Idempotence #

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

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

• Shuttle.Idempotence.Client
• Shuttle.Idempotence.Server

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 #

When operations, or in our case messages, can be applied multiple times with the same result they are said to be idempotent. Idempotence is something you should strive to implement directly on your endpoint by keeping track of some unique property of each message and whether the operation has been completed for that unique property.

An IIdempotenceService implementation can assist with this from a technical point-of-view by allowing a particular message id to be handled only once. This works fine for our at-least-once delivery mechanism where, in some edge case, we may receive the same message again. However, it will not aid us when two messages are going to be sent, each with its own message id, but they contain the same data.

In this guide we'll create the following projects:

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

Messages #

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

Note: remember to change the Solution name.

RegisterMember #

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

namespace Shuttle.Idempotence.Messages
{
	public class RegisterMember
	{
		public string UserName { get; set; }
	}
}

Client #

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

Install the Shuttle.Esb.AzureStorageQueues nuget package.

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

Install the Microsoft.Extensions.Configuration.Json nuget package.

This will provide the ability to read the appsettings.json file.

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

Program #

Implement the main client code as follows:

using System;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Shuttle.Core.Pipelines;
using Shuttle.Esb;
using Shuttle.Esb.AzureStorageQueues;
using Shuttle.Idempotence.Messages;

namespace Shuttle.Idempotence.Client
{
	internal class Program
	{
		private static void Main(string[] args)
		{
			var services = new ServiceCollection();

			var configuration = new ConfigurationBuilder().AddJsonFile("appsettings.json").Build();

			services.AddSingleton<IConfiguration>(configuration);

			services.AddServiceBus(builder =>
			{
				configuration.GetSection(ServiceBusOptions.SectionName).Bind(builder.Options);
			});

			services.AddAzureStorageQueues(builder =>
			{
				builder.AddOptions("azure", new AzureStorageQueueOptions
				{
					ConnectionString = configuration.GetConnectionString("azure")
				});
			});

			Console.WriteLine("Type some characters and then press [enter] to submit; an empty line submission stops execution:");
			Console.WriteLine();

			var serviceProvider = services.BuildServiceProvider();
			var pipelineFactory = serviceProvider.GetRequiredService<IPipelineFactory>();
			var messageSender = serviceProvider.GetRequiredService<IMessageSender>();
			var transportMessagePipeline = pipelineFactory.GetPipeline<TransportMessagePipeline>();

			using (var bus = serviceProvider.GetRequiredService<IServiceBus>().Start())
			{
				string userName;

				while (!string.IsNullOrEmpty(userName = Console.ReadLine()))
				{
					var command = new RegisterMember
					{
						UserName = userName
					};

					transportMessagePipeline.Execute(command, null, null);

					var transportMessage = transportMessagePipeline.State.GetTransportMessage();

					for (var i = 0; i < 5; i++)
					{
						messageSender.Dispatch(transportMessage, null); // will be processed only once since message id is the same
					}

					bus.Send(command); // will be processed since it has a new message id
					bus.Send(command); // will also be processed since it too has a new message id
				}
			}
		}
	}
}

Keep in mind that the when you Send a message a TransportMessage envelope is created with a unique message id (Guid). In the above code we first manually create a TransportMessage so that we can send technically identical messages (with the same message id).

The next two Send operations do not use the TransportMessage but rather send individual messages. These will each have a TransportMessage envelope and, therefore, each have its own unique message id.

Client configuration file #

Add an appsettings.json file as follows:

{
  "ConnectionStrings": {
    "azure": "UseDevelopmentStorage=true;"
  },
  "Shuttle": {
    "ServiceBus": {
      "MessageRoutes": [
        {
          "Uri": "azuresq://azure/shuttle-server-work",
          "Specifications": [
            {
              "Name": "StartsWith",
              "Value": "Shuttle.Idempotence.Messages"
            }
          ]
        }
      ]
    }
  }
}

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

Server #

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

Install the Shuttle.Esb.AzureStorageQueues nuget package.

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

Install the Microsoft.Extensions.Hosting nuget package.

This allows a console application to be hosted using the .NET generic host.

Install the Microsoft.Extensions.Configuration.Json nuget package.

This will provide the ability to read the appsettings.json file.

Install the Shuttle.Esb.Sql.Idempotence package.

We will also have access to the Sql implementation of the IIdempotenceService.

Install the Microsoft.Data.SqlClient nuget package.

This will provide a connection to our Sql Server.

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

Program #

Implement the Program class as follows:

using System.Data.Common;
using Microsoft.Data.SqlClient;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Shuttle.Core.Data;
using Shuttle.Esb;
using Shuttle.Esb.AzureStorageQueues;
using Shuttle.Esb.Sql.Idempotence;

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

            Host.CreateDefaultBuilder()
                .ConfigureServices(services =>
                {
                    var configuration = new ConfigurationBuilder().AddJsonFile("appsettings.json").Build();

                    services.AddSingleton<IConfiguration>(configuration);

                    services.AddDataAccess(builder =>
                    {
                        builder.AddConnectionString("Idempotence", "Microsoft.Data.SqlClient");
                    });

                    services.AddServiceBus(builder =>
                    {
                        configuration.GetSection(ServiceBusOptions.SectionName).Bind(builder.Options);
                    });

                    services.AddSqlIdempotence();

                    services.AddAzureStorageQueues(builder =>
                    {
                        builder.AddOptions("azure", new AzureStorageQueueOptions
                        {
                            ConnectionString = configuration.GetConnectionString("azure")
                        });
                    });
                })
                .Build()
                .Run();
        }
    }
}

Database #

We need a store for our idempotence tracking. In this example we will be using Sql Server. If you use the express version remember to change the data source value to .\sqlexpress from the standard ..

When you reference the Shuttle.Esb.Sql.Idempotence package a scripts folder is included in the relevant package folder. Click on the NuGet referenced assembly in the Dependencies and navigate to the package folder (in the Path property) 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}\IdempotenceServiceCreate.sql in the newly created database.

Server configuration file #

Add an appsettings.json file as follows:

{
  "ConnectionStrings": {
    "azure": "UseDevelopmentStorage=true;",
    "Idempotence": "server=.;database=shuttle;user id=sa;password=Pass!000;TrustServerCertificate=True"
  },
  "Shuttle": {
    "ServiceBus": {
      "Inbox": {
        "WorkQueueUri": "azuresq://azure/shuttle-server-work",
        "DeferredQueueUri": "azuresq://azure/shuttle-server-deferre",
        "ErrorQueueUri": "azuresq://azure/shuttle-error"
      }
    }
  }
}

RegisterMemberHandler #

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

using System;
using Shuttle.Esb;
using Shuttle.Idempotence.Messages;

namespace Shuttle.Idempotence.Server
{
	public class RegisterMemberHandler : IMessageHandler<RegisterMember>
	{
		public void ProcessMessage(IHandlerContext<RegisterMember> context)
		{
			Console.WriteLine();
			Console.WriteLine("[MEMBER REGISTERED] : user name = '{0}' / message id = '{1}'",
				context.Message.UserName,
				context.TransportMessage.MessageId);
			Console.WriteLine();
		}
	}
}

This will write out some information to the console window.

Run #

Set both the client and server 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:

You have now implemented message idempotence.