# OPC Foundation UA .NET Standard Library - Console Reference Subscriber

## Introduction

This OPC application was created to provide the sample code for creating Subscriber applications using the OPC Foundation UA .NET Standard PubSub Library. There is a .NET Core 3.1 (2.1) console version of the Subscriber which runs on any OS supporting [.NET Standard](https://docs.microsoft.com/en-us/dotnet/articles/standard).
The Reference Subscriber is configured to run in parallel with the [Console Reference Publisher](../ConsoleReferencePublisher/README.md)

## How to build and run the Windows OPC UA Reference Server from Visual Studio

1. Open the solution **UA.slnx** with Visual Studio 2026.
2. Choose the project `ConsoleReferenceSubscriber` in the Solution Explorer and set it with a right click as `Startup Project`.
3. Hit `F5` to build and execute the sample.

## How to build and run the console OPC UA Reference Subscriber on Windows, Linux and iOS

This section describes how to run the **ConsoleReferenceSubscriber**.

Please follow instructions in this [article](https://aka.ms/dotnetcoregs) to setup the dotnet command line environment for your platform.

## Start the Subscriber

1. Open a command prompt.
2. Navigate to the folder **Applications/ConsoleReferenceSubscriber**.
3. To run the Subscriber sample type

`dotnet run --project ConsoleReferenceSubscriber.csproj --framework net10.0.`

The Subscriber will start and listen for network messages sent by the Reference Publisher.

## Command Line Arguments for *ConsoleReferenceSubscriber*

 **ConsoleReferenceSubscriber** can be executed using the following command line arguments:

- -h|help - Shows usage information
- -m|mqtt_json - Creates a connection using there MQTT with Json encoding Profile. This is the default option.
- -u|udp_uadp - Creates a connection using there UDP with UADP encoding Profile.

To run the Subscriber sample using a connection with MQTT with Json encoding execute:

  dotnet run --project ConsoleReferenceSubscriber.csproj --framework net10.0

  or

  dotnet run --project ConsoleReferenceSubscriber.csproj --framework net10.0 -m

To run the Subscriber sample using a connection with the UDP with UADP encoding execute:

  dotnet run --project ConsoleReferenceSubscriber.csproj --framework net10.0 -u

## Programmer's Guide

To create a new OPC UA Subscriber application:

- Open Microsoft Visual Studio 2019 environment,
- Create a new project and give it a name,
- Add a reference to the [OPCFoundation.NetStandard.Opc.Ua.PubSub NuGet package](https://www.nuget.org/packages/OPCFoundation.NetStandard.Opc.Ua.PubSub/),
- Initialize Subscriber application (see [Subscriber Initialization](#subscriber-initialization)).

### Subscriber Initialization

The following four steps are required to implement a functional Subscriber:

 1. Create [Subscriber Configuration](#subscriber-configuration).

    ```csharp
        // Create configuration using UDP protocol and UADP Encoding
        PubSubConfigurationDataType pubSubConfiguration = CreateSubscriberConfiguration_UdpUadp();
    ```

    Or use the alternative configuration object for MQTT with JSON encoding

    ```csharp
        // Create configuration using MQTT protocol and JSON Encoding
        PubSubConfigurationDataType pubSubConfiguration = CreateSubscriberConfiguration_MqttJson();
    ```

    The CreateSubscriberConfiguration methods can be found in  [ConsoleReferenceSubscriber/Program.cs](./Program.cs) file.

 2. Create an instance of the [UaPubSubApplication Class](../../Docs/PubSub.md#uapubsubapplication-class) using the configuration data from step 1.

    ```csharp
        // Subscribe to data events
        UaPubSubApplication uaPubSubApplication = UaPubSubApplication.Create(pubSubConfiguration);
    ```

 3. Provide the event handler for the *DataReceived*  event. This event will be raised when data sets matching the subscriber configuration arrive over the network. See the DataReceived Event section for more details.

    ```csharp
        // Create an instance of UaPubSubApplication
        uaPubSubApplication.DataReceived += PubSubApplication_DataReceived;
    ```

 4. Start PubSub application

    ```csharp
        // Start the publisher
        uaPubSubApplication.Start();
    ```

After this step the *Subscriber* will listen for *NetworkMessages* as configured.

### Subscriber Configuration

The Subscriber configuration is a subset of the [PubSub Configuration](../../Docs/PubSub.md#pubsub-configuration). A functional *Subscriber* application needs to have a configuration (*PubSubConfigurationDataType* instance) that contains at least one connection (*PubSubConnectionDataType* instance) with at least one reader group configuration (*ReaderGroupDataType* instance). The reader group contains at least one data set reader (*DataSetReaderDataType* instance) that describes a published data set that can be processed and retrieved by the *Subscriber* application.
The diagram shows the subset of classes involved in an *OPC UA Publisher* configuration.

![SubscriberConfigClasses](../../Docs/Images/SubscriberConfigClasses.png)