IHttphandler之防止图片盗链

同样IHttpHandler原理见“IHttphandler子Url重写”一文。

web.config设置如下：

<httpHandlers>
      <add verb="*" path="*.gif" type="MyHttpHandler.PreventAntiLeechHandler,MyHttpHandler"/>    </httpHandlers>

如果请求的路径为gif图片（*.gif）则经过MyHttpHandler.PreventAntiLeechHandler处理后返回。

PreventAntiLeechHandler实现如下：

 

using  System;
using  System.Collections.Generic;
using  System.Text;
using  System.Web;
using  System.Web.UI;
using  System.Drawing;
using  System.IO;

namespace  MyHttpHandler
{
     class  PreventAntiLeechHandler : IHttpHandler
    {
         #region  IHttpHandler 成员

         public   bool  IsReusable
        {
             get  {  return   false ; }
        }

         public   void  ProcessRequest(HttpContext context)
        {
             if  (context.Request.Url.Authority  ==  context.Request.UrlReferrer.Authority)
            {
                CommonDeal.DealImageRequest(context);
            }
             else
            {
                CommonDeal.ReturnErrorImage(context);
            }
        }

         #endregion
    }
}

CommonDeal实现如下：

using  System;
using  System.Collections.Generic;
using  System.Text;
using  System.Web;
using  System.Web.UI;
using  System.IO;
using  System.Drawing;
using  System.Drawing.Imaging;

namespace  MyHttpHandler
{
     internal   class  CommonDeal
    {
         public   static   void  DealImageRequest(HttpContext context)
        {
            Font titleFont  =   new  Font( " 黑体 " ,  12 , FontStyle.Bold); // 标题字体 
            Font font  =   new  Font( " Consolas " ,  8 , FontStyle.Regular); // 数字0字有斜线的字体:WST_Ital,  01 DigitGraphics , 00 Starmap Truetype,Consolas,
             // Font font = new Font("WST_Engl", 8); // 正文字体 
            Font headerFont  =   new  Font( " 黑体 " ,  12 , FontStyle.Bold); // 列名标题 
            Font footerFont  =   new  Font( " Arial " ,  8 ); // 页脚显示页数的字体 
            Font upLineFont  =   new  Font( " Arial " ,  9 , FontStyle.Bold); // 当header分两行显示的时候，上行显示的字体。 
            Font underLineFont  =   new  Font( " Arial " ,  8 ); // 当header分两行显示的时候，下行显示的字
            Font enFont  =   new  Font( " Times New Roman " ,  12 );

            MemoryStream ms  =   new  MemoryStream();

             string  filePath  =  context.Server.MapPath( " Image "   +  context.Request.Path);
             try
            {
                Image image  =  Image.FromFile(filePath);
                 if  (IsPixelFormatIndexed(image.PixelFormat))
                {
                    Bitmap bmp  =   new  Bitmap(image.Width, image.Height, PixelFormat.Format32bppArgb);
                     using  (Graphics graphic  =  Graphics.FromImage(bmp))
                    {
                        graphic.InterpolationMode  =  System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        graphic.SmoothingMode  =  System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        graphic.CompositingQuality  =  System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                        graphic.DrawImage(image,  0 ,  0 );
                        graphic.DrawString( " pangxiaoliang " , enFont,  new  SolidBrush(Color.LightGray),  2 ,  2 );
                        graphic.DrawString( " pangxiaoliang " , enFont,  new  SolidBrush(Color.Black),  0 ,  0 );

                    }
                    bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                    bmp.Dispose();
                }
                 else
                {
                     using  (Graphics graphic  =  Graphics.FromImage(image))
                    {
                        graphic.DrawString( " pangxiaoliang " , enFont,  new  SolidBrush(Color.LightGray),  2 ,  2 );
                        graphic.DrawString( " pangxiaoliang " , enFont,  new  SolidBrush(Color.Black),  0 ,  0 );

                    }

                    Bitmap theBitmap  =   new  Bitmap(image);
                    theBitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                    theBitmap.Dispose();
                }

                context.Response.ClearContent();
                context.Response.ContentType  =   " image/jpg " ;
                context.Response.BinaryWrite(ms.ToArray());

            }
             catch
            {
                Bitmap error  =   new  Bitmap(context.Server.MapPath( " Image/error.bmp " ));
                error.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                error.Dispose();
                context.Response.ClearContent();
                context.Response.ContentType  =   " image/jpg " ;
                context.Response.BinaryWrite(ms.ToArray());
            }
             finally
            {
                ms.Close();
                ms.Dispose();
                context.Response.End();
            }
        }

         public   static   void  ReturnErrorImage(HttpContext context)
        {
            MemoryStream ms  =   new  MemoryStream();
             try
            {
                Bitmap error  =   new  Bitmap(context.Server.MapPath( " error.bmp " ));
                error.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                error.Dispose();
                context.Response.ClearContent();
                context.Response.ContentType  =   " image/jpg " ;
                context.Response.BinaryWrite(ms.ToArray());
            }
             catch
            {
            }
             finally
            {
                ms.Close();
                ms.Dispose();
                context.Response.End();
            }
        }

         ///   <summary>
         ///  会产生graphics异常的PixelFormat
         ///   </summary>
         private   static  PixelFormat[] indexedPixelFormats  =  { PixelFormat.Undefined, PixelFormat.DontCare,
                                            PixelFormat.Format16bppArgb1555, PixelFormat.Format1bppIndexed, PixelFormat.Format4bppIndexed,
                                            PixelFormat.Format8bppIndexed
                                            };

         ///   <summary>
         ///  判断图片的PixelFormat 是否在 引发异常的 PixelFormat 之中
         ///   </summary>
         ///   <param name="imgPixelFormat"> 原图片的PixelFormat </param>
         ///   <returns></returns>
         private   static   bool  IsPixelFormatIndexed(PixelFormat imgPixelFormat)
        {
             foreach  (PixelFormat pf  in  indexedPixelFormats)
            {
                 if  (pf.Equals(imgPixelFormat))  return   true ;
            }

             return   false ;
        }
    }


}

防止盗链关键点在：

if (context.Request.Url.Authority == context.Request.UrlReferrer.Authority)
{
      CommonDeal.DealImageRequest(context);
}
else
{
      CommonDeal.ReturnErrorImage(context);
}

客户端请求gif图像路径“http://localhost:2868/Image/logo.gif”,则：

1)如果是本站内请求

context.Request.Url.Authority是请求的地址，即“http://localhost:2868”。

context.Request.UrlReferrer.Authority是引用地址（请求的站点），即“http://localhost:2868”。

所以此时返回客户端的是带有水印的正确图像。

2）如果是其他站盗链（“http://localhost:9999”）

context.Request.Url.Authority是请求的地址，即“http://localhost:2868”。

context.Request.UrlReferrer.Authority是引用地址（请求的站点），即“http://localhost:9999”。

所以此时返回客户端的是提示请勿盗链图像。