用Asp隐藏文件路径实现防盗链

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如果我们知道一个静态文件的实际路径如：http://www.xx.com/download/51windows.pdf，如果服务器没有作特别的限制设置，我们就可以毫不费力的把它下载下来！当网站提供51windows.pdf下载时，怎么样才能让下载者无法得到他的实际路径呢！本文就来介绍如何使用Asp来隐藏文件的实际下载路径。

　　我们在管理网站文件时，可以把扩展名一样的文件放在同一个目录下，起一个比较特别名字，例如放pdf文件目录为the_pdf_file_s，把下面代码另存为down.asp，他的网上路径为http://www.xx.com/down.asp，我们就可以用http://www.xx.com/down.asp?FileName=51windows.pdf来下载这个文件了，而且下载者无法看到这个文件实际下载路径的！在down.asp中我们还可以设置下载文件是否需要登陆，判断下载的来源页是否为外部网站，从而可以做到防止文件被盗链。

示例代码：

<%
From_url = Cstr(Request.ServerVariables("HTTP_REFERER"))
Serv_url = Cstr(Request.ServerVariables("SERVER_NAME"))
if mid(From_url,8,len(Serv_url)) <> Serv_url then
response.write "非法链接！" '防止盗链
response.end
end if

if Request.Cookies("Logined")="" then
response.redirect "/login.asp" '需要登陆！

end if
Function GetFileName(longname)'/folder1/folder2/file.asp=>file.asp
while instr(longname,"/")
  longname = right(longname,len(longname)-1)
wend
GetFileName = longname
End Function
Dim Stream
Dim Contents
Dim FileName
Dim TrueFileName
Dim FileExt
Const adTypeBinary = 1
FileName = Request.QueryString("FileName")
if FileName = "" Then
    Response.Write "无效文件名！"
    Response.End
End if
FileExt = Mid(FileName, InStrRev(FileName, ".") + 1)
Select Case UCase(FileExt)
    Case "ASP", "ASA", "ASPX", "ASAX", "MDB"
        Response.Write "非法操作！"
        Response.End
End Select
Response.Clear
if lcase(right(FileName,3))="gif" or lcase(right(FileName,3))="jpg" or lcase(right(FileName,3))="png" then
Response.ContentType = "image/*" '对图像文件不出现下载对话框
else
Response.ContentType = "application/ms-download"
end if
Response.AddHeader "content-disposition", "attachment; filename=" & GetFileName(Request.QueryString("FileName"))
Set Stream = server.CreateObject("ADODB.Stream")
Stream.Type = adTypeBinary
Stream.Open
if lcase(right(FileName,3))="pdf" then '设置pdf类型文件目录
TrueFileName = "/the_pdf_file_s/"&FileName
end if
if lcase(right(FileName,3))="doc" then '设置DOC类型文件目录
TrueFileName = "/my_D_O_C_file/"&FileName
end if
if lcase(right(FileName,3))="gif" or lcase(right(FileName,3))="jpg" or lcase(right(FileName,3))="png" then
TrueFileName = "/all_images_/"&FileName '设置图像文件目录
end if
Stream.LoadFromFile Server.MapPath(TrueFileName)
While Not Stream.EOS
    Response.BinaryWrite Stream.Read(1024 * 64)
Wend
Stream.Close
Set Stream = Nothing
Response.Flush