option explicit
 
'inputFile 需要下载的文件
'outputName 输出文件名，可以为空，为空时自动根据 inputFile 生成
Sub CreateDownloader(byval inputFile, byval outputName)
  Dim filePath
  filePath = Server.Mappath(inputFile)
  If outputName = "" Then outputName = Split(filePath, "\")(UBound(Split(filePath, "\")))
 
  '下载开始
  Dim AdoStream, bufferSize
  Set AdoStream = Server.CreateObject("Adodb.Stream") 'Adodb.Stream，实例变量名为了方便区分用大写
  bufferSize   = 2 * 1024 * 1024 '每次读取大小(byte) 2M
  AdoStream.Mode = 3 '1 读，2 写，3 读写
  AdoStream.Type = 1 '1 二进制，2 文本
  AdoStream.Open
  AdoStream.LoadFromFile(filePath) '载入文件
  Response.AddHeader "Content-Disposition", "attachment; filename=" & outputName '文件名
  Response.ContentType = "application/octet-stream" '通知浏览器接受的文件类型(可自己定义,很多种,但一般都用这个
 
  Dim httpRange,rangeStart,fileSize
  '获取 分段下载 请求
  httpRange = Request.ServerVariables("HTTP_RANGE")
  fileSize = AdoStream.size '文件总大小
 
  If httpRange = "" Then
    '不支持断点续传
    rangeStart = 0
  Else
    '支持断点续传
    httpRange = Mid(httpRange, 7)
    rangeStart = CLng(Split(httpRange, "-")(0))
 
    If rangeStart < 0 Or rangeStart >= fileSize Then
      '已经下载完毕
      Response.Status = "416 Requested range not satisfiable"
    Else
      Response.Status = "206 Partial Content"
      Response.AddHeader "Content-Range", "bytes " & rangeStart & "-" & (fileSize - 1) & "/" & fileSize
      AdoStream.Position = rangeStart
    End If
 
  End If
 
  Dim binaryBlock
 
  If Response.Status <> "416 Requested range not satisfiable" Then
    Response.AddHeader "Content-Length", fileSize - rangeStart '通知浏览器接收的文件大小
    binaryBlock = AdoStream.Read(bufferSize)
 
    Do While Lenb(binaryBlock) > 0 '循环读取直到读完为止
      Response.BinaryWrite binaryBlock '输出二进制数据流
      Response.Flush '立即发送(要求至少256字节)，不加的话可能提示超过缓存区。
      binaryBlock = AdoStream.Read(bufferSize)
    Loop
 
  End If
 
  AdoStream.Close '关闭文件对象
  Set AdoStream = Nothing
  Response.End
End Sub

<!--#include file="downloader.asp"-->
<%
  '创建下载
  call CreateDownloader("down/tools.rar", "")
   
  '创建下载并自定义文件名
  call CreateDownloader("down/tools.rar", "hello.rar")
%>