asp.net mvc如何實現(xiàn)文件下載

仰望//45度微笑 2012-05-29

展開全文

public static bool DownloadFile(HttpContext httpContext, string filePath, long speed)
{
    bool ret = true;
    try
    {
      #region--驗證：HttpMethod，請求的文件是否存在
        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 定義局部變量
         long startBytes = 0;
        int packSize = 1024 * 10; //分塊讀取，每塊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);//毫秒數(shù)：讀取下一數(shù)據(jù)塊的時間間隔
        string lastUpdateTiemStr = File.GetLastWriteTimeUtc(filePath).ToString("r");
        string eTag = HttpUtility.UrlEncode(fileName, Encoding.UTF8) + lastUpdateTiemStr;//便于恢復(fù)下載時提取請求頭;
        #endregion

        #region--驗證：文件是否太大，是否是續(xù)傳，且在上次被請求的日期之后是否被修
        if (myFile.Length > Int32.MaxValue)
        {//-------文件太大了-------
            httpContext.Response.StatusCode = 413;//請求實體太大
            return false;
        }

        if (httpContext.Request.Headers["If-Range"] != null)//對應(yīng)響應(yīng)頭ETag：文件名+文件最后修改時間
        {
            //----------上次被請求的日期之后被修改過--------------
            if (httpContext.Request.Headers["If-Range"].Replace("\"", "") != eTag)
            {//文件修改過
                httpContext.Response.StatusCode = 412;//預(yù)處理失敗
                return false;
            }
        }
        #endregion

        try
        {
         #region -------添加重要響應(yīng)頭、解析請求頭、相關(guān)驗證-------------------
            httpContext.Response.Clear();
            httpContext.Response.Buffer = false;
            httpContext.Response.AddHeader("Content-MD5", GetMD5Hash(myFile));//用于驗證文件
            httpContext.Response.AddHeader("Accept-Ranges", "bytes");//重要：續(xù)傳必須
            httpContext.Response.AppendHeader("ETag", "\"" + eTag + "\"");//重要：續(xù)傳必須
            httpContext.Response.AppendHeader("Last-Modified", lastUpdateTiemStr);//把最后修改日期寫入響應(yīng)
            httpContext.Response.ContentType = "application/octet-stream";//MIME類型：匹配任意文件類型
            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)
            {//------如果是續(xù)傳請求，則獲取續(xù)傳的起始位置，即已經(jīng)下載到客戶端的字節(jié)數(shù)------
                httpContext.Response.StatusCode = 206;//重要：續(xù)傳必須，表示局部范圍響應(yīng)。初始下載時默認(rèn)為200
                string[] range = httpContext.Request.Headers["Range"].Split(new char[] { '=', '-' });//"bytes=1474560-"
                startBytes = Convert.ToInt64(range[1]);//已經(jīng)下載的字節(jié)數(shù)，即本次下載的開始位置
                if (startBytes < 0 || startBytes >= fileLength)
                {//無效的起始位置
                    return false;
                }
            }
            if (startBytes > 0)
            {//------如果是續(xù)傳請求，告訴客戶端本次的開始字節(jié)數(shù)，總長度，以便客戶端將續(xù)傳數(shù)據(jù)追加到startBytes位置后----------
                httpContext.Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
            }
            #endregion

            #region -------向客戶端發(fā)送數(shù)據(jù)塊-------------------
            br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
            int maxCount = (int)Math.Ceiling((fileLength - startBytes + 0.0) / packSize);//分塊下載，剩余部分可分成的塊數(shù)
            for (int i = 0; i < maxCount && httpContext.Response.IsClientConnected; i++)
            {//客戶端中斷連接，則暫停
                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;
}