3.1. Initialize Anjay Lite client

3.1.1. Project structure

Create the following directory layout for your client project:

example/
  ├── CMakeLists.txt
  └── src/
      └── main.c

Note

All code found in this tutorial is available under examples/tutorial/BC* in Anjay Lite source directory. Each tutorial project follows the same project directory layout.

3.1.2. Configure the build system

We are going to use CMake as a build system. Create a CMakeLists.txt file in the root of your project directory with the following content:

cmake_minimum_required(VERSION 3.6.0)

project(anjay_lite_bc_initialization C)

set(CMAKE_C_STANDARD 99)
set(CMAKE_C_EXTENSIONS OFF)

if (CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
    set(anjay_lite_DIR "../../../cmake")
    find_package(anjay_lite REQUIRED)
endif()

add_executable(anjay_lite_bc_initialization src/main.c)
target_include_directories(anjay_lite_bc_initialization PUBLIC
    "${CMAKE_SOURCE_DIR}"
    )

target_link_libraries(anjay_lite_bc_initialization PRIVATE
                      anj
                      anj_extra_warning_flags)

This file configures the CMake build system to compile your client and link it with the Anjay Lite library.

3.1.3. Implement the Hello World client

Now, we can begin the actual client implementation. Create a main.c file in the src/ directory with the following content:

#include <stdbool.h>
#include <stdio.h>
#include <unistd.h>

#include <anj/core.h>
#include <anj/log/log.h>

#define log(...) anj_log(example_log, __VA_ARGS__)

int main(int argc, char *argv[]) {
    if (argc != 2) {
        log(L_ERROR, "No endpoint name given");
        return -1;
    }

    anj_t anj;
    anj_configuration_t config = {
        .endpoint_name = argv[1]
    };

    if (anj_core_init(&anj, &config)) {
        log(L_ERROR, "Failed to initialize Anjay Lite");
        return -1;
    }

    while (true) {
        anj_core_step(&anj);
        usleep(50 * 1000);
    }
    return 0;
}

Note

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

Code explanation:

• The anj_core_init() function is used to initialize the Anjay Lite instance. You must pass a anj_configuration_t structure with the basic runtime configuration.

• The example program configures only one basic value: endpoint_name. This endpoint name is used to uniquely identify the client to a LwM2M server.

• After initializing the library, a loop calls anj_core_step() continuously. This function handles all LwM2M client tasks. It is non-blocking unless a blocking network API is used.

Note

Anjay Lite does not allocate resources that require cleanup. You do not need to call a shutdown or cleanup function.

3.1.4. Build and run the client

In your project directory, build the client:

$ cmake . && make

If the build succeeds, you can run the client. Provide an endpoint name as an argument. When the communication with the server takes place later in the project this will be a name that the client uses to identify itself to the server. At this point, you can use the local hostname to simulate an endpoint name:

$ ./anjay_lite_bc_initialization urn:dev:os:$(hostname)

The program will log errors about the missing Server instance and may appear idle. This is expected at this stage, as no server is configured yet.

The connection to the LwM2M Server will be described in the next steps.