paho_iot_pnp_sample.c

// Copyright (c) Microsoft Corporation. All rights reserved.
// SPDX-License-Identifier: MIT

/*
 * This sample connects an IoT Plug and Play enabled device.
 *
 * IoT Plug and Play requires the device to advertise its capabilities in a device model. This
 * sample's model is available in
 * https://github.com/Azure/opendigitaltwins-dtdl/blob/master/DTDL/v2/samples/Thermostat.json. See
 * the sample README for more information on this model. For more information about IoT Plug and
 * Play, see https://aka.ms/iotpnp.
 *
 * The sample loops listening for incoming commands and property updates and periodically (every
 * MQTT_TIMEOUT_RECEIVE_MS milliseconds) will send a telemetry event.  After
 * MQTT_TIMEOUT_RECEIVE_MAX_MESSAGE_COUNT loops without any service initiated operations, the sample
 * will exit.
 *
 * An X509 self-signed certificate is used for authentication, directly to IoT Hub.
 *
 */

#ifdef _MSC_VER
#pragma warning(push)
// warning C4201: nonstandard extension used: nameless struct/union
#pragma warning(disable : 4201)
#endif
#include <MQTTClient.h>
#ifdef _MSC_VER
#pragma warning(pop)
#endif

#include <azure/core/az_result.h>
#include <azure/core/az_span.h>
#include <azure/iot/az_iot_hub_client.h>

#include "iot_sample_common.h"
#include "paho_iot_pnp_sample_common.h"

#define SAMPLE_TYPE PAHO_IOT_HUB
#define SAMPLE_NAME PAHO_IOT_PNP_SAMPLE

// The model this device implements
static az_span const model_id = AZ_SPAN_LITERAL_FROM_STR("dtmi:com:example:Thermostat;1");
static iot_sample_environment_variables env_vars;
static char mqtt_client_username_buffer[256];

//
// Functions
//
static void create_and_configure_mqtt_client(void);
static void connect_mqtt_client_to_iot_hub(void);
static void disconnect_mqtt_client_from_iot_hub(void);

int main(void)
{
  // The initial functions setup the MQTT connection to Azure IoT Hub, based
  // on environment variable settings.
  create_and_configure_mqtt_client();
  IOT_SAMPLE_LOG_SUCCESS("Client created and configured.");

  connect_mqtt_client_to_iot_hub();
  IOT_SAMPLE_LOG_SUCCESS("Client connected to IoT Hub.");

  // The device's main loop including primary Plug and Play interaction is
  // in paho_iot_pnp_sample_device_implement.
  paho_iot_pnp_sample_device_implement();
  IOT_SAMPLE_LOG_SUCCESS("Completed sample device implementation run.");

  // Disconnect the MQTT connection.
  disconnect_mqtt_client_from_iot_hub();
  IOT_SAMPLE_LOG_SUCCESS("Client disconnected from IoT Hub.");

  return 0;
}

// create_and_configure_mqtt_client reads configuration variables from the environment,
// makes calls to the Azure SDK for C for initial setup, and initiates an MQTT client
// from Paho.
static void create_and_configure_mqtt_client(void)
{
  int rc;

  // Reads in environment variables set by user for purposes of running sample.
  iot_sample_read_environment_variables(SAMPLE_TYPE, SAMPLE_NAME, &env_vars);

  // Build an MQTT endpoint c-string.
  char mqtt_endpoint_buffer[HUB_ENDPOINT_BUFFER_LENGTH];
  iot_sample_create_mqtt_endpoint(
      SAMPLE_TYPE, &env_vars, mqtt_endpoint_buffer, sizeof(mqtt_endpoint_buffer));

  // The Plug and Play model ID is specified as an option during initial client initialization.
  az_iot_hub_client_options options = az_iot_hub_client_options_default();
  options.model_id = model_id;

  rc = az_iot_hub_client_init(&hub_client, env_vars.hub_hostname, env_vars.hub_device_id, &options);
  if (az_result_failed(rc))
  {
    IOT_SAMPLE_LOG_ERROR("Failed to initialize hub client: az_result return code 0x%08x.", rc);
    exit(rc);
  }

  // Get the MQTT client id used for the MQTT connection.
  char mqtt_client_id_buffer[CLIENT_ID_BUFFER_LENGTH];
  rc = az_iot_hub_client_get_client_id(
      &hub_client, mqtt_client_id_buffer, sizeof(mqtt_client_id_buffer), NULL);
  if (az_result_failed(rc))
  {
    IOT_SAMPLE_LOG_ERROR("Failed to get MQTT client id: az_result return code 0x%08x.", rc);
    exit(rc);
  }

  // Create the Paho MQTT client.
  rc = MQTTClient_create(
      &mqtt_client, mqtt_endpoint_buffer, mqtt_client_id_buffer, MQTTCLIENT_PERSISTENCE_NONE, NULL);
  if (rc != MQTTCLIENT_SUCCESS)
  {
    IOT_SAMPLE_LOG_ERROR("Failed to create MQTT client: MQTTClient return code %d.", rc);
    exit(rc);
  }
}

// connect_mqtt_client_to_iot_hub sets up basic security and MQTT topics and then
// initiates an MQTT connection to Azure IoT Hub.
static void connect_mqtt_client_to_iot_hub(void)
{
  int rc;

  // Get the MQTT client username.
  rc = az_iot_hub_client_get_user_name(
      &hub_client, mqtt_client_username_buffer, sizeof(mqtt_client_username_buffer), NULL);
  if (az_result_failed(rc))
  {
    IOT_SAMPLE_LOG_ERROR("Failed to get MQTT client username: az_result return code 0x%08x.", rc);
    exit(rc);
  }

  IOT_SAMPLE_LOG("MQTT client username: %s\n", mqtt_client_username_buffer);

  // Set MQTT connection options.
  MQTTClient_connectOptions mqtt_connect_options = MQTTClient_connectOptions_initializer;
  mqtt_connect_options.username = mqtt_client_username_buffer;
  mqtt_connect_options.password = NULL; // This sample uses x509 authentication.
  mqtt_connect_options.cleansession = false; // Set to false so can receive any pending messages.
  mqtt_connect_options.keepAliveInterval = AZ_IOT_DEFAULT_MQTT_CONNECT_KEEPALIVE_SECONDS;

  MQTTClient_SSLOptions mqtt_ssl_options = MQTTClient_SSLOptions_initializer;
  mqtt_ssl_options.verify = 1;
  mqtt_ssl_options.enableServerCertAuth = 1;
  mqtt_ssl_options.keyStore = (char*)az_span_ptr(env_vars.x509_cert_pem_file_path);
  if (az_span_size(env_vars.x509_trust_pem_file_path) != 0) // Is only set if required by OS.
  {
    mqtt_ssl_options.trustStore = (char*)az_span_ptr(env_vars.x509_trust_pem_file_path);
  }
  mqtt_connect_options.ssl = &mqtt_ssl_options;

  // Connect MQTT client to the Azure IoT Hub.  This will block until the connection
  // is established or fails.
  rc = MQTTClient_connect(mqtt_client, &mqtt_connect_options);
  if (rc != MQTTCLIENT_SUCCESS)
  {
    IOT_SAMPLE_LOG_ERROR(
        "Failed to connect: MQTTClient return code %d.\n"
        "If on Windows, confirm the AZ_IOT_DEVICE_X509_TRUST_PEM_FILE_PATH environment variable is "
        "set correctly.",
        rc);
    exit(rc);
  }
}

// disconnect_mqtt_client_from_iot_hub disconnects and destroys the underlying MQTT connection and
// Paho handle.
static void disconnect_mqtt_client_from_iot_hub(void)
{
  int rc = MQTTClient_disconnect(mqtt_client, MQTT_TIMEOUT_DISCONNECT_MS);
  if (rc != MQTTCLIENT_SUCCESS)
  {
    IOT_SAMPLE_LOG_ERROR("Failed to disconnect MQTT client: MQTTClient return code %d.", rc);
    exit(rc);
  }

  MQTTClient_destroy(&mqtt_client);
}