Asp.Net 分段，断点，下载

public static void DownloadFile(HttpContext context, string filePath)
        {
            UtilLite.Guard<ArgumentNullException>(context == null);
            FileInfo file = new FileInfo(filePath);
            UtilLite.Guard<FileNotFoundException>(!file.Exists);
            context.Response.Clear();
            context.Response.Buffer = false;
            context.Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(Encoding.UTF8.GetBytes(file.Name)));
            context.Response.AppendHeader("Content-Length", file.Length.ToString());
            context.Response.ContentType = "application/octet-stream";
            context.Response.WriteFile(filePath);
            context.Response.Flush();
            context.Response.End();
        }

        public static void Range(HttpContext context, string filePath)
        {
            UtilLite.Guard<ArgumentNullException>(context == null);
            HttpRequest Request = context.Request;
            HttpResponse Response = context.Response;
            Response.Clear();
            Response.Buffer = false;
            Response.AddHeader("Accept-Ranges", "bytes");
            int bufferSize = 4096;
            byte[] buffer = new byte[bufferSize];
            using (FileStream stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize))
            {
                long p = 0L, l = stream.Length;
                #region Resolve Range
                string range = Request.Headers["Range"];
                if (range != null)
                {
                    //Range:bytes=1024-
                    //Range:bytes=1024-2048
                    //Range:bytes=-1024
                    //Range:bytes=0-512,1024-2048
                    int index = range.IndexOf("=");
                    if (index != -1)
                    {
                        string[] ranges = range.Substring(index + 1).Split(',');
                        if (ranges.Length > 1)
                        {
                            //not supported multipart/byterange
                        }
                        else
                        {
                            bool flag = false;
                            if (ranges[0].StartsWith("-"))
                            {
                                long _p, _absp;
                                if (long.TryParse(ranges[0], out _p) && (_absp = Math.Abs(_p)) <= l)
                                {
                                    if (_p < 0)
                                    {
                                        p = l - _absp;
                                        l = _absp;
                                        flag = true;
                                    }
                                }
                            }
                            else
                            {
                                ranges = ranges[0].Split('-');
                                if (ranges.Length == 2)
                                {
                                    long _p, _l;
                                    if (ranges[1] == string.Empty)
                                    {
                                        if (long.TryParse(ranges[0], out _p) && _p <= l)
                                        {
                                            p = _p;
                                            flag = true;
                                        }
                                    }
                                    else if (long.TryParse(ranges[0], out _p) && long.TryParse(ranges[1], out _l) && _p > 0 && _l > 0 && _p < _l && _l < l)
                                    {
                                        p = _p;
                                        l = _l + 1;
                                        flag = true;
                                    }
                                }
                            }
                            if (flag)
                            {
                                Response.StatusCode = 206;
                                Response.AddHeader("Content-Range", "bytes " + p.ToString() + "-" + l.ToString() + "/" + stream.Length.ToString());
                            }
                            else
                            {
                                Response.StatusCode = 416;  //Requested range not satisfiable
                            }
                        }
                    }
                }
                #endregion
                Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(Encoding.UTF8.GetBytes(Path.GetFileName(filePath))));
                Response.AddHeader("Content-Length", l.ToString());
                Response.ContentType = "application/octet-stream";
                stream.Position = p;
                int read;
                while (Response.IsClientConnected && p < l)
                {
                    Response.OutputStream.Write(buffer, 0, read = stream.Read(buffer, 0, bufferSize));
                    Response.Flush();
                    p += read;
                }
            }
            Response.End();
        }