Minimal Mediator is a lightweight library for implementing the mediator pattern in .NET Minimal APIs.

Lightweight and fast, it is designed to be used in high-performance applications with no overhead.

Minimal Mediator runs in-process without any serialization or reflection.

Native AOT compilation is supported.

Support for publishing/sending messages.

Support for streaming requests and responses based on System.Threading.Channels and IAsyncEnumerable.

The implementation provides a simple middleware pipeline workflow for handling requests and responses that is easy to extend and customize.

Install the MinimalMediator NuGet package.

dotnet add package MinimalMediator

Minimal Mediator supports Microsoft.Extensions.DependencyInjection and Microsoft.Extensions.Hosting for dependency injection and configuration.

There are three possible ways to initialize the mediator services:

• using Source Generators - automatically by scanning the assembly for handlers and generating the mediator code

builder.Services.AddMinimalMediator(config => config.UseSourceGenerator());

• using Reflection - automatically by scanning the assembly for handlers and registering them in the service collection

builder.Services.AddMinimalMediator(config => config.UseReflection(typeof(Program)));

• Manually by registering the mediator and handlers in the service collection

builder.Services.AddMinimalMediator(config =>
{
    config.AddConsumer(typeof(IConsumer<TestMessage>), typeof(Consumer2));
    config.AddMiddleware(typeof(IAfterPublishMiddleware<TestMessage>), typeof(AfterMiddleware1));
    config.AddReceiver(typeof(IReceiver<TestMessage, TestResponse>), typeof(ReceiverTest));
});

Minimal Mediator supports two types of invocations:

• Publish/Subscribe - broadcast a message to all consumers
• Request/Response - send a message and receive a response. This also supports streaming requests and responses.

Minimal Mediator supports publishing messages to all consumers that implement the IConsumer<TMessage> interface.

public interface IConsumer<TMessage>
{
    Task ConsumeAsync(TMessage message, CancellationToken cancellationToken);
}

The mediator will invoke all consumers in parallel.

Because the mediator implements middleware pipelines, it is possible to add middleware that will be invoked before and after the message is published.

This behavior is only valid for the Publish/Subscribe invocation. The Request/Response invocation does not support middleware.

There are three types of middleware:

• IBeforePublishMiddleware - invoked before the message is published
• IAfterPublishMiddleware - invoked after the message is published
• IExceptionHandlerMiddleware - invoked if an exception is thrown during the message publishing

Multiple middleware can be registered of a specific type/message and they will be invoked in the order they are registered.

To control the order of middleware, use the Order property of the MinimalMediatorAttribute class. The order is important only for middleware of the same type.

The presence of this attribute is not required. If it is not present, the middleware will be invoked in the order they are registered.

[MinimalMediator(Order = 2)]
public class AfterMiddleware2 : IAfterPublishMiddleware<TestMessage>
{
    ...
}

Minimal Mediator supports sending and receiving messages and streams. The functionalities are provided by the following interfaces:

• IReceiver<TMessage, TResponse> - used for sending a message and receiving a response
• IReceiverStreamAsync<TMessage, TResponse> - used for sending a IAsyncEnumerable stream of messages and receiving a TResponse message
• IReceiverStreamChannel<TMessage, TResponse> - used for sending a ChannelReader stream of messages and receiving a TResponse message
• IReceiverConsumeStreamAsync<TMessage, TResponse> - used for sending a TMessage message and receiving a IAsyncEnumerable stream of messages
• IReceiverConsumeStreamChannel<TMessage, TResponse> - used for sending a TMessage message and receiving a ChannelReader stream of messages

See the sample project and tests for more details.

The default lifetime of the IMediator service is Singleton. There is also a Scoped lifetime available that can be enabled from the configuration.

builder.Services.AddMinimalMediator(config => config.UseSourceGenerator(), ServiceLifetime.Scoped);

When IMediator registered as Scoped lifetime, the mediator creates/manages its own scope that has the same lifetime as the IMediator instance.

MIT