c# - 装饰 ASP.NET Web API IHttpController

Question

我试图用装饰器包装 Web API Controller (IHttpController 实现)，但是当我这样做时，Web API 抛出异常，因为不知何故它期待实际的实现。

将装饰器应用于 Controller 是我成功应用于 MVC Controller 的一个技巧，显然我喜欢在 Web API 中做同样的事情。

我创建了一个自定义 IHttpControllerActivator，它允许解析修饰的 IHttpController 实现。这是一个剥离的实现:

public class CrossCuttingConcernHttpControllerActivator : IHttpControllerActivator {
    private readonly Container container;
    public CrossCuttingConcernHttpControllerActivator(Container container) {
        this.container = container;
    }

    public IHttpController Create(HttpRequestMessage request, 
        HttpControllerDescriptor controllerDescriptor, Type controllerType)
    {
        var controller = (IHttpController)this.container.GetInstance(controllerType);

        // Wrap the instance in one or multiple decorators. Note that in reality, the 
        // decorator is applied by the container, but that doesn't really matter here.
        return new MyHttpControllerDecorator(controller);
    }
}

我的装饰器看起来像这样:

public class MyHttpControllerDecorator : IHttpController {
    private readonly IHttpController decoratee;
    public MyHttpControllerDecorator(IHttpController decoratee) {
        this.decoratee = decoratee;
    }

    public Task<HttpResponseMessage> ExecuteAsync(
        HttpControllerContext controllerContext,
        CancellationToken cancellationToken)
    {
        // this decorator does not add any logic. Just the minimal amount of code to
        // reproduce the issue.
        return this.decoratee.ExecuteAsync(controllerContext, cancellationToken);
    }
}

但是，当我运行我的应用程序并请求 ValuesController 时，Web API 向我抛出以下 InvalidCastException:

Unable to cast object of type 'WebApiTest.MyHttpControllerDecorator' to type 'WebApiTest.Controllers.ValuesController'.

堆栈跟踪:

at lambda_method(Closure , Object , Object[] )
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass13.<GetExecutor>b__c(Object instance, Object[] methodParameters)
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.<>c__DisplayClass5.<ExecuteAsync>b__4()
at System.Threading.Tasks.TaskHelpers.RunSynchronously[TResult](Func`1 func, CancellationToken cancellationToken)

就好像 Web API 为我们提供了 IHttpController 抽象但跳过它并仍然依赖于实现本身。这当然会严重违反依赖倒置原则，并使抽象完全无用。所以我可能做错了什么。

我做错了什么？如何愉快地装饰我的 API Controller ？

Answer 1

我想说的是，如何在 ASP.NET Web API 中实现此行为的自然设计方式是使用 Custom Message Handlers / Delegation Handlers

例如，我确实有这个 DelegationHandler

public class AuthenticationDelegationHandler : DelegatingHandler
{
    protected override System.Threading.Tasks.Task<HttpResponseMessage> 
        SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // I. do some stuff to create Custom Principal
        // e.g.
        var principal = CreatePrincipal();
        ...

        // II. return execution to the framework            
        return base.SendAsync(request, cancellationToken).ContinueWith(t =>
        {
            HttpResponseMessage resp = t.Result;
            // III. do some stuff once finished
            // e.g.:
            // SetHeaders(resp, principal);

            return resp;
        });
    }

这是将其注入(inject)结构的方法:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.MessageHandlers.Add(new AuthenticationDelegationHandler());