图片地址防盗链,通过IHttpHandler实现

/*
 * 
 * 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
 * 
 * 
 * 
 *
 * 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
    ///
    /// </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;
                }
            }

        }

    }

}
http://www.cnblogs.com/zhouxujian/archive/2006/10/12/527673.html