求助，关于断点续传
最近在做一个能够断点续传的下载器，其中遇到了一个问题
比如要下载的文件大小是100k
那么下载到50k的时候我中断下载，下次续传的时候，下载完成是文件大小为150k
同样，下载到30k中断，续传完成的文件就是130k
用的代码不多，在论坛上面找的，反复核查都没发现问题所在
希望能有大神给指点下迷津，谢了
下面是代码~~~
class classDownloader { private string strURL; //待下载文件链接 private string strSavePath; //待下载文件存放路径 private long lContentLenth = 0; //文件的大小 private long lStartPos = 0; //文件下载的起始位置 private System.IO.FileStream fs; private System.IO.Stream ns; private System.Net.HttpWebRequest request; private System.Net.WebRequest req; private const int NBuff = 512;//下载流缓冲池大小 private void SetURL(string temp) //获取待下载文件链接 { strURL = temp; } private void SetSavePath(string temp) //获取待下载文件存放路径 { strSavePath = temp; } private void StartDownload() //开始下载 { //打开网络连接 try { // req = System.Net.HttpWebRequest.Create(strURL); // req.Method = "HEAD"; request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(strURL); System.Net.WebResponse resp = request.GetResponse(); long.TryParse(resp.Headers.Get("Content-Length"), out lContentLenth);//获取待下载文件的大小 //判断是新文件或续传文件或已经下好了 if (System.IO.File.Exists(strSavePath)) { fs = System.IO.File.OpenWrite(strSavePath); lStartPos = fs.Length; if (lStartPos >= lContentLenth) { MessageBox.Show("已经下好了"); return; } //lStartPos -= 10240; fs.Seek(lStartPos, System.IO.SeekOrigin.Current); } else { fs = new System.IO.FileStream(strSavePath, System.IO.FileMode.Create); lStartPos = 0; } if (lStartPos > 0) { request.AddRange((int)lStartPos); //设置range值 } //向服务器请求，获得服务器回应数据流 ns = request.GetResponse().GetResponseStream(); byte[] nbytes = new byte[NBuff]; int nReadSize = 0; nReadSize = ns.Read(nbytes, 0, NBuff); while (nReadSize > 0) { fs.Write(nbytes, 0, nReadSize); nReadSize = ns.Read(nbytes, 0, NBuff); Program.a.progressBar1.Value = (int)(((float)fs.Length / (float)lContentLenth) * 100); int resault = (int)((float)fs.Length / (float)lContentLenth*100); Program.a.label2.Text = "已下载" + resault+"%"; //Program.a.label2.Text = "已下载" + fs.Length + "/" + lContentLenth; } //MessageBox.Show("下载完成"); } catch (Exception ex) { MessageBox.Show("下载中出错" + ex.ToString()); } finally { if (!(lStartPos >= lContentLenth)) { ns.Close(); fs.Close(); } //req.Abort(); request.Abort(); } } public void update() { classWebRequest webrequest = new classWebRequest(); webrequest.WebReqVer(); /* DataSet dataset = new DataSet(); DataTable datatable = new DataTable("UpdataContext"); datatable.Columns.Add(new DataColumn ("No.",typeof (int))); datatable.Columns.Add(new DataColumn ("FileName",typeof (string))); datatable.Columns.Add(new DataColumn ("Status",typeof (string))); DataRow datarow; for (int j = 1; j < webrequest.VerList.Count; j++) { datarow = datatable.NewRow(); datarow["No."]=j; datarow["FileName"]="ZZV" + webrequest .VerList[j] + ".pcg"; datatable.Rows.Add(datarow); } dataset .Tables.Add(datatable); Program .a.dataGridView1 .DataSource =dataset.Tables ["UpdataContext"]; */ int i = 1; while (i < webrequest .VerList .Count ) { Program.a.dataGridView1.Rows[i-1].Cells[2].Value ="正在下载中"; SetSavePath("d:\\ZZV" + webrequest .VerList[i] + ".pcg.dat"); SetURL("http://www.autososcn.com/webservice/soft/zzv" + webrequest .VerList [i] + ".zip"); StartDownload(); //解压 ZipData.UnZipFile("d:\\ZZV" + webrequest.VerList[i] + ".pcg.dat", "d:\\temp\\"); //释放 classChangeFile.UnPackage("d:\\temp\\ZZV" + webrequest.VerList[i] + ".pcg","e:\\aaaa\\"); Program.a.dataGridView1.Rows[i - 1].Cells[2].Value = "已下载"; i++; } MessageBox .Show ("所有更新文件下载完成"); } }
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strURL);request.AddRange((int)position);//这里的position就是断点