文件下载代码

文件下载代码,Copy 别人的.

Codepublic static bool DownloadFile(HttpContext httpContext, string filePath, long speed)

        {

            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;

                }

                if (!File.Exists(filePath))

                {

                    httpContext.Response.StatusCode = 404;

                    return false;

                }

                #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;

                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 = File.GetLastWriteTimeUtc(filePath).ToString("r");

                string eTag = HttpUtility.UrlEncode(fileName, 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/octet-stream";//MIME类型：匹配任意文件类型 

                    httpContext.Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(fileName, Encoding.UTF8).Replace("+", "%20"));

                    httpContext.Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());

                    httpContext.Response.AddHeader("Connection", "Keep-Alive");

                    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;

                        }

                    }

                    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));

                    }

                    #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;

        }