Configuration Extensions

Wolverine supports the concept of extensions for modularizing Wolverine configuration with implementations of the IWolverineExtension interface:

/// <summary>
///     Use to create loadable extensions to Wolverine applications
/// </summary>
public interface IWolverineExtension
{
    /// <summary>
    ///     Make any alterations to the WolverineOptions for the application
    /// </summary>
    /// <param name="options"></param>
    void Configure(WolverineOptions options);
}

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Here's a sample:

public class SampleExtension : IWolverineExtension
{
    public void Configure(WolverineOptions options)
    {
        // Add service registrations
        options.Services.AddTransient<IFoo, Foo>();

        // Alter settings within the application
        options
            .UseNewtonsoftForSerialization(settings => settings.TypeNameHandling = TypeNameHandling.None);
    }
}

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Extensions can be applied programmatically against the WolverineOptions like this:

using var host = await Host.CreateDefaultBuilder()
    .UseWolverine(opts =>
    {
        // Including a single extension
        opts.Include<SampleExtension>();
        
        // Or add a Wolverine extension that needs
        // to use IoC services
        opts.Services.AddWolverineExtension<ConfigurationUsingExtension>();

    })
    
    .ConfigureServices(services =>
    {
        // This is the same logical usage, just showing that it
        // can be done directly against IServiceCollection
        services.AddWolverineExtension<ConfigurationUsingExtension>();
    })
    
    .StartAsync();

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Lastly, you can also add IWolverineExtension types to your IoC container registration that will be applied to WolverineOptions just before bootstrapping Wolverine at runtime. This was originally added to allow for test automation scenarios where you might want to override part of the Wolverine setup during tests. As an example, consider this common usage for disabling external transports during testing:

// This is using Alba to bootstrap a Wolverine application
// for integration tests, but it's using WebApplicationFactory
// to do the actual bootstrapping
await using var host = await AlbaHost.For<Program>(x =>
{
    // I'm overriding 
    x.ConfigureServices(services => services.DisableAllExternalWolverineTransports());
});

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Behind the scenes, Wolverine has a small extension like this:

internal class DisableExternalTransports : IWolverineExtension
{
    public void Configure(WolverineOptions options)
    {
        options.ExternalTransportsAreStubbed = true;
    }
}

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And that extension is just added to the application's IoC container at test bootstrapping time like this:

public static IServiceCollection DisableAllExternalWolverineTransports(this IServiceCollection services)
{
    services.AddSingleton<IWolverineExtension, DisableExternalTransports>();
    return services;
}

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In usage, the IWolverineExtension objects added to the IoC container are applied after the inner configuration inside your application's UseWolverine() set up.

As another example, IWolverineExtension objects added to the IoC container can also use services injected into the extension object from the IoC container as shown in this example that uses the .NET IConfiguration service:

public class ConfigurationUsingExtension : IWolverineExtension
{
    private readonly IConfiguration _configuration;

    // Use constructor injection from your DI container at runtime
    public ConfigurationUsingExtension(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public void Configure(WolverineOptions options)
    {
        // Configure the wolverine application using 
        // the information from IConfiguration
    }
}

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There's also a small helper method to register Wolverine extensions like so:

Modifying Transport Configuration

If your Wolverine extension needs to apply some kind of extra configuration to the transport integration, most of the transport packages support a WolverineOptions.ConfigureTransportName() extension method that will let you make additive configuration changes to the transport integration for items like declaring extra queues, topics, exchanges, subscriptions or overriding dead letter queue behavior. For example:

1. ConfigureRabbitMq()
2. ConfigureKafka()
3. ConfigureAzureServiceBus()
4. ConfigureAmazonSqs()

Asynchronous Extensions

TIP

This was added to Wolverine 2.3, specifically for a user needing to use the Feature Flag library from Microsoft.

There is also any option for creating Wolverine extensions that need to use asynchronous methods to configure the WolverineOptions using the IAsyncWolverineExtension library. A sample is shown below:

public class SampleAsyncExtension : IAsyncWolverineExtension
{
    private readonly IFeatureManager _features;

    public SampleAsyncExtension(IFeatureManager features)
    {
        _features = features;
    }

    public async ValueTask Configure(WolverineOptions options)
    {
        if (await _features.IsEnabledAsync("Module1"))
        {
            // Make any kind of Wolverine configuration
            options
                .PublishMessage<Module1Message>()
                .ToLocalQueue("module1-high-priority")
                .Sequential();
        }
    }
}

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Which can be added to your application with this extension method on IServiceCollection:

using var host = await Host.CreateDefaultBuilder()
    .UseWolverine(opts =>
    {
        opts.Services.AddFeatureManagement();
        opts.Services.AddSingleton(featureManager);

        // Adding the async extension to the underlying IoC container
        opts.Services.AddAsyncWolverineExtension<SampleAsyncExtension>();

    }).StartAsync();

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Asynchronous Extensions and Wolverine.HTTP

Just a heads up, there's a timing issue between the application of asynchronous Wolverine extensions and the usage of the Wolverine.HTTP MapWolverineEndpoints() method. If you need the asynchronous extensions to apply to the HTTP configuration, you need to help Wolverine out by explicitly calling this method in your Program file after building the WebApplication, but before calling MapWolverineEndpoints() like so:

var app = builder.Build();

// In order for async Wolverine extensions to apply to Wolverine.HTTP configuration,
// you will need to explicitly call this *before* MapWolverineEndpoints()
await app.Services.ApplyAsyncWolverineExtensions();

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Wolverine Plugin Modules

TIP

Use this sparingly, but it might be advantageous for adding extra instrumentation or extra middleware

If you want to create a Wolverine extension assembly that automatically loads itself into an application just by being referenced by the project, you can use a combination of IWolverineExtension and the [WolverineModule] assembly attribute.

Assuming that you have an implementation of IWolverineExtension named Module1Extension, you can mark your module library with this attribute to automatically add that extension to Wolverine:

[assembly: WolverineModule(typeof(Module1Extension))]

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