Download of file with open/save dialog box

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Web;
using System.IO;
using System.Net;
using System.Text;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;

using System.Windows.Forms;

namespace WindowsFormsApplicationDW
{
    public partial class Form1 : Form
    {
        
        string sWebPath = "http://www.miosito.it/"; //change this path with WebApplicationTest's virtual path
        string sLocalPath = @"c:\"; //change this path, physical path of a file downloading  (write permission)
        string sMyName = "erika";
        string sPageLogin = "login.aspx";
        string sPageDw = "dw.aspx";
        bool bFirstTime;
        StreamWriter swWriterL;

        [DllImport("wininet.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern bool InternetGetCookieEx(string pchURL, string pchCookieName, StringBuilder pchCookieData, ref uint pcchCookieData, int dwFlags, IntPtr lpReserved);
        
        const int INTERNET_COOKIE_HTTPONLY = 0x00002000;  
        
        private string GetGlobalCookies(string uri)
        {
            uint uiDataSize = 2048;
            StringBuilder sbCookieData = new StringBuilder((int)uiDataSize);
            if (InternetGetCookieEx(uri, null, sbCookieData, ref uiDataSize, INTERNET_COOKIE_HTTPONLY, IntPtr.Zero) && sbCookieData.Length > 0)
            {
                return sbCookieData.ToString().Replace(";", ",");
            }
            else
            {
                return null;
            }
        }

        public Form1()
        {
            InitializeComponent();
            bFirstTime = true;
            timer1.Start(); // Then I start timer
            swWriterL = new StreamWriter(System.AppDomain.CurrentDomain.BaseDirectory + "log.log", true); // Inizializate log
            swWriterL.WriteLine("---------------------------------");
            swWriterL.WriteLine("Start working session " + DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss"));
            webBrowser1.Navigate(sWebPath + sPageLogin);
        }


        private void timer1_Tick(object sender, EventArgs e)
        {
            swWriterL.WriteLine("Error timeout application");
            swWriterL.Close();
            timer1.Stop();
            this.Close();
            Application.Exit();

        }
        //extract __VIEWSTATE __EVENTVALIDATION from input type hidden
        private string ExtractInputHidden(string str, string name)
        {
            string sRit = "";
            string sPattern = "(?<=" + name  + "\" value=\")(?<val>.*?)(?=\")";
            Match match = Regex.Match(str, sPattern);
            if (match.Success)
            {
                sRit = match.Groups["val"].Value;
                sRit = HttpUtility.UrlEncodeUnicode(sRit);
            }
            return sRit;
        }
        
        
        private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
          //login page
            if ((bFirstTime == true) && (e.Url.ToString().Contains(sPageLogin))) //only first time
           {
                bFirstTime = false;
                HtmlElement heElement;
                heElement = (HtmlElement)webBrowser1.Document.GetElementById("UserEmail");
                heElement.InnerText = "name";
                heElement = (HtmlElement)webBrowser1.Document.GetElementById("UserPass");
                heElement.InnerText = "pass";
                System.Threading.Thread.Sleep(2000);
                heElement = (HtmlElement)webBrowser1.Document.GetElementById("Submit1");
                heElement.InvokeMember("click");
                System.Threading.Thread.Sleep(2000);
                webBrowser1.Navigate(sWebPath + sPageDw);
            }
            else
                if (e.Url.ToString().Contains(sPageDw) == true)
                {
                    try
                    {
                        //first request to extract __VIEWSTATE and __EVENTVALIDATION and cookie use get
                
                        string sPageData;
                        string PathRemote = sWebPath + sPageDw;
                        string sTmpCookieString =  GetGlobalCookies(webBrowser1.Url.AbsoluteUri);
                        HttpWebRequest fstRequest = (HttpWebRequest)WebRequest.Create(PathRemote);
                        fstRequest.Method = "GET";
                        fstRequest.CookieContainer = new System.Net.CookieContainer();
                        fstRequest.CookieContainer.SetCookies(webBrowser1.Document.Url, sTmpCookieString);
                        HttpWebResponse fstResponse = (HttpWebResponse)fstRequest.GetResponse();
                        StreamReader sr = new StreamReader(fstResponse.GetResponseStream());
                        sPageData = sr.ReadToEnd();
                        sr.Close();

                        string sViewState = ExtractInputHidden(sPageData, "__VIEWSTATE");
                        string sEventValidation = this.ExtractInputHidden(sPageData, "__EVENTVALIDATION");
                        
                        //second request post all values and save generated file
                        string sUrl = sWebPath + sPageDw;
                        HttpWebRequest hwrRequest = (HttpWebRequest)WebRequest.Create(sUrl);
                        hwrRequest.Method = "POST";
                        hwrRequest.CookieContainer = new System.Net.CookieContainer();

                        string sPostData = "__EVENTTARGET=&__EVENTARGUMENT=&__VIEWSTATE=" + sViewState + "&__EVENTVALIDATION=" + sEventValidation + "&Name=" + sMyName + "&Button1=Button";

                        byte[] bByteArray = Encoding.UTF8.GetBytes(sPostData);
                        hwrRequest.ContentType = "application/x-www-form-urlencoded";
                        hwrRequest.CookieContainer.SetCookies(webBrowser1.Document.Url, sTmpCookieString);
                        hwrRequest.ContentLength = bByteArray.Length;
                        Stream sDataStream = hwrRequest.GetRequestStream();
                        sDataStream.Write(bByteArray, 0, bByteArray.Length);
                        sDataStream.Close();
                        using (WebResponse response = hwrRequest.GetResponse())
                        {
                            using (sDataStream = response.GetResponseStream())
                            {
                                StreamReader reader = new StreamReader(sDataStream);
                                {
                                    //get original file name
                                    string sHeader = response.Headers["Content-Disposition"];
                                    int iFileNameStartIndex = sHeader.IndexOf("filename=") + "filename=".ToString().Length;
                                    int iFileNameLength = sHeader.Length - iFileNameStartIndex;
                                    string sFileName = sHeader.Substring(iFileNameStartIndex, iFileNameLength); 
                                    string sResponseFromServer = reader.ReadToEnd();
                                    //save the file
                                    FileStream fs = File.Open(sLocalPath + sFileName, FileMode.OpenOrCreate, FileAccess.Write);
                                    Byte[] info = new System.Text.UTF8Encoding(true).GetBytes(sResponseFromServer);
                                    fs.Write(info, 0, info.Length);
                                    fs.Close();

                                    swWriterL.WriteLine("saved");
                                    reader.Close();
                                    sDataStream.Close();
                                    response.Close();
                                } //end StreamReader
                            } //end dataStream
                        }//end WebResponse
                    }//end try
                    catch (Exception eccezione)
                    {
                        swWriterL.WriteLine("Error: " + eccezione.Message);
                        swWriterL.Close();
                    }
                    swWriterL.Close();
                    this.Close(); //close form
                    Application.Exit();  //close app
                }
            }
    }
}