Convert a RFC time string into TDateTime and VV

Problem/Question/Abstract:

How to convert a RFC time string into TDateTime and vv.

Answer:

Conversion of date & time formats: RFC <-> TDateTime (local & UNC) RFC: e.g. 03.01.2001 05:45:00 -0500

TDateTime -> RFC use

DateTimeToRfcTime(date, diff, gmt)

RFC -> TDateTime  use

RfcTimeToDateTime(time, gmt)

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;