ASP.NET MVC ETag & Cache等优化方法

背景

最近有一个项目是用SmartAdmin + Jquery + EasyUI 一个ASP.NET MVC5的项目,一直存在一个性能问题,加载速度比较慢,第一次加载需要(在没有cache的情况下)需要4-5秒完成全部的加载.

如下图就是用Chrome PageSpeed 测试的结果

有几个非常重要的指标

Fist Contentfu Paint:第一次绘出页面,需要4秒,前4秒都是白屏,确实有点长

Fist Meaningfull Paint:第一次绘出有意义的内容,需要8.6秒,才出现可见的操作页面.

Eliminate render-blocking resources:阻塞加载资源文件,因为的项目在head中加载了jquery和css,因为有些代码必须先执行导致的

Remove unused css:存在大量的没用的css样式定义,这也很难避免.

分析一下原因

出现上述问题的主要原因,页面本身的大小,所有资源加起来超过3.2M,Jquery EasyUI的JS+css 就接近3M,另外页面里有嵌入了好几个PartialView,还有就是执行js的时间,EasyUI DataGrid需要从后台抓起数据并生成复杂的Dom结构这都需要时间.

一般的优化手段

Cache

第一想到的就是使用cache,单只能解决第二次访问的速度问题,对少有点用,我一般会这样做,设置的方法有

添加outputcache 例如:

[OutputCache(Duration = 360, VaryByParam = "none")]
public ActionResult Index() => this.View();

web.Config 添加对静态文件的缓存

<system.webServer>
        <staticContent>
            <remove fileExtension=".js" />
            <mimeMap fileExtension=".js" mimeType="text/javascript" />
            <remove fileExtension=".ico" />
            <mimeMap fileExtension=".ico" mimeType="image/x-icon" />
            <remove fileExtension=".eot" />
            <mimeMap fileExtension=".eot" mimeType="application/vnd.ms-fontobject" />
            <remove fileExtension=".woff" />
            <mimeMap fileExtension=".woff" mimeType="application/x-font-woff" />
            <remove fileExtension=".woff2" />
            <mimeMap fileExtension=".woff2" mimeType="application/x-font-woff2" />
            <remove fileExtension=".svg" />
            <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
            <remove fileExtension=".ttf" />
            <mimeMap fileExtension=".ttf" mimeType="application/x-font-ttf" />
            <clientCache cacheControlMode="UseMaxAge" httpExpires="365.00:00:00" cacheControlMaxAge="365.00:00:00" />
        </staticContent>
</system.webServer>

压缩和合并资源文件

尽量减少资源文件的大小和请求次数,通常的做法就是使用BundleConfig.cs合并和压缩js,css文件.我现在使用bundleconfig.json配置代替System.Web.Optimization.配置灵活一点,如果使用bundleconfig.json 编译压缩还需要解决客户端更新的缓存的问题,我使用一下代码添加一个指纹标志

public class Fingerprint
    {
        public static string Tag(string rootRelativePath)
        {
            if (HttpRuntime.Cache[rootRelativePath] == null)
            {
                string absolute = HostingEnvironment.MapPath("~" + rootRelativePath);

                DateTime date = File.GetLastWriteTime(absolute);
                int index = rootRelativePath.LastIndexOf('/');

                string result = rootRelativePath.Insert(index, "/v-" + date.Ticks);
                HttpRuntime.Cache.Insert(rootRelativePath, result, new CacheDependency(absolute));
            }

            return HttpRuntime.Cache[rootRelativePath] as string;
        }
    }

<system.webServer>
   <urlCompression doStaticCompression="true" doDynamicCompression="true" dynamicCompressionBeforeCache="false" />
   <rewrite>
      <rules>
        <rule name="fingerprint">
          <match url="([S]+)(/v-[0-9]+/)([S]+)" />
          <action type="Rewrite" url="{R:1}/{R:3}" />
        </rule>
      </rules>
    </rewrite>
 </system.webServer>

<link rel="stylesheet" href="@Fingerprint.Tag("/content/site.css")" />

ETag

ETags 是用于 Web 缓存验证的工具，允许有条件的客户端请求。通过 ETags，浏览器可以判断某项资源是否被需要。如果不需要，浏览器就不会向 Web 服务器发送请求，从而最小化请求数量。配置方法

全局方案,自定义一个HttpModule

  public class ETagHttpModule : IHttpModule
  {
    #region IHttpModule Members
    void IHttpModule.Dispose()
    {
      // Nothing to dispose; 
    }
    void IHttpModule.Init(HttpApplication context)
    {
      context.BeginRequest += new EventHandler(context_BeginRequest);
      WebPageHttpHandler.DisableWebPagesResponseHeader = true;
    }
    #endregion
    void context_BeginRequest(object sender, EventArgs e)
    {
      HttpApplication app = sender as HttpApplication;

      //if (app.Request.CurrentExecutionFilePath.EndsWith("/") || app.Request.CurrentExecutionFilePath.EndsWith(".cshtml"))
      //{
        app.Response.Filter = new ETagStream(app.Response, app.Request);
      //}
    }
    #region Stream filter
    public class ETagStream : MemoryStream
    {
      private HttpResponse _response = null;
      private HttpRequest _request;
      private Stream _filter = null;
      public ETagStream(HttpResponse response, HttpRequest request)
      {
        _response = response;
        _request = request;
        _filter = response.Filter;
      }
      private string GetToken(Stream stream)
      {
        var checksum = new byte[0];
        checksum = MD5.Create().ComputeHash(stream);
        return Convert.ToBase64String(checksum, 0, checksum.Length);
      }
      public override void Write(byte[] buffer, int offset, int count)
      {
        var data = new byte[count];
        Buffer.BlockCopy(buffer, offset, data, 0, count);
        var token = GetToken(new MemoryStream(data));
        var clientToken = _request.Headers["If-None-Match"];
        if (token != clientToken)
        {
          _response.AddHeader("ETag", token);
          _filter.Write(data, 0, count);
        }
        else
        {
          _response.SuppressContent = true;
          _response.StatusCode = 304;
          _response.StatusDescription = "Not Modified";
          _response.AddHeader("Content-Length", "0");
        }
      }
    }
    #endregion
  }

<modules>
            <remove name="FormsAuthentication" />
            <!--<add type="WhitespaceModule" name="WhitespaceModule" />-->
           <add type="WebApp.ETagHttpModule" name="ETagHttpModule" />
</modules>

Action页面级

public class ETagAttribute : ActionFilterAttribute
  {
    public override void OnActionExecuting(ActionExecutingContext filterContext) => filterContext.HttpContext.Response.Filter = new ETagFilter(filterContext.HttpContext.Response, filterContext.RequestContext.HttpContext.Request);
  }

  public class ETagFilter : MemoryStream
  {
    private HttpResponseBase _response = null;
    private HttpRequestBase _request;
    private Stream _filter = null;

    public ETagFilter(HttpResponseBase response, HttpRequestBase request)
    {
      _response = response;
      _request = request;
      _filter = response.Filter;
    }

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

    public override void Write(byte[] buffer, int offset, int count)
    {
      var data = new byte[count];

      Buffer.BlockCopy(buffer, offset, data, 0, count);

      var token = GetToken(new MemoryStream(data));
      var clientToken = _request.Headers["If-None-Match"];

      if (token != clientToken)
      {
        _response.AddHeader("ETag", token);
        _filter.Write(data, 0, count);
      }
      else
      {
        _response.SuppressContent = true;
        _response.StatusCode = 304;
        _response.StatusDescription = "Not Modified";
        _response.AddHeader("Content-Length", "0");
      }
    }

   
  }

//[OutputCache(Duration = 360, VaryByParam = "none")]
[ETag]
public ActionResult Index() => this.View();

效果图,回发的字节数确实减少了很多,单响应时间差不多,不是很明显.

总结

优化方案有很多,但是感觉效果都不是很理想,要做到极致的用户体验,可能真的要抛弃Jquery,EasyUI,这类肥大又复杂的类库.

问题

另外大家有没有非常好用又简单的方法解决初始加载白屏的问题,我试过用js preloading图层动画,但是效果还是不理想.但看过一些网址和APP做的效果非常好,不知道具体是如何实现的,在Asp.net mvc环境下能不能用

参考文章

(ASP.NET MVC 应用提速的十种方法)http://blog.oneapm.com/apm-tech/679.html