PLCcom.Opc.Ua.PubSub 10.6.2

PLCcom.Opc.Ua.PubSub

An add-on for building OPC UA PubSub publisher and subscriber applications. It runs cross-platform on .NET Framework 4.7.2+, .NET Standard 2.1, .NET 8, .NET 9, and .NET 10.

Requires PLCcom.Opc.Ua.Sdk with a Client + PubSub or Client + Server + PubSub license.

What PLCcom.Opc.Ua.PubSub has to offer

PLCcom.Opc.Ua.PubSub implements the OPC UA PubSub specification (Part 14) with a simple, fluent API. Publishers and subscribers are configured with a builder pattern and started with a single call — no low-level stack configuration required.

Supported transports:

• UDP unicast (brokerless, point-to-point)
• UDP multicast (brokerless, one-to-many)
• MQTT with UADP binary encoding (broker-based)
• MQTT with JSON encoding (broker-based, cloud-ready)
• sMQTT (MQTT over TLS) for all broker-based transports

Key features:

• Fluent builder API — configure publisher or subscriber in a few lines
• Automatic metadata exchange — subscribers discover field layouts dynamically
• PKI-based TLS certificate management — same model as PLCcom.Opc.Ua.Sdk
• CertificateValidation event — same pattern as UaClient
• Mutual TLS (mTLS) support for broker authentication
• Configurable reconnect interval for MQTT connections

Getting started

1. Install the NuGet package

Install-Package PLCcom.Opc.Ua.PubSub

2. Import namespaces

using PLCcom.Opc.Ua;
using PLCcom.Opc.Ua.PubSub.Sdk;

Publisher

UDP Unicast (brokerless)

string LicenseUserName = "<Enter your UserName here>";
string LicenseSerial   = "<Enter your Serial here>";

var config = UaPublisherConfiguration.Build("MyPublisher", "opcua:MyMachine")
    .WithNetworkInterface(NetworkInterfaces.All)
    .WithTransport(PubSubTransportMode.DirectUnicast, "opc.udp://192.168.1.10:4840")
    .WithPublishingInterval(1000)
    .AddDataSet("Sensors", ds => ds
        .AddField("Temperature", new NodeId(1001, 2))
        .AddField("Pressure",    new NodeId(1002, 2))
        .WithKeyFrameCount(10)
        .WithInterval(1000));

using var publisher = new UaPublisher(LicenseUserName, LicenseSerial, config);
publisher.Start();

publisher.WriteValue("Sensors", "Temperature", 23.5);
publisher.WriteValue("Sensors", "Pressure",    1.013);

MQTT with JSON encoding (broker-based)

var config = UaPublisherConfiguration.Build("MyPublisher", "opcua:MyMachine")
    .WithNetworkInterface(NetworkInterfaces.All)
    .WithTransport(PubSubTransportMode.BrokerMqttJson, "mqtt://broker.local:1883")
    .WithPublishingInterval(1000)
    .AddDataSet("Sensors", ds => ds
        .AddField("Temperature", new NodeId(1001, 2))
        .AddField("Pressure",    new NodeId(1002, 2))
        .WithKeyFrameCount(10)
        .WithInterval(1000));

using var publisher = new UaPublisher(LicenseUserName, LicenseSerial, config);
publisher.Start();

sMQTT (MQTT over TLS)

var config = UaPublisherConfiguration.Build("MyPublisher", "opcua:MyMachine")
    .WithNetworkInterface(NetworkInterfaces.All)
    .WithTransport(PubSubTransportMode.BrokerMqttUadp, "mqtts://broker.local:8883")
    .WithMqttTls("./pki")
    .WithPublishingInterval(1000)
    .AddDataSet("Sensors", ds => ds
        .AddField("Temperature", new NodeId(1001, 2))
        .WithKeyFrameCount(10)
        .WithInterval(1000));

using var publisher = new UaPublisher(LicenseUserName, LicenseSerial, config);

// Accept broker certificate (for testing - use PKI store in production)
publisher.CertificateValidation += (sender, e) => e.Accept = true;

publisher.Start();

Subscriber

UDP Multicast (brokerless)

var config = UaSubscriberConfiguration.Build("MySubscriber")
    .WithNetworkInterface(NetworkInterfaces.All)
    .WithTransport(PubSubTransportMode.DirectMulticast, "opc.udp://239.0.0.1:4840")
    .AddDataSetReader("opcua:MyMachine", "Sensors", ds => ds
        .AddField("Temperature", BuiltInType.Double)
        .AddField("Pressure",    BuiltInType.Double));

using var subscriber = new UaSubscriber(LicenseUserName, LicenseSerial, config);

subscriber.DataReceived += (sender, e) =>
{
    Console.WriteLine($"Temperature = {e.Fields["Temperature"].Value}");
    Console.WriteLine($"Pressure    = {e.Fields["Pressure"].Value}");
};

subscriber.Start();

MQTT with dynamic field discovery

For MQTT transports, the publisher publishes DataSetMetaData with the RETAIN flag. The subscriber can omit AddField() — the field layout is received automatically:

var config = UaSubscriberConfiguration.Build("MySubscriber")
    .WithNetworkInterface(NetworkInterfaces.All)
    .WithTransport(PubSubTransportMode.BrokerMqttJson, "mqtt://broker.local:1883")
    // No AddField() needed - field layout received via MQTT RETAIN metadata
    .AddDataSetReader("opcua:MyMachine", "Sensors");

sMQTT Subscriber

var config = UaSubscriberConfiguration.Build("MySubscriber")
    .WithNetworkInterface(NetworkInterfaces.All)
    .WithTransport(PubSubTransportMode.BrokerMqttUadp, "mqtts://broker.local:8883")
    .WithMqttTls("./pki")
    .AddDataSetReader("opcua:MyMachine", "Sensors", ds => ds
        .AddField("Temperature", BuiltInType.Double));

using var subscriber = new UaSubscriber(LicenseUserName, LicenseSerial, config);

subscriber.CertificateValidation += (sender, e) => e.Accept = true;

subscriber.DataReceived += (sender, e) =>
{
    foreach (var field in e.Fields)
        Console.WriteLine($"{field.Key} = {field.Value.Value}");
};

subscriber.Start();

Transport modes

Use mqtts:// scheme with .WithMqttTls() for TLS on any broker transport.

PKI Certificate Management (TLS)

WithMqttTls(pkiBase) uses the standard OPC UA PKI directory convention:

./pki/trusted/certs/   - directly trusted broker certificates
./pki/trusted/crl/     - certificate revocation lists
./pki/issuers/certs/   - trusted CA/issuer certificates
./pki/issuers/crl/     - issuer revocation lists
./pki/rejected/        - certificates rejected on first contact

On first connection, the broker certificate is placed in rejected/. Copy the broker's CA certificate to issuers/certs/ to trust it permanently.

For mutual TLS (mTLS), load a client certificate and pass it to WithMqttTls():

var clientResult = UaPubSubCertificate.LoadOwnCertificate(
    "./pki", "mqtt_client", "password",
    UaPubSubCertificate.CertificateFormat.Pfx);

config.WithMqttTls("./pki", clientResult.Certificate);

System Requirements

Supported platforms:

• Microsoft .NET Framework 4.7.2 or higher (up to 4.8.1)
• Microsoft .NET 5.0 to 7.0 via .NET Standard 2.1
• Microsoft .NET 8.0
• Microsoft .NET 9.0
• Microsoft .NET 10.0

Prerequisites:

• PLCcom.Opc.Ua.Sdk NuGet package (installed automatically as dependency)
• A valid PLCcom license with PubSub add-on (Client + PubSub or Client + Server + PubSub)

Additional Documentation

Online class reference: https://docs.plccom.net/help_opc_ua_sdk/net/help/html/R_Project_PLCcom_Opc_Ua_Sdk_Documentation.htm

Quick-start examples on GitHub: https://github.com/indi-an-gmbh/PLCcom-OpcUaSdk-examples-dotnet

Feedback

To provide feedback or report issues, please write to: support@indi-an.com