C#通过登录从web下载文件

我已经可以用这个代码通过重定向登录到网页（我正在保存cookie）

   CookieCollection cookies = new CookieCollection();
        HttpWebRequest cookieRequest = (HttpWebRequest)WebRequest.Create("https://www.loginpage.com/"); 
        cookieRequest.CookieContainer = new CookieContainer();
        cookieRequest.CookieContainer.Add(cookies);
        HttpWebResponse cookieResponse = (HttpWebResponse)cookieRequest.GetResponse();
        cookies = cookieResponse.Cookies;
        string postData = "name=********&password=*********&submit=submit";
        HttpWebRequest loginRequest = (HttpWebRequest)WebRequest.Create("https://www.loginpage.com/");
        loginRequest.CookieContainer = new CookieContainer();
        loginRequest.CookieContainer.Add(cookies);
        loginRequest.Method = WebRequestMethods.Http.Post;
        loginRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2";
        loginRequest.AllowWriteStreamBuffering = true;
        loginRequest.ProtocolVersion = HttpVersion.Version11;
        loginRequest.AllowAutoRedirect = true;
        loginRequest.ContentType = "application/x-www-form-urlencoded";
        byte[] byteArray = Encoding.ASCII.GetBytes(postData);
        loginRequest.ContentLength = byteArray.Length;
        Stream newStream = loginRequest.GetRequestStream(); //open connection
        newStream.Write(byteArray, 0, byteArray.Length); // Send the data.
        newStream.Close();

这很好，但我需要从那里下载.xls文件，它位于这里（例如）

https://www.loginpage.com/export_excel.php?export_type=list

为此，我尝试了这个代码

     HttpWebRequest wr = (HttpWebRequest)HttpWebRequest.Create("https://www.loginpage.com/export_excel.php?export_type=list");
        HttpWebResponse ws = (HttpWebResponse)wr.GetResponse();
        Stream str = ws.GetResponseStream();
        byte[] inBuf = new byte[100000];
        int bytesReadTotal = 0;
        string path = @"d:'test.xlsx";
        FileStream fstr = new FileStream(path, FileMode.Create, FileAccess.Write);
        while (true)
        {
            int n = str.Read(inBuf, 0, 100000);
            if ((n == 0) || (n == -1))
            {
                break;
            }
            fstr.Write(inBuf, 0, n);
            bytesReadTotal += n;
        }
        str.Close();
        fstr.Close();

但它不起作用，现在我被这个卡住了

        string dLink = "https://www.loginpage.com/export_excel.php?export_type=list";
        HttpWebRequest fileRequest = (HttpWebRequest)HttpWebRequest.Create(dLink);
        fileRequest.CookieContainer = new CookieContainer();
        fileRequest.CookieContainer.Add(cookies);
        fileRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2";
        HttpWebResponse fileResponse = (HttpWebResponse)fileRequest.GetResponse();
        for (int i = 0; i < fileResponse.Headers.Count; ++i)
        richTextBox1.Text += "'nHeader Name: " + fileResponse.Headers.Keys[i] + ", Value :" + fileResponse.Headers[i];

当然不是下载文件。我现在正试图获取标题，以了解我从网络上得到了什么？我已经从文件共享页面（如rghost或filehippo）下载了一些带有脚本的文件，但这一个不起作用。

        CookieContainer cookieJar = new CookieContainer();
        CookieAwareWebClient http = new CookieAwareWebClient(cookieJar);
        string postData = "name=********&password=*********&submit=submit";
        string response = http.UploadString("https://www.loginpage.com/", postData);
        // validate your login! 
        http.DownloadFile("https://www.loginpage.com/export_excel.php?export_type=list", "my_excel.xls");

public class CookieAwareWebClient : WebClient
{
    public CookieContainer CookieContainer { get; set; }
    public Uri Uri { get; set; }
    public CookieAwareWebClient()
        : this(new CookieContainer())
    {
    }
    public CookieAwareWebClient(CookieContainer cookies)
    {
        this.CookieContainer = cookies;
    }
    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest request = base.GetWebRequest(address);
        if (request is HttpWebRequest)
        {
            (request as HttpWebRequest).CookieContainer = this.CookieContainer;
        }
        HttpWebRequest httpRequest = (HttpWebRequest)request;
        httpRequest.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
        return httpRequest;
    }
    protected override WebResponse GetWebResponse(WebRequest request)
    {
        WebResponse response = base.GetWebResponse(request);
        String setCookieHeader = response.Headers[HttpResponseHeader.SetCookie];
        if (setCookieHeader != null)
        {
            //do something if needed to parse out the cookie.
            if (setCookieHeader != null)
            {
                Cookie cookie = new Cookie(); //create cookie
                this.CookieContainer.Add(cookie);
            }
        }
        return response;
    }
}

WebClient Client=new WebClient();
Client.UseDefaultCredentials=true;
Client.DownloadFile(url, destination);