4.2. Installing mandatory Objects

In order to be able to connect to some LwM2M Server and handle incoming packets our client has to have at least LwM2M Security (/0) and LwM2M Server (/1) Objects implemented.

Fortunately, Anjay provides both of these Objects in the form of pre-implemented modules, and they can be used easily.

Note

It doesn’t impact on Anjay flexibility – i.e., users can still provide their own implementation of these Objects if necessary.

When Anjay is first instantiated (as in our previous hello world example), it has no knowledge about the Data Model, i.e., no LwM2M Objects are registered within it. Security and Server objects can be registered using installation mechanism, presented in the next subsection.

4.2.1. Installing Objects

Each LwM2M Object is defined by an instance of the anjay_dm_object_def_t structure. To add support for a new Object, you’d need to:

  • fill the anjay_dm_object_def_t structure,

  • implement appropriate callback functions,

  • register created object in Anjay.

However, for now, we are going to install our pre-implemented LwM2M Objects (Security, Server), so that you don’t have to worry about initializing the structure and object registration on your own. In case you are interested in this topic, Implementing standard Object section provides more information on this subject.

To install the Objects we are going to use anjay_security_object_install() and anjay_server_object_install() functions.

Important

Remember to include anjay/security.h and anjay/server.h headers to use the functions mentioned above.

4.2.2. Setting up Server and Security Objects

Now we are going to create functions which install Server and Security Objects and add instances of them. We modify the code from the previous tutorial.

The first one will be setup_security_object(). In this tutorial, we will use the Coiote IoT Device Management platform as the hard-coded server URI. You can go to https://avsystem.com/coiote-iot-device-management-platform/ to create an account, and after logging in, add the device entry for your application. If you wish to use another server, then you must replace coap://eu.iot.avsystem.cloud:5683 with a valid value.

For now, we will establish non-secure connection, a secure one will be described later.

// Installs Security Object and adds and instance of it.
// An instance of Security Object provides information needed to connect to
// LwM2M server.
static int setup_security_object(anjay_t *anjay) {
    if (anjay_security_object_install(anjay)) {
        return -1;
    }

    const anjay_security_instance_t security_instance = {
        .ssid = 1,
        .server_uri = "coap://eu.iot.avsystem.cloud:5683",
        .security_mode = ANJAY_SECURITY_NOSEC
    };

    // Anjay will assign Instance ID automatically
    anjay_iid_t security_instance_id = ANJAY_ID_INVALID;
    if (anjay_security_object_add_instance(anjay, &security_instance,
                                           &security_instance_id)) {
        return -1;
    }

    return 0;
}

Both Security and Server instances are linked together by the Short Server ID Resource (ssid). That is why we keep SSID matched in both setup_server_object() and setup_security_object().

// Installs Server Object and adds and instance of it.
// An instance of Server Object provides the data related to a LwM2M Server.
static int setup_server_object(anjay_t *anjay) {
    if (anjay_server_object_install(anjay)) {
        return -1;
    }

    const anjay_server_instance_t server_instance = {
        // Server Short ID
        .ssid = 1,
        // Client will send Update message often than every 60 seconds
        .lifetime = 60,
        // Disable Default Minimum Period resource
        .default_min_period = -1,
        // Disable Default Maximum Period resource
        .default_max_period = -1,
        // Disable Disable Timeout resource
        .disable_timeout = -1,
        // Sets preferred transport to UDP
        .binding = "U"
    };

    // Anjay will assign Instance ID automatically
    anjay_iid_t server_instance_id = ANJAY_ID_INVALID;
    if (anjay_server_object_add_instance(anjay, &server_instance,
                                         &server_instance_id)) {
        return -1;
    }

    return 0;
}

Now we are ready to call these functions from main().

int main(int argc, char *argv[]) {
    if (argc != 2) {
        avs_log(tutorial, ERROR, "usage: %s ENDPOINT_NAME", argv[0]);
        return -1;
    }

    const anjay_configuration_t CONFIG = {
        .endpoint_name = argv[1],
        .in_buffer_size = 4000,
        .out_buffer_size = 4000,
        .msg_cache_size = 4000
    };

    anjay_t *anjay = anjay_new(&CONFIG);
    if (!anjay) {
        avs_log(tutorial, ERROR, "Could not create Anjay object");
        return -1;
    }

    int result = 0;
    // Setup necessary objects
    if (setup_security_object(anjay) || setup_server_object(anjay)) {
        result = -1;
    }

    if (!result) {
        result = anjay_event_loop_run(
                anjay, avs_time_duration_from_scalar(1, AVS_TIME_S));
    }

    anjay_delete(anjay);
    return result;
}

Note

anjay_delete() will automatically delete installed modules after destruction of Anjay instance.

Note

Complete code of this example can be found in examples/tutorial/BC-MandatoryObjects subdirectory of main Anjay project repository.

After running the client, you should see registration successful, location = /rd/<server-dependent identifier> once and registration successfully updated every 30 seconds in logs. It means, that the client has connected to the server and successfully sends Update messages. Now you can perform some Reads for example from the LwM2M Server side.

4.2.3. Application events

The code above handles all events that may happen within the Anjay library itself. Of course, the application usually needs to handle its own functionality. Some ways to do this will be handled later in the Notifications support tutorial.