C#下载文件通用方法,支持大文件、续传、速度限制。

支持续传的响应头Accept-Ranges、ETag,请求头Range 。


Accept-Ranges:响应头,向客户端指明,此进程支持可恢复下载.实现后台智能传输服务(BITS),值为:bytes;
ETag:响应头,用于对客户端的初始(200)响应,以及来自客户端的恢复请求,
必须为每个文件提供一个唯一的ETag值(可由文件名和文件最后被修改的日期组成),这使客户端软件能够验证它们已经下载的字节块是否仍然是最新的。
Range:续传的起始位置,即已经下载到客户端的字节数,值如:bytes=1474560- 。
另外:UrlEncode编码后会把文件名中的空格转换中 ( 转换为%2b),但是浏览器是不能理解加号为空格的,所以在浏览器下载得到的文件,空格就变成了加号;
解决办法:UrlEncode 之后, 将 " " 替换成 "%20",因为浏览器将%20转换为空格



001using System;
002using System.Collections.Generic;
003using System.Linq;
004using System.Web;
005using System.IO;
006using System.Text;
007using System.Threading;
008 
009namespace AutoHome.CommonHelper
010{
011    public class FileDownHelper
012    {
013        //C#下载文件帮助类 支持大文件、续传、速度限制
014        /// <summary>
015        /// 下载文件,支持大文件、续传、速度限制。支持续传的响应头Accept-Ranges、ETag,请求头Range 。
016        /// Accept-Ranges:响应头,向客户端指明,此进程支持可恢复下载.实现后台智能传输服务(BITS),值为:bytes;
017        /// ETag:响应头,用于对客户端的初始(200)响应,以及来自客户端的恢复请求,
018        /// 必须为每个文件提供一个唯一的ETag值(可由文件名和文件最后被修改的日期组成),这使客户端软件能够验证它们已经下载的字节块是否仍然是最新的。
019        /// Range:续传的起始位置,即已经下载到客户端的字节数,值如:bytes=1474560- 。
020        /// 另外:UrlEncode编码后会把文件名中的空格转换中 ( 转换为%2b),但是浏览器是不能理解加号为空格的,所以在浏览器下载得到的文件,空格就变成了加号;
021        /// 解决办法:UrlEncode 之后, 将 " " 替换成 "%20",因为浏览器将%20转换为空格
022        /// </summary>
023        /// <param name="httpContext">当前请求的HttpContext</param>
024        /// <param name="filePath">下载文件的物理路径,含路径、文件名</param>
025        /// <param name="speed">下载速度:每秒允许下载的字节数</param>
026        /// <returns>true下载成功,false下载失败</returns>
027        public static bool DownloadFile(HttpContext httpContext, string filePath, long speed)
028        {
029            httpContext.Response.Clear();
030            bool ret = true;
031            try
032            {
033                switch (httpContext.Request.HttpMethod.ToUpper())
034                { //目前只支持GET和HEAD方法
035                    case "GET":
036                    case "HEAD":
037                        break;
038                    default:
039                        httpContext.Response.StatusCode = 501;
040                        return false;
041                }
042                if (!File.Exists(filePath))
043                {
044                    httpContext.Response.StatusCode = 404;
045                    return false;
046                }
047                //定义局部变量#region 定义局部变量#region 定义局部变量#region 定义局部变量
048                long startBytes = 0;
049                long stopBytes = 0;
050                int packSize = 1024 * 10; //分块读取,每块10K bytes
051                string fileName = Path.GetFileName(filePath);
052                FileStream myFile = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
053                BinaryReader br = new BinaryReader(myFile);
054                long fileLength = myFile.Length;
055                int sleep = (int)Math.Ceiling(1000.0 * packSize / speed);//毫秒数:读取下一数据块的时间间隔
056                string lastUpdateTiemStr = File.GetLastWriteTimeUtc(filePath).ToString("r");
057                string eTag = HttpUtility.UrlEncode(fileName, Encoding.UTF8)   lastUpdateTiemStr;//便于恢复下载时提取请求头;
058 
059                // --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改过#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改过
060                if (myFile.Length > long.MaxValue)
061                {//-------文件太大了-------
062                    httpContext.Response.StatusCode = 413;//请求实体太大
063                    return false;
064                }
065                //
066                if (httpContext.Request.Headers["If-Range"] != null)//对应响应头ETag:文件名 文件最后修改时间
067                {
068                    //----------上次被请求的日期之后被修改过--------------
069                    if (httpContext.Request.Headers["If-Range"].Replace("\"", "") != eTag)
070                    {//文件修改过
071                        httpContext.Response.StatusCode = 412;//预处理失败
072                        return false;
073                    }
074                }
075                try
076                {
077                    //-------添加重要响应头、解析请求头、相关验证#region -------添加重要响应头、解析请求头、相关验证
078                    httpContext.Response.Clear();
079                    if (httpContext.Request.Headers["Range"] != null)
080                    {//------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------
081                        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
082                        string[] range = httpContext.Request.Headers["Range"].Split(new char[] { '=', '-' });//"bytes=1474560-"
083                        startBytes = Convert.ToInt64(range[1]);//已经下载的字节数,即本次下载的开始位置 
084                        if (startBytes < 0 || startBytes >= fileLength)
085                        {//无效的起始位置
086                            return false;
087                        }
088                        if (range.Length == 3)
089                        {
090                            stopBytes = Convert.ToInt64(range[2]);//结束下载的字节数,即本次下载的结束位置 
091                            if (startBytes < 0 || startBytes >= fileLength)
092                            {
093                                return false;
094                            }
095                        }
096                    }
097                    httpContext.Response.Buffer = false;
098                    httpContext.Response.AddHeader("Content-MD5", GetMD5HashFromFile(filePath));//用于验证文件
099                    httpContext.Response.AddHeader("Accept-Ranges", "bytes");//重要:续传必须
100                    httpContext.Response.AppendHeader("ETag", "\""   eTag   "\"");//重要:续传必须
101                    httpContext.Response.AppendHeader("Last-Modified", lastUpdateTiemStr);//把最后修改日期写入响应               
102                    httpContext.Response.ContentType = "application/octet-stream";//MIME类型:匹配任意文件类型
103                    httpContext.Response.AddHeader("Content-Disposition", "attachment;filename="   HttpUtility.UrlEncode(fileName, Encoding.UTF8).Replace(" ", "%20"));
104                    httpContext.Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
105                    httpContext.Response.AddHeader("Connection", "Keep-Alive");
106                    httpContext.Response.ContentEncoding = Encoding.UTF8;
107                    if (startBytes > 0)
108                    {//------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----------
109                        httpContext.Response.AddHeader("Content-Range", string.Format("bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
110                    }
111                    // -------向客户端发送数据块-------------------#region -------向客户端发送数据块-------------------
112                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
113                    int maxCount = (int)Math.Ceiling((fileLength - startBytes   0.0) / packSize);//分块下载,剩余部分可分成的块数
114                    for (int i = 0; i < maxCount && httpContext.Response.IsClientConnected; i  )
115                    {//客户端中断连接,则暂停
116                        httpContext.Response.BinaryWrite(br.ReadBytes(packSize));
117                        httpContext.Response.Flush();
118                        if (sleep > 1)
119                            Thread.Sleep(sleep);
120                    }
121                }
122                catch
123                {
124                    ret = false;
125                }
126                finally
127                {
128                    br.Close();
129                    myFile.Close();
130                }
131            }
132            catch
133            {
134                ret = false;
135            }
136            return ret;
137        }
138        public static string GetMD5HashFromFile(string fileName)
139        {
140            try
141            {
142                FileStream file = new FileStream(fileName, FileMode.Open);
143                System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
144                byte[] retVal = md5.ComputeHash(file);
145                file.Close();
146 
147                StringBuilder sb = new StringBuilder();
148                for (int i = 0; i < retVal.Length; i  )
149                {
150                    sb.Append(retVal[i].ToString("x2"));
151                }
152                return sb.ToString();
153            }
154            catch (Exception ex)
155            {
156                throw new Exception("GetMD5HashFromFile() fail,error:"   ex.Message);
157            }
158        }
159    }
160}



原文链接:C#下载文件帮助类 支持大文件、续传、速度限制