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I needed to parse RSS/Atom feeds and I was rather surprised to find that the standard .NET class libraries do not include a convenient way to successfully parse strings like "Tue, 01 Dec 2009 10:22:00 EST". The problem lies in the last part that says EST (or some other abbreviation). Based on my experiments, it is appearing in feed pubDate values every now and then. I don't know what the specs say about the time formats, but the dominant format seems to be like this: "Mon, 19 Mar 2007 23:48:18 -0700", which gets fortunately parsed correctly by DateTime.Parse().

So, I needed a way to parse the "incorrectly formatted" string. Another surprise was that .NET class libraries do not even seem to include those abbreviated timezones either (TimeZoneInfo class comes close though). So I ended up writing this to solve the problem:

// Handles cases like "Tue, 01 Dec 2009 10:22:00 EST" which cannot be parsed by DateTime.TryParse()
private static DateTime ParseSpecialDateTime(string datetimeString)
{
    Dictionary<string, int> knownTimeZoneAbbreviations = new Dictionary<string, int>()
    {
        {"AST", -4},
        {"ADT", -3},
        {"EST", -5},
        {"EDT", -4},
        {"CST", -6},
        {"CDT", -5},
        {"MST", -7},
        {"MDT", -6},
        {"PST", -8},
        {"PDT", -7},
        {"AKST", -9},
        {"AKDT", -8},
        {"HAST", -10},
        {"HADT", -9}
    };

    foreach (String key in knownTimeZoneAbbreviations.Keys)
    {
        DateTime dt;
        if (datetimeString.Contains(key))
        {
            string withoutAbbr = datetimeString.Replace(key, "");
            if (DateTime.TryParse(withoutAbbr, out dt) == true)
            {
                dt = dt.AddHours(knownTimeZoneAbbreviations[key]);
                return dt;
            }
            else
                break;
        }
    }
    return DateTime.Now;
}

If anybody knows a better way to do this, feel free to write a comment or email me at aali.alikoski (at) avanade.com