Paypal IPN integration issues - asp.net

Question

I am trying to process the response from paypal on my page. I found this code from paypal documentation itself. When the response is valid, some parameters needs to be processed like txn_id and payment_completed. How should i do that??
the code is as follows
string strSandbox = "https://www.sandbox.paypal.com/cgi-bin/webscr";
// string strLive = "https://www.paypal.com/cgi-bin/webscr";
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(strSandbox);
//Set values for the request back
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
byte[] param = Request.BinaryRead(HttpContext.Current.Request.ContentLength);
string strRequest = Encoding.ASCII.GetString(param);
strRequest += "&cmd=_notify-validate";
req.ContentLength = strRequest.Length;
//for proxy
//WebProxy proxy = new WebProxy(new Uri("http://url:port#"));
//req.Proxy = proxy;
//Send the request to PayPal and get the response
StreamWriter streamOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
streamOut.Write(strRequest);
streamOut.Close();
StreamReader streamIn = new StreamReader(req.GetResponse().GetResponseStream());
string strResponse = streamIn.ReadToEnd();
streamIn.Close();
if (strResponse == "VERIFIED")
{
//UPDATE YOUR DATABASE
//TextWriter txWriter = new StreamWriter(Server.MapPath("../uploads/") + Session["orderID"].ToString() + ".txt");
//txWriter.WriteLine(strResponse);
//txWriter.Close();
//check the payment_status is Completed
//check that txn_id has not been previously processed
//check that receiver_email is your Primary PayPal email
//check that payment_amount/payment_currency are correct
//process payment
}
else if (strResponse == "INVALID")
{
//UPDATE YOUR DATABASE
//TextWriter txWriter = new StreamWriter(Server.MapPath("../uploads/") + Session["orderID"].ToString() + ".txt");
//txWriter.WriteLine(strResponse);
////log for manual investigation
//txWriter.Close();
}
else
{ //UPDATE YOUR DATABASE
//TextWriter txWriter = new StreamWriter(Server.MapPath("../uploads/") + Session["orderID"].ToString() + ".txt");
//txWriter.WriteLine("Invalid");
////log response/ipn data for manual investigation
//txWriter.Close();
}
}
Give me some inputs please. Thanks

Answer 1

After you get the response and you know that is valid, the parameters have been posted to you and you can get them using the .Form For example:
if (strResponse == "VERIFIED")
{
// Now All informations are on
HttpContext.Current.Request.Form;
// for example you get the invoice like this
HttpContext.Current.Request.Form["invoice"]
// or the payment_status like
HttpContext.Current.Request.Form["payment_status"]
}
else
{
//log for manual investigation
}