function DateTimeToRfcTime(
 dt: TDateTime;
 iDiff: integer;
 blnGMT: boolean = false): string;
{*
Explanation:
iDiff is the local offset to GMT in minutes
if blnGMT then Result is UNC time else local time
e.g. local time zone: ET = GMT - 5hr = -300 minutes
  dt is TDateTime of 3 Jan 2001 5:45am
  blnGMT = true -> Result = 'Wed, 03 Jan 2001 05:45:00 GMT'
  blnGMT = false -> Result = 'Wed, 03 Jan 2001 05:45:00 -0500'
*}
const
 Weekday: array[1..7] of string =
 ('Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat');
 Month: array[1..12] of string = (
  'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
  'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec');
var
 iDummy: Word;
 iYear: Word;
 iMonth: Word;
 iDay: Word;
 iHour: Word;
 iMinute: Word;
 iSecond: Word;
 strZone: string;
begin
 if blnGMT then
 begin
  dt := dt - iDiff / 1440;
  strZone := 'GMT';
 end
 else
 begin
  iDiff := (iDiff div 60) * 100 + (iDiff mod 60);
  if iDiff < 0 then
  strZone := Format('-%.4d', [-iDiff])
  else
  strZone := Format('+%.4d', [iDiff]);
 end;
 DecodeDate(dt, iYear, iMonth, iDay);
 DecodeTime(dt, iHour, iMinute, iSecond, iDummy);
 Result := Format('%s, %.2d %s %4d %.2d:%.2d:%.2d %s', [
  Weekday[DayOfWeek(dt)], iDay, Month[iMonth], iYear,
  iHour, iMinute, iSecond, strZone]);
end;
function RfcTimeToDateTime(
 strTime: string;
 blnGMT: boolean = true): TDateTime;
{*
Explanation:
if blnGMT then Result is UNC time else local time
e.g. local time zone: ET = GMT - 5hr = -0500
  strTime = 'Wed, 03 Jan 2001 05:45:00 -0500'
  blnGMT = true -> FormatDateTime('...', Result) = '03.01.2001 10:45:00'
  blnGMT = false -> FormatDateTime('...', Result) = '03.01.2001 05:45:00'
*}
const
 wd = 'sun#mon#tue#wed#thu#fri#sat';
 month = 'janfebmaraprmayjunjulaugsepoctnovdec';
var
 s: string;
 dd: Word;
 mm: Word;
 yy: Word;
 hh: Word;
 nn: Word;
 ss: Word;
begin
 s := LowerCase(Copy(strTime, 1, 3));
 if Pos(s, wd) > 0 then
  Delete(strTime, 1, Pos(' ', strTime));
 s := Trim(Copy(strTime, 1, Pos(' ', strTime)));
 Delete(strTime, 1, Length(s) + 1);
 dd := StrToIntDef(s, 0);
 s := LowerCase(Copy(strTime, 1, 3));
 Delete(strTime, 1, 4);
 mm := (Pos(s, month) div 3) + 1;
 s := Copy(strTime, 1, 4);
 Delete(strTime, 1, 5);
 yy := StrToIntDef(s, 0);
 Result := EncodeDate(yy, mm, dd);
 s := strTime[1] + strTime[2];
 hh := StrToIntDef(strTime[1] + strTime[2], 0);
 nn := StrToIntDef(strTime[4] + strTime[5], 0);
 ss := StrToIntDef(strTime[7] + strTime[8], 0);
 Delete(strTime, 1, 9);
 Result := Result + EncodeTime(hh, nn, ss, 0);
 if (CompareText(strTime, 'gmt') <> 0) and blnGMT then
 begin
  hh := StrToIntDef(strTime[2] + strTime[3], 0);
  nn := StrToIntDef(strTime[4] + strTime[5], 0);
  if strTime[1] = '+' then
  Result := Result - EncodeTime(hh, nn, 0, 0)
  else
  Result := Result + EncodeTime(hh, nn, 0, 0);
 end;
end;

function RFC1123ToDateTime(Date: string): TDateTime;
var
 day, month, year: Integer;
 strMonth: string;
 Hour, Minute, Second: Integer;
begin
 try
  day := StrToInt(Copy(Date, 6, 2));
  strMonth := Copy(Date, 9, 3);
  if strMonth = 'Jan' then month := 1
  else if strMonth = 'Feb' then month := 2
  else if strMonth = 'Mar' then month := 3
  else if strMonth = 'Apr' then month := 4
  else if strMonth = 'May' then month := 5
  else if strMonth = 'Jun' then month := 6
  else if strMonth = 'Jul' then month := 7
  else if strMonth = 'Aug' then month := 8
  else if strMonth = 'Sep' then month := 9
  else if strMonth = 'Oct' then month := 10
  else if strMonth = 'Nov' then month := 11
  else if strMonth = 'Dec' then month := 12;
  year := StrToInt(Copy(Date, 13, 4));
  hour := StrToInt(Copy(Date, 18, 2));
  minute := StrToInt(Copy(Date, 21, 2));
  second := StrToInt(Copy(Date, 24, 2));
  Result := 0;
  Result := EncodeTime(hour, minute, second, 0);
  Result := Result + EncodeDate(year, month, day);
 except
  Result := now;
 end;
end;

function DateTimeToRFC1123(aDate: TDateTime): string;
const
 StrWeekDay: string = 'MonTueWedThuFriSatSun';
 StrMonth: string = 'JanFebMarAprMayJunJulAugSepOctNovDec';
var
 Year, Month, Day: Word;
 Hour, Min, Sec, MSec: Word;
 DayOfWeek: Word;
begin
 DecodeDate(aDate, Year, Month, Day);
 DecodeTime(aDate, Hour, Min, Sec, MSec);
 DayOfWeek := ((Trunc(aDate) - 2) mod 7);
 Result := Copy(StrWeekDay, 1 + DayOfWeek * 3, 3) + ', ' +
  Format('%2.2d %s %4.4d %2.2d:%2.2d:%2.2d',
  [Day, Copy(StrMonth, 1 + 3 * (Month - 1), 3),
  Year, Hour, Min, Sec]);
end;