.NET断点下载

女爷i 2022-05-25 23:42 99阅读 0赞

场景：最近由于公司项目中需要使用到断点续传这一功能，并且需要将文件和服务器的文件进行，只好自己去学习和了解一些有关断点续传的知识，其中，主要需要学习的是HTTP相关的知识，比如Header，其实这里面的Range属性就是用来实现断点下载的，下面直接贴代码：

其中服务器端的代码主要是使用ASP.NET MVC写的，如下所示：

/// <summary>  
    /// 下载的方法  
    /// </summary>  
    /// <param name="filename">下载文件的路径</param>  
    
    public ActionResult Reget(string filename)
    {
    	long start = 0L, end = 0L;
    	Stream iStream = null;
    	var result = GetMD5(filename, out string message);
    	// 分块读取，每块512 bytes   
    	byte[] buffer = new Byte[512];
    	//文件的大小  
    	int length;
    	// 文件的字节数  
    	long dataToRead;
    
    	// 得到服务器上面的文件
    	var path = Server.MapPath("/Files/Files/");
    	string filepath = path + filename;
    
    	try
    	{
    		Response.Clear();
    		Response.ClearHeaders();
    
    		//打开文件  
    		iStream = new FileStream(filepath, FileMode.Open,
    			FileAccess.Read, FileShare.Read);
    
    		// 总字节  
    		dataToRead = iStream.Length;
    
    		if (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  
    			Response.StatusCode = 206;
    			//重要：续传必须，表示局部范围响应。  
    			var range = Request.Headers["Range"].ToString();
    			var startRange = range.Substring(6);
    			start = Convert.ToInt64(startRange.Substring(0, startRange.LastIndexOf("-")));
    			end = Convert.ToInt64(range.Substring(startIndex: range.LastIndexOf("-") + 1));
    
    		}
    		//不是从最开始下载,  
    		响应的格式是:Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小]  
    		Response.AddHeader("Range", "bytes=" + start + "-" + end);
    		Response.AddHeader("Connection", "Keep-Alive");
    		Response.ContentType = "application/octet-stream";   //MIME类型：匹配任意文件类型   
    		Response.ContentType = "application/octet-stream";
    		Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(filename));
    		Response.AddHeader("Content-Length", string.Format("{0}", iStream.Length));
    		Response.AddHeader("Content-MD5", message);//用于验证文件
    		iStream.Position = start;
    		dataToRead = end - start;
    		// 读字节  
    		while (dataToRead > 0)
    		{
    			//确认客户端连接  
    			if (Response.IsClientConnected)
    			{
    				// Read the data in buffer.  
    				length = iStream.Read(buffer, 0, (int)dataToRead);
    				// Write the data to the current output stream.  
    				Response.OutputStream.Write(buffer, 0, length);
    				// Flush the data to the HTML output.  
    				Response.Flush();
    				buffer = new Byte[length];
    				dataToRead = dataToRead - length;
    			}
    			else
    			{
    				//prevent infinite loop if user disconnects  
    				dataToRead = -1;
    			}
    		}
    
    	}
    	catch (Exception ex)
    	{
    		// Trap the error, if any.  
    		return Content("Error : " + ex.Message);
    	}
    	finally
    	{
    		if (iStream != null)
    		{
    			//关闭流  
    			iStream.Close();
    		}
    		Response.Close();
    	}
    	return new EmptyResult();
    }

接下来就展示客户端的代码，并且对文件进行MD5校验：

using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using System.Security.Cryptography;
    using System.Text;
    using System.Threading;
    using System.Threading.Tasks;
    
    namespace DownloadTaskDemo
    {
    	class Program
    	{
    		static void Main(string[] args)
    		{
    			//1、查看文件是否已下载过和配置文件是否已生成
    			//2、已下载或已生成文件，直接读取它们
    			//3、否则，从零开始下载，并生成配置文件
    			//4、通过对请求头的Range属性进行配置来获取文件某一段内容，服务器并返回内容，同时将已下载的部分记录在配置文件中
    			//5、判断文件是否下载完成，下载完成就根据服务器返回的MD5进行校验，并记录到配置文件
    			long start = 0L, end = 0L;
    			string fn = "";
    			long contentLength = 0L;
    			string md5 = "";
    			var isComplate = false;
    			string StrFileName = @"d:\my.tmp";
    			string StrUrl = "http://localhost:56159/Upload/Reget?filename=f512b5fa8cab41b9e8940107ca657862.jar";
    			// StrUrl = "http://localhost:56159/Upload/Reget?filename=Paper20180412.docx";
    			//打开上次下载的文件或新建文件
    			long lStartPos = 0;
    			FileStream fs;
    			if (File.Exists(StrFileName))
    			{
    				fs = File.OpenWrite(StrFileName);
    				lStartPos = fs.Length;
    				fs.Seek(lStartPos, SeekOrigin.Current);   //移动文件流中的当前指针
    			}
    			else
    			{
    				fs = new FileStream(StrFileName, FileMode.Create);
    				lStartPos = 0;
    			}
    			//打开网络连接
    			try
    			{
    				System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(StrUrl);
    				request.AddRange(lStartPos, lStartPos + 512);
    				Stream ns;
    				//向服务器请求，获得服务器回应数据流
    				int i = 1;
    				while (!isComplate)
    				{
    					i++;
    					if (start != 0 && end != 0 && contentLength != 0)
    					{
    						request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(StrUrl);
    						//矫正range
    						if (end > contentLength)
    						{
    							request.AddRange(start, contentLength);
    						}
    						else
    						{
    							request.AddRange(start, end);
    						}
    					}
    					var response = request.GetResponse();
    					if (response.Headers["Content-Length"] != null)
    					{
    						contentLength = Convert.ToInt64(response.Headers["Content-Length"]);
    					}
    					md5 = response.Headers["Content-MD5"];
    					Console.WriteLine(md5);
    					if (response.Headers["Range"] != null)
    					{
    						var range = response.Headers["Range"].ToString();
    						var startRange = range.Substring(6);
    						start = Convert.ToInt64(startRange.Substring(0, startRange.LastIndexOf("-")));
    						end = Convert.ToInt64(range.Substring(startIndex: range.LastIndexOf("-") + 1));
    						Console.WriteLine(start + "-" + end);
    					}
    					var cd = response.Headers["Content-Disposition"];
    					fn = cd.Substring(cd.LastIndexOf("=") + 1);
    					ns = response.GetResponseStream();
    					byte[] nbytes = new byte[512];
    					int nReadSize = 0;
    					nReadSize = ns.Read(nbytes, 0, 512);
    					while (nReadSize > 0)
    					{
    						//同时向同一个记录里面取数据  并将数据从相同位置写
    						fs.Write(nbytes, 0, nReadSize);
    						nReadSize = ns.Read(nbytes, 0, 512);
    					}
    					//下载完成就退出
    					if (end == contentLength)
    					{
    						isComplate = true;
    						break;
    					}
    					start = end;
    					end = end + 512;
    					//获取剩余512字节的数据
    					ns.Close();
    				}
    
    				fs.Close();
    				var valMd5 = GetMD5(filePath: StrFileName);
    				Console.WriteLine(valMd5);
    				if (md5.Equals(valMd5))
    				{
    					Console.WriteLine("校验成功");
    				}
    				else
    				{
    					Console.WriteLine("校验失败");
    				}
    				File.Move(StrFileName, @"d:\" + fn);
    				Console.WriteLine("下载完成");
    			}
    			catch (Exception ex)
    			{
    				fs.Close();
    				Console.WriteLine("下载过程中出现错误:" + ex.Message);
    			}
    			Console.Read();
    		}
    
    		/// <summary>
    		/// MD5校验
    		/// </summary>
    		/// <param name="fileName"></param>
    		/// <param name="message"></param>
    		/// <returns></returns>
    		public static string GetMD5(string filePath)
    		{
    			string path = filePath;
    			string message = "";
    			try
    			{
    				FileStream file = new FileStream(path, System.IO.FileMode.Open);
    				MD5 md5 = new MD5CryptoServiceProvider();
    				byte[] retVal = md5.ComputeHash(file);
    				file.Close();
    				string result = BitConverter.ToString(retVal);
    				message = result.Replace("-", "");
    				return message;
    			}
    			catch (Exception ex)
    			{
    				message = "错误信息" + ex.Message;
    				return message;
    			}
    		}
    
    	}
    }

在这里，主要涉及的知识有HTTP的相关知识可以参考：https://en.wikipedia.org/wiki/List\_of\_HTTP\_header\_fields