一 介绍
断点续传搜索大部分都是下载的断点续传，涉及到HTTP协议1.1的Range和Content-Range头。
来个简单的介绍
所谓断点续传，也就是要从文件已经下载的地方开始继续下载。在以前版本的 HTTP 协议是不支持断点的，HTTP/1.1 开始就支持了。一般断点下载时才用到 Range 和 Content-Range 实体头。
Range
用于请求头中，指定第一个字节的位置和最后一个字节的位置，一般格式：
Range:(unit=first byte pos)-[last byte pos]
Content-Range
用于响应头，指定整个实体中的一部分的插入位置，他也指示了整个实体的长度。在服务器向客户返回一个部分响应，它必须描述响应覆盖的范围和整个实体长度。一般格式：
Content-Range: bytes (unit first byte pos) – [last byte pos]/[entity legth]
请求下载整个文件:
- GET /test.rar HTTP/1.1
- Connection: close
- Host: 116.1.219.219
- Range: bytes=0-801 //一般请求下载整个文件是bytes=0- 或不用这个头
一般正常回应
- HTTP/1.1 200 OK
- Content-Length: 801
- Content-Type: application/octet-stream
- Content-Range: bytes 0-800/801 //801:文件总大小
而今天要说的是上传的断点续传，用到了Content-Range头
上传的续传原理跟下载的续传同理。
就是在上传前把文件拆分后上传。服务器端接收合并，即使上传断了。下次上传依然从服务器端的文件现有字节后合并文件。最终上传完成。
二 实现
服务器端
服务端是webapi实现。或是mvc,webform皆可。
服务端的原理就是接收上传数据流。保存文件。如果此文件已存在。就是合并现有文件。
这里文件的文件名是采用客户端传过来的数据。
文件名称是文件的MD5，保证文件的唯一性。
[HttpGet]
public HttpResponseMessage GetResumFile()
{
//用于获取当前文件是否是续传。和续传的字节数开始点。
var md5str = HttpContext.Current.Request.QueryString["md5str"];
var saveFilePath = HttpContext.Current.Server.MapPath("~/Images/") + md5str;
if(System.IO.File.Exists(saveFilePath))
{
var fs = System.IO.File.OpenWrite(saveFilePath);
var fslength = fs.Length.ToString();
fs.Close();
return new HttpResponseMessage { Content = new StringContent(fslength, System.Text.Encoding.UTF8, "text/plain") };
}
return new HttpResponseMessage(HttpStatusCode.OK);
}
[HttpPost]
public HttpResponseMessage Rsume()
{
var file = HttpContext.Current.Request.InputStream;
var filename = HttpContext.Current.Request.QueryString["filename"];
this.SaveAs(HttpContext.Current.Server.MapPath("~/Images/") + filename, file);
HttpContext.Current.Response.StatusCode = 200;
// For compatibility with IE's "done" event we need to return a result as well as setting the context.response
return new HttpResponseMessage(HttpStatusCode.OK);
}
private void SaveAs(string saveFilePath,System.IO.Stream stream)
{
long lStartPos = 0;
int startPosition = 0;
int endPosition = 0;
var contentRange = HttpContext.Current.Request.Headers["Content-Range"];
//bytes 10000-19999/1157632
if (!string.IsNullOrEmpty(contentRange))
{
contentRange = contentRange.Replace("bytes", "").Trim();
contentRange = contentRange.Substring(0, contentRange.IndexOf("/"));
string[] ranges = contentRange.Split('-');
startPosition = int.Parse(ranges[0]);
endPosition = int.Parse(ranges[1]);
}
System.IO.FileStream fs;
if (System.IO.File.Exists(saveFilePath))
{
fs = System.IO.File.OpenWrite(saveFilePath);
lStartPos = fs.Length;
}
else
{
fs = new System.IO.FileStream(saveFilePath, System.IO.FileMode.Create);
lStartPos = 0;
}
if (lStartPos > endPosition)
{
fs.Close();
return;
}
else if (lStartPos < startPosition)
{
lStartPos = startPosition;
}
else if (lStartPos > startPosition && lStartPos < endPosition)
{
lStartPos = startPosition;
}
fs.Seek(lStartPos, System.IO.SeekOrigin.Current);
byte[] nbytes = new byte[512];
int nReadSize = 0;
nReadSize = stream.Read(nbytes, 0, 512);
while (nReadSize > 0)
{
fs.Write(nbytes, 0, nReadSize);
nReadSize = stream.Read(nbytes, 0, 512);
}
fs.Close();
}
客户端
这里的客户端是winform，功能就是选择文件后即刻上传。如果中途网络，断点等因素没有传成功。
可以再次选择此文件上传。服务器会合并之前传送的文件字节。实现断点续传。
private void btnSelectFile_Click(object sender, EventArgs e)
{
OpenFileDialog openFileDialog = new OpenFileDialog();
openFileDialog.InitialDirectory = "c:\";
openFileDialog.RestoreDirectory = true;
openFileDialog.FilterIndex = 1;
if (openFileDialog.ShowDialog() == DialogResult.OK)
{
var fName = openFileDialog.FileName;
FileStream fStream = new FileStream(fName, FileMode.Open, FileAccess.Read);
var mdfstr = GetStreamMd5(fStream);
fStream.Close();
var startpoint = isResume(mdfstr, Path.GetExtension(fName));
MessageBox.Show(UpLoadFile(fName, url, 64, startpoint,mdfstr));
}
}
/// <summary>
/// 根据文件名获取是否是续传和续传的下次开始节点
/// </summary>
/// <param name="md5str"></param>
/// <param name="fileextname"></param>
/// <returns></returns>
private int isResume(string md5str, string fileextname)
{
System.Net.WebClient WebClientObj = new System.Net.WebClient();
var url = "http://localhost:13174/api/file/GetResumFile?md5str="+md5str+fileextname;
byte[] byRemoteInfo = WebClientObj.DownloadData(url);
string result = System.Text.Encoding.UTF8.GetString(byRemoteInfo);
if(string.IsNullOrEmpty(result))
{
return 0;
}
return Convert.ToInt32(result);
}
#region
/// <summary>
/// 上传文件（自动分割）
/// </summary>
/// <param name="filePath">待上传的文件全路径名称</param>
/// <param name="hostURL">服务器的地址</param>
/// <param name="byteCount">分割的字节大小</param>
/// <param name="cruuent">当前字节指针</param>
/// <returns>成功返回"";失败则返回错误信息</returns>
public string UpLoadFile(string filePath, string hostURL, int byteCount, long cruuent, string mdfstr)
{
string tmpURL = hostURL;
byteCount = byteCount * 1024;
System.Net.WebClient WebClientObj = new System.Net.WebClient();
FileStream fStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
BinaryReader bReader = new BinaryReader(fStream);
long length = fStream.Length;
string sMsg = "上传成功";
string fileName = filePath.Substring(filePath.LastIndexOf('\') + 1);
try
{
#region 续传处理
byte[] data;
if (cruuent > 0)
{
fStream.Seek(cruuent, SeekOrigin.Current);
}
#endregion
#region 分割文件上传
for (; cruuent <= length; cruuent = cruuent + byteCount)
{
if (cruuent + byteCount > length)
{
data = new byte[Convert.ToInt64((length - cruuent))];
bReader.Read(data, 0, Convert.ToInt32((length - cruuent)));
}
else
{
data = new byte[byteCount];
bReader.Read(data, 0, byteCount);
}
try
{
//*** bytes 21010-47021/47022
WebClientObj.Headers.Remove(HttpRequestHeader.ContentRange);
WebClientObj.Headers.Add(HttpRequestHeader.ContentRange, "bytes " + cruuent + "-" + (cruuent + byteCount) + "/" + fStream.Length);
hostURL = tmpURL + "?filename=" + mdfstr + Path.GetExtension(fileName);
byte[] byRemoteInfo = WebClientObj.UploadData(hostURL, "POST", data);
string sRemoteInfo = System.Text.Encoding.Default.GetString(byRemoteInfo);
// 获取返回信息
if (sRemoteInfo.Trim() != "")
{
sMsg = sRemoteInfo;
break;
}
}
catch (Exception ex)
{
sMsg = ex.ToString();
break;
}
#endregion
}
}
catch (Exception ex)
{
sMsg = sMsg + ex.ToString();
}
try
{
bReader.Close();
fStream.Close();
}
catch (Exception exMsg)
{
sMsg = exMsg.ToString();
}
GC.Collect();
return sMsg;
}
public static string GetStreamMd5(Stream stream)
{
var oMd5Hasher = new MD5CryptoServiceProvider();
byte[] arrbytHashValue = oMd5Hasher.ComputeHash(stream);
//由以连字符分隔的十六进制对构成的String，其中每一对表示value 中对应的元素；例如“F-2C-4A”
string strHashData = BitConverter.ToString(arrbytHashValue);
//替换-
strHashData = strHashData.Replace("-", "");
string strResult = strHashData;
return strResult;
}