C99 Connector library which provides easy connectivity to WolkAbout IoT Platform.
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WolkAbout C99 Connector library for connecting devices to WolkAbout IoT platform.

WolkConnect-C is transportation layer agnostic which means it is up to the user of the library to open socket to WolkAbout IoT platform, configure SSL if desired, and forward read/write implementation to WolkConnect-C Connector. WolkConnect-C Connector is not thread safe, and is written with cooperative scheduling in mind. This allows WolkConnect-C Connector to work on wide variety of systems, bare metal to OS based ones.

Given examples are intended to be run on Debian based system.

Supported protocol(s):

  • JSON single


Following tools/libraries are required in order to build WolkConnect-C Connector

  • cmake - version 2.8 or later

Former can be installed on Debian based system from terminal by invoking

apt-get install cmake

When dependencies are installed, Unix Makefiles build system can generated by invoking ./configure

Generated build system is located inside 'build' directory

WolkConnect-C Connector is built to out/lib directory, and example application is built to out/bin directory.

Example Usage

Initialize WolkConnect-C Connector

Create a device on WolkAbout IoT platform by importing simple-example-manifest.json located in examples/simple/. This manifest fits simple example and demonstrates the sending of a temperature sensor reading.

static const char *device_key = "device_key";
static const char *device_password = "some_password";
static const char *hostname = "api-demo.wolkabout.com";
static int portno = 1883;

/* Sample in-memory persistence storage - size 1MB */
static uint8_t persistence_storage[1024*1024];

/* WolkConnect-C Connector context */
static wolk_ctx_t wolk;


wolk_init(&wolk,                                             /* Context */
          send_buffer,                                       /* See send_func_t */
          receive_buffer,                                    /* See recv_func_t */
          actuation_handler,                                 /* Actuation handler        - see actuation_handler_t */
          actuator_status_provider,                          /* Actuator status provider - see actuator_status_provider_t */
          device_key, device_password,                       /* Device key and password provided by WolkAbout IoT Platform upon device creation */
          PROTOCOL_JSON_SINGLE,                              /* Protocol specified for device */
          actuator_references,                               /* Array of actuator references */
          num_actuator_references);                          /* Number of actuator references */

wolk_init_in_memory_persistence(&wolk,                       /* Context */
                                persistence_storage,         /* Address to start of the memory which will be used by persistence mechanism */
                                sizeof(persistence_storage), /* Size of memory in bytes */
                                true);                       /* If storage is full overwrite oldest item when pushing */

Considering that WolkConnect C Connector is transportation layer agnostic, it is up to the user of it to open connection to WolkAbout IoT Platform, optionally setup TLS, and forward read/write callbacks WolkConnect-C Connector in initialization step.

See send_func_t and send_func_t in sources/wolk_connector.h

Establishing connection with WolkAbout IoT platform:


Adding sensor readings:

wolk_add_numeric_sensor_reading(&wolk, "T", 23.4, 0);

Data publish strategy:

Sensor reading is pushed to WolkAbout IoT platform on demand by calling


Disconnecting from the platform:


Cooperative scheduling:

Fuction wolk_process(wolk_ctx_t *ctx) is non-blocking in order to comply with cooperative scheduling, and it must to be called periodically.

wolk_process(&wolk, 5);

Data persistence:

WolkConnect-C provides mechanism for persisting data in situations where readings can not be sent to WolkAbout IoT platform. Default implementation can work with in-memory or memory mapped storage.

Persisted readings are sent to WolkAbout IoT platform, in batches, on publish function call.

In cases when provided persistence implementation is suboptimal, one can use custom persistence by providing custom implementation.

                             persistence_peek_impl, persistence_pop_impl,

For more info on persistence mechanism see sources/persistence.h and sources/in_memory_persistence.h files.

Additional functionality

WolkConnect-C library has integrated additional features which can perform full WolkAbout IoT platform potential. Read more about full feature set example HERE.