Chain of Responsibility

Namespace: DesignPatterns.Behavioral

Overview

Ordered handlers process a shared context. Each handler can short-circuit (skip calling next) or continue the pipeline. Async-first: ValueTask + CancellationToken.

Runtime

Type	Role
IHandler<TContext>	InvokeAsync(context, next, cancellationToken)
HandlerPipelineBuilder<TContext>	Use(handler) / Use(delegate), then Build()
HandlerPipeline<TContext>	Immutable pipeline — InvokeAsync, InvokeTracedAsync
HandlerPipelineTrace	Per-invocation step list
HandlerPipelineStep	Index, handler display name, HandlerPipelineStepStatus
HandlerPipelineStepStatus	Completed / ShortCircuited / NotReached

var pipeline = new HandlerPipelineBuilder<RequestContext>()
    .Use(new LoggingHandler())
    .Use(new AuthorizationHandler())
    .Use(new ResourceHandler())
    .Build();

await pipeline.InvokeAsync(context, cancellationToken);

Short-circuit

• Calls await next(context, ct) → later handlers run.
• Does not call next → remaining handlers are skipped.

Traced invocation (InvokeTracedAsync)

Use when debugging auth blocks or early exits without adding a full middleware framework:

var trace = await pipeline.InvokeTracedAsync(context, cancellationToken);

foreach (var step in trace.Steps)
{
    Console.WriteLine($"{step.Index}: {step.Name} → {step.Status}");
}

Status	Meaning
Completed	Handler ran and called next
ShortCircuited	Handler ran but did not call next
NotReached	Handler never ran (an earlier handler short-circuited)

InvokeTracedAsync does not change execution order or short-circuit rules — it only returns a trace. Delegate handlers appear as "<delegate>".

Source generator

Mark handlers with [HandlerOrder(n, typeof(TContext))] on a shared contract. The generator emits {Context}HandlerPipeline wiring handlers by order.

[HandlerOrder(0, typeof(IRequestContext))]
public sealed class LoggingHandler : IRequestHandler { ... }

[HandlerOrder(1, typeof(IRequestContext))]
public sealed class AuthorizationHandler : IRequestHandler { ... }

Diagnostics

DP005, DP008–DP009, DP024 (Info + CodeFix for missing [HandlerOrder]).

Sample

DesignPatterns.Samples.Chain

Maintainer doc: docs/ChainOfResponsibility.md (中文).