhost:1883" #define CLIENTID "ExampleClientPub" #define TOPIC "MQTT Examples" #define PAYLOAD "Hello World!" #define QOS 1 #define TIMEOUT 10000L int main(int argc, char* argv[]) { MQTTClient client; MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer; MQTTClient_message pubmsg = MQTTClient_message_initializer; MQTTClient_deliveryToken token; int rc; MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL); conn_opts.keepAliveInterval = 20; conn_opts.cleansession = 1; if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) { printf("Failed to connect, return code %d\n", rc); exit(-1); } pubmsg.payload = PAYLOAD; pubmsg.payloadlen = strlen(PAYLOAD); pubmsg.qos = QOS; pubmsg.retained = 0; MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token); printf("Waiting for up to %d seconds for publication of %s\n" "on topic %s for client with ClientID: %s\n", (int)(TIMEOUT/1000), PAYLOAD, TOPIC, CLIENTID); rc = MQTTClient_waitForCompletion(client, token, TIMEOUT); printf("Message with delivery token %d delivered\n", token); MQTTClient_disconnect(client, 10000); MQTTClient_destroy(&client); return rc; } * @endcode * * @page pubasync Asynchronous publication example @code{.c} #include "stdio.h" #include "stdlib.h" #include "string.h" #include "MQTTClient.h" #define ADDRESS "tcp://localhost:1883" #define CLIENTID "ExampleClientPub" #define TOPIC "MQTT Examples" #define PAYLOAD "Hello World!" #define QOS 1 #define TIMEOUT 10000L volatile MQTTClient_deliveryToken deliveredtoken; void delivered(void *context, MQTTClient_deliveryToken dt) { printf("Message with token value %d delivery confirmed\n", dt); deliveredtoken = dt; } int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_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'); MQTTClient_freeMessage(&message); MQTTClient_free(topicName); return 1; } void connlost(void *context, char *cause) { printf("\nConnection lost\n"); printf(" cause: %s\n", cause); } int main(int argc, char* argv[]) { MQTTClient client; MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer; MQTTClient_message pubmsg = MQTTClient_message_initializer; MQTTClient_deliveryToken token; int rc; MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL); conn_opts.keepAliveInterval = 20; conn_opts.cleansession = 1; MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered); if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) { printf("Failed to connect, return code %d\n", rc); exit(-1); } pubmsg.payload = PAYLOAD; pubmsg.payloadlen = strlen(PAYLOAD); pubmsg.qos = QOS; pubmsg.retained = 0; deliveredtoken = 0; MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token); printf("Waiting for publication of %s\n" "on topic %s for client with ClientID: %s\n", PAYLOAD, TOPIC, CLIENTID); while(deliveredtoken != token); MQTTClient_disconnect(client, 10000); MQTTClient_destroy(&client); return rc; } * @endcode * @page subasync Asynchronous subscription example @code #include "stdio.h" #include "stdlib.h" #include "string.h" #include "MQTTClient.h" #define ADDRESS "tcp://localhost:1883" #define CLIENTID "ExampleClientSub" #define TOPIC "MQTT Examples" #define PAYLOAD "Hello World!" #define QOS 1 #define TIMEOUT 10000L volatile MQTTClient_deliveryToken deliveredtoken; void delivered(void *context, MQTTClient_deliveryToken dt) { printf("Message with token value %d delivery confirmed\n", dt); deliveredtoken = dt; } int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_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'); MQTTClient_freeMessage(&message); MQTTClient_free(topicName); return 1; } void connlost(void *context, char *cause) { printf("\nConnection lost\n"); printf(" cause: %s\n", cause); } int main(int argc, char* argv[]) { MQTTClient client; MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer; int rc; int ch; MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL); conn_opts.keepAliveInterval = 20; conn_opts.cleansession = 1; MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered); if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) { printf("Failed to connect, return code %d\n", rc); exit(-1); } printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n" "Press Q to quit\n\n", TOPIC, CLIENTID, QOS); MQTTClient_subscribe(client, TOPIC, QOS); do { ch = getchar(); } while(ch!='Q' && ch != 'q'); MQTTClient_disconnect(client, 10000); MQTTClient_destroy(&client); return rc; } * @endcode * @page tracing Tracing * * Runtime tracing is controlled by environment variables. * * Tracing is switched on by setting MQTT_C_CLIENT_TRACE. 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. * * ### 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 */