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;
                }
            }

        }

    }

}