Shuttle.Esb

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Publish / Subscribe

INFO

Remember that you can download the samples from the GitHub repository.

This sample makes use of Shuttle.Esb.AzureMQ for the message queues. Local Azure Storage Queues should be provided by Azurite.

Once you have opened the Shuttle.PublishSubscribe.sln solution in Visual Studio set the following projects as startup projects:

  • Shuttle.PublishSubscribe.Client
  • Shuttle.PublishSubscribe.Server
  • Shuttle.PublishSubscribe.Subscriber

You will also need to create and configure a Sql Server database for this sample and remember to update the App.config connectionString settings to point to your database. Please reference the Database section below.

Implementation

Events are interesting things that happen in our system that other systems may be interested in. There may be 0..N number of subscribers for an event. Typically there should be at least one subscriber to an event.

In this guide we'll create the following projects:

  • Shuttle.PublishSubscribe.Client (Console Application)
  • Shuttle.PublishSubscribe.Server (Console Application)
  • Shuttle.PublishSubscribe.Subscriber (Console Application)
  • Shuttle.PublishSubscribe.Messages (Class Library)

Messages

Create a new class library called Shuttle.PublishSubscribe.Messages with a solution called Shuttle.PublishSubscribe

Note: remember to change the Solution name.

RegisterMemberCommand

Rename the Class1 default file to RegisterMemberCommand and add a UserName property.

namespace Shuttle.PublishSubscribe.Messages
{
	public class RegisterMemberCommand
	{
		public string UserName { get; set; }
	}
}

MemberRegisteredEvent

Add a new class called MemberRegisteredEvent also with a UserName property.

namespace Shuttle.PublishSubscribe.Messages
{
	public class MemberRegisteredEvent
	{
		public string UserName { get; set; }
	}
}

Client

Add a new Console Application to the solution called Shuttle.PublishSubscribe.Client.

Install the Shuttle.Esb.AzureMQ nuget package.

This will provide access to the Azure Storage Queues IQueue implementation and also include the required dependencies.

Install the Shuttle.Core.StructureMap nuget package.

This will provide access to the StructureMap dependency injection container.

Add a reference to the Shuttle.PublishSubscribe.Messages project.

Program

Implement the main client code as follows:

using System;
using Shuttle.Core.Container;
using Shuttle.Core.StructureMap;
using Shuttle.Esb;
using Shuttle.Esb.AzureMQ;
using Shuttle.PublishSubscribe.Messages;
using StructureMap;

namespace Shuttle.PublishSubscribe.Client
{
	internal class Program
	{
		private static void Main(string[] args)
		{
			var registry = new Registry();
			var componentRegistry = new StructureMapComponentRegistry(registry);

			componentRegistry.Register<IAzureStorageConfiguration, DefaultAzureStorageConfiguration>();
			componentRegistry.RegisterServiceBus();

			using (var bus = new StructureMapComponentResolver(new Container(registry)).Resolve<IServiceBus>().Start())
			{
				string userName;

				while (!string.IsNullOrEmpty(userName = Console.ReadLine()))
				{
					bus.Send(new RegisterMemberCommand
					{
						UserName = userName
					});
				}
			}
		}
	}
}

App.config

Create the relevant configuration as follows:

<?xml version="1.0" encoding="utf-8"?>

<configuration>
	<configSections>
		<section name='serviceBus' type="Shuttle.Esb.ServiceBusSection, Shuttle.Esb" />
	</configSections>

	<appSettings>
		<add key="azure" value="UseDevelopmentStorage=true;" />
	</appSettings>

	<serviceBus>
		<messageRoutes>
			<messageRoute uri="azuremq://azure/shuttle-server-work">
				<add specification="StartsWith" value="Shuttle.PublishSubscribe.Messages" />
			</messageRoute>
		</messageRoutes>
	</serviceBus>
</configuration>

This tells the service bus that all messages sent having a type name starting with Shuttle.PublishSubscribe.Messages should be sent to endpoint azuremq://azure/shuttle-server-work.

Server

Add a new Console Application to the solution called Shuttle.PublishSubscribe.Server.

Install the Shuttle.Esb.AzureMQ nuget package.

This will provide access to the Azure Storage Queues IQueue implementation and also include the required dependencies.

Install the Shuttle.Core.WorkerService nuget package.

This allows a console application to be hosted as a Windows Service or Systemd Unit while running as a normal console application when debugging.

Install the Shuttle.Core.StructureMap nuget package.

This will provide access to the StructureMap dependency injection container.

Install the Shuttle.Esb.Sql.Subscription nuget package.

This will provide access to the Sql-based ISubscriptionManager implementation.

Install the Microsoft.Data.SqlClient nuget package.

This will provide a connection to our Sql Server.

Add a reference to the Shuttle.PublishSubscribe.Messages project.

Program

Implement the Program class as follows:

using System.Data.Common;
using Microsoft.Data.SqlClient;
using Shuttle.Core.WorkerService;

namespace Shuttle.PublishSubscribe.Server
{
    public class Program
    {
        public static void Main()
        {
            DbProviderFactories.RegisterFactory("Microsoft.Data.SqlClient", SqlClientFactory.Instance);

            ServiceHost.Run<Host>();
        }
    }
}

This will simply run the Host implementation.

Host

Add a Host class and implement the IServiceHost interface as follows:

using Shuttle.Core.Container;
using Shuttle.Core.Data;
using Shuttle.Core.StructureMap;
using Shuttle.Core.WorkerService;
using Shuttle.Esb;
using Shuttle.Esb.AzureMQ;
using Shuttle.Esb.Sql.Subscription;
using StructureMap;

namespace Shuttle.PublishSubscribe.Server
{
    public class Host : IServiceHostStart
    {
        private IServiceBus _bus;

        public void Start()
        {
            var registry = new Registry();
            var componentRegistry = new StructureMapComponentRegistry(registry);

            componentRegistry.Register<IAzureStorageConfiguration, DefaultAzureStorageConfiguration>();
            componentRegistry.RegisterDataAccess();
            componentRegistry.RegisterSubscription();
            componentRegistry.RegisterServiceBus();

            _bus = new StructureMapComponentResolver(new Container(registry)).Resolve<IServiceBus>().Start();
        }

        public void Stop()
        {
            _bus?.Dispose();
        }
    }
}

Database

We need a store for our subscriptions. In this example we will be using Sql Server. Remember to make any required changges to the relevant connection strings.

When you reference the Shuttle.Esb.Sql.Subscription package a scripts folder is included in the relevant package folder. Click on the Nuget referenced assembly in the References or Dependencies (depending on your project type) and navigate to the package folder to find the scripts folder.

The {version} bit will be in a semver format.

Create a new database called Shuttle and execute the script {provider}\SubscriptionManagerCreate.sql in the newly created database.

This will create the required structures that the subscription manager will use to store the subcriptions.

Whenever the Publish method is invoked on the ServiceBus instance the registered ISubscriptionManager instance is asked for the subscribers to the published message type. These are retrieved from the Sql Server database for the implementation we are using.

App.config

Add an Application Configuration File item to create the App.config and populate as follows:

<?xml version="1.0" encoding="utf-8"?>

<configuration>
	<configSections>
		<section name='serviceBus' type="Shuttle.Esb.ServiceBusSection, Shuttle.Esb" />
	</configSections>

	<appSettings>
		<add key="azure" value="UseDevelopmentStorage=true;" />
	</appSettings>

	<connectionStrings>
		<add name="Subscription"
		     connectionString="server=.;database=shuttle;user id=sa;password=Pass!000;TrustServerCertificate=True"
		     providerName="Microsoft.Data.SqlClient" />
	</connectionStrings>

	<serviceBus>
		<inbox
			workQueueUri="azuremq://azure/shuttle-server-work"
			errorQueueUri="azuremq://azure/shuttle-error" />
	</serviceBus>
</configuration>

The Sql Server implementation of the ISubscriptionManager that we are using by default will try to find a connection string with a name of Subscription. However, you can override this. See the [Sql Server configuration options][sql-server] for details about how to do this.

RegisterMemberHandler

Add a new class called RegisterMemberHandler that implements the IMessageHandler<RegisterMemberCommand> interface as follows:

using System;
using Shuttle.Esb;
using Shuttle.PublishSubscribe.Messages;

namespace Shuttle.PublishSubscribe.Server
{
	public class RegisterMemberHandler : IMessageHandler<RegisterMemberCommand>
	{
		public void ProcessMessage(IHandlerContext<RegisterMemberCommand> context)
		{
			Console.WriteLine();
			Console.WriteLine("[MEMBER REGISTERED] : user name = '{0}'", context.Message.UserName);
			Console.WriteLine();

			context.Publish(new MemberRegisteredEvent
			{
				UserName = context.Message.UserName
			});
		}
	}
}

This will write out some information to the console window and publish the MemberRegisteredEvent message.

Subscriber

Add a new Console Application to the solution called Shuttle.PublishSubscribe.Subscriber.

Install the Shuttle.Esb.AzureMQ nuget package.

This will provide access to the Azure Storage Queues IQueue implementation and also include the required dependencies.

Install the Shuttle.Core.WorkerService nuget package.

This allows a console application to be hosted as a Windows Service or Systemd Unit while running as a normal console application when debugging.

Install the Shuttle.Core.StructureMap nuget package.

This will provide access to the StructureMap dependency injection container.

Install the Shuttle.Esb.Sql.Subscription nuget package.

This will provide access to the Sql-based ISubscriptionManager implementation.

Install the Microsoft.Data.SqlClient nuget package.

This will provide a connection to our Sql Server.

Add a reference to the Shuttle.PublishSubscribe.Messages project.

Program

Implement the Program class as follows:

using System.Data.Common;
using Microsoft.Data.SqlClient;
using Shuttle.Core.WorkerService;

namespace Shuttle.PublishSubscribe.Subscriber
{
    public class Program
    {
        public static void Main()
        {
            DbProviderFactories.RegisterFactory("Microsoft.Data.SqlClient", SqlClientFactory.Instance);

            ServiceHost.Run<Host>();
        }
    }
}

This will simply run the Host implementation.

Host

Add a Host class and implement the IServiceHost interface as follows:

using Shuttle.Core.Container;
using Shuttle.Core.Data;
using Shuttle.Core.StructureMap;
using Shuttle.Core.WorkerService;
using Shuttle.Esb;
using Shuttle.Esb.AzureMQ;
using Shuttle.Esb.Sql.Subscription;
using Shuttle.PublishSubscribe.Messages;
using StructureMap;

namespace Shuttle.PublishSubscribe.Subscriber
{
    public class Host : IServiceHostStart
    {
        private IServiceBus _bus;

        public void Start()
        {
            var registry = new Registry();
            var componentRegistry = new StructureMapComponentRegistry(registry);

            componentRegistry.Register<IAzureStorageConfiguration, DefaultAzureStorageConfiguration>();
            componentRegistry.RegisterDataAccess();
            componentRegistry.RegisterSubscription();
            componentRegistry.RegisterServiceBus();

            var resolver = new StructureMapComponentResolver(new Container(registry));

            resolver.Resolve<ISubscriptionManager>().Subscribe<MemberRegisteredEvent>();

            _bus = resolver.Resolve<IServiceBus>().Start();
        }

        public void Stop()
        {
            _bus.Dispose();
        }
    }
}

Here we register the subscription by calling the ISubscriptionManager implementation's Subscribe<MemberRegisteredEvent>(); method. Since we are using the Sql Server implementation of the ISubscriptionManager interface an entry will be created in the SubscriberMessageType table associating the inbox work queue uri with the message type.

It is important to note that in a production environment one would not typically register subscriptions in this manner as they may be somewhat more sensitive as we do not want any arbitrary subscriber listening in on the messages being published. For this reason the connection string should be read-only and the subscription should be registered manually or via a deployment script. Should the subscription not yet exist the creation of the subscription will fail, indicating that the subscription should be registered out-of-band.

App.config

Add an Application Configuration File item to create the App.config and populate as follows:

<?xml version="1.0" encoding="utf-8"?>

<configuration>
	<configSections>
		<section name='serviceBus' type="Shuttle.Esb.ServiceBusSection, Shuttle.Esb" />
		<section name="subscription" type="Shuttle.Esb.Sql.Subscription.SubscriptionSection, Shuttle.Esb.Sql.Subscription" />
	</configSections>

	<appSettings>
		<add key="azure" value="UseDevelopmentStorage=true;" />
	</appSettings>

	<connectionStrings>
		<add name="Subscription"
		     connectionString="server=.;database=shuttle;user id=sa;password=Pass!000;TrustServerCertificate=True"
		     providerName="Microsoft.Data.SqlClient" />
	</connectionStrings>

	<serviceBus>
		<inbox
			workQueueUri="azuremq://azure/shuttle-subscriber-work"
			errorQueueUri="azuremq://azure/shuttle-error" />
	</serviceBus>
</configuration>

MemberRegisteredHandler

Add a new class called MemberRegisteredHandler that implements the IMessageHandler<MemberRegisteredHandler> interface as follows:

using System;
using Shuttle.Esb;
using Shuttle.PublishSubscribe.Messages;

namespace Shuttle.PublishSubscribe.Subscriber
{
	public class MemberRegisteredHandler : IMessageHandler<MemberRegisteredEvent>
	{
		public void ProcessMessage(IHandlerContext<MemberRegisteredEvent> context)
		{
			Console.WriteLine();
			Console.WriteLine("[EVENT RECEIVED] : user name = '{0}'", context.Message.UserName);
			Console.WriteLine();
		}
	}
}

This will write out some information to the console window.

Run

Set the client, server, and subscriber projects as startup projects.

Execute

Execute the application.

The client application will wait for you to input a user name. For this example enter my user name and press enter:

INFO

You will observe that the server application has processed the message.

INFO

The subscriber application will then process the event published by the server.

You have now completed a full publish / subscribe call chain.