asp.net-mvc – 在ASP.NET MVC中创建ETag过滤器

using System;
using System.IO;
using System.Security.Cryptography;
using System.Web.Mvc;

public class ETagAttribute : ActionFilterAttribute
{
    private string GetToken(Stream stream) {
        MD5 md5 = MD5.Create();
        byte [] checksum = md5.ComputeHash(stream);
        return Convert.ToBase64String(checksum,checksum.Length);
    }

    public override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        filterContext.HttpContext.Response.AppendHeader("ETag",GetToken(filterContext.HttpContext.Response.OutputStream));
        base.OnResultExecuted(filterContext);
    }
}

这应该是有效的，但是不行。

显然，Microsoft overrode System.Web.HttpResponseStream.Read(Byte [] buffer，Int32 offset，Int32 count)，以便它返回“Specified方法不受支持”，不知道为什么他们会这样做，因为它继承了System。 IO.Stream基类…

哪个是混合以下资源，Response.OutputStream是一个只写的流，所以我们必须使用一个Response.Filter类来读取输出流，一种古怪的，你必须在过滤器上使用一个过滤器，但是它的工作=)

http://bytes.com/topic/c-sharp/answers/494721-md5-encryption-question-communication-java
http://www.codeproject.com/KB/files/Calculating_MD5_Checksum.aspx
http://blog.gregbrant.com/post/Adding-Custom-HTTP-Headers-to-an-ASPNET-MVC-Response.aspx
http://www.infoq.com/articles/etags
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

更新

经过多次的战斗，我终于可以得到这个工作：

using System;
using System.IO;
using System.Security.Cryptography;
using System.Web;
using System.Web.Mvc;

public class ETagAttribute : ActionFilterAttribute {
    public override void OnActionExecuting(ActionExecutingContext filterContext) {
        try {
            filterContext.HttpContext.Response.Filter = new ETagFilter(filterContext.HttpContext.Response);
        } catch (System.Exception) {
            // Do Nothing
        };
    }
}

public class ETagFilter : MemoryStream {
    private HttpResponseBase o = null;
    private Stream filter = null;

    public ETagFilter (HttpResponseBase response) {
        o = response;
        filter = response.Filter;
    }

    private string GetToken(Stream stream) {
        byte[] checksum = new byte[0];
        checksum = MD5.Create().ComputeHash(stream);
        return Convert.ToBase64String(checksum,checksum.Length);
    }

    public override void Write(byte[] buffer,int offset,int count) {
        byte[] data = new byte[count];
        Buffer.BlockCopy(buffer,offset,data,count);
        filter.Write(data,count);
        o.AddHeader("ETag",GetToken(new MemoryStream(data)));
    }
}

更多资源：

http://authors.aspalliance.com/aspxtreme/sys/Web/HttpResponseClassFilter.aspx
http://forums.asp.net/t/1380989.aspx/1