Question

我们最近安装了Robohash作为Gravatar的一个伟大后备：

enter image description here

http://static2.scirra.net/avatars/128/5df4bf5d460c9497fdb35578e923ad1f.png

正如你所看到的，robohashes非常出色，并且来自我们的静态域。实际上重写了URL：

<action type="Rewrite" url="gravatar.ashx?hash={R:2}&amp;size={R:1}" appendQueryString="false" />

在同一个web.config文件中，我们有缓存配置文件：

<staticContent>
    <clientCache httpExpires="Sun, 29 Mar 2020 00:00:00 GMT" cacheControlMode="UseExpires" />
</staticContent>
<caching>
    <profiles>
        <add extension=".ashx" policy="CacheForTimePeriod"  kernelCachePolicy="DontCache" duration="01:00:00" />
        <add extension=".png" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" location="Any" />
        <add extension=".jpg" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" location="Any" />
        <add extension=".gif" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" location="Any" />
        <add extension=".ico" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" location="Any" />
    </profiles>
</caching>

为了更好地衡量gravatar.ashx文件，我们还设置了缓存策略：

<%@ WebHandler Language="C#" Class="GravatarImage" %>

using System;
using System.Web;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using System.Net;

public class GravatarImage : IHttpHandler {

    public void ProcessRequest (HttpContext context) {

        // Adds document content type        
        context.Response.Cache.SetCacheability(HttpCacheability.Public);
        context.Response.Cache.SetExpires(DateTime.Now.AddMinutes(60));
        context.Response.Cache.SetMaxAge(new TimeSpan(1, 0, 0));
        context.Response.AddHeader("Last-Modified", DateTime.Now.ToLongDateString());

        // Get params and send initial request to gravatar
        string Hash = context.Request.QueryString["hash"];
        string Size = context.Request.QueryString["size"];
        string URL = "http://www.gravatar.com/avatar/" + Hash + "?r=pg&s=" + Size + "&d=404";

        // Make request to gravatar
        bool Fetched = makeAvatarRequest(URL);

        // Backup to robo hash
        if (!Fetched)
        {
            URL = "http://robohash.org/" + Hash + ".png?size=" + Size + "x" + Size + "&bgset=bg2";
            Fetched = makeAvatarRequest(URL);
        }

        // Fallback if gravatar doesn't match and robohash is down
        if (!Fetched)
        {

        }

        // Cache this handler response for 1 hour.
        HttpCachePolicy c = context.Response.Cache;
        c.SetCacheability(HttpCacheability.Public);
        c.SetMaxAge(new TimeSpan(1, 0, 0));
    }

    // Attempt a request for avatar
    private bool makeAvatarRequest(string URL)
    {        
        try
        {
            WebRequest request = WebRequest.Create(URL);
            using (WebResponse response = request.GetResponse())
            {
                using (Stream responseStream = response.GetResponseStream())
                {
                    displayImage(responseStream);
                    return true;
                }
            }
        }
        catch (WebException ex)
        {
            return false;
        }
    }

    // Display the image from stream
    private void displayImage(Stream stream)
    {
        HttpContext.Current.Response.ContentType = "image/png";
        Image img = Image.FromStream(stream);
        MemoryStream temp = new MemoryStream();
        img.Save(temp, ImageFormat.Png);
        byte[] buffer = temp.GetBuffer();
        HttpContext.Current.Response.OutputStream.Write(buffer, 0, buffer.Length);

        img.Dispose();
        temp.Dispose();        
    }

    public bool IsReusable {
        get {
            return false;
        }
    }

}

请注意，我们在底部使用Response.cache AND CachePolicy

当我使用YSlow时，页面上的每个图像都有一个未来的到期日期，除了这些没有过期日期的头像。每次请求页面时，都会再次获取它们。

脚本的想法是从外部URL获取头像并将其缓存1小时。然后从我们的网站上提供。

任何人都可以帮助我们吗？在没有缓存的情况下使用头像的示例页面是： http://www.scirra.com/forum/construct-in-ludum-dare-21_topic44523.html

Answer 1

因为您正在使用处理程序，所以您需要在自己的代码中处理缓存头，即返回304 repsonse。因此，请根据文件检查标题上的日期，并在适当的时候返回304。

我们在一些图像处理程序的开头有类似于以下的代码

var lastModified = this.LastModifiedFileTime(path);
var isNotModified = this.WriteConditional304(context, lastModified);
if (isNotModified)
    return;

使用的两种方法大致如下所示。

protected bool WriteConditional304(HttpContext context, DateTime lastWrite)
    {
        if (context.Request.Headers[since] != null || context.Request.Headers[eTag] != null)
        {
            try
            {
                DateTime date = context.Request.Headers[since] != null ? DateTime.Parse(context.Request.Headers[since]) : new DateTime(long.Parse(context.Request.Headers[eTag]));

                if (lastWrite <= date)
                {
                    Write304(context);
                    return true;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
        return false;
    }



protected DateTime LastModifiedFileTime(string path)
    {
        FileInfo fi = new FileInfo(path);
        var modificationTime = fi.LastWriteTime;
        // negates the smaller parts of the date as the header doesnt carry them
        var date = new DateTime(modificationTime.Year, modificationTime.Month, modificationTime.Day, modificationTime.Hour,
            modificationTime.Minute, modificationTime.Second);
        return date;
    }

ASP.net ashx处理程序没有缓存

1 个答案: