Question

How do I convert a DateTime structure to its equivalent RFC 822 date-time formatted string representation and parse this string representation back to a DateTime structure in .NET? The RFC-822 date-time format is used in a number of specifications such as the RSS Syndication Format.

Answer 1

This is an implementation in C# of how to parse and convert a DateTime to and from its RFC-822 representation. The only restriction it has is that the DateTime is in Coordinated Universal Time (UTC). I agree that this is not very elegant code, but it does the job.

/// <summary> /// Provides methods for converting <see cref='DateTime'/> structures  /// to and from the equivalent <a href='http://www.w3.org/Protocols/rfc822/#z28'>RFC 822</a>  /// string representation. /// </summary> public class Rfc822DateTime {     //============================================================     //  Private members     //============================================================     #region Private Members     /// <summary>     /// Private member to hold array of formats that RFC 822 date-time representations conform to.     /// </summary>     private static string[] formats = new string[0];     /// <summary>     /// Private member to hold the DateTime format string for representing a DateTime in the RFC 822 format.     /// </summary>     private const string format     = 'ddd, dd MMM yyyy HH:mm:ss K';     #endregion      //============================================================     //  Public Properties     //============================================================     #region Rfc822DateTimeFormat     /// <summary>     /// Gets the custom format specifier that may be used to represent a <see cref='DateTime'/> in the RFC 822 format.     /// </summary>     /// <value>A <i>DateTime format string</i> that may be used to represent a <see cref='DateTime'/> in the RFC 822 format.</value>     /// <remarks>     /// <para>     /// This method returns a string representation of a <see cref='DateTime'/> that utilizes the time zone      /// offset (local differential) to represent the offset from Greenwich mean time in hours and minutes.      /// The <see cref='Rfc822DateTimeFormat'/> is a valid date-time format string for use      /// in the <see cref='DateTime.ToString(String, IFormatProvider)'/> method.     /// </para>     /// <para>     /// The <a href='http://www.w3.org/Protocols/rfc822/#z28'>RFC 822</a> Date and Time specification      /// specifies that the year will be represented as a two-digit value, but the      /// <a href='http://www.rssboard.org/rss-profile#data-types-datetime'>RSS Profile</a> recommends that      /// all date-time values should use a four-digit year. The <see cref='Rfc822DateTime'/> class      /// follows the RSS Profile recommendation when converting a <see cref='DateTime'/> to the equivalent      /// RFC 822 string representation.     /// </para>     /// </remarks>     public static string Rfc822DateTimeFormat     {         get         {             return format;         }     }     #endregion      #region Rfc822DateTimePatterns     /// <summary>     /// Gets an array of the expected formats for RFC 822 date-time string representations.     /// </summary>     /// <value>     /// An array of the expected formats for RFC 822 date-time string representations      /// that may used in the <see cref='DateTime.TryParseExact(String, string[], IFormatProvider, DateTimeStyles, out DateTime)'/> method.     /// </value>     /// <remarks>     /// The array of the expected formats that is returned assumes that the RFC 822 time zone      /// is represented as or converted to a local differential representation.     /// </remarks>     /// <seealso cref='ConvertZoneToLocalDifferential(String)'/>     public static string[] Rfc822DateTimePatterns     {         get         {             if (formats.Length > 0)             {                 return formats;             }             else             {                 formats = new string[35];                  // two-digit day, four-digit year patterns                 formats[0]  = 'ddd',' dd MMM yyyy HH':'mm':'ss'.'fffffff zzzz';                 formats[1]  = 'ddd',' dd MMM yyyy HH':'mm':'ss'.'ffffff zzzz';                 formats[2]  = 'ddd',' dd MMM yyyy HH':'mm':'ss'.'fffff zzzz';                 formats[3]  = 'ddd',' dd MMM yyyy HH':'mm':'ss'.'ffff zzzz';                 formats[4]  = 'ddd',' dd MMM yyyy HH':'mm':'ss'.'fff zzzz';                 formats[5]  = 'ddd',' dd MMM yyyy HH':'mm':'ss'.'ff zzzz';                 formats[6]  = 'ddd',' dd MMM yyyy HH':'mm':'ss'.'f zzzz';                 formats[7]  = 'ddd',' dd MMM yyyy HH':'mm':'ss zzzz';                  // two-digit day, two-digit year patterns                 formats[8]  = 'ddd',' dd MMM yy HH':'mm':'ss'.'fffffff zzzz';                 formats[9]  = 'ddd',' dd MMM yy HH':'mm':'ss'.'ffffff zzzz';                 formats[10] = 'ddd',' dd MMM yy HH':'mm':'ss'.'fffff zzzz';                 formats[11] = 'ddd',' dd MMM yy HH':'mm':'ss'.'ffff zzzz';                 formats[12] = 'ddd',' dd MMM yy HH':'mm':'ss'.'fff zzzz';                 formats[13] = 'ddd',' dd MMM yy HH':'mm':'ss'.'ff zzzz';                 formats[14] = 'ddd',' dd MMM yy HH':'mm':'ss'.'f zzzz';                 formats[15] = 'ddd',' dd MMM yy HH':'mm':'ss zzzz';                  // one-digit day, four-digit year patterns                 formats[16] = 'ddd',' d MMM yyyy HH':'mm':'ss'.'fffffff zzzz';                 formats[17] = 'ddd',' d MMM yyyy HH':'mm':'ss'.'ffffff zzzz';                 formats[18] = 'ddd',' d MMM yyyy HH':'mm':'ss'.'fffff zzzz';                 formats[19] = 'ddd',' d MMM yyyy HH':'mm':'ss'.'ffff zzzz';                 formats[20] = 'ddd',' d MMM yyyy HH':'mm':'ss'.'fff zzzz';                 formats[21] = 'ddd',' d MMM yyyy HH':'mm':'ss'.'ff zzzz';                 formats[22] = 'ddd',' d MMM yyyy HH':'mm':'ss'.'f zzzz';                 formats[23] = 'ddd',' d MMM yyyy HH':'mm':'ss zzzz';                  // two-digit day, two-digit year patterns                 formats[24] = 'ddd',' d MMM yy HH':'mm':'ss'.'fffffff zzzz';                 formats[25] = 'ddd',' d MMM yy HH':'mm':'ss'.'ffffff zzzz';                 formats[26] = 'ddd',' d MMM yy HH':'mm':'ss'.'fffff zzzz';                 formats[27] = 'ddd',' d MMM yy HH':'mm':'ss'.'ffff zzzz';                 formats[28] = 'ddd',' d MMM yy HH':'mm':'ss'.'fff zzzz';                 formats[29] = 'ddd',' d MMM yy HH':'mm':'ss'.'ff zzzz';                 formats[30] = 'ddd',' d MMM yy HH':'mm':'ss'.'f zzzz';                 formats[31] = 'ddd',' d MMM yy HH':'mm':'ss zzzz';                  // Fall back patterns                 formats[32] = 'yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffffffK'; // RoundtripDateTimePattern                 formats[33] = DateTimeFormatInfo.InvariantInfo.UniversalSortableDateTimePattern;                 formats[34] = DateTimeFormatInfo.InvariantInfo.SortableDateTimePattern;                  return formats;             }         }     }     #endregion      //============================================================     //  Public Methods     //============================================================     #region Parse(string s)     /// <summary>     /// Converts the specified string representation of a date and time to its <see cref='DateTime'/> equivalent.     /// </summary>     /// <param name='s'>A string containing a date and time to convert.</param>     /// <returns>     /// A <see cref='DateTime'/> equivalent to the date and time contained in <paramref name='s'/>,      /// expressed as <i>Coordinated Universal Time (UTC)</i>.     /// </returns>     /// <remarks>     /// The string <paramref name='s'/> is parsed using formatting information in the <see cref='DateTimeFormatInfo.InvariantInfo'/> object.     /// </remarks>     /// <exception cref='ArgumentNullException'><paramref name='s'/> is a <b>null</b> reference (Nothing in Visual Basic).</exception>     /// <exception cref='ArgumentNullException'><paramref name='s'/> is an empty string.</exception>     /// <exception cref='FormatException'><paramref name='s'/> does not contain a valid RFC 822 string representation of a date and time.</exception>     public static DateTime Parse(string s)     {         //------------------------------------------------------------         //  Validate parameter         //------------------------------------------------------------         if (String.IsNullOrEmpty(s))         {           throw new ArgumentNullException('s');         }          DateTime result;         if (Rfc822DateTime.TryParse(s, out result))         {             return result;         }         else         {             throw new FormatException(String.Format(null, '{0} is not a valid RFC 822 string representation of a date and time.', s));         }     }     #endregion      #region ConvertZoneToLocalDifferential(string s)     /// <summary>     /// Converts the time zone component of an RFC 822 date and time string representation to its local differential (time zone offset).     /// </summary>     /// <param name='s'>A string containing an RFC 822 date and time to convert.</param>     /// <returns>A date and time string that uses local differential to describe the time zone equivalent to the date and time contained in <paramref name='s'/>.</returns>     /// <exception cref='ArgumentNullException'><paramref name='s'/> is a <b>null</b> reference (Nothing in Visual Basic).</exception>     /// <exception cref='ArgumentNullException'><paramref name='s'/> is an empty string.</exception>     public static string ConvertZoneToLocalDifferential(string s)     {         string zoneRepresentedAsLocalDifferential   = String.Empty;          //------------------------------------------------------------         //  Validate parameter         //------------------------------------------------------------         if (String.IsNullOrEmpty(s))         {           throw new ArgumentNullException('s');         }          if(s.EndsWith(' UT', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' UT') + 1) ), '+00:00');         }         else if (s.EndsWith(' GMT', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' GMT') + 1 ) ), '+00:00');         }         else if (s.EndsWith(' EST', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' EST') + 1)), '-05:00');         }         else if (s.EndsWith(' EDT', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' EDT') + 1)), '-04:00');         }         else if (s.EndsWith(' CST', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' CST') + 1)), '-06:00');         }         else if (s.EndsWith(' CDT', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' CDT') + 1)), '-05:00');         }         else if (s.EndsWith(' MST', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' MST') + 1)), '-07:00');         }         else if (s.EndsWith(' MDT', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' MDT') + 1)), '-06:00');         }         else if (s.EndsWith(' PST', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' PST') + 1)), '-08:00');         }         else if (s.EndsWith(' PDT', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' PDT') + 1)), '-07:00');         }         else if (s.EndsWith(' Z', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' Z') + 1)), '+00:00');         }         else if (s.EndsWith(' A', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' A') + 1)), '-01:00');         }         else if (s.EndsWith(' M', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' M') + 1)), '-12:00');         }         else if (s.EndsWith(' N', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' N') + 1)), '+01:00');         }         else if (s.EndsWith(' Y', StringComparison.OrdinalIgnoreCase))         {             zoneRepresentedAsLocalDifferential  = String.Concat(s.Substring(0, (s.LastIndexOf(' Y') + 1)), '+12:00');         }         else         {             zoneRepresentedAsLocalDifferential  = s;         }          return zoneRepresentedAsLocalDifferential;     }     #endregion      #region ToString(DateTime utcDateTime)     /// <summary>     /// Converts the value of the specified <see cref='DateTime'/> object to its equivalent string representation.     /// </summary>     /// <param name='utcDateTime'>The Coordinated Universal Time (UTC) <see cref='DateTime'/> to convert.</param>     /// <returns>A RFC 822 string representation of the value of the <paramref name='utcDateTime'/>.</returns>     /// <exception cref='ArgumentException'>The specified <paramref name='utcDateTime'/> object does not represent a <see cref='DateTimeKind.Utc'>Coordinated Universal Time (UTC)</see> value.</exception>     public static string ToString(DateTime utcDateTime)     {         if (utcDateTime.Kind != DateTimeKind.Utc)         {             throw new ArgumentException('utcDateTime');         }          return utcDateTime.ToString(Rfc822DateTime.Rfc822DateTimeFormat, DateTimeFormatInfo.InvariantInfo);     }     #endregion      #region TryParse(string s, out DateTime result)     /// <summary>     /// Converts the specified string representation of a date and time to its <see cref='DateTime'/> equivalent.     /// </summary>     /// <param name='s'>A string containing a date and time to convert.</param>     /// <param name='result'>     /// When this method returns, contains the <see cref='DateTime'/> value equivalent to the date and time      /// contained in <paramref name='s'/>, expressed as <i>Coordinated Universal Time (UTC)</i>,      /// if the conversion succeeded, or <see cref='DateTime.MinValue'>MinValue</see> if the conversion failed.      /// The conversion fails if the s parameter is a <b>null</b> reference (Nothing in Visual Basic),      /// or does not contain a valid string representation of a date and time.      /// This parameter is passed uninitialized.     /// </param>     /// <returns><b>true</b> if the <paramref name='s'/> parameter was converted successfully; otherwise, <b>false</b>.</returns>     /// <remarks>     /// The string <paramref name='s'/> is parsed using formatting information in the <see cref='DateTimeFormatInfo.InvariantInfo'/> object.      /// </remarks>     public static bool TryParse(string s, out DateTime result)     {         //------------------------------------------------------------         //  Attempt to convert string representation         //------------------------------------------------------------         bool wasConverted   = false;         result              = DateTime.MinValue;          if (!String.IsNullOrEmpty(s))         {             DateTime parseResult;             if (DateTime.TryParseExact(Rfc822DateTime.ConvertZoneToLocalDifferential(s), Rfc822DateTime.Rfc822DateTimePatterns, DateTimeFormatInfo.InvariantInfo, DateTimeStyles.AdjustToUniversal, out parseResult))             {                 result          = DateTime.SpecifyKind(parseResult, DateTimeKind.Utc);                 wasConverted    = true;             }         }          return wasConverted;     }     #endregion }