How to generate command output in IoT Central Azure SDK C

Question

I am using IoT Central and am able to successfully send command to the device as well as receive confirmation code. This is executed using the following line:

azure_iot_send_command_response(azure_iot, command.request_id, response_code, AZ_SPAN_EMPTY);

AZ_SPAN_EMPTY is the payload portion that can be replaces with the JSON formatted response.

Most other actions have sub-routines defined to generate such response (such as: generate_telemetry_payload, generate_device_info_payload, generate_properties_update_response...etc).

I cannot see out of the box generate_command_response.

Am I missing something, can I reuse one of the existing routines or do I have to create my own? What is the common way of passing back payload on command execution?

Tried using functions to generate az_span_from_string etc but they do not generate the whole payload.

Tried formattign it using

static const az_span cmd = AZ_SPAN_LITERAL_FROM_STR("Hello world");

but the error is always:

Device XXXXXXX sent a response payload with a syntax error for method XXXXXXXXX in application XXXXXXX Error code: 400.070.002.052 / s6p8v199hr.2

The annoying part is that I cannot see the raw data to be able to figure out where the syntax problem is...hence my desire to use az_span standard method.

Answer 1

IoT Central Azure with C

I Referred this MSDOC for IoT Hub and for IoT central referred this link

    void myCommandCallback(IOTContextHandle context_handle, const char* component_name, const char* command_name, const char* payload, size_t payload_len) {
    printf("Command received: %s\n", command_name);

    IoTCCommandResponseHandle response_handle = IoTCCommandResponse_create(component_name, command_name);
    IoTCCommandResponse_setStatus(response_handle, 200);
    IoTCCommandResponse_setMessage(response_handle, "Command executed successfully");
    IoTCCommandResponse_send(response_handle);
    IoTCCommandResponse_destroy(response_handle);
}
 int main() {
    IoTCInit();
    IoTCDeviceCreateInfo device_info;
    device_info.deviceId = "my-device-id";
    device_info.scopeId = "my-scope-id";
    device_info.deviceKey = "my-device-key";
    device_info.primaryThumbprint = NULL;
    device_info.secondaryThumbprint = NULL;
    IoTCDeviceClientHandle device_client =  IoTCDeviceClient_create(&device_info);
    IoTCDeviceClient_connect(device_client);
    IoTCCommandRequestCallback myCommandRequestCallback = {
        .callback = myCommandCallback
    };
    IoTCDeviceClient_registerCommandRequestCallback(myCommandRequestCallback);
    while (1)
       {
        IoTCDeviceClient_doWork(device_client);
        IoTCSleep(10);
        }

     IoTCDeviceClient_destroy(device_client);
    return 0;
}

• Creating the IoT central and added the device.

• I tried IoT Device message with IoT Central and able to send message.

• For More details for IoT Central Refer this MSDOC