如何从未知位置下载文件

我有一个问题，我一直在努力解决，但似乎找不到答案，所以希望有人在这里可以帮助我找到一个答案。

问题是，我试图从一个动态生成下载文件的网站创建一个网络抓取。本网站需要输入各种参数，以便对您的数据请求进行分类。一旦你点击提交按钮，网站就会根据你的参数动态生成数据请求，并将结果下载到文件中。

当尝试用c#这样做时，我的代码成功地提交了带有所需参数的请求，并捕获了HTML响应，但似乎无法捕获文件下载响应。远程URL上的文件下载位置被屏蔽。下载文件名以"Inquiry_currentdate_currenttime.xml"格式动态生成。文件大小可以根据所提交的数据请求而变化。

这个远程URL将数据文件推送给我，而不是我使用c# DownloadFile从URL中提取数据。我如何捕获这个"被推送"的文件?

到目前为止，我所尝试的代码如下。此代码成功提交请求并获得Html响应。

    foreach (string fy in lstFY)
    {
      foreach (string st in lstState)
      {
        HtmlHandler b = new HtmlHandler();
        b.Get(gWebTgtName);
        b.FormElements["ctl00$ContentPlaceHolder$ddlFundingYear"] = fy;
        b.FormElements["ctl00$ContentPlaceHolder$ddlState"] = st;
        //set reporting format (XML)      radiobutton
        b.FormElements["ctl00$ContentPlaceHolder$rblReportFormat"] = "xml";
        //set "select data points"        ckbx
        b.FormElements["ctl00$ContentPlaceHolder$cbSelectDatapoints"] = "on";
        //set "select All Data Points"    ckbx
        b.FormElements["ctl00$ContentPlaceHolder$cbAll"] = "on";
        //set "submit button"
        b.FormElements["ctl00$ContentPlaceHolder$bSearch"] = "Build Data File!";
        //SUBMIT (build data file)
        string resp3 = b.Post(gWebTgtName);
        //RESPONSE
        //save XMLfile
        //process XMLfile
      }
    }

    public string Post(string url)
    {
      _isPost = true;
      CreateWebRequestObject().Load(url, "POST");
      return _htmlDoc.DocumentNode.InnerHtml;
    }
    private HtmlWeb CreateWebRequestObject()
    {
      HtmlWeb web = new HtmlWeb();
      web.UseCookies = true;
      web.PreRequest = new HtmlWeb.PreRequestHandler(OnPreRequest);
      web.PostResponse = new HtmlWeb.PostResponseHandler(OnAfterResponse);
      web.PreHandleDocument = new HtmlWeb.PreHandleDocumentHandler(OnPreHandleDocument);
      return web;
    }
    protected bool OnPreRequest(HttpWebRequest rqst)
    {
      AddCookiesTo(rqst);               // Add cookies that were saved from previous requests
      if (_isPost) AddPostDataTo(rqst); // We only need to add post data on a POST request
      return true;
    }
    protected void OnAfterResponse(HttpWebRequest rqst, HttpWebResponse resp)
    {
      SaveCookiesFrom(resp); // Save cookies for subsequent requests
      GetDownload(DRTCollector.gWebTgtName);
      string sWebPage = string.Empty;
      // get correct charset and encoding from the server's header
      string sCharset = resp.CharacterSet;
      Encoding encoding = Encoding.GetEncoding(sCharset);
      // read response
      using (StreamReader sr = new StreamReader(resp.GetResponseStream(), encoding))
      {
        sWebPage = sr.ReadToEnd();
        // Close and clean up the StreamReader
        sr.Close();
        XmlDocument xdoc = new XmlDocument();
        xdoc.LoadXml(sWebPage);
      }
    }
    private void AddCookiesTo(HttpWebRequest rqst)
    {
      if (Cookies != null && Cookies.Count > 0)
      {
        rqst.CookieContainer.Add(Cookies);
      }
    }
    private void AddPostDataTo(HttpWebRequest rqst)
    {
      string payload = FormElements.AssemblePostPayload();
      byte[] buff = Encoding.UTF8.GetBytes(payload.ToCharArray());
      rqst.ContentLength = buff.Length;
      rqst.ContentType = "application/x-www-form-urlencoded";
      rqst.Accept = "image/png,image/*;q=0.8,*/*;q=0.5";
      //rqst.ContentType = "application/xml";
      //rqst.Accept = "application/xml";
      System.IO.Stream reqStream = rqst.GetRequestStream();
      reqStream.Write(buff, 0, buff.Length);
    }