c# download file

download.cs

public bool download(HttpContextBase httpContext, int id)
        {
            long speed = 1024*1024;
            bool ret = true;
            try
            {
                #region--验证：HttpMethod，请求的文件是否存在
                switch (httpContext.Request.HttpMethod.ToUpper())
                { //目前只支持GET和HEAD方法   
                    case "GET":
                    case "HEAD":
                        break;
                    default:
                        httpContext.Response.StatusCode = 501;
                        return false;
                }
                string filePath = GetPath(id);
                #endregion

                #region 定义局部变量
                long startBytes = 0;
                int packSize = 1024 * 10; //分块读取，每块10K bytes   
                string fileName = Path.GetFileName(filePath);
                FileStream myFile = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                BinaryReader br = new BinaryReader(myFile);
                long fileLength = myFile.Length;

                String deliveryName = id + ".zip";

                int sleep = (int)Math.Ceiling(1000.0 * packSize / speed);//毫秒数：读取下一数据块的时间间隔   
                string lastUpdateTiemStr = System.IO.File.GetLastWriteTimeUtc(filePath).ToString("r");
                string eTag = HttpUtility.UrlEncode(deliveryName, Encoding.UTF8) + lastUpdateTiemStr;//便于恢复下载时提取请求头;   
                #endregion

                #region--验证：文件是否太大，是否是续传，且在上次被请求的日期之后是否被修
                if (myFile.Length > Int32.MaxValue)
                {//-------文件太大了-------   
                    httpContext.Response.StatusCode = 413;//请求实体太大   
                    return false;
                }

                if (httpContext.Request.Headers["If-Range"] != null)//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--------------   
                    if (httpContext.Request.Headers["If-Range"].Replace("\"", "") != eTag)
                    {//文件修改过   
                        httpContext.Response.StatusCode = 412;//预处理失败   
                        return false;
                    }
                }
                #endregion

                try
                {
                    #region -------添加重要响应头、解析请求头、相关验证-------------------
                    httpContext.Response.Clear();
                    httpContext.Response.Buffer = false;
                    //httpContext.Response.AddHeader("Content-MD5", GetMD5Hash(myFile));//用于验证文件   
                    httpContext.Response.AddHeader("Accept-Ranges", "bytes");//重要：续传必须   
                    httpContext.Response.AppendHeader("ETag", "\"" + eTag + "\"");//重要：续传必须   
                    httpContext.Response.AppendHeader("Last-Modified", lastUpdateTiemStr);//把最后修改日期写入响应                   
                    httpContext.Response.ContentType = "application/x-zip-compressed";//MIME类型：匹配任意文件类型   
                    httpContext.Response.AddHeader("Content-Disposition", "attachment;filename=\"" + HttpUtility.UrlEncode(deliveryName, Encoding.UTF8)+ "\"");
                    httpContext.Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
                    httpContext.Response.AddHeader("Connection", "Keep-Alive");
                    //httpContext.Response.AddHeader("Connection", "close");
                    httpContext.Response.ContentEncoding = Encoding.UTF8;
                    if (httpContext.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------   
                        httpContext.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 = httpContext.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 >= fileLength)
                        {//无效的起始位置   
                            return false;
                        }
                    }
                    else
                    {
                        DownloadLogManager.LogDownlad(id);
                    }
                    if (startBytes > 0)
                    {//------如果是续传请求，告诉客户端本次的开始字节数，总长度，以便客户端将续传数据追加到startBytes位置后----------   
                        httpContext.Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
                    }

                    ServiceLog.Log(ServiceLog.Level.Info, string.Format("Response Header:{0}", Response.Headers));
                    #endregion

                    #region -------向客户端发送数据块-------------------
                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
                    int maxCount = (int)Math.Ceiling((fileLength - startBytes + 0.0) / packSize);//分块下载，剩余部分可分成的块数   
                    for (int i = 0; i < maxCount && httpContext.Response.IsClientConnected; i++)
                    {//客户端中断连接，则暂停   
                        httpContext.Response.BinaryWrite(br.ReadBytes(packSize));
                        httpContext.Response.Flush();
                        if (sleep > 1) Thread.Sleep(sleep);
                    }
                    #endregion
                }
                catch
                {
                    ret = false;
                }
                finally
                {
                    br.Close();
                    myFile.Close();
                }
            }
            catch
            {
                ret = false;
            }
            return ret;
        }


        public void DownloadFile(int id)
        {
            var success = download(this.HttpContext, id);
            ServiceLog.Log(ServiceLog.Level.Info, string.Format("Request Header:{0}",Request.Headers));
        }