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。