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Pipeline Behaviors

Pipeline behaviors wrap handler execution, forming a chain:

Behavior1 → Behavior2 → … → Handler

Each behavior can run logic before and after the next step in the pipeline. The next parameter is an IRequestHandler — calling next.Handle(request, ct) advances the chain via interface dispatch (virtual call) instead of a delegate invocation, enabling zero-allocation behavior pipelines.

Pipeline Allocation

Allocations stay flat at 72 B regardless of pipeline depth:

xychart-beta
    title "Allocation vs Pipeline Depth"
    x-axis "Behaviors" [0, 1, 3, 5]
    y-axis "Bytes" 0 --> 100
    line [72, 72, 72, 72]

Behaviors	DSoft (alloc)	MediatR (alloc)
0	72 B	272 B
1	72 B	544 B
3	72 B	800 B
5	72 B	1,088 B

Example

public class LoggingBehavior<TRequest, TResponse>
    : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    public async ValueTask<TResponse> Handle(
        TRequest request,
        IRequestHandler<TRequest, TResponse> next,
        CancellationToken ct)
    {
        Console.WriteLine($"Handling {typeof(TRequest).Name}");
        return await next.Handle(request, ct);
    }
}

Register behaviors as open generics:

services.AddTransient(typeof(IPipelineBehavior<,>), typeof(LoggingBehavior<,>));

Behaviors execute in registration order. The first registered behavior is the outermost wrapper.

See Also

• Pipeline Patterns — logging, transactions, and other real-world patterns
• Pre/Post Processors — simpler hooks when you don’t need the full chain
• Performance Design — why interface dispatch keeps allocations at zero
• Registration Order — register behaviors before PrecompilePipelines()