Working with Yandex IoT Core in C#

In this scenario, you'll learn how to connect to Yandex IoT Core using the Paho library written in C#. It assumes that you know how to develop apps on .NET in C#.

Once connected, you can:

• Send messages.
• Subscribe a device or registry to receive messages.

To connect to Yandex IoT Core and start messaging:

• Create the required Yandex IoT Core resources:
  • Create a registry and add a certificate to it.
  • Create a device and add a certificate to it.
• Connect to Yandex IoT Core.
• Authenticate in Yandex IoT Core:
  • Authentication using certificates.
  • Authentication by username and password.
• Establish a connection.
• Subscribe to a topic and receive messages.
• Send a message.
• Terminate the connection.

Getting startedGetting started

1. If you do not have the Yandex Cloud command line interface yet, install and initialize it.
2. Download and install a development environment for .Net, e.g., Microsoft Visual Studio.

Create the required Yandex IoT Core resourcesCreate the required Yandex IoT Core resources

Create a registry and add a certificate to itCreate a registry and add a certificate to it

If you already have a certificate, start with the second step.

1. Create a certificate for the registry (skip this step if you already have a registry certificate):

   openssl req -x509 \
     -newkey rsa:4096 \
     -keyout registry-key.pem \
     -out registry-cert.pem \
     -nodes \
     -days 365 \
     -subj '/CN=localhost'
   

2. Create a registry:

   yc iot registry create --name my-registry
   

3. Add a certificate to the registry:

   yc iot registry certificate add \
     --registry-name my-registry \ # Registry name.
     --certificate-file registry-cert.pem # Path to the public part of the certificate.
   

Create a device and add a certificate to itCreate a device and add a certificate to it

If you already have a certificate, start with the second step.

1. (optional) Create a certificate for the device:

   openssl req -x509 \
     -newkey rsa:4096 \
     -keyout device-key.pem \
     -out device-cert.pem \
     -nodes \
     -days 365 \
     -subj '/CN=localhost'
   

2. Review a list of the registries where you can create a device or create a new registry.

3. Create a device:

   yc iot device create --registry-name my-registry --name my-device
   

4. Add a certificate to the device:

   yc iot device certificate add \
     --device-name my-device \ # Device name.
     --certificate-file device-cert.pem # Path to the public part of the certificate.
   

Connect to Yandex IoT CoreConnect to Yandex IoT Core

Before connecting, configure the connection parameters using the following code:

// Setting up a TLS connection
MqttClientOptionsBuilderTlsParameters tlsOptions = new MqttClientOptionsBuilderTlsParameters
{
  SslProtocol = SslProtocols.Tls12,
  UseTls = true
};

// Enabling the server validation event handler
tlsOptions.CertificateValidationCallback += CertificateValidationCallback;

// Setting up the connection parameters
var options = new MqttClientOptionsBuilder()
    .WithClientId($"Test_C#_Client_{Guid.NewGuid()}")
    .WithTcpServer(MqttServer, MqttPort)
    .WithTls(tlsOptions)
    .WithCleanSession()
    .WithCredentials(id, password)
    .WithKeepAlivePeriod(TimeSpan.FromSeconds(90))
    .WithKeepAliveSendInterval(TimeSpan.FromSeconds(60))
    .Build();

var factory = new MqttFactory();
IMqttClient mqttClient = factory.CreateMqttClient();

// Enabling the data receipt event handler
mqttClient.UseApplicationMessageReceivedHandler(DataHandler);

// Enabling the event handler for connections to Yandex IoT Core
mqttClient.UseConnectedHandler(ConnectedHandler);

// Enabling the event handler for losing connections to Yandex IoT Core
mqttClient.UseDisconnectedHandler(DisconnectedHandler);

Where:

• MqttClientOptionsBuilderTlsParameters is a class that specifies the parameters for using TLS when connecting to Yandex IoT Core.
• MqttClientOptionsBuilder is a constructor class for setting connection options. You can use the default settings, but we recommend setting the WithKeepAlivePeriod and WithKeepAliveSendInterval parameters. The values of these parameters determine:

  • The frequency of sending PINGREQ commands.

  • The client's response time to a broken connection.

    The lower the values of these parameters, the faster the client realizes that a connection terminated abnormally. However, this increases the frequency of sending payable PINGREQ commands.

Authenticate in Yandex IoT CoreAuthenticate in Yandex IoT Core

There are two authentication methods:

• Using X.509 certificates.
• Using a username and password.

Authentication using certificatesAuthentication using certificates

When authenticating with X.509 certificates, it is most convenient to use PKCS#12 certificates in PFX format. To generate a certificate in PKCS#12 format from PEM certificates, run the command:

openssl pkcs12 -export -out cert.pfx -inkey key.pem -in cert.pem

To load certificates in your project, use the following code:

X509Certificate2 certificate = new X509Certificate2(certPath);

The client certificate used for authentication on the server is specified when setting up a TLS connection:

X509Certificate2 certificate = new X509Certificate2(certPath);
List<byte[]> certificates = new List<byte[]>();
certificates.Add(certificate.Export(X509ContentType.SerializedCert));

// Setting up a TLS connection
MqttClientOptionsBuilderTlsParameters tlsOptions = new MqttClientOptionsBuilderTlsParameters
{
  Certificates = certificates,
  SslProtocol = SslProtocols.Tls12,
  UseTls = true
};

The certificate used for server authentication is used in the server validation event handler:

private static X509Certificate2 rootCrt = new X509Certificate2("rootCA.crt");

private static bool CertificateValidationCallback(X509Certificate cert, X509Chain chain, SslPolicyErrors errors, IMqttClientOptions opts)
{
  try
  {
    if (errors == SslPolicyErrors.None)
    {
      return true;
    }

    if (errors == SslPolicyErrors.RemoteCertificateChainErrors)
    {
      chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
      chain.ChainPolicy.VerificationFlags = X509VerificationFlags.NoFlag;
      chain.ChainPolicy.ExtraStore.Add(rootCrt);

      chain.Build((X509Certificate2)rootCrt);
      // Comparing certificate thumbprints
      var res = chain.ChainElements.Cast<X509ChainElement>().Any(a => a.Certificate.Thumbprint == rootCrt.Thumbprint);
      return res;
    }
  }
  catch { }

  return false;
}

Authenticating by username and passwordAuthenticating by username and password

Authentication with a username and password in Yandex IoT Core requires the TLS protocol. To do this, use the MqttClientOptionsBuilderTlsParameters class:

// Setting up a TLS connection
MqttClientOptionsBuilderTlsParameters tlsOptions = new MqttClientOptionsBuilderTlsParameters
{
  SslProtocol = SslProtocols.Tls12,
  UseTls = true
};

// Enabling the server validation event handler
tlsOptions.CertificateValidationCallback += CertificateValidationCallback;

In the connection settings, using the WithCredentials method, set the username to id (registry or device ID) and the password to password:

// Setting up the connection parameters
var options = new MqttClientOptionsBuilder()
    .WithClientId($"Test_C#_Client_{Guid.NewGuid()}")
    .WithTcpServer(MqttServer, MqttPort)
    .WithTls(tlsOptions)
    .WithCleanSession()
    .WithCredentials(id, password)
    .WithKeepAlivePeriod(TimeSpan.FromSeconds(90))
    .WithKeepAliveSendInterval(TimeSpan.FromSeconds(60))
    .Build();

Establish a connectionEstablish a connection

Establish a connection to Yandex IoT Core using the following code:

mqttClient.ConnectAsync(options, CancellationToken.None);

Subscribe to a topic and get messagesSubscribe to a topic and get messages

Use a callback function to receive messages:

...
  mqttClient.UseApplicationMessageReceivedHandler(DataHandler);
...

private Task DataHandler(MqttApplicationMessageReceivedEventArgs arg)
{
  return Task.CompletedTask;
}

Subscribe to a topic using the following code. In the SubscribeAsync method, specify the topic that you want to subscribe to and the level of quality of service (QoS).

mqttClient.SubscribeAsync(topic, qos);

Send a messageSend a message

Send a message using the following code. In the PublishAsync method, specify the topic that you want to send a message to, the message text, and the desired level of quality of service (qos).

mqttClient.PublishAsync(topic, "Your message text.", qos);

Handle connection loss events and track message delivery using callback functions:

...
  mqttClient.UseConnectedHandler(ConnectedHandler);
  mqttClient.UseDisconnectedHandler(DisconnectedHandler);
...

private Task ConnectedHandler(MqttClientConnectedEventArgs arg)
{
  return Task.CompletedTask;
}

private static Task DisconnectedHandler(MqttClientDisconnectedEventArgs arg)
{
  return Task.CompletedTask;
}

Terminate the connectionTerminate the connection

Disconnect from Yandex IoT Core using the following code:

mqttClient.DisconnectAsync();