download程序C#源码，支持断点续传

    class Downfile
    { 
        public Downfile(string url,string username,string userpwd,string savename,string proxyip,string proxyport)
        {
            Durl = url;
            Dusername = username;
            Duserpwd = userpwd;
            Dsavename = savename;
            Dproxyip = proxyip;
            Dproxyport = proxyport;
        }

        public Downfile(string url, string username, string userpwd, string savename)
        {
            Durl = url;
            Dusername = username;
            Duserpwd = userpwd;
            Dsavename = savename;
        }

        public void Work()//download file no matter the file is exist or not
        {
            try
            {
                Uri uri = new Uri(Durl);
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);

                if (!(string.IsNullOrEmpty(Dproxyip) || string.IsNullOrEmpty(Dproxyport)))
                {
                    WebProxy myproxy = new WebProxy(Dproxyip, Convert.ToInt32(Dproxyport));

                    myproxy.BypassProxyOnLocal = true;
                    request.Proxy = myproxy;
                }
 
                NetworkCredential credentials = new NetworkCredential(Dusername, Duserpwd);
                request.Credentials = credentials;
                WebResponse v = request.GetResponse();
                Stream rStream = v.GetResponseStream();



                byte[] buffer = new byte[4096];
                Stream outStream = File.Create(Dsavename);

                int len;
                do
                {
                    len = rStream.Read(buffer, 0, buffer.Length);
                    if (len > 0)
                        outStream.Write(buffer, 0, len);
                } while (len > 0);

                outStream.Close();
                rStream.Close();
               
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message + "\n");
                if (WriteLog.LOgIsFine())