C# http下载（支持断点续传）

分享下项目里面自己封装的一个http下载类

功能如下：

1、支持断点续传

2、下载失败自动重试

3、超时等异常处理

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
public class HttpManager
{
    const int bytebuff = 1024;
    const int ReadWriteTimeOut = 2 * 1000;//超时等待时间
    const int TimeOutWait = 5 * 1000;//超时等待时间
    const int MaxTryTime = 12;
    static Dictionary<string,int> TryNumDic = new Dictionary<string,int>();
　　
    /// <summary>
    /// 下载文件（同步）  支持断点续传
    /// </summary>
    /// <param name="url">文件url</param>
    /// <param name="savepath">本地保存路径</param>
    /// <param name="progress">下载进度（百分比）</param>
    /// <param name="size">下载文件大小</param>
    public static void DowLoadFile(string url,string savepath,ref int progress,long size = 0)
    {
        //打开上次下载的文件
        long lStartPos = 0;
        FileStream fs;
        if(File.Exists(savepath))
        {
            fs = File.OpenWrite(savepath);
            lStartPos = fs.Length;
            fs.Seek(lStartPos,SeekOrigin.Current);//移动文件流中的当前指针
        }
        else
        {
            string direName = Path.GetDirectoryName(savepath);
            if(!Directory.Exists(direName))//如果不存在保存文件夹路径，新建文件夹
            {
                Directory.CreateDirectory(direName);
            }
            fs = new FileStream(savepath, FileMode.Create);
            lStartPos = 0;
        }

        HttpWebRequest request = null;
        try{
            if(size == 0)
            {
                size = GetFileContentLength(url);
            }
            if(size != 0 && size == lStartPos)
            {
                //下载完成
                fs.Close();
                return;
            }

            request = (HttpWebRequest)WebRequest.Create(url);
            request.ReadWriteTimeout = ReadWriteTimeOut;
            request.Timeout = TimeOutWait;
            if(lStartPos>0)
                request.AddRange((int)lStartPos);//设置Range值，断点续传

            //向服务器请求，获得服务器回应数据流
            WebResponse respone = request.GetResponse();
            long totalSize = respone.ContentLength + lStartPos;
            long curSize  = lStartPos;
            progress  = (int)(curSize / totalSize *100);

            Stream ns = respone.GetResponseStream();

            byte[] nbytes = new byte[bytebuff];
            int nReadSize = 0;
            while(nReadSize > 0)
            {
                fs.Write(nbytes, 0, nReadSize);
                nReadSize = ns.Read(nbytes, 0 ,bytebuff);

                curSize += nReadSize;
                //下载进度计算
                if (progress < (int)((double)curSize / totalSize * 100))
                    progress = (int)((double)curSize / totalSize * 100);
                fs.Flush();
                ns.Close();
                fs.Close();
                if(curSize!=totalSize)//文件长度不等于下载长度，下载出错
                {
                    throw new Exception();
                }
                if(request != null)
                {
                    request.Abort();
                }
                TryNumDic.Remove(url);
            }
        }
        catch 
        {
            if(request!=null)
            {
                request.Abort();
            }
            
            fs.Close();
            if(TryNumDic.ContainsKey(url))
            {
                if(TryNumDic[url]>MaxTryTime)
                {
                    TryNumDic.Remove(url);
                    throw new Exception();
                }
                else
                {
                    TryNumDic[url]++;
                }
            }
            else
            {
                TryNumDic.Add(url,1);
            }
            DowLoadFile(url, savepath, ref progress, size);
        }
    }

    /// <summary>
    /// 获取下载文件长度
    /// </summary>
    /// <param name="url"></param>
    /// <returns></returns>
    public static long GetFileContentLength(string url)
    {
        HttpWebRequest request = null;
        try
        {
            request = (HttpWebRequest)HttpWebRequest.Create(url);
            request.Timeout = TimeOutWait;
            request.ReadWriteTimeout = ReadWriteTimeOut;
            //向服务器请求，获得服务器回应数据流
            WebResponse respone = request.GetResponse();
            request.Abort();
            return respone.ContentLength;
        }
        catch(Exception e)
        {
            if(request != null)
                request.Abort();
            return 0;
        }
    }

}