usage of IoTHubDeviceClient_LL_DeviceMethodResponse In C client device IoT Hub SDK


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!

Azure IoT Hub
Azure IoT Hub
An Azure service that enables bidirectional communication between internet of things (IoT) devices and applications.
1,136 questions
Azure IoT SDK
Azure IoT SDK
An Azure software development kit that facilitates building applications that connect to Azure IoT services.
208 questions
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Accepted answer
  1. António Sérgio Azevedo 7,666 Reputation points Microsoft Employee

    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:

    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)  
        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;  
            // 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:

    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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