用于错误处理和丢失图像的HttpModule

Question

我有一个HttpModule,我把它从一些不同的在线源码拼凑在一起,形成了(大部分)与传统的ASP.NET应用程序以及ASP.NET MVC应用程序一起工作的东西.其中最大的部分来自CodePlex上的kigg项目.我的问题是处理由于图像丢失导致的404错误.在下面的代码中,我必须通过HttpContext的Request对象中的AcceptedTypes集合显式查找请求的图像.如果我没有进行此检查,即使丢失的图像也会导致重定向到Web.config中我的部分中定义的404页面.

这种方法的问题是(除了它闻到的事实)是这只是图像.我基本上必须对可以想象的每种内容类型执行此操作,我不希望发生此重定向行为.

看看下面的代码,是否有人可以推荐某种重构,这可能会使非页面请求变得更宽松？我仍然希望它们在IIS日志中(所以我可能不得不删除ClearError()调用),但我不认为破坏的图像会影响用户体验,直到将它们重定向到错误页面.

代码如下:

/// <summary>
/// Provides a standardized mechanism for handling exceptions within a web application.
/// </summary>
public class ErrorHandlerModule : IHttpModule
{
    #region Public Methods

    /// <summary>
    /// Disposes of the resources (other than memory) used by the module that implements 
    /// <see cref="T:System.Web.IHttpModule"/>.
    /// </summary>
    public void Dispose()
    {
    }

    /// <summary>
    /// Initializes a module and prepares it to handle requests.
    /// </summary>
    /// <param name="context">
    /// An <see cref="T:System.Web.HttpApplication"/> that provides access to the methods, properties, and events 
    /// common to all application objects within an ASP.NET application.</param>
    public void Init(HttpApplication context)
    {
        context.Error += this.OnError;
    }

    #endregion

    /// <summary>
    /// Called when an error occurs within the application.
    /// </summary>
    /// <param name="source">The source.</param>
    /// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
    private void OnError(object source, EventArgs e)
    {
        var httpContext = HttpContext.Current;

        var imageRequestTypes =
            httpContext.Request.AcceptTypes.Where(a => a.StartsWith("image/")).Select(a => a.Count());

        if (imageRequestTypes.Count() > 0)
        {
            httpContext.ClearError();
            return;
        }

        var lastException = HttpContext.Current.Server.GetLastError().GetBaseException();
        var httpException = lastException as HttpException;
        var statusCode = (int)HttpStatusCode.InternalServerError;

        if (httpException != null)
        {
            statusCode = httpException.GetHttpCode();
            if ((statusCode != (int)HttpStatusCode.NotFound) && (statusCode != (int)HttpStatusCode.ServiceUnavailable))
            {
                // TODO: Log exception from here.
            }
        }

        var redirectUrl = string.Empty;

        if (httpContext.IsCustomErrorEnabled)
        {
            var errorsSection = WebConfigurationManager.GetSection("system.web/customErrors") as CustomErrorsSection;
            if (errorsSection != null)
            {
                redirectUrl = errorsSection.DefaultRedirect;

                if (httpException != null && errorsSection.Errors.Count > 0)
                {
                    var item = errorsSection.Errors[statusCode.ToString()];

                    if (item != null)
                    {
                        redirectUrl = item.Redirect;
                    }
                }
            }
        }

        httpContext.Response.Clear();
        httpContext.Response.StatusCode = statusCode;
        httpContext.Response.TrySkipIisCustomErrors = true;
        httpContext.ClearError();

        if (!string.IsNullOrEmpty(redirectUrl))
        {
            var mvcHandler = httpContext.CurrentHandler as MvcHandler;
            if (mvcHandler == null)
            {
                httpContext.Server.Transfer(redirectUrl);                    
            }
            else
            {
                var uriBuilder = new UriBuilder(
                    httpContext.Request.Url.Scheme, 
                    httpContext.Request.Url.Host, 
                    httpContext.Request.Url.Port, 
                    httpContext.Request.ApplicationPath);

                uriBuilder.Path += redirectUrl;

                string path = httpContext.Server.UrlDecode(uriBuilder.Uri.PathAndQuery);
                HttpContext.Current.RewritePath(path, false);
                IHttpHandler httpHandler = new MvcHttpHandler();

                httpHandler.ProcessRequest(HttpContext.Current);
            }
        }
    }
}

对于任何反馈,我们都表示感谢.我目前正在使用的应用程序是一个ASP.NET MVC应用程序,但就像我提到的那样,它被编写为与MVC处理程序一起使用,但仅当CurrentHandler属于该类型时.

编辑:我忘了在这种情况下提到"hack"将是OnError()中的以下行:

        var imageRequestTypes =
        httpContext.Request.AcceptTypes.Where(a => a.StartsWith("image/")).Select(a => a.Count());

    if (imageRequestTypes.Count() > 0)
    {
        httpContext.ClearError();
        return;
    }

Answer 1

最终,问题是由于不区分传统ASP.NET应用程序和ASP.NET MVC应用程序提供的不同类型的Context.通过提供检查来确定我正在处理的上下文类型,我能够做出相应的回应.

我为HttpTransfer和MvcTransfer添加了单独的方法,允许我重定向到错误页面,特别是在需要时.我也改变了逻辑,以便我可以轻松地在我的本地和开发机器上获得我的YSOD,而不会让处理程序吞噬异常.

除了用于将异常记录到数据库的代码(由TODO注释表示)之外,我们使用的最终代码是:

using System;
using System.Net;
using System.Security.Principal;
using System.Web;
using System.Web.Configuration;
using System.Web.Mvc;

using Diagnostics;

/// <summary>
/// Provides a standardized mechanism for handling exceptions within a web application.
/// </summary>
public sealed class ErrorHandlerModule : IHttpModule
{
    #region Public Methods

    /// <summary>
    /// Disposes of the resources (other than memory) used by the module that implements 
    /// <see cref="T:System.Web.IHttpModule"/>.
    /// </summary>
    public void Dispose()
    {
    }

    /// <summary>
    /// Initializes a module and prepares it to handle requests.
    /// </summary>
    /// <param name="context">
    /// An <see cref="T:System.Web.HttpApplication"/> that provides access to the methods, properties, and events 
    /// common to all application objects within an ASP.NET application.</param>
    public void Init(HttpApplication context)
    {
        context.Error += OnError;
    }

    #endregion

    #region Private Static Methods

    /// <summary>
    /// Performs a Transfer for an MVC request.
    /// </summary>
    /// <param name="url">The URL to transfer to.</param>
    /// <param name="currentContext">The current context.</param>
    private static void HttpTransfer(string url, HttpContext currentContext)
    {
        currentContext.Server.TransferRequest(url);
    }

    /// <summary>
    /// Performs a Transfer for an MVC request.
    /// </summary>
    /// <param name="url">The URL to transfer to.</param>
    /// <param name="currentContext">The current context.</param>
    private static void MvcTransfer(string url, HttpContext currentContext)
    {
        var uriBuilder = new UriBuilder(
            currentContext.Request.Url.Scheme,
            currentContext.Request.Url.Host,
            currentContext.Request.Url.Port,
            currentContext.Request.ApplicationPath);

        uriBuilder.Path += url;

        string path = currentContext.Server.UrlDecode(uriBuilder.Uri.PathAndQuery);
        HttpContext.Current.RewritePath(path, false);
        IHttpHandler httpHandler = new MvcHttpHandler();

        httpHandler.ProcessRequest(HttpContext.Current);
    }

    #endregion

    #region Private Methods

    /// <summary>
    /// Called when an error occurs within the application.
    /// </summary>
    /// <param name="source">The source.</param>
    /// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
    private static void OnError(object source, EventArgs e)
    {
        var httpContext = HttpContext.Current;
        var lastException = HttpContext.Current.Server.GetLastError().GetBaseException();
        var httpException = lastException as HttpException;
        var statusCode = (int)HttpStatusCode.InternalServerError;

        if (httpException != null)
        {
            if (httpException.Message == "File does not exist.")
            {
                httpContext.Response.StatusCode = (int)HttpStatusCode.NotFound;
                httpContext.ClearError();
                return;
            }

            statusCode = httpException.GetHttpCode();
        }

        if ((statusCode != (int)HttpStatusCode.NotFound) && (statusCode != (int)HttpStatusCode.ServiceUnavailable))
        {
            // TODO : Your error logging code here.
        }

        var redirectUrl = string.Empty;

        if (!httpContext.IsCustomErrorEnabled)
        {
            return;
        }

        var errorsSection = WebConfigurationManager.GetSection("system.web/customErrors") as CustomErrorsSection;
        if (errorsSection != null)
        {
            redirectUrl = errorsSection.DefaultRedirect;

            if (httpException != null && errorsSection.Errors.Count > 0)
            {
                var item = errorsSection.Errors[statusCode.ToString()];

                if (item != null)
                {
                    redirectUrl = item.Redirect;
                }
            }
        }

        httpContext.Response.Clear();
        httpContext.Response.StatusCode = statusCode;
        httpContext.Response.TrySkipIisCustomErrors = true;
        httpContext.ClearError();

        if (!string.IsNullOrEmpty(redirectUrl))
        {
            var mvcHandler = httpContext.CurrentHandler as MvcHandler;
            if (mvcHandler == null)
            {
                try
                {
                    HttpTransfer(redirectUrl, httpContext);
                }
                catch (InvalidOperationException)
                {
                    MvcTransfer(redirectUrl, httpContext);
                }
            }
            else
            {
                MvcTransfer(redirectUrl, httpContext);
            }
        }
    }

    #endregion
}