HermesMediator.Testing 1.0.2

Hermes

High-performance mediator for .NET 10 — zero-reflection hot path, built-in OpenTelemetry, compile-time safety.

Por que Hermes?

Instalação

dotnet add package Hermes
dotnet add package Hermes.Testing  # apenas em projetos de teste

Configuração

builder.Services.AddHermes(cfg => cfg
    .RegisterServicesFromAssembly(typeof(Program).Assembly)
    .AddOpenBehavior(typeof(LoggingBehavior<,>)));

Uso

Request com retorno

public record GetUserQuery(int Id) : IRequest<User>;

public class GetUserQueryHandler : IRequestHandler<GetUserQuery, User>
{
    public Task<User> Handle(GetUserQuery request, CancellationToken ct)
        => _db.Users.FindAsync(request.Id, ct);
}

// Envio
var user = await mediator.Send(new GetUserQuery(42));

Command (sem retorno)

public record CreateUserCommand(string Name) : IRequest;

public class CreateUserCommandHandler : IRequestHandler<CreateUserCommand>
{
    public async Task<Unit> Handle(CreateUserCommand request, CancellationToken ct)
    {
        await _db.Users.AddAsync(new User(request.Name), ct);
        return Unit.Value;
    }
}

Notificações

public record UserCreated(int UserId) : INotification;

// Múltiplos handlers — todos recebem a notificação
public class SendWelcomeEmail : INotificationHandler<UserCreated> { ... }
public class UpdateAuditLog  : INotificationHandler<UserCreated> { ... }

await mediator.Publish(new UserCreated(userId));

Streams

public record GetOrdersQuery(int CustomerId) : IStreamRequest<Order>;

public class GetOrdersHandler : IStreamRequestHandler<GetOrdersQuery, Order>
{
    public async IAsyncEnumerable<Order> Handle(GetOrdersQuery request, CancellationToken ct)
    {
        await foreach (var order in _db.GetOrdersAsync(request.CustomerId, ct))
            yield return order;
    }
}

await foreach (var order in mediator.CreateStream(new GetOrdersQuery(customerId)))
    Process(order);

Pipeline Behaviors

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

// Registro
cfg.AddOpenBehavior(typeof(LoggingBehavior<,>));

Behavior Condicional

public class CacheBehavior<TRequest, TResponse>(ICache cache)
    : IConditionalBehavior<TRequest, TResponse>
    where TRequest : ICacheableRequest
{
    // Se retornar false, o behavior é pulado automaticamente — sem overhead
    public bool ShouldHandle(TRequest request) => !request.BypassCache;

    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken ct)
    {
        if (cache.TryGet(request.CacheKey, out TResponse? cached)) return cached!;
        var result = await next();
        cache.Set(request.CacheKey, result);
        return result;
    }
}

Atributos

Timeout automático

[RequestTimeout(5000)] // cancela automaticamente após 5 segundos
public record GetReportQuery : IRequest<Report>;

Ignorar behavior por request

[IgnoreBehavior(typeof(LoggingBehavior<,>))]
public record HealthCheckQuery : IRequest<bool>;

Tratamento de Exceções

Handler (pode suprimir a exceção)

public class NotFoundHandler : IRequestExceptionHandler<GetUserQuery, User, NotFoundException>
{
    public Task Handle(GetUserQuery request, NotFoundException ex,
        RequestExceptionHandlerState<User> state, CancellationToken ct)
    {
        state.SetHandled(User.Anonymous); // suprime a exceção e retorna alternativo
        return Task.CompletedTask;
    }
}

Action (side-effect, sempre relança)

public class ErrorLogger : IRequestExceptionAction<GetUserQuery, Exception>
{
    public Task Execute(GetUserQuery request, Exception ex, CancellationToken ct)
    {
        logger.LogError(ex, "Erro ao processar {Request}", request);
        return Task.CompletedTask; // exceção é repropagada automaticamente
    }
}

Pre/Post Processors

public class ValidationPreProcessor<TRequest>(IValidator<TRequest> validator)
    : IRequestPreProcessor<TRequest>
    where TRequest : notnull
{
    public async Task Process(TRequest request, CancellationToken ct)
    {
        var result = await validator.ValidateAsync(request, ct);
        if (!result.IsValid) throw new ValidationException(result.Errors);
    }
}

Contexto de Pipeline

public class AuditBehavior<TRequest, TResponse>(IPipelineContextAccessor accessor)
    : IPipelineBehavior<TRequest, TResponse>
    where TRequest : notnull
{
    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken ct)
    {
        accessor.Context!.Set("userId", GetCurrentUserId());
        return await next();
    }
}

// No handler ou em outro behavior:
var userId = accessor.Context?.Get<string>("userId");

Dispatch Dinâmico

// Útil quando o tipo é descoberto em runtime (ex: mediator genérico)
object request = ResolveRequest(commandName);
object? result = await mediator.Send(request);

object notification = new SomeEvent();
await mediator.Publish(notification);

Estratégias de Publicação

cfg.DefaultPublishStrategy = PublishStrategy.ForeachAwait;       // sequencial (padrão)
cfg.DefaultPublishStrategy = PublishStrategy.WhenAll;            // paralelo, agrega exceções
cfg.DefaultPublishStrategy = PublishStrategy.WhenAllContinueOnError; // paralelo, ignora falhas

TypeEvaluator — Filtrar Assembly Scanning

cfg.RegisterServicesFromAssembly(typeof(Program).Assembly)
   .TypeEvaluator = t => !t.Namespace?.StartsWith("MyApp.Legacy") ?? true;

Source Generator (registro zero-reflection)

O Hermes inclui um Source Generator que escaneia o assembly em compile-time e gera um método AddHermesGenerated() com registro estático de todos os handlers.

Isso elimina completamente o assembly scanning em runtime — startup instantâneo.

O generator é automaticamente incluído ao instalar o pacote Hermes.

Analyzer HRM001

Quando um IRequest não tem handler correspondente, o analyzer emite um aviso em compile-time:

warning HRM001: 'CreateUserCommand' implementa 'IRequest<Unit>' mas não existe
'IRequestHandler<CreateUserCommand, Unit>' neste projeto.

OpenTelemetry

Hermes emite traces e métricas automaticamente. Configure o seu provider:

services.AddOpenTelemetry()
    .WithTracing(b => b.AddSource(HermesDiagnostics.ActivitySourceName))
    .WithMetrics(b => b.AddMeter(HermesDiagnostics.MeterName));

Métricas expostas:

• hermes.requests.total — total de requests enviados
• hermes.requests.failed — requests com falha
• hermes.request.duration — duração em ms (histograma)
• hermes.notifications.total — notificações publicadas
• hermes.timeouts.total — requests cancelados por timeout

Hermes.Testing

var fake = new FakeMediator()
    .Setup<GetUserQuery, User>(q => new User(q.Id, "Alice"))
    .Returns<DeleteUserCommand, Unit>(Unit.Value);

// Verificações
Assert.True(fake.WasSent<GetUserQuery>());
Assert.True(fake.WasSent<GetUserQuery>(q => q.Id == 42));
Assert.Equal(1, fake.CountSent<GetUserQuery>());
Assert.True(fake.WasPublished<UserDeleted>());

Licença

MIT