1

您好，我刚开始使用ASP.NET MVC 4，我是一家企业的实习生，他告诉我创建一个没有服务器的基本网上商店，然后使用YSlow验证 HTML 和网站的速度。

我一直很忙，当我完成网店后，我开始使用 YSlow 将速度应用于网站，但有一件事我似乎无法修复，那就是错误配置的 ETag：
“有 5 个组件的 ETag 配置错误”<-这些是我的 CSS 文件和我用过的图片。我一直在研究 ETag 是什么，但仍然不完全了解它们的作用。

我知道在Apache中你可以通过说 FileETag none 来关闭它们，但在这种情况下，我没有使用服务器，我仍然想关闭它们，因为它们对 99 的分数不满意。

我正在寻找的是对 ETags 究竟做什么的答案以及对我的问题的修复。

谢谢

4

1 回答 1

1

根据下面的评论，这是一个练习，显然 PC 的性能不会很好。您可以使用 httpHandler。这是我用于图像的一个，这将有助于您的 yslow（但请注意，这不能保证性能，并且旨在为非常繁忙的站点提供指导）

public class ImageHandler : IHttpHandler
    {
        public void ProcessRequest(HttpContext context)
        {
            context.Response.Cache.SetCacheability(HttpCacheability.Public);
            context.Response.Cache.SetMaxAge(new TimeSpan(28, 0, 0, 0, 0));

            // Setting the last modified date to the creation data of the assembly
        Assembly thisAssembly = Assembly.GetExecutingAssembly();
        string thisPath = thisAssembly.CodeBase.Replace(@"file:///", "");
        string assemblyName = "yourAssembly";
        string assemblyPath = thisPath.Replace(thisAssembly.ManifestModule.ScopeName, assemblyName);

        var assemblyInfo = new FileInfo(assemblyPath);
        var creationDate = assemblyInfo.CreationTime;
        string eTag = GetFileETag(assemblyPath, creationDate);      
        // set cache info
        context.Response.Cache.SetCacheability(HttpCacheability.Private);
        context.Response.Cache.VaryByHeaders["If-Modified-Since"] = true;
        context.Response.Cache.VaryByHeaders["If-None-Match"] = true;
        context.Response.Cache.SetLastModified(creationDate);
        context.Response.Cache.SetETag(eTag);
if (IsFileModified(assemblyPath, creationDate, eTag, context.Request))
        {
            //context.Response.ContentType = <specify content type>;
            // Do resource processing here
            context.Response.TransmitFile(context.Request.PhysicalPath);
        }
        else
        {
            // File hasn't changed, so return HTTP 304 without retrieving the data 
            context.Response.StatusCode = 304;
            context.Response.StatusDescription = "Not Modified";

            // Explicitly set the Content-Length header so the client doesn't wait for
            //  content but keeps the connection open for other requests 
            context.Response.AddHeader("Content-Length", "0");         
        }


        context.Response.End();


        }


        public bool IsReusable
        {
            get { return false; }
        }


        /// <summary>
        /// Checks if the resource assembly has been modified based on creation date.
        /// </summary>
        /// <remarks>
        /// </remarks>
        /// <seealso cref="GetFileETag"/>
        private bool IsFileModified(string fileName, DateTime modifyDate, string eTag, HttpRequest request)
        {
            // Assume file has been modified unless we can determine otherwise 
            bool FileDateModified = true;
            DateTime ModifiedSince;
            TimeSpan ModifyDiff;
            bool ETagChanged;

            // Check If-Modified-Since request header, if it exists 
            string ifModifiedSince = request.Headers["If-Modified-Since"];
            if (!string.IsNullOrEmpty(ifModifiedSince) && ifModifiedSince.Length > 0 && DateTime.TryParse(ifModifiedSince, out ModifiedSince))
            {
                FileDateModified = false;
                if (modifyDate > ModifiedSince)
                {
                    ModifyDiff = modifyDate - ModifiedSince;
                    // Ignore time difference of up to one seconds to compensate for date encoding
                    FileDateModified = ModifyDiff > TimeSpan.FromSeconds(1);
                }
            }
            // Check the If-None-Match header, if it exists. This header is used by FireFox to validate entities based on the ETag response header 
            ETagChanged = false;
            string ifNoneMatch = request.Headers["If-None-Match"];
            if (!string.IsNullOrEmpty(ifNoneMatch) && ifNoneMatch.Length > 0)
            {
                ETagChanged = ifNoneMatch != eTag;
            }
            return ETagChanged || FileDateModified;
        }

        /// <summary>
        /// Generates a caching ETag based on file name and creation date.
        /// </summary>
        /// <remarks>
        /// </remarks>
        /// <seealso cref="GetFileETag"/>
        private string GetFileETag(string fileName, DateTime modifyDate)
        {
            string fileString;
            Encoder stringEncoder;
            int byteCount;
            Byte[] stringBytes;

            // Use file name and modify date as the unique identifier 
            fileString = fileName + modifyDate.ToString();

            // Get string bytes 
            stringEncoder = Encoding.UTF8.GetEncoder();
            byteCount = stringEncoder.GetByteCount(fileString.ToCharArray(), 0, fileString.Length, true);
            stringBytes = new Byte[byteCount];

            stringEncoder.GetBytes(fileString.ToCharArray(), 0, fileString.Length, stringBytes, 0, true);

            //{ Hash string using MD5 and return the hex-encoded hash }
            MD5 Enc = MD5CryptoServiceProvider.Create();
            return "\"" + BitConverter.ToString(Enc.ComputeHash(stringBytes)).Replace("-", string.Empty) + "\"";

        }
    }
}

然后在您的配置中指定处理程序（如果不使用 iis7，也可以在 httphandlers 下执行）

  <add name="pngs" verb="*" path="*.png" type="yourAssembly.HttpHandlers.ImageHandler, hcs.web" preCondition="managedHandler" />
  <add name="jpgs" verb="*" path="*.jpg" type="yourAssembly.HttpHandlers.ImageHandler, hcs.web" preCondition="managedHandler" />
  <add name="gif" verb="*" path="*.gif" type="yourAssembly.HttpHandlers.ImageHandler, hcs.web" preCondition="managedHandler" />
于 2012-11-21T08:38:32.257 回答