如何覆盖Owin中的默认未处理异常输出？

Question

我使用Owin Self-hosting和WebApi编写了简单的服务器:

namespace OwinSelfHostingTest
{
    using System.Threading;
    using System.Web.Http;
    using Microsoft.Owin.Hosting;
    using Owin;

    public class Startup
    {
        public void Configuration(IAppBuilder builder)
        {
            var config = new HttpConfiguration();

            config.Routes.MapHttpRoute(
                "Default",
                "{controller}/{id}",
                new { id = RouteParameter.Optional }
                );

            builder.UseWebApi(config);
        }
    }

    public class Server
    {
        private ManualResetEvent resetEvent = new ManualResetEvent(false);
        private Thread thread;

        private const string ADDRESS = "http://localhost:9000/";

        public void Start()
        {
            this.thread = new Thread(() =>
                {
                    using (var host = WebApp.Start<Startup>(ADDRESS))
                    {
                        resetEvent.WaitOne(Timeout.Infinite, true);
                    }
                });
            thread.Start();
        }

        public void Stop()
        {
            resetEvent.Set();
        }
    }

}

当控制器中出现异常时,Owin会返回如下的XML响应:

<Error>
    <Message>An error has occurred.</Message>
    <ExceptionMessage>Attempted to divide by zero.</ExceptionMessage>
    <ExceptionType>System.DivideByZeroException</ExceptionType>
    <StackTrace> 
        ...
    </StackTrace>
</Error>

但我想要不同的输出 - 所以我怎么能覆盖这个？

Answer 1

您可以通过创建OWIN MiddleWare并将其挂钩到管道中来实现:

public class CustomExceptionMiddleware : OwinMiddleware
{
   public CustomExceptionMiddleware(OwinMiddleware next) : base(next)
   {}

   public override async Task Invoke(IOwinContext context)
   {
      try
      {
          await Next.Invoke(context);
      }
      catch(Exception ex)
      {
          // Custom stuff here
      }
   }
 }

并在启动时挂钩:

public class Startup
{
    public void Configuration(IAppBuilder builder)
    {
        var config = new HttpConfiguration();

        config.Routes.MapHttpRoute(
            "Default",
            "{controller}/{id}",
            new { id = RouteParameter.Optional }
            );

        builder.Use<CustomExceptionMiddleware>().UseWebApi(config);
    }
}

这样,任何未处理的异常都将被中间件捕获,并允许您自定义输出结果.

需要注意的一件重要事情是:如果托管的东西有自己的异常处理逻辑,就像WebAPI那样,异常不会传播.此处理程序适用于任何由托管的基础服务无法处理的异常.