用Asp隐藏文件路径实现防盗链

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。

<%
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
Response.End
%>