usage of IoTHubDeviceClient_LL_DeviceMethodResponse In C client device IoT Hub SDK

Question

I am looking for support since there is not much information online, I am trying to program an ESP32 microcontroller using the C SDK port for the Arduino framework, by connecting it to a central IoT App.

I managed to make the device respond to the call of a method through a command sent from central IoT but I have not been able to send a response from the device to the cloud, I would infinitely appreciate if someone could explain to me how "IoTHubDeviceClient_LL_DeviceMethodResponse" works

Thanks for your time and patience!

Answer 1

Thank you for asking your question here @Anonymous !

If you research on the azure iot sdk for C you will find some samples and there is one explaining how Direct Methods work:

https://github.com/Azure/azure-iot-sdk-c/tree/master/iothub_client/samples/iothub_client_device_twin_and_methods_sample

Here is the piece of code that you should pay attention for your described scenario:

static int deviceMethodCallback(const char* method_name, const unsigned char* payload, size_t size, unsigned char** response, size_t* response_size, void* userContextCallback)  
{  
    (void)userContextCallback;  
    (void)payload;  
    (void)size;  
  
    int result;  
  
    if (strcmp("getCarVIN", method_name) == 0)  
    {  
        const char deviceMethodResponse[] = "{ \"Response\": \"1HGCM82633A004352\" }";  
        *response_size = sizeof(deviceMethodResponse)-1;  
        *response = malloc(*response_size);  
        (void)memcpy(*response, deviceMethodResponse, *response_size);  
        result = 200;  
    }  
    else  
    {  
        // All other entries are ignored.  
        const char deviceMethodResponse[] = "{ }";  
        *response_size = sizeof(deviceMethodResponse)-1;  
        *response = malloc(*response_size);  
        (void)memcpy(*response, deviceMethodResponse, *response_size);  
        result = -1;  
    }  
  
    return result;  
}  

Would strongly advise you to take a look at the following doc as well to better Understand how to invoke direct methods from IoT Hub: https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-direct-methods

Despites mentioning IoT Hub, would work the same for IoT Central since the technology behind IoT Central is using IoT Hub ;).

Hope I could help you continue with your project.

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