asp.net c# 断点续传 下载 Accept-Ranges

转自：http://www.cnblogs.com/90nice/p/3489287.html

1.因为要下载大文件 需要断点续传，使用多线程 分段下载 效率比较高，节省资源。

发点牢骚：下载可以用多线程，如果是上传 我觉得没必要了。如果是普通用户(adsl) 上传速度只有50KB/s  据我所知100MB光纤 家庭用户下载理论值能达到12.5MB/S 但是上传目前却只有 256kb/s   这点速度够干啥的。希望以后 上传下载速度能一致。

下面是一个简单的例子：

服务端：

如果是分段下载 在http Header 头文件里 要有Range ，下面会有 客户端的例子。

var range = Request.Headers["Range"];
 if (null == range)
 { //正常情况 200
 Response.StatusCode = 200;
 Response.ContentType = "application/x-zip-compressed";
 Response.AddHeader("Content-Disposition", "attachment;filename=" + fName);
 FileStream fs = new FileStream(fUrl, FileMode.Open);
 long len = fs.Length;
 fs.Close();
 fs.Dispose();
 Response.AddHeader("Accept-Ranges", len.ToString());
 Response.TransmitFile(fUrl);
 }
 else
 { //Accept - Range 情况
string[] re = range.Split('=');
 string[] r = re[1].Split('-');
 long start = 0;
 long alength = 0;
 long fslength = 0;
 // 如果开始为空 从0开始取
if (string.IsNullOrEmpty(r[0]))
 start = 0;
 else
 start = Convert.ToInt64(r[0]);
 //取文件总长度
FileStream fs = new FileStream(fUrl, FileMode.Open);
 fslength = fs.Length;
 fs.Close();
 fs.Dispose();
 // 字节长度 
if (string.IsNullOrEmpty(r[1]))
 alength = fslength - start;
 else
 alength = Convert.ToInt64(r[1]) - start;
 Response.StatusCode = 206;  //分段下载状态
Response.ContentType = "application/x-zip-compressed";
 Response.AddHeader("Content-Disposition", "attachment;filename=" + fName);
 Response.AddHeader("Accept-Ranges", (alength - start).ToString());
 Response.AddHeader("Content-Range", "bytes " + start + "-" + (start + alength) + "/" + fslength.ToString()); //Content-Range： bytes 100-200/1024 告诉客户端 本次请求的文件位置和总文件大小
// 文件路径 开始位置 取多少字节
Response.TransmitFile(fUrl, start, alength);

客户端 例子：

创建一个 http请求 并 写入请求的文件段

var request = (HttpWebRequest)WebRequest.Create("http://localhost:40337/PublicPage/ZrqPublicImg.zip");
 request.AddRange(0, 500);
 try
 {
 //获取HTTP回应，注意HttpWebResponse继承自IDisposable
 using (var response = (HttpWebResponse)request.GetResponse())
 {
 if (response.StatusCode == HttpStatusCode.OK)
 throw new Exception("文件不支持Range部分下载");
 //设置接收信息的缓冲器
var bytes = new byte[5000];
 //获取回应的Stream（字节流）
using (var stream = response.GetResponseStream())
 {//FileMode.Append 我这里是从文件末尾处写入        如果是多线程 就要根据具体的请求的位置 写入文件
using (var outStream = new FileStream(@"D:222.jpg", FileMode.Append, FileAccess.Write, FileShare.None))
 {
 const int bufferLen = 4096;
 byte[] buffer = new byte[bufferLen];
 int count = 0;

while ((count = stream.Read(buffer, 0, bufferLen)) > 0)
 {
 outStream.Write(buffer, 0, count);
 }
 outStream.Close();
 stream.Close();
 }
 }
 }
 }
 catch (Exception ex)
 {
 Console.WriteLine("错误信息：{0}", ex.Message);
 }

 以下摘自：http://www.sufeinet.com/forum.php?mod=viewthread&tid=2258&extra=page%3D1%26filter%3Dtypeid%26typeid%3D284%26typeid%3D284

另附支持限速下载的方法（服务器代码）：

/// <summary>
        ///  输出硬盘文件，提供下载 支持大文件、续传、速度限制、资源占用小
        /// </summary>
        /// <param name="_Request">;Page.Request对象</param>
        /// <param name="_Response">;Page.Response对象</param>
        /// <param name="_fileName">下载文件名</param>
        /// <param name="_fullPath">带文件名下载路径</param>
        /// <param name="_speed">每秒允许下载的字节数</param>
        /// <returns>返回是否成功</returns>
        //---------------------------------------------------------------------
        //调用：
        // string FullPath=Server.MapPath("count.txt");
        // ResponseFile(this.Request,this.Response,"count.txt",FullPath,100);
        //---------------------------------------------------------------------
        public static bool ResponseFile(HttpRequest _Request, HttpResponse _Response, string _fileName, string _fullPath, long _speed)
        {
            try
            {
                FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                BinaryReader br = new BinaryReader(myFile);
                try
                {
                    _Response.AddHeader("Accept-Ranges", "bytes");
                    _Response.Buffer = false;
 
                    long fileLength = myFile.Length;
                    long startBytes = 0;
                    int pack = 10240;  //10K bytes
                    int sleep = (int)Math.Floor((double)(1000 * pack / _speed)) + 1;
 
                    if (_Request.Headers["Range"] != null)
                    {
                        _Response.StatusCode = 206;
                        string[] range = _Request.Headers["Range"].Split(new char[] { '=', '-' });
                        startBytes = Convert.ToInt64(range[1]);
                    }
                    _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
                    if (startBytes != 0)
                    {
                        _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
                    }
 
                    _Response.AddHeader("Connection", "Keep-Alive");
                    _Response.ContentType = "application/octet-stream";
                    _Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(_fileName, System.Text.Encoding.UTF8));
 
                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
                    int maxCount = (int)Math.Floor((double)((fileLength - startBytes) / pack)) + 1;
 
                    for (int i = 0; i < maxCount; i++)
                    {
                        if (_Response.IsClientConnected)
                        {
                            _Response.BinaryWrite(br.ReadBytes(pack));
                            Thread.Sleep(sleep);
                        }
                        else
                        {
                            i = maxCount;
                        }
                    }
                }
                catch
                {
                    return false;
                }
                finally
                {
                    br.Close();
                    myFile.Close();
                }
            }
            catch
            {
                return false;
            }
            return true;
        }
    }