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public 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; } |
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