.net Mvc文件下载的功能，大文件下载完成之后修改数据库功能

原文:.net Mvc文件下载的功能，大文件下载完成之后修改数据库功能

我服务器上文件只能下载一次，下载了之后就不能下载了，大文件或网速不好时，可能服务端文件流发送完了，客户端还没下载完，导致下载失败，

那么最好的办法就是：在续传时不判断（If-Range，或If-Match 不为空时不判断，仍然发送对应的文件流）就行了，这样有一个漏洞，就是一个文件没下载完时，可以同时下载很多次，但是没办法，客户使用浏览器下载不好控制（如果记录用户开始下载的次数，逻辑上也不行—他可以下载到一半，然后时间不够不下载了，下次再重新下载，这在业务上也是允许他没下载完时重新下载的）。

        #region 下载文件处理-downfiledeal
        /// <summary>
        /// 下载文件处理
        /// </summary>
        /// <param name="ResourceID">资源id</param>
        /// <param name="UserID">用户id</param>
        /// <param name="downtype">下载类型：1-购买，2-今日免费，3-订阅用户</param>
        /// <param name="webtitle">提示页面titie</param>
        /// <param name="ResourceType">资源类型（暂时不考虑）</param>
        /// <returns></returns>
        private string downfiledeal(string ResourceID, string UserID, string downtype, string webtitle, string ResourceType = "")
        {
            TopicInformationBLL bll_tf = new TopicInformationBLL();
            TopicInformation tf = bll_tf.GetById(ResourceID);
            bll_tf.Dispose();
            string FilePath = "";
            FilePath = tf.TopicSourceFile.ToLower();
            if (FilePath.StartsWith("http://www.***.com"))//不是外网文件夹服务器路径
            {
                FilePath = FilePath.Replace("http://www.***.com", "");
            }
            if (!FilePath.StartsWith("/")) FilePath = "/" + FilePath;
            FilePath = Server.MapPath(FilePath);
            FileInfo DownloadFile = new FileInfo(FilePath);
            System.IO.Stream iStream = null;
            int downsize = 1024;//读取web.config中的配置
            try { downsize = Convert.ToInt32(System.Configuration.ConfigurationManager.AppSettings["downsize"]); }
            catch { downsize = 1024; }
            int buffersize = 1024 * downsize;//默认每次发送1K;
            byte[] buffer = new Byte[buffersize];// Buffer to read 10K bytes in chunk:
            int currentlength;// Length of each read to buffer:
            long dataToRead;// Total bytes to read:
            long dataSended;//已发送的字节
            long datalength;//文件字节总长度
            string filename = System.IO.Path.GetFileName(FilePath); // Identify the file name.
            try
            {
                System.Collections.Specialized.NameValueCollection hds = Request.Headers;
                long startBytes = 0;
                Response.Clear();
                Response.ClearHeaders();
                if (Request.Headers["Range"] != null)
                {//------如果是续传请求，则获取续传的起始位置，即已经下载到客户端的字节数------
                    Response.StatusCode = 206;//重要：续传必须，表示局部范围响应。初始下载时默认为200
                    string[] range = Request.Headers["Range"].Split(new char[] { '=', '-' });//"bytes=1474560-"
                    startBytes = Convert.ToInt64(range[1]);//已经下载的字节数，即本次下载的开始位置
                    if (startBytes < 0 || startBytes >= DownloadFile.Length)
                    {//无效的起始位置
                        startBytes = 0;
                    }
                }
                iStream = new System.IO.FileStream(FilePath, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read);// Open the file.
                dataSended = 0;
                datalength =
                dataToRead = iStream.Length - startBytes;// Total bytes to read:
                Response.Buffer = true;
                string lastUpdateTiemStr = System.IO.File.GetLastWriteTimeUtc(FilePath).ToString("r");
                string eTag = HttpUtility.UrlEncode(filename, Encoding.UTF8) + lastUpdateTiemStr;
                Response.AppendHeader("ETag", "\"" + eTag + "\"");//重要：续传必须
                if (startBytes > 0)
                {
                    if (Request.Headers["If-Range"] != null)//（IE,360）对应响应头ETag：文件名+文件最后修改时间
                    {
                        //----------上次被请求的日期之后被修改过--------------
                        string If_Range = Request.Headers["If-Range"].Replace("\"", "");
                        if (If_Range != eTag)
                        {//文件修改过
                            Response.StatusCode = 412;//预处理失败
                            return "文件名验证失败";
                        }
                    }
                    else if (Request.Headers["If-Match"] != null)//（火狐）对应响应头ETag：文件名+文件最后修改时间
                    {
                        //----------上次被请求的日期之后被修改过--------------
                        string If_Match = Request.Headers["If-Match"].Replace("\"", "");
                        if (If_Match != eTag)
                        {//文件修改过
                            Response.StatusCode = 412;//预处理失败
                            return "文件名验证失败";
                        }
                    }
                    iStream.Seek(startBytes, SeekOrigin.Begin);
                    Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, DownloadFile.Length - 1, DownloadFile.Length));
                    Response.AddHeader("Accept-Ranges", "bytes");//重要：续传必须
                }
                Response.AppendHeader("Content-Length", (DownloadFile.Length - startBytes).ToString());

                Response.ContentType = "application/octet-stream";
                Response.AddHeader("Connection", "Keep-Alive");
                Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);
                while (dataToRead > 0)// Read the bytes.
                {
                    if (Response.IsClientConnected)// Verify that the client is connected.
                    {
                        currentlength = iStream.Read(buffer, 0, buffersize);// Read the data in buffer.
                        Response.OutputStream.Write(buffer, 0, currentlength); // Write the data to the current output stream.
                        //Response.BinaryWrite(buffer);
                        Response.Flush();// Flush the data to the HTML output.
                        //buffer = new Byte[10000];
                        dataToRead = dataToRead - currentlength;
                        dataSended = dataSended + currentlength;
                        Thread.Sleep(1000);//每秒钟发送一次
                    }
                    else
                    {
                        dataToRead = -1;//prevent infinite loop if user disconnects
                    }
                }
                if (dataToRead == 0 && dataSended>0)//发送、下载完成datalength == dataSended
                {
                    //UpdateOrderWhenDownloaded(ResourceID, UserID, downtype);//下载完成，修改数据库状态
                }
                return "";
            }
            catch (Exception ex)
            {
                CommonFun.WritetTxtLog("下载出错：" + ex.Message);
                return CommonFun.GetInformationHtml(webtitle, "下载出错 : " + ex.Message);
            }
            finally
            {

                if (iStream != null)
                {
                    iStream.Close();//Close the file.
                }
            }
        }
        #endregion

        #region 返回显示标题的网页提示文本
        /// <summary>
        /// 返回显示标题的网页提示文本
        /// </summary>
        /// <param name="title">网站title</param>
        /// <param name="body">显示的文字</param>
        /// <returns></returns>
        public static string GetInformationHtml(string title, string body)
        {
            StringBuilder sb = new StringBuilder();
            sb.Append("<html>");
            sb.Append("<head>");
            sb.AppendFormat("<title>{0}</title>",title);
            sb.Append("<style type=\"text/css\">");
            sb.Append(".fixed_div { position:absolute; z-index:2008; bottom:0px; left:0px; width:100%;text-align:center;height:20px; border:0px solid #e5e5e5; background:#e5e5e5; }");
            sb.Append(".margin_auto{margin:-7px auto;width:980px;height:100%;overflow:hidden;}");
            sb.Append(".nounderline{text-decoration:none;}");
            sb.Append(".info{color:red;border:0px solid #e5e5e5; background:#e5e5e5;height:100%;}");
            sb.Append("</style>");
            sb.Append("</head>");
            sb.Append("<body>");
            sb.Append("<div class=\"margin_auto\">");
            sb.Append("<div class=\"info\">");
            sb.Append("<span style=\"font-style:italic;\">提示信息：</span><br/>");
            sb.Append(body);
            sb.Append("</div>");
            sb.Append("<div class=\"fixed_div\">Power By <a href=\"http://www.***.com\" target=\"_blank\" class=\"nounderline\">www.kinpan.com</a><div>");
            sb.Append("</div>");
            sb.Append("</body>");
            sb.Append("</html>");
            return sb.ToString() ;
        }
        #endregion

如果response.writefile,或mvc 中的返回 fileresult,谁知道它下载完成了，这很难控制，现在这样发送，发送完成之后就下载完成了，还能续传，比较精确。。