C# 文件下载断点续传

C# 文件下载断点续传的一个类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Net;

namespace CHD.Framework
{
   public class HttpDownLoadExtender
    {
       public static string PERSIST_EXP = ".cdel";

       public static void download(string url, string path)
       {
           if (File.Exists(path))
           {
               print("文件己存在！是否重新下载？");
               return;
           }
           else
           {
               path = path + PERSIST_EXP;

               simpleDownload(url, path);//开始下载
           }
       }
       /// <summary>
        /// 下载网络资源(支持断点续传)
        /// </summary>
        /// <param name="url"></param>
        /// <param name="path"></param>
        public static void simpleDownload(string url, string path)
        {
            HttpWebRequest request = httpClient.getWebRequest(url, 0);
            request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.110 Safari/537.36";
            WebResponse response = null;

            FileStream writer = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write);
            long lStartPos = writer.Length; ;//当前文件大小
            long currentLength = 0;
            long totalLength = 0;//总大小 

            if (File.Exists(path))//断点续传
            {
                response = request.GetResponse();
                long sTotal = response.ContentLength;

                if (sTotal == lStartPos) {

                    close(writer);
                    File.Move(path, path.Replace(PERSIST_EXP, ""));
                    print("下载完成!");
                    return;

                }
                request = httpClient.getWebRequest(url, (int)lStartPos);//设置Range值

                writer.Seek(lStartPos, SeekOrigin.Begin);//指针跳转
                response = request.GetResponse();

                totalLength = response.ContentLength + lStartPos; //总长度
                currentLength = lStartPos; //当前长度
            }
            else
            {
                response = request.GetResponse();
                totalLength = response.ContentLength;
            }

            Stream reader = response.GetResponseStream();

            byte[] buff = new byte[1024];
            int c = 0; //实际读取的字节数

            while ((c = reader.Read(buff, 0, buff.Length)) > 0)
            {
                currentLength += c;
                writer.Write(buff, 0, c);
                progressBar(currentLength, totalLength);//进度条

                writer.Flush();
            }
            close(writer);
            if (currentLength == totalLength)
            {
                File.Move(path, path.Replace(PERSIST_EXP, ""));
                print("下载完成!");
            }

            if (reader != null)
            {
                reader.Close();
                reader.Dispose();
                response.Close();
            }
        }
        private static void close(FileStream writer)
        {
            if (writer != null)
            {
                writer.Close();
                writer.Dispose();
            }
        }
        /// <summary>
        /// 进度条
        /// </summary>
        /// <param name="currentLength">当前长度</param>
        /// <param name="totalLength">总长度</param>
        public static void progressBar(Object currentLength, Object totalLength)
        {
            double aaa = System.Convert.ToDouble(currentLength);
            double bbb = System.Convert.ToDouble(totalLength);
            print(currentLength + "/" + totalLength + "__" + (aaa / bbb).ToString("0.00 %"));
        }
        /// <summary>
        /// 系统输出
        /// </summary>
        /// <param name="obj"></param>
        public static void print(Object obj){
            Console.WriteLine(obj);
        }
        public static void printStr(string[] str)
        {
            foreach (string d in str)
            {
                print(d);
            }
        }
        /// <summary>
        /// 文件写
        /// </summary>
        /// <param name="path">文件路径</param>
        /// <param name="content">要写入的内容</param>
        public static void fileWriter(string path,string content,Encoding encoding)
        {
            if (File.Exists(path))
            {
                StreamWriter sw = new StreamWriter(path, true, encoding);

                sw.WriteLine(content);

                sw.Flush();
                sw.Close();
            }
        }
        /// <summary>
        /// 读文件，返回内容
        /// </summary>
        /// <param name="path">文件路径</param>
        /// <param name="enCoding">默认编码格式</param>
        /// <returns></returns>
        public static string fileReader(string path,Encoding enCoding) {
            StringBuilder sb = new StringBuilder();
            if(enCoding == null){
                enCoding = Encoding.Default;
            }
            //读取文件
            StreamReader sr = new StreamReader(path, enCoding);
                string s = "";
                while ((s = sr.ReadLine()) != null)
                {
                    sb.AppendLine(s);
                }
                if(sr != null)
                    sr.Close();

            return sb.ToString();
        }
        /// <summary>
        /// 获取文件编码格式
        /// </summary>
        /// <param name="path">文件路径</param>
        /// <param name="defaultEncoding">默认编码</param>
        /// <returns></returns>
        public static string getFileEncoding(string path, string defaultEncoding) {
            string ed = defaultEncoding;
            if (File.Exists(path)) {
                FileStream fs = new FileStream(path, FileMode.Open);
                ed = GetEncoding(fs, defaultEncoding);
                if (fs != null)
                    fs.Close();
            }
            return ed;
        }
        /// <summary>
        /// 取得一个文本文件流的编码方式。
        /// </summary>
        /// <param name="stream">文本文件流。</param>
        /// <param name="defaultEncoding">默认编码方式。当该方法无法从文件的头部取得有效的前导符时，将返回该编码方式。</param>
        /// <returns></returns>
        public static string GetEncoding(FileStream stream, string defaultEncoding)
        {
            string targetEncoding = defaultEncoding;
            if (stream != null && stream.Length >= 2)
            {
                //保存文件流的前4个字节
                byte byte1 = 0;
                byte byte2 = 0;
                byte byte3 = 0;
                byte byte4 = 0;
                //保存当前Seek位置
                long origPos = stream.Seek(0, SeekOrigin.Begin);
                stream.Seek(0, SeekOrigin.Begin);

                int nByte = stream.ReadByte();
                byte1 = Convert.ToByte(nByte);
                byte2 = Convert.ToByte(stream.ReadByte());
                if (stream.Length >= 3)
                {
                    byte3 = Convert.ToByte(stream.ReadByte());
                }
                if (stream.Length >= 4)
                {
                    byte4 = Convert.ToByte(stream.ReadByte());
                }
                //根据文件流的前4个字节判断Encoding
                //Unicode {0xFF, 0xFE};
                //BE-Unicode {0xFE, 0xFF};
                //UTF8 = {0xEF, 0xBB, 0xBF};
                if (byte1 == 0xFE && byte2 == 0xFF)//UnicodeBe
                {
                    targetEncoding = Encoding.BigEndianUnicode.BodyName;
                }
                if (byte1 == 0xFF && byte2 == 0xFE && byte3 != 0xFF)//Unicode
                {
                    targetEncoding = Encoding.Unicode.BodyName;
                }
                if (byte1 == 0xEF && byte2 == 0xBB && byte3 == 0xBF)//UTF8
                {
                    targetEncoding = Encoding.UTF8.BodyName;
                }
                //恢复Seek位置
                stream.Seek(origPos, SeekOrigin.Begin);
            }
            return targetEncoding;
        }

    }

   class httpClient
   {
       /// <summary>
       /// 获取基础WebRequest
       /// </summary>
       /// <param name="url">请求地址</param>
       /// <param name="lStartPos">请求的开始位置</param>
       /// <returns></returns>
       public static HttpWebRequest getWebRequest(string url, int lStartPos)
       {
           HttpWebRequest request = null;
           try
           {
               request = (System.Net.HttpWebRequest)HttpWebRequest.Create(url);
               request.AddRange(lStartPos); //设置Range值
           }
           catch (Exception ex)
           {
              // Program.print(ex.Message);
           }

           return request;
       }
   }
}