iFinity

Written by:
Wednesday, January 06, 2010 6:27 PM 

I recently had a problem writing a PayPal Instant Payment Notification (IPN) listener.  The problem was that the PayPal Sandbox environment (now puzzlingly called x.com) would process my IPN requests OK, but any ‘live’ request that came through my site ended in error.

Now the PayPal support people assured me that this wasn’t possible, but after dumping most of the actual code out of my module, and replacing it with highly-sensitive ‘gotcha’ error capturing code, I worked out the problem was due to a slight difference in the date formats between the Sandbox and Live environments.

The Sandbox date looked like this:

22:40:29 Dec. 16, 2009 PST

The live date looked like this:

13:02:26 Dec 21, 2009 PST

Eagle eyed readers will detect the difference straight away.  It was a bit more difficult for me, as I was looking through raw logs and all I could see was 22%3A40%3A29+Dec.+16%2C+2009+PST as the values are encoded.  It was a surprise for me, but I guess I should have been more prepared for wide and varied date formats – they’re always the problem child of data handling and validation.  At least they have a text month to differentiate from dd/mm and mm/dd formats – they’re always fun.

Converting a PayPal Date to a .NET DateTime value

The format of the PayPal date isn’t one of the ones that you can easily just convert to a .NET DateTime type by doing a DateTime.TryParse call.  I looked into writing a customised date parser to supply with the DateTime.Parse routine, but it all just looked too hard for something that was (supposed) to be coming in with a standard format.

What I originally wrote (and which caused all the problems between Sandbox and Live environments) was a date parsing routine that worked out which bit of the date was which, all done by splitting up the string into substrings – one for the time, date and timezone.  This worked on the sandbox because it didn’t have the ‘.’ at the end of the month.  But move it into the live environment, and it didn’t work at all, because it was out by one character.  The resulting error wasn’t handled well (my fault) and so the whole thing mysteriously failed.

A better .NET / PayPal Date Parsing routine

Instead of fiddling around with brittle substring functions, I decided to turn to my old friend Regex, which thrives on this sort of fixed-format string parsing.  I quickly wrote this regex expression, which worked almost straight away.  The routine splits out the time, date and timezone, and within those individual groups, split out the hours, minutes, days, months and years.  Turns out I didn’t need the individual pieces, but by then the expression was written anyway.

Here’s the expression:

(?<time>\d{1,2}:\d{2}:\d{2})\s(?<date>(?<Mmm>[A-Za-z\.]{3,5})\s(?<dd>\d{1,2}),?\s(?<yyyy>\d{4}))\s(?<tz>[A-Z]{0,3})

A routine to convert a PayPal date to a .NET DateTime value using Regex

Here’s the full routine in C# to convert a PayPal date into a .NET DateTime value

/// <summary>
/// Converts a PayPal datestring into a valid .net datetime value
/// </summary>
/// <param name="dateValue">a string containing a PayPal date</param>
/// <param name="localUtcOffset">the number of hours from UTC/GMT the local 
/// time is (ie, the timezone where the computer is)</param>
/// <returns>Valid DateTime value if successful, DateTime.MinDate if not</returns>
private static DateTime ConvertFromPayPalDate(string rawPayPalDate, int localUtcOffset)
{
    /* regex pattern splits paypal date into
     * time : hh:mm:ss
     * date : Mmm dd yyyy
     * timezone : PST/PDT
     */
     const string payPalDateRegex = @"(?<time>\d{1,2}:\d{2}:\d{2})\s(?<date>(?<
Mmm>[A-Za-z\.]{3,5})\s(?<dd>\d{1,2}),?\s(?<yyyy>\d{4}))\s(?<tz>[A-Z]{0,3})";  
    //!important : above line broken over two lines for formatting - rejoin in code editor
    //example 05:49:56 Oct. 18, 2009 PDT
    //        20:48:22 Dec 25, 2009 PST
    Match dateMatch = Regex.Match(rawPayPalDate, payPalDateRegex, RegexOptions.IgnoreCase);
    DateTime time, date = DateTime.MinValue;
    //check to see if the regex pattern matched the supplied string
    if (dateMatch.Success)
    {
        //extract the relevant parts of the date from regex match groups
        string rawDate = dateMatch.Groups["date"].Value;
        string rawTime = dateMatch.Groups["time"].Value;
        string tz = dateMatch.Groups["tz"].Value;

        //create date and time values
        if (DateTime.TryParse(rawTime, out time) && DateTime.TryParse(rawDate, out date))
        {
            //add the time to the date value to get the datetime value
            date = date.Add(new TimeSpan(time.Hour, time.Minute, time.Second));
            //adjust for the pdt timezone.  Pass 0 to localUtcOffset to get UTC/GMT
            int offset = localUtcOffset + 7; //pdt = utc-7, pst = utc-8
            if (tz == "PDT")//pacific daylight time
                date = date.AddHours(offset);
            else  //pacific standard time
                date = date.AddHours(offset + 1);
        }
    }
    return date;
}

You can use this routine quite simply by extracting a field which contains a PayPal date, and transforming it into a .NET DateTime value, like this:

    //Get the payment date of the request.  Note 0 hours to return UTC time of payment
    DateTime paymentDate = ConvertFromPayPalDate(Request.Form["payment_date"], 0);

Feel free to use the code as-is, if you find any problems let me know via the comments.

Trackback Print

Tags:

Categories:

Location: Blogs Crafty Code

Your name:
Your email:
	(Optional) Email used only to show Gravatar.
Your website:
Title:
Comment:
Add Comment   Cancel