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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;
     
                double 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(int.Parse(pack.ToString())));
                        Thread.Sleep(sleep);
                    }
                    else
                    ...{
                        i=maxCount; 
                    }
                }
            }
            catch
            ...{
             return false;
            }
            finally
            ...{
                br.Close();

                myFile.Close();
            }
        }
        catch
        ...{
            return false;
        }
        return true;
    }