WebApi中用于响应的DelegatingHandler

Question

我目前正在使用几个委托处理程序(从DelegatingHandler派生的类)在发送请求之前对其进行处理，比如验证签名等。这非常好，因为我不必在所有调用中重复签名验证(例如)。

我想在同一个web请求的响应上使用相同的原则。响应是否有类似于DelegatingHandler的内容？在某种程度上，在响应返回到方法之前捕获响应的方法？

附加信息:我正在使用HttpClient.PutAsync(...)调用web api

Answer 1

是。您可以在continuation任务中执行此操作。

我来解释一下，here。

例如，此代码(来自上面的博客)跟踪请求URI，并向响应添加一个虚拟标头。

public class DummyHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // work on the request 
       Trace.WriteLine(request.RequestUri.ToString());

       var response = await base.SendAsync(request, cancellationToken);
       response.Headers.Add("X-Dummy-Header", Guid.NewGuid().ToString());
       return response;
    }
}

Answer 2

下面是一个截取请求和响应的示例。被覆盖的方法SendAsync用于捕获原始请求，而名为ResponseHandler的方法用于捕获响应。

捕获原始请求和响应的示例

using System.Net.Http;
using System.Threading.Tasks;
namespace webAPI_Test
{
    public class MessageInterceptor : DelegatingHandler
    {
        protected override System.Threading.Tasks.Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
        {
            // CATCH THE REQUEST BEFORE SENDING TO THE ROUTING HANDLER
            var headers = request.ToString();
            var body = request.Content.ReadAsStringAsync().Result;
            var fullRequest = headers + "\n" + body;

            // SETUP A CALLBACK FOR CATCHING THE RESPONSE - AFTER ROUTING HANDLER, AND AFTER CONTROLLER ACTIVITY
            return base.SendAsync(request, cancellationToken).ContinueWith(
                        task =>
                        {
                            // GET THE COPY OF THE TASK, AND PASS TO A CUSTOM ROUTINE
                            ResponseHandler(task);

                            // RETURN THE ORIGINAL RESULT
                            var response = task.Result;
                            return response;
                        }
            );
        }

        public void ResponseHandler(Task<HttpResponseMessage> task)
        {
            var headers = task.Result.ToString();
            var body = task.Result.Content.ReadAsStringAsync().Result;

            var fullResponse = headers + "\n" + body;
        }
    }
}

要使用此方法，需要标识类并将其注册为MessageHandler。我将以下行添加到我的Global.asax文件中...

示例如何注册新的MessageInterceptor类

GlobalConfiguration.Configuration.MessageHandlers.Add(new MessageInterceptor());

这是我的完整Global.asax文件。注意MessageInterceptor是如何被引用的……

显示MessageInterceptor集成的Global.asax的完整版

using System.Web.Http;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;
namespace webAPI_Test
{
    // Note: For instructions on enabling IIS6 or IIS7 classic mode, 
    // visit http://go.microsoft.com/?LinkId=9394801

    public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();

            WebApiConfig.Register(GlobalConfiguration.Configuration);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);

            GlobalConfiguration.Configuration.MessageHandlers.Add(new MessageInterceptor());
        }
    }
}