SkathIO.Rogue

AOT-safe, source-generated CQRS/mediator for .NET. Free and MIT-licensed forever.

Rogue is a drop-in alternative to MediatR built for the modern .NET ecosystem: reflection-free dispatch via Roslyn source generation, Native AOT support, zero-allocation on the hot path, and a ValueTask-based pipeline — with no commercial license required, now or ever.

---

Why Rogue?

	MediatR	martinothamar/Mediator	SkathIO.Rogue
License	Commercial (v13+)	MIT	MIT
Dispatch	Reflection	Source-gen (monomorphized)	Source-gen (DI-resolved)
Native AOT	No	Yes	Yes
Pipeline behaviors	Open generic	Open generic	Open generic + [BehaviorOrder]
Streaming	No	No	IAsyncEnumerable<T>
Migration path from MediatR	—	Manual	One-line + compat shim

Benchmarks: Rogue meets or beats MediatR across the measured warm-path scenarios (single-handler Send, notification fan-out at N = 2 / 5 / 20, and validated Send with a real FluentValidation behavior) and leads cold-start by ~18.5×. See docs/benchmarks.md and bench/RESULTS.md for the full measured tables and methodology.

---

Installation

dotnet add package SkathIO.Rogue

For library authors who only need the interfaces (no source generator or DI wiring):

dotnet add package SkathIO.Rogue.Abstractions

Optional integration packages (v1.0):

dotnet add package SkathIO.Rogue.Logging
dotnet add package SkathIO.Rogue.Validation.FluentValidation

---

Quick start

1. Register

// Program.cs
builder.Services.AddRogue();

The source generator discovers all IQueryHandler<,>, ICommandHandler<> / ICommandHandler<,>, IEventHandler<>, and IStreamQueryHandler<,> types in your project at compile time — no assembly scanning, no reflection.

2. Define requests and handlers

// Queries return data
public record GetUserQuery(int Id) : IQuery<User>;

public class GetUserQueryHandler : IQueryHandler<GetUserQuery, User>
{
    public ValueTask<User> Handle(GetUserQuery query, CancellationToken ct)
        => ValueTask.FromResult(new User(query.Id, "Alice"));
}

// Commands signal intent
public record CreateOrderCommand(string ProductId, int Qty) : ICommand<OrderId>;

public class CreateOrderCommandHandler : ICommandHandler<CreateOrderCommand, OrderId>
{
    public async ValueTask<OrderId> Handle(CreateOrderCommand cmd, CancellationToken ct)
    {
        // ... create the order
        return new OrderId(Guid.NewGuid());
    }
}

// Events fan out to all handlers
public record OrderPlacedEvent(OrderId OrderId) : IEvent;

public class SendOrderConfirmationHandler : IEventHandler<OrderPlacedEvent>
{
    public ValueTask Handle(OrderPlacedEvent @event, CancellationToken ct)
    {
        // ... send email
        return ValueTask.CompletedTask;
    }
}

3. Send

// Inject ISender / IPublisher via DI
public class OrderController(ISender sender, IPublisher publisher)
{
    public async Task<IActionResult> PlaceOrder(PlaceOrderRequest req)
    {
        var orderId = await sender.Send(new CreateOrderCommand(req.ProductId, req.Qty));
        await publisher.Publish(new OrderPlacedEvent(orderId));
        return Ok(orderId);
    }
}

4. Stream

public record PagedProductsQuery(int PageSize) : IStreamQuery<Product>;

public class PagedProductsHandler : IStreamQueryHandler<PagedProductsQuery, Product>
{
    public async IAsyncEnumerable<Product> Handle(
        PagedProductsQuery query,
        [EnumeratorCancellation] CancellationToken ct)
    {
        await foreach (var product in FetchPagedAsync(query.PageSize, ct))
            yield return product;
    }
}

// Usage
await foreach (var product in sender.CreateStream(new PagedProductsQuery(50)))
    Console.WriteLine(product.Name);

---

Scoped dispatch

AddRogue() registers ISender / IMediator (and the underlying dispatcher) as Scoped — one mediator instance per request/scope, matching the standard mediator-pattern lifetime. That means ISender/IMediator must be resolved from within a scope, not from the root IServiceProvider.

For ASP.NET Core controllers/minimal-API handlers, constructor/parameter injection already resolves from the current request's scope — no extra work needed (see the Quick start example above). The failure case is code that runs outside a request scope: hosted services, background workers, and startup/seeding code.

// Wrong — throws at resolution time
public class OutboxProcessor(IServiceProvider provider) : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken ct)
    {
        var sender = provider.GetRequiredService<ISender>(); // throws
        ...
    }
}

// Right — create a scope first
public class OutboxProcessor(IServiceScopeFactory scopeFactory) : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            using var scope = scopeFactory.CreateScope();
            var sender = scope.ServiceProvider.GetRequiredService<ISender>();
            await sender.Send(new ProcessOutboxCommand(), ct);
            await Task.Delay(TimeSpan.FromSeconds(30), ct);
        }
    }
}

Resolving ISender/IMediator from the root provider throws:

System.InvalidOperationException: Cannot resolve scoped service 'SkathIO.Rogue.ISender' from root provider.

This is standard Microsoft.Extensions.DependencyInjection scope-validation behavior for any Scoped service resolved from the root container — it applies equally with or without any optional Rogue integration package (e.g. SkathIO.Rogue.Validation.FluentValidation) installed, since it's a property of the mediator's own Scoped registration, not of any particular pipeline behavior.

Note: the .NET Generic Host only enables this scope validation (ValidateScopes) by default in the Development environment. Outside Development — the default in most deployed configurations — resolving from the root provider does not throw; it silently succeeds with an instance captured against the root container, effectively a singleton mediator that never sees per-request scoped state. That's a worse failure mode than the exception above precisely because it's silent. Create a scope regardless of environment; don't rely on the exception as your only signal.

---

Pipeline behaviors

Behaviors wrap every request in the pipeline — use them for logging, validation, caching, or any cross-cutting concern.

public class LoggingBehavior<TRequest, TResponse>(ILogger<LoggingBehavior<TRequest, TResponse>> logger)
    : IPipelineBehavior<TRequest, TResponse>
    where TRequest : notnull
{
    public async ValueTask<TResponse> Handle(
        TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken ct)
    {
        logger.LogInformation("Handling {Request}", typeof(TRequest).Name);
        var result = await next();
        logger.LogInformation("Handled {Request}", typeof(TRequest).Name);
        return result;
    }
}

Register open behaviors — they apply to all request types automatically:

builder.Services.AddRogue(opts =>
    opts.AddOpenBehavior(typeof(LoggingBehavior<,>)));

Control pipeline order with [BehaviorOrder] (lower = outermost, executes first):

[BehaviorOrder(-10)]  // outermost — runs before everything else
public class TracingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse> { ... }

[BehaviorOrder(10)]   // inner — runs just before the handler
public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse> { ... }

Validators: zero wiring, unlike behaviors

A custom behavior sometimes needs an explicit AddOpenBehavior call, as above. A FluentValidation validator never does. SkathIO.Rogue.Validation.FluentValidation discovers every AbstractValidator<T> at compile time and registers it into DI automatically — no AddOpenBehavior, no AddValidatorsFromAssembly-style scan, nothing:

public sealed class CreateOrderCommandValidator : AbstractValidator<CreateOrderCommand>
{
    public CreateOrderCommandValidator() => RuleFor(x => x.Quantity).GreaterThan(0);
}

// Program.cs — unchanged. Referencing the package and writing the validator above is the entire
// contract; there is no corresponding AddRogue(o => ...) call to add.
builder.Services.AddRogue();

ValidationBehavior<TRequest, TResponse> itself is still auto-woven into the pipeline the same way LoggingBehavior is above — referencing SkathIO.Rogue.Validation.FluentValidation is enough. See Validation behavior for the full contract, an important note if you're upgrading from a version that predates validator auto-discovery, and the ExcludeAssets="analyzers" opt-out.

---

Performance

Rogue dispatches via source-generated, DI-resolved methods — no reflection on the hot path.

• 0 bytes allocated on the generated concrete dispatch path (RogueDispatcher.Send{Request}) for a behavior-free, synchronously-completing handler; the portable ISender.Send<T> path boxes one ValueTask<T> by design
• Faster than MediatR on the measured warm paths (single-handler Send, notification fan-out at N = 2 / 5 / 20) and ~19× faster cold-start — no runtime assembly scan
• Native AOT compatible — no dynamic code generation, no Expression.Compile(), no MakeGenericMethod
• ValueTask-based throughout — avoids unnecessary heap allocations vs Task

Full benchmark results and methodology: docs/benchmarks.md and bench/RESULTS.md.

---

Migration from MediatR

Most MediatR code migrates in one step:

- services.AddMediatR(cfg => cfg.RegisterServicesFromAssemblyContaining<Program>());
+ services.AddRogue();

Rogue's native core is CQS-explicit (IQuery<T>, ICommand / ICommand<T>, IEvent, IStreamQuery<T>). For drop-in migration, the SkathIO.Rogue.MediatR package provides the MediatR-shaped surface (IRequest<T>, IRequestHandler<,>, INotification, INotificationHandler<>, IStreamRequest<T>, …) under the SkathIO.Rogue.Compatibility namespace, plus an AddMediatR(...) shim so existing IMediator injection points keep working. A bundled Roslyn analyzer (ROGM001–006) ships code-fixes — including rewrites to the native CQS contracts.

See the migration guide and the before/after sample.

---

Packages

Package	Purpose
SkathIO.Rogue	Core library — source generator + DI wiring + dispatcher
SkathIO.Rogue.Abstractions	Interfaces only — for library authors
SkathIO.Rogue.Logging	LoggingBehavior<,> — structured request/response logging (v1.0)
SkathIO.Rogue.Validation.FluentValidation	ValidationBehavior<,> — FluentValidation pipeline integration (v1.0)
SkathIO.Rogue.MediatR	MediatR compatibility shim — IMediator adapter (v1.0)

---

Requirements

• .NET 8.0+ (or .NET Standard 2.0 for library authors)
• C# 10+ (source generator produces modern C#)
• Supports Native AOT on .NET 8+

---

Contributing

See CONTRIBUTING.md. All contributions are welcome — open an issue before starting large changes.

---

License

MIT — free forever, no exceptions.