防盜鏈IHttpHandler

/*
*
* 防盜鏈IHttpHandler
*
*
* 增加了對檔案關鍵字的選擇(即僅對檔案名稱存在某些關鍵字或不存在某些關鍵字進行過濾)
* 設定web.config中<appSettings>節以下值
* string eWebapp_NoLink 如果檔案名稱符合該正確表態式將進行過濾(不設定對所有進行過濾)
* string eWebapp_AllowLink 如果檔案名稱符合該正確表態式將不進行過濾(優先權高於AllowLink,不設定則服從AllowLink)
* bool eWebapp_ AllowOnlyFile 如果為False,(預設true)則不允許使用者直接對該檔案進行訪問建議為true
*
*
* :)以下設定均可省略,設定只是為了增加靈活性與體驗
* eWebapp_NoLink_Message 錯誤資訊提示:預設為Link From:網域名稱
* eWebapp_Error_Width 錯誤資訊提示圖片寬
* eWebapp_Error_Height 錯誤資訊提示圖片高
*
*
*
* 垃圾豬 2005-9-11 建立
* 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>
/// 防盜鏈IHttpHandler
/// 參考http://www.softat.org/archiver/tid-52114.html
/// 垃圾豬 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: 在此處添加建構函式邏輯
//
}

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>
/// 輸出錯誤資訊
/// </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>
/// 輸出真實檔案
/// </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();

//這裡選擇輸出的檔案格式
//可以參考http://ewebapp.cnblogs.com/articles/234756.html增加對更多檔案格式的支援.

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>
/// 確認字串是否為空白
/// </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>
/// 檢查是否是非法連結
/// </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是否存在網站的IP或網域名稱
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
{
//這裡使用正則表達對規則進行匹配
try
{
Regex myRegex ;

//檢查允許匹配
if(!Empty(eWebapp_AllowLink))
{

myRegex = new Regex(eWebapp_AllowLink);

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

}

//檢查禁止匹配
if(!Empty(eWebapp_NoLink))
{

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

}

return true;

}
catch
{
//如果匹配出錯，連結錯誤
return true;
}
}
}
else
{
//是否允許直接存取檔案
if(eWebapp_AllowOnlyFile)
{
return false;
}
else
{
return true;
}
}
}
}
}
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