Stratara.Mediator 4.0.2

Stratara.Mediator

Derived. The behaviour described here is specified under openspec/specs/. Those specifications are the source; this page explains and illustrates them.

License: MIT.

In-process mediator with DI-resolved handlers and pipeline behaviors. Drop-in replacement for MediatR-style routing without the runtime cost of MethodInfo.Invoke — uses a typed wrapper cache and direct DI dispatch.

Quick start

// The mediator traces every dispatch, so an OpenTelemetry Tracer must be resolvable.
// AddMediator() does not register one — pick your own instrumentation name:
services.AddSingleton(TracerProvider.Default.GetTracer("Your.App"));

services.AddMediator()
    .AddCommandHandlersFromAssemblyContaining<Program>()
    .AddQueryHandlersFromAssemblyContaining<Program>()
    .AddPipelineBehaviorWithResult(typeof(LoggingBehavior<,>))
    .AddPipelineBehavior(typeof(LoggingBehavior<>));

// Optional: wrap in authorization decorator
services.AddAuthorizingMediator<MyAuthorizationProvider>();

IMediator is registered scoped. Resolve it from a scope (a request scope in ASP.NET Core, or an explicit IServiceProvider.CreateScope() in a console host) — resolving it from the root provider throws.

What's in the box

• IMediator.HandleAsync<TResult>(IRequest<TResult>, CancellationToken) — routes queries and commands-with-result to IQueryHandler<TRequest, TResult> through any registered IPipelineBehavior<TRequest, TResult> chain.
• IMediator.HandleAsync<TRequest>(TRequest, CancellationToken) — routes void commands to ICommandHandler<TRequest> through any registered IPipelineBehavior<TRequest> chain.
• AuthorizingMediator decorator — checks [RequireRole] attributes via IAuthorizationProvider and [RequirePermission] attributes via IPermissionResolver (both AND) on the request's runtime type before delegating to the inner mediator. Its startup validator fails fast when a permission-guarded type is registered without an authorizing mediator or without a resolver, so a guard can never be silently skipped.
• BucketLockPool — concurrency primitive that serialises IAggregateScopedCommand dispatch per bucket id. Used by message-bus consumers (e.g. the MediatorCommandWorker in Stratara.Outbox.RabbitMQ) to keep aggregate writes single-writer.

Pipeline behavior contract

Behaviors run outer-to-inner in DI registration order:

public sealed class LoggingBehavior<TRequest, TResult> : IPipelineBehavior<TRequest, TResult>
    where TRequest : IRequest<TResult>
{
    public async Task<TResult> HandleAsync(
        TRequest request, Func<Task<TResult>> next, CancellationToken cancellationToken)
    {
        // before
        var result = await next();
        // after
        return result;
    }
}

Tenant isolation

AddStrataraTenantIsolation() registers a pipeline behavior that enforces tenant isolation at the mediator entrance — before the handler runs — for any request that opts in by implementing the ITenantScopedRequest marker. Requests that do not implement the marker pass through untouched.

public sealed record GetCustomerQuery(Guid CustomerId, Guid TenantId)
    : IQuery<CustomerDto>, ITenantScopedRequest;

services
    .AddStrataraValidation()           // validation stays outermost
    .AddStrataraTenantIsolation();     // then tenant isolation

The behavior compares the request's TenantId (the data owner) against the ambient session's data-owner tenant (SessionContext.TenantId), not the actor tenant (SessionContext.ActorTenantId). A request whose payload names a different tenant than the established session subject is rejected with TenantAccessDeniedException (translated to HTTP 403 on ASP.NET hosts that register AddStrataraProblemDetails() from Stratara.ServiceDefaults.AspNetCore; surfaced through the message-failure path on workers).

Default vs. strict mode

• TenantIsolationMode.Default — enforces only the subject match. A privileged cross-tenant operation (actor tenant ≠ data-owner tenant) passes, because the calling endpoint is expected to have promoted the session's data-owner tenant to the target before dispatch.
• TenantIsolationMode.Strict — additionally routes every cross-tenant operation through an ICrossTenantAuthorizer. Stratara registers a deny-all default (via TryAdd), so strict mode rejects all cross-tenant access until you register your own authorizer that grants it:

services.AddStrataraTenantIsolation(o => o.Mode = TenantIsolationMode.Strict);
services.AddScoped<ICrossTenantAuthorizer, PlatformAdminCrossTenantAuthorizer>();

internal sealed class PlatformAdminCrossTenantAuthorizer(IHttpContextAccessor http)
    : ICrossTenantAuthorizer
{
    public ValueTask<bool> IsCrossTenantAllowedAsync(SessionContext session, CancellationToken ct) =>
        ValueTask.FromResult(http.HttpContext?.User.IsInRole("PlatformAdmin") ?? false);
}

The behavior runs both in-process (queries via IMediator at the endpoint, where HttpContext is available) and worker-side (commands dispatched through the outbox, where there is no HttpContext). An ICrossTenantAuthorizer that needs request-role state should be applied on the in-process path; the worker path must base its decision on the SessionContext alone.

Dependencies

• Stratara.Abstractions — for IMediator/IRequest/ICommand/IQuery/IPipelineBehavior contracts, plus ITenantScopedRequest/ICrossTenantAuthorizer/TenantAccessDeniedException.
• Stratara.Diagnostics — log-event IDs for the tenant-isolation behavior.
• Microsoft.Extensions.DependencyInjection.Abstractions.
• Microsoft.Extensions.Logging.Abstractions.
• OpenTelemetry.Api — emits an Activity per dispatch under the Stratara.Application source.

No EF Core, no message bus, no event sourcing. Library-safe.