parse static method

DateTime parse(String date)

Parse a date string in either of the formats RFC-1123, RFC-850 or ANSI C's asctime() format. These formats are listed here.

Thu, 1 Jan 1970 00:00:00 GMT
Thursday, 1-Jan-1970 00:00:00 GMT
Thu Jan  1 00:00:00 1970

For more information see RFC-2616 section 3.1.1.

Implementation

static DateTime parse(String date) {
  final int SP = 32;
  const List wkdays = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
  const List weekdays = [
    'Monday',
    'Tuesday',
    'Wednesday',
    'Thursday',
    'Friday',
    'Saturday',
    'Sunday'
  ];
  const List months = [
    'Jan',
    'Feb',
    'Mar',
    'Apr',
    'May',
    'Jun',
    'Jul',
    'Aug',
    'Sep',
    'Oct',
    'Nov',
    'Dec'
  ];
  const List wkdaysLowerCase = [
    'mon',
    'tue',
    'wed',
    'thu',
    'fri',
    'sat',
    'sun'
  ];
  const List weekdaysLowerCase = [
    'monday',
    'tuesday',
    'wednesday',
    'thursday',
    'friday',
    'saturday',
    'sunday'
  ];
  const List monthsLowerCase = [
    'jan',
    'feb',
    'mar',
    'apr',
    'may',
    'jun',
    'jul',
    'aug',
    'sep',
    'oct',
    'nov',
    'dec'
  ];

  final int formatRfc1123 = 0;
  final int formatRfc850 = 1;
  final int formatAsctime = 2;

  int index = 0;
  String tmp;
  int? format;

  void expect(String s) {
    if (date.length - index < s.length) {
      throw Exception('Invalid HTTP date $date');
    }
    String tmp = date.substring(index, index + s.length);
    if (tmp != s) {
      throw Exception('Invalid HTTP date $date');
    }
    index += s.length;
  }

  int expectWeekday() {
    int weekday;
    // The formatting of the weekday signals the format of the date string.
    int pos = date.indexOf(',', index);
    if (pos == -1) {
      int pos = date.indexOf(' ', index);
      if (pos == -1) throw Exception('Invalid HTTP date $date');
      tmp = date.substring(index, pos);
      index = pos + 1;
      weekday = wkdays.indexOf(tmp);
      if (weekday != -1) {
        format = formatAsctime;
        return weekday;
      }
    } else {
      tmp = date.substring(index, pos);
      index = pos + 1;
      weekday = wkdays.indexOf(tmp);
      if (weekday != -1) {
        format = formatRfc1123;
        return weekday;
      }
      weekday = weekdays.indexOf(tmp);
      if (weekday != -1) {
        format = formatRfc850;
        return weekday;
      }
    }
    throw Exception('Invalid HTTP date $date');
  }

  int expectMonth(String separator) {
    int pos = date.indexOf(separator, index);
    if (pos - index != 3) throw Exception('Invalid HTTP date $date');
    tmp = date.substring(index, pos);
    index = pos + 1;
    int month = months.indexOf(tmp);
    if (month != -1) return month;
    throw Exception('Invalid HTTP date $date');
  }

  int expectNum(String separator) {
    int pos;
    if (separator.length > 0) {
      pos = date.indexOf(separator, index);
    } else {
      pos = date.length;
    }
    String tmp = date.substring(index, pos);
    index = pos + separator.length;
    try {
      int value = int.parse(tmp);
      return value;
    } on FormatException catch (e) {
      throw Exception('Invalid HTTP date $date');
    }
  }

  void expectEnd() {
    if (index != date.length) {
      throw Exception('Invalid HTTP date $date');
    }
  }

  int weekday = expectWeekday();
  int day;
  int month;
  int year;
  int hours;
  int minutes;
  int seconds;
  if (format == formatAsctime) {
    month = expectMonth(' ');
    if (date.codeUnitAt(index) == SP) index++;
    day = expectNum(' ');
    hours = expectNum(':');
    minutes = expectNum(':');
    seconds = expectNum(' ');
    year = expectNum('');
  } else {
    expect(' ');
    day = expectNum(format == formatRfc1123 ? ' ' : '-');
    month = expectMonth(format == formatRfc1123 ? ' ' : '-');
    year = expectNum(' ');
    hours = expectNum(':');
    minutes = expectNum(':');
    seconds = expectNum(' ');
    expect('GMT');
  }
  expectEnd();
  return DateTime.utc(year, month + 1, day, hours, minutes, seconds, 0);
}