ASP.NET提供文件下载函数（支持大文件、续传、速度限制、资源占用小）

 // 输出硬盘文件，提供下载
  // 输入参数 _Request: Page.Request对象，  _Response: Page.Response对象， _fileName: 下载文件名， _fullPath: 带文件名下载路径， _speed 每秒允许下载的字节数
  // 返回是否成功
  public static bool ResponseFile(HttpRequest _Request,HttpResponse _Response,string _fileName,string _fullPath, long _speed)
  {
   try
   {
    FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
    BinaryReader br = new BinaryReader(myFile);
    try
    {
     _Response.AddHeader("Accept-Ranges", "bytes");
     _Response.Buffer = false;
     long fileLength = myFile.Length;
     long startBytes = 0;
     
     int pack = 10240; //10K bytes
     //int sleep = 200;   //每秒5次   即5*10K bytes每秒
     int sleep = (int)Math.Floor(1000 * pack / _speed) + 1;
     if (_Request.Headers["Range"] != null)
     {
      _Response.StatusCode = 206;
      string[] range = _Request.Headers["Range"].Split(new char[] {'=', '-'});
      startBytes = Convert.ToInt64(range[1]);
     }
     _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
     if (startBytes != 0)
     {
      _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength-1, fileLength));
     }
     _Response.AddHeader("Connection", "Keep-Alive");
     _Response.ContentType = "application/octet-stream";
     _Response.AddHeader("Content-Disposition","attachment;filename=" + HttpUtility.UrlEncode(_fileName,System.Text.Encoding.UTF8) );
 
     br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
     int maxCount = (int) Math.Floor((fileLength - startBytes) / pack) + 1;

     for (int i = 0; i < maxCount; i++)
     {
      if (_Response.IsClientConnected)
      {
       _Response.BinaryWrite(br.ReadBytes(pack));
       Thread.Sleep(sleep);
      }
      else
      {
       i=maxCount; 
      }
     }
    }
    catch
    {
     return false;
    }
    finally
    {
     br.Close();
     myFile.Close();
    }
   }
   catch
   {
    return false;
   }
   return true;
  }

调用例

   Page.Response.Clear();
     
   bool success = ResponseFile(Page.Request, Page.Response, "filename", @"C:\download.date", 1024000);
  
   if(!success)
    Response.Write("下载文件出错！");
   Page.Response.End();

作者Blog：http://blog.csdn.net/nickycheng/

下面是vb.net 版本

        Public Function ResponseFile(ByVal FRequest As HttpRequest, ByVal FResponse As HttpResponse, ByVal fileName As String, ByVal fullPath As String, ByVal speed As Long) As Boolean
            Try
                Dim myFile As FileStream = New FileStream(fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
                Dim br As BinaryReader = New BinaryReader(myFile)
                Try
                    FResponse.AddHeader("Accept-Ranges", "bytes")

                    FResponse.Buffer = False '關閉存後送出
                    Dim fileLength As Long = myFile.Length
                    Dim startBytes As Long = 0

                    Dim pack As Integer = 10240  '10K bytes
                    'int sleep = 200;   //每秒5次   即5*10K bytes每秒
                    Dim sleep As Integer = CType(Math.Floor(1000 * pack / speed) + 1, Integer)
                    If (FRequest.Headers("Range") <> Nothing) Then
                        FResponse.StatusCode = 206
                        Dim range() As String = FRequest.Headers("Range").Split(New Char() {"="c, "-"c})
                        startBytes = Convert.ToInt64(range(1))

                    End If
                    FResponse.AddHeader("Content-Length", (fileLength - startBytes).ToString())
                    If (startBytes <> 0) Then
                        FResponse.AddHeader("Content-Range", String.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength))
                    End If
                    FResponse.AddHeader("Connection", "Keep-Alive")
                    FResponse.ContentType = "application/octet-stream"
                    FResponse.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8))

                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin)
                    Dim maxCount As Integer = CType(Math.Floor((fileLength - startBytes) / pack) + 1, Integer)
                    Dim i As Integer
                    For i = 0 To maxCount - 1 Step i + 1
                        If (FResponse.IsClientConnected) Then
                            FResponse.BinaryWrite(br.ReadBytes(pack))
                            Thread.Sleep(sleep)
                        Else
                            i = maxCount
                        End If
                    Next
                Catch
                    Return False
                Finally
                    br.Close()
                    myFile.Close()
                End Try
            Catch
                Return False
            End Try
            Return True
        End Function

調用時:
            Page.Response.Clear()
            Me.ResponseFile(Page.Request, Page.Response, filename, Server.MapPath(fileurl), 10240)
            Page.Response.End()