An (almost) RFC 822/2822 Compliant Date Parser

Introduction

In .NET Framework 1.1, there's a DateTime object with a parse(exact) method. Unfortunately, you can't use it to get a DateTime from an email.

The RFC2822DateTime class can be used in this case.

RFC 822/2822

You can find here how date's defined in RFC 822 (the first RFC for "electronic mail" ) and RFC2822 (which supersedes RFC822).

The Code

You'll need System.Text.RegularExpressions and System.DateTime to make it work.

public class RFC2822DateTime 
/*
 * Copyright (c)  vendredi13@007.freesurf.fr
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
{
    static public System.DateTime fromString(string adate) 
    {
        string tmp;
        string [] resp;
        string dayName;
        string dpart;
        string hour, minute;
        string timeZone;
        System.DateTime dt=System.DateTime.Now ;
        //--- strip comments
        //--- XXX : FIXME : how to handle nested comments ?
        tmp = Regex.Replace(adate, "(\\([^(].*\\))", "");

        // strip extra white spaces
        tmp = Regex.Replace(tmp, "\\s+", " ");
        tmp = Regex.Replace(tmp, "^\\s+","");
        tmp = Regex.Replace(tmp, "\\s+$","");

        // extract week name part
        resp = tmp.Split(new char[] {','},2);
        if (resp.Length==2) 
        {
            // there's week name
            dayName = resp[0];
            tmp = resp[1];
        } else dayName = "";

        try 
        {
            // extract date and time
            int pos = tmp.LastIndexOf(" ");
            if (pos < 1) throw new FormatException("probably not a date");
            dpart = tmp.Substring(0,pos-1);
            timeZone = tmp.Substring(pos+1);
            dt = Convert.ToDateTime(dpart);

            // check weekDay name
            // this must be done before convert to GMT 
            if (dayName!=string.Empty) 
            {
                if ((dt.DayOfWeek==DayOfWeek.Friday && dayName!="Fri") ||
                    (dt.DayOfWeek==DayOfWeek.Monday && dayName!="Mon") ||
                    (dt.DayOfWeek==DayOfWeek.Saturday && dayName!="Sat") ||
                    (dt.DayOfWeek==DayOfWeek.Sunday && dayName!="Sun") ||
                    (dt.DayOfWeek==DayOfWeek.Thursday && dayName!="Thu") ||
                    (dt.DayOfWeek==DayOfWeek.Tuesday&& dayName!="Tue") ||
                    (dt.DayOfWeek==DayOfWeek.Wednesday && dayName!="Wed")
                    )
                    throw new FormatException("invalid week of day");
            }

            // adjust to localtime
            if (Regex.IsMatch(timeZone, "[+\\-][0-9][0-9][0-9][0-9]")) 
            {
                // it's a modern ANSI style timezone
                int factor = 0;
                hour = timeZone.Substring(1,2);
                minute = timeZone.Substring(3,2);
                if (timeZone.Substring(0,1)=="+") factor = 1;
                else if (timeZone.Substring(0,1)=="-") factor = -1;
                else throw new FormatException("incorrect time zone");
                dt = dt.AddHours(factor * Convert.ToInt32(hour));
                dt = dt.AddMinutes(factor * Convert.ToInt32(minute));
            } else {
                // it's a old style military time zone ?
                switch (timeZone) 
                {
                    case "A" : dt = dt.AddHours(1); break;
                    case "B" : dt = dt.AddHours(2); break;
                    case "C" : dt = dt.AddHours(3); break;
                    case "D" : dt = dt.AddHours(4); break;
                    case "E" : dt = dt.AddHours(5); break;
                    case "F" : dt = dt.AddHours(6); break;
                    case "G" : dt = dt.AddHours(7); break;
                    case "H" : dt = dt.AddHours(8); break;
                    case "I" : dt = dt.AddHours(9); break;
                    case "K" : dt = dt.AddHours(10); break;
                    case "L" : dt = dt.AddHours(11); break;
                    case "M" : dt = dt.AddHours(12); break;
                    case "N" : dt = dt.AddHours(-1); break;
                    case "O" : dt = dt.AddHours(-2); break;
                    case "P" : dt = dt.AddHours(-3); break;
                    case "Q" : dt = dt.AddHours(-4); break;
                    case "R" : dt = dt.AddHours(-5); break;
                    case "S" : dt = dt.AddHours(-6); break;
                    case "T" : dt = dt.AddHours(-7); break;
                    case "U" : dt = dt.AddHours(-8); break;
                    case "V" : dt = dt.AddHours(-9); break;
                    case "W" : dt = dt.AddHours(-10); break;
                    case "X" : dt = dt.AddHours(-11); break;
                    case "Y" : dt = dt.AddHours(-12); break;
                    case "Z" :  
                    case "UT" : 
                    case "GMT" :  break;    // It's UTC
                    case "EST" : dt = dt.AddHours(5); break;
                    case "EDT" : dt = dt.AddHours(4); break;
                    case "CST" : dt = dt.AddHours(6); break;
                    case "CDT" : dt = dt.AddHours(5); break;
                    case "MST" : dt = dt.AddHours(7); break;
                    case "MDT" : dt = dt.AddHours(6); break;
                    case "PST" : dt = dt.AddHours(8); break;
                    case "PDT" : dt = dt.AddHours(7); break;
                    default: throw new FormatException("invalid time zone");
                }
            }
        } 
        catch (Exception e) 
        {
            throw new FormatException(string.Format("Invalid date:{0}:{1}", 
		e.Message, adate));
        }
        return dt;
    }
}

Bug and Limitation

This code is tested with a 300000 mails box, and no error was seen.

As specified in the code, nested comments like (comment (comment inside) outside) are left as a reader's exercise.

This code is not designed for speed, but it should consume reasonable resources.

History

• 23^rd June, 2006: Initial post