ASP.NET 防盗链源码

防盗链原理：

http标准协议中有专门的字段记录referer

一来可以追溯上一个入站地址是什么

二来对于资源文件，可以跟踪到包含显示他的网页地址是什么。

因此所有防盗链方法都是基于这个Referer字段

解决方法：
(一)创建一个继承了System.Web.IHttpHandler接口的类
在System.Web.IHttpHandler接口有两个成员ProcessRequest()方法和IsReusable()属性。ProcessRequest(System.Web.HttpContext context) 方法，除了用户自定义中被要求处理的特殊的http请求。其中的参数 System.Web.HttpContext 类的实例装入了一个http请求中http协议中要求的所有信息。其中System.Web.HttpContext 类中包含有属性 Request 使得从客户端发送过来的http请求信息的值可以被方便地读取；属性Response 它封装了需要返回给客户端的信息和操作。
IsReusable()属性要置为true.

(二) 创建一个资源图片的方法Real()
1．若是盗链服务器给其错误图片。
2．若不是盗链服务器给其正常的图片。
在Real()方法中用到了FileInfo 这个类去取得图片的扩展名并用来判断图片的类型.

(三) 注意页面的缓存(response.Expires=1;获取和设置浏览器上缓存的页过期之前的分钟数.如果用户在页过期之前返回同一页,则显示缓存的内容)

(四)配置应用程序扩展名映射
因为IIS在接收到aspx页面请求时，会为其自动加载一个C：\WINDOWS\Micosoft.NET\Framework\v1.1.4322
\aspnet_isapi.dll文件。
虚拟目录和文件夹的属性里面的”执行许可”改为“纯脚本”。
若是有多个Web.config那么只要在总目录下有就可以了，其它地方的均可删除。
(五)在 Web.config这个网络应用程序配置文件中加入注册信息
<system.web>
<httpHandlers>
<add verb = "*" path = "*.jpg\.ief\.jpg\.jepg\.bmp\.png\.tif\.emf\.ras\.pnm\.pbm\.pgm
\.ppm\.rgb\.xbm\.xpm\.xwd\.did\.ico\.emf"type="eWebapp.NoLink,eWebapp"/>
.
.
</httpHandlers>
</system.web>\

/*
*
* 防盗链IHttpHandler
*
*
* 增加了对文件关键字的选择(即仅对文件名存在某些关键字或不存在某些关键字进行过滤)
* 设置web.config中<appSettings>节以下值
* string eWebapp_NoLink 如果文件名符合该正确表态式将进行过滤(不设置对所有进行过滤)
* string eWebapp_AllowLink 如果文件名符合该正确表态式将不进行过滤(优先权高于AllowLink,不设置则服从AllowLink)
* bool eWebapp_ AllowOnlyFile 如果为False,(默认true)则不允许用户直接对该文件进行访问建议为true
*
*
* :)以下设置均可省略,设置只是为了增加灵活性与体验
* eWebapp_NoLink_Message 错误信息提示:默认为Link From:域名
* eWebapp_Error_Width 错误信息提示图片宽
* eWebapp_Error_Height 错误信息提示图片高
*
*
*
* 垃圾猪 2005-9-11 创建
* http://ewebapp.net/
*/

using System;
using System.Web;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Configuration;
using System.Text.RegularExpressions;

namespace eWebapp
{
    /// <summary>
    /// 防盗链IHttpHandler
    /// 参考http://www.softat.org/archiver/tid-52114.html
    /// 垃圾猪 2005-9-12 修正
    /// </summary>
    public class NoLink : IHttpHandler
    {
        private string eWebapp_NoLink = string.Empty;
        private string eWebapp_AllowLink = string.Empty;
        private bool eWebapp_AllowOnlyFile = true;

        private string eWebapp_NoLink_Message = string.Empty;
        private bool error = false;

        public NoLink()
        {
            //
            // TODO: 在此处添加构造函数逻辑
            //
        }

        public void ProcessRequest(HttpContext context)
        {
            eWebapp_NoLink_Message = ConfigurationSettings.AppSettings["eWebapp_NoLink_Message"];

            string myDomain = string.Empty;

            error = errorLink(context, out myDomain);

            if (Empty(eWebapp_NoLink_Message))
            {
                eWebapp_NoLink_Message = "Link from :" + myDomain;
            }

            if (error)
            {
                //Jpg(context.Response,eWebapp_NoLink_Message);
                Jpg(context.Response, eWebapp_NoLink_Message);
            }
            else
            {
                Real(context.Response, context.Request);
            }

        }

        public bool IsReusable
        {
            get
            {
                return true;
            }
        }

        /// <summary>
        /// 输出错误信息
        /// </summary>
        /// <param name="Response"></param>
        /// <param name="_word"></param>
        private void Jpg(HttpResponse Response, string _word)
        {

            int myErrorWidth = _word.Length * 15;
            int myErrorHeight = 16;
            try
            {
                int _myErrorWidth = Convert.ToInt32(ConfigurationSettings.AppSettings["eWebapp_Error_Width"]);
                if (_myErrorWidth > 0)
                {
                    myErrorWidth = _myErrorWidth;
                }

            }
            catch
            {

            }
            try
            {
                int _myErrorHeight = Convert.ToInt32(ConfigurationSettings.AppSettings["eWebapp_Error_Height"]);
                if (_myErrorHeight > 0)
                {
                    myErrorHeight = _myErrorHeight;
                }
            }
            catch
            {

            }
            Bitmap Img = null;
            Graphics g = null;
            MemoryStream ms = null;
            Img = new Bitmap(myErrorWidth, myErrorHeight);
            g = Graphics.FromImage(Img);
            g.Clear(Color.White);
            Font f = new Font("Arial", 9);
            SolidBrush s = new SolidBrush(Color.Red);
            g.DrawString(_word, f, s, 3, 3);
            ms = new MemoryStream();
            Img.Save(ms, ImageFormat.Jpeg);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            Img.Dispose();
            Response.End();
        }

        /// <summary>
        /// 输出真实文件
        /// </summary>
        /// <param name="response"></param>
        /// <param name="context"></param>
        private void Real(HttpResponse response, HttpRequest request)
        {
            FileInfo file = new System.IO.FileInfo(request.PhysicalPath);

            response.Clear();

            response.AddHeader("Content-Disposition", "filename=" + file.Name);

            response.AddHeader("Content-Length", file.Length.ToString());

            string fileExtension = file.Extension.ToLower();

            //这里选择输出的文件格式
            //可以参考http://ewebapp.cnblogs.com/articles/234756.html增加对更多文件格式的支持.

            switch (fileExtension)
            {

            case "mp3":
                response.ContentType = "audio/mpeg3";
                break;

            case "mpeg":

                response.ContentType = "video/mpeg";
                break;

            case "jpg":

                response.ContentType = "image/jpeg";
                break;

            case "bmp":

                response.ContentType = "image/bmp";
                break;

            case "gif":

                response.ContentType = "image/gif";
                break;

            case "doc":

                response.ContentType = "application/msword";

                break;
            case "css":

                response.ContentType = "text/css";
                break;

            default:

                response.ContentType = "application/octet-stream";
                break;

            }

            response.WriteFile(file.FullName);

            response.End();
        }

        /// <summary>
        /// 确认字符串是否为空
        /// </summary>
        /// <param name="_value"></param>
        /// <returns></returns>
        private bool Empty(string _value)
        {
            if (_value == null | _value == string.Empty | _value == "")
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        /// <summary>
        /// 检查是否是非法链接
        /// </summary>
        /// <param name="context"></param>
        /// <param name="_myDomain"></param>
        /// <returns></returns>
        private bool errorLink(HttpContext context, out string _myDomain)
        {
            HttpResponse response = context.Response;
            string myDomain = context.Request.ServerVariables["SERVER_NAME"];
            _myDomain = myDomain;
            string myDomainIp = context.Request.UserHostAddress;

            eWebapp_NoLink = ConfigurationSettings.AppSettings["eWebapp_NoLink"];
            eWebapp_AllowLink = ConfigurationSettings.AppSettings["eWebapp_AllowLink"];

            try
            {
                eWebapp_AllowOnlyFile = Convert.ToBoolean(ConfigurationSettings.AppSettings["eWebapp_AllowOnlyFile"]);
            }
            catch
            {
                eWebapp_AllowOnlyFile = true;
            }

            if (context.Request.UrlReferrer != null)
            {

                //判定referDomain是否存在网站的IP或域名
                string referDomain = context.Request.UrlReferrer.AbsoluteUri.Replace(context.Request.UrlReferrer.AbsolutePath, "");
                string myPath = context.Request.RawUrl;

                if (referDomain.IndexOf(myDomainIp) >= 0 | referDomain.IndexOf(myDomain) >= 0)
                {
                    return false;
                }
                else
                {
                    //这里使用正则表达对规则进行匹配
                    try
                    {
                        Regex myRegex;

                        //检查允许匹配
                        if (!Empty(eWebapp_AllowLink))
                        {

                            myRegex = new Regex(eWebapp_AllowLink);

                            if (myRegex.IsMatch(myPath))
                            {
                                return false;
                            }

                        }

                        //检查禁止匹配
                        if (!Empty(eWebapp_NoLink))
                        {

                            myRegex = new Regex(eWebapp_NoLink);
                            if (myRegex.IsMatch(myPath))
                            {
                                return true;
                            }
                            else
                            {
                                return false;
                            }

                        }

                        return true;

                    }
                    catch
                    {
                        //如果匹配出错，链接错误
                        return true;
                    }
                }
            }
            else
            {
                //是否允许直接访问文件
                if (eWebapp_AllowOnlyFile)
                {
                    return false;
                }
                else
                {
                    return true;
                }
            }

        }

    }

}