不断收到PayPal的无效回复

Question

I keep getting an INVALID response. Here's my code:

    protected void Page_Load(object sender, EventArgs e)
    {
        ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
        ServicePointManager.Expect100Continue = true;
        mclog.Info("entered PayPalListener Page_Load");

        //Post back to either sandbox or live

        string strSandbox = "https://www.sandbox.paypal.com/cgi-bin/webscr";
        string strLive = "https://www.paypal.com/cgi-bin/webscr";
        mclog.Info(string.Format("strSandbox = [{0}]", strSandbox));

        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 = strRequest + "&cmd=_notify-validate";
        req.ContentLength = strRequest.Length;

        mclog.Info(string.Format("strRequest = [{0}]", strRequest));

        //Send the request to PayPal and get the response
        StreamWriter streamOut = new StreamWriter(req.GetRequestStream(), Encoding.ASCII);
        streamOut.Write(strRequest);
        streamOut.Close();
        StreamReader streamIn = new StreamReader(req.GetResponse().GetResponseStream());
        string strResponse = streamIn.ReadToEnd();
        streamIn.Close();
        mclog.Info(string.Format("Response was [{0}]", strResponse));

        if (strResponse == "VERIFIED")
        {
            //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")
        {
            //log for manual investigation
        }
        else
        {
            //Response wasn't VERIFIED or INVALID, log for manual investigation
        }

I've included the log output and also quoted the result displayed on the Sandbox page:

2016-07-19 16:16:54:870 W15 INFO MyPayPal.PayPal.PayPalListener.Page_Load.0 entered PayPalListener Page_Load 
2016-07-19 16:16:54:870 W15 INFO MyPayPal.PayPal.PayPalListener.Page_Load.0 strSandbox = [https://www.sandbox.paypal.com/cgi-bin/webscr] 
2016-07-19 16:16:54:870 W15 INFO MyPayPal.PayPal.PayPalListener.Page_Load.0 strRequest = [payment_type=instant&payment_date=Wed%20Jul%2020%202016%2008%3A08%3A21%20GMT+0930%20%28AUS%20Central%20Standard%20Time%29&payment_status=Completed&address_status=confirmed&payer_status=verified&first_name=John&last_name=Smith&payer_email=buyer@paypalsandbox.com&payer_id=TESTBUYERID01&address_name=John%20Smith&address_country=United%20States&address_country_code=US&address_zip=95131&address_state=CA&address_city=San%20Jose&address_street=123%20any%20street&business=seller@paypalsandbox.com&receiver_email=seller@paypalsandbox.com&receiver_id=seller@paypalsandbox.com&residence_country=US&item_name1=something&item_number1=AK-1234&tax=2.02&mc_currency=USD&mc_fee=0.44&mc_gross=12.34&mc_gross_1=12.34&mc_handling=2.06&mc_handling1=1.67&mc_shipping=3.02&mc_shipping1=1.02&txn_type=cart&txn_id=919215415&notify_version=2.1&custom=xyz123&invoice=abc1234&test_ipn=1&verify_sign=AFcWxV21C7fd0v3bYYYRCpSSRl31Ak5zhWFvRQAir0SAm0lY6s-KEoQl&cmd=_notify-validate] 
2016-07-19 16:16:55:448 W15 INFO MyPayPal.PayPal.PayPalListener.Page_Load.0 Response was [INVALID] 

I've also tried Encoding.UTF8 in both the decoding and encoding however doing so fails when used in both receiving and sending but not in receiving only. When sending UTF8, the handshake fails altogether.

Answer 1

The issue has been caused by the "+" sign inserted by the IPN Simulator in the payment_date field. In my case it was Sat Jul 23 2016 08:52:03 GMT+0930 (AUS Central Standard Time) Taking out the "+" fixes the problem.

Essentially, the plus is being stripped out:

string payment_date = Form.Request["payment_date"];

2016-07-22 16:09:33:751 W15 INFO MyPayPal.PayPal.PayPalListener.Page_Load.0 payment_date = [Sat Jul 23 2016 08:38:14 GMT 0930 (AUS Central Standard Time)]

Returning the parameter to PayPal without the plus was enough to invalidate the request.

I will search here and elsewhere to try and figure out a way to allow for this however the plus (and presumably) a minus don't seem to feature in MSDN or RFC DateTime formats so how I can check it's original existence is a worry.