Setting the MQTT keepalive using a *_SetOption function

[bertulli]

Hi, thank you for your work. I'm trying to set up an Azure IotHub client with the C SDK, and I noticed that if I don't send out a new MQTT message every 10 seconds, the connection to the Hub is closed. I'd like to increase this timeout, and I think the option I need is "keepalive" (OPTION_KEEP_ALIVE, see this doc page). However, if I try to do

IOTHUB_DEVICE_CLIENT_LL_HANDLE device_ll_handle;
// [...]
int keepalive = 20;
IoTHubTransport_MQTT_Common_SetOption(device_ll_handle, OPTION_KEEP_ALIVE, &keepalive);
// [...]
device_ll_handle = IoTHubDeviceClient_LL_CreateFromConnectionString(connection_string, iothub_transport)

in the code opening the device handle, I end up with a SEGFAULT, because it detects the connection as already open, and it tries to disconnect with DisconnectFromClient(transport_data). I can't find in the doc how to set this option: where should I set it? Thanks!

A MWE:

typedef struct CLIENT_SAMPLE_INFO_TAG
{
  PROV_DEVICE_LL_HANDLE handle;
  unsigned int sleep_time_msec;
  char* iothub_uri;
  char* device_id;
  bool registration_complete;
} CLIENT_SAMPLE_INFO;

PROV_DEVICE_TRANSPORT_PROVIDER_FUNCTION prov_transport;

CLIENT_SAMPLE_INFO azure_init() {

  CLIENT_SAMPLE_INFO user_ctx;

  (void)IoTHub_Init();
  (void)prov_dev_security_init(SECURE_DEVICE_TYPE_X509);

  memset(&user_ctx, 0, sizeof(CLIENT_SAMPLE_INFO));

  // Protocol to USE
  prov_transport = Prov_Device_MQTT_Protocol;

  user_ctx.registration_complete = false;
  user_ctx.sleep_time_msec = 10;

  LOG(INFO) << "Provisioning API Version: " << Prov_Device_LL_GetVersionString();
  LOG(INFO) << "Iothub API Version: " << IoTHubClient_GetVersionString();

  return user_ctx;
}

IOTHUB_DEVICE_CLIENT_LL_HANDLE open_iothub(const std::string &connection_string,
                                           const CLIENT_SAMPLE_INFO &azure_ctx,
                                           const std::string &x509_certificate,
                                           const std::string &x509_key) {
  const CLIENT_SAMPLE_INFO user_ctx{azure_ctx};
  IOTHUB_DEVICE_CLIENT_LL_HANDLE device_ll_handle;

  // Protocol to USE
  iothub_transport = MQTT_Protocol;

  // int keepalive = 20;
  // IoTHubTransport_MQTT_Common_SetOption(device_ll_handle, OPTION_KEEP_ALIVE, &keepalive);

  LOG(INFO) << "Creating IoTHub Device handle";  
  if ((device_ll_handle = IoTHubDeviceClient_LL_CreateFromConnectionString(connection_string.c_str(), iothub_transport) ) == NULL)
    {
      LOG(ERROR) << "failed create IoTHub client " << user_ctx.iothub_uri << "!";
      return nullptr;
    }
  else
    {
      iothub_info.stop_running = false;
      iothub_info.connected = false;

      (void)IoTHubDeviceClient_LL_SetConnectionStatusCallback(device_ll_handle, iothub_connection_status, &iothub_info);

      // Set any option that are necessary.
      // For available options please see the iothub_sdk_options.md documentation
      bool traceOn = true;
      IoTHubDeviceClient_LL_SetOption(device_ll_handle, OPTION_LOG_TRACE, &traceOn);
      int keepalive = 20;
      IoTHubTransport_MQTT_Common_SetOption(device_ll_handle, OPTION_KEEP_ALIVE, &keepalive);

      //Setting the auto URL Encoder (recommended for MQTT). Please use this option unless
      //you are URL Encoding inputs yourself.
      //ONLY valid for use with MQTT
      bool urlEncodeOn = true;
      (void)IoTHubDeviceClient_LL_SetOption(device_ll_handle, OPTION_AUTO_URL_ENCODE_DECODE, &urlEncodeOn);

      // Set the X509 certificates in the SDK
      if (
          (IoTHubDeviceClient_LL_SetOption(device_ll_handle, OPTION_X509_CERT, x509_certificate.c_str()) != IOTHUB_CLIENT_OK) ||
          (IoTHubDeviceClient_LL_SetOption(device_ll_handle, OPTION_X509_PRIVATE_KEY, x509_key.c_str()) != IOTHUB_CLIENT_OK)
          )
        {
          LOG(ERROR) << "failure to set options for x509, aborting";
        }

        (void)IoTHubDeviceClient_LL_SetMessageCallback(
            device_ll_handle, receive_msg_callback, &iothub_info);
        LOG(INFO) << "Opened IoTHub connection via connection string " << connection_string;
      return device_ll_handle;
    }  
}

int main() {

    auto azure_connection = azure_helpers::azure_init();

    auto iot_handle = azure_helpers::open_iothub("HostName=XXXXXXXXXXXXXX.azure-devices.net;DeviceId=test2;x509=true",
                                                 azure_connection,
                                                 x509certificate, // read from file
                                                 x509privatekey); // read from file

}

with output

Provisioning API Version: 1.14.0
Iothub API Version: 1.14.0
Creating IoTHub Device handle
Error: Time:Tue Jan 20 09:41:58 2025 File:/home/abertulli/<project_root>/azure-iot-sdk-c/iothub_client/src/iothub_client_authorization.c Func:IoTHubClient_Auth_Get_Credential_Type Line:361 Invalid Parameter handle: (nil)
Segmentation fault