Middleman 1.0.4

Middleman 🤝

Middleman is a lightweight, in-process mediator library for .NET focused on CQRS-style request/query dispatching and notification (event) publication.

Installation

dotnet add package Middleman

Target Frameworks

• Middleman: net9.0, netstandard2.0
• Middleman.FluentValidation: net9.0

Core Concepts

• IMiddleman: Main dispatcher interface (send, publish, stream).
• IRequest<TResponse>: Request/query with a single response.
• IRequest: Request with no response.
• IStreamRequest<TResponse>: Request/query that returns IAsyncEnumerable<TResponse>.
• INotification: Marker for published events/notifications.

Quick Start

1) Define Contracts

using Middleman;

public sealed class CreateUserRequest : IRequest<Guid>
{
    public CreateUserRequest(string name) => Name = name;
    public string Name { get; }
}

public sealed class UserCreatedNotification : INotification
{
    public UserCreatedNotification(Guid userId) => UserId = userId;
    public Guid UserId { get; }
}

2) Implement Handlers

using Middleman;

public sealed class CreateUserRequestHandler : IRequestHandler<CreateUserRequest, Guid>
{
    private readonly IMiddleman _middleman;

    public CreateUserRequestHandler(IMiddleman middleman)
    {
        _middleman = middleman;
    }

    public async Task<Guid> Handle(CreateUserRequest message, CancellationToken cancellationToken)
    {
        var id = Guid.NewGuid();
        await _middleman.Publish(new UserCreatedNotification(id), cancellationToken);
        return id;
    }
}

public sealed class UserCreatedLogger : INotificationHandler<UserCreatedNotification>
{
    public Task Handle(UserCreatedNotification notification, CancellationToken cancellationToken)
    {
        Console.WriteLine($"User created: {notification.UserId}");
        return Task.CompletedTask;
    }
}

3) Register in DI

using System.Reflection;
using Middleman;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddMiddleman(Assembly.GetExecutingAssembly(), options =>
{
    options.PublishStrategy = NotificationPublishStrategy.Parallel;
    options.ContinueOnException = false;
});

// Optional: enable in-memory request response caching
builder.Services.AddMiddlemanCaching();

4) Dispatch

var id = await middleman.Send(new CreateUserRequest("joao"), cancellationToken);

Release Notes (March 2026)

Added

• Core package multi-target support for net9.0 and netstandard2.0

• Centralized exception handling behavior

  • IExceptionHandler<TRequest, TResponse>
  • IExceptionHandler<TRequest>
  • ExceptionHandlingBehavior<TRequest, TResponse>
  • ExceptionHandlingBehavior<TRequest>

• Response caching behavior for requests

  • ICacheableRequest<TResponse>
  • CachingBehavior<TRequest, TResponse>
  • AddMiddlemanCaching()

• Configurable notification publish strategies

  • MiddlemanOptions
  • NotificationPublishStrategy.Parallel
  • NotificationPublishStrategy.Sequential
  • ContinueOnException

• Async stream request support

  • IStreamRequest<TResponse>
  • IStreamRequestHandler<TRequest, TResponse>
  • CreateStream<TResponse>(...) on sender/dispatcher

Internal Improvements

• Safer reflective invocation for handlers and pipeline behaviors.
• Expanded xUnit coverage for exception handling, caching, publish strategy, and streaming.

API Overview

Contributing

Contributions are welcome. Open an issue or submit a pull request.

License

This project is licensed under the MIT License. See LICENSE for details.