使用全局异常处理会扰乱DelegatingHandler

Question

当ovveride进行IExceptionHandler时，当发生意外异常时，响应不会到达DelegatingHandler。我怎么才能解决这个问题？

在webapi 2中，我想为请求和响应消息实现一个审计记录器。我还想添加一个全局异常处理程序。但是，当我用自定义实现替换IExceptionHandler时。响应永远不会到达DelegatingHandler -on异常，因此响应的审计将丢失。

在WebApiConfig中

// add custom audittrail logger
config.MessageHandlers.Add(new AuditLogHandler());
// replace global exception handeling
config.Services.Replace(typeof(IExceptionHandler), new WebAPiExceptionHandler());

自定义异常处理程序

public class WebAPiExceptionHandler : ExceptionHandler
{
    //A basic DTO to return back to the caller with data about the error
    private class ErrorInformation
    {
        public string Message { get; set; }
        public DateTime ErrorDate { get; set; }
    }

    public override void Handle(ExceptionHandlerContext context)
    {
        context.Result = new ResponseMessageResult(context.Request.CreateResponse(HttpStatusCode.InternalServerError,
        new ErrorInformation { Message = "Iets is misgegaan", ErrorDate = DateTime.UtcNow }));
    }
}

定制审计记录器

public class AuditLogHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        if (request.Content != null)
        {
            var task = await request.Content.ReadAsStringAsync();

            // .. code for loggign request
        }

        var result = await base.SendAsync(request, cancellationToken);

        // .. code for logging response
        // when I do not replace WebAPiExceptionHandler, code is reachred here
        // When I Do use WebAPiExceptionHandler, code is not reached here

        return result;
    }
}

在webapi中抛出异常的代码

public class Values_v2Controller : ApiController
{
    public string Get(int id)
    {
        throw new Exception("haha");
    }
}

Answer 1

不要使用ExceptionHandler作为基类，实现接口IExceptionHandler

public class WebAPiExceptionHandler : IExceptionHandler
{
    public Task HandleAsync(ExceptionHandlerContext context, CancellationToken cancellationToken)
    {
        var fout = new ErrorInformation
        {
            Message = "Iets is misgegaan"
            , ErrorDate = DateTime.UtcNow
        };

        var httpResponse = context.Request.CreateResponse(HttpStatusCode.InternalServerError, fout);

        context.Result = new ResponseMessageResult(httpResponse);

        return Task.FromResult(0);
    }

    private class ErrorInformation
    {
        public string Message { get; set; }
        public DateTime ErrorDate { get; set; }
    }
}

Answer 2

问题是，ExceptionHandler只在Handle(ExceptionHandlerContext context)返回true时才执行ShouldHandle(ExceptionHandlerContext context)方法。

重写bool ShouldHandle(ExceptionHandlerContext context)，始终返回true，为我修复问题。