rfc3339ToTimestamp function

Map<String, Object?> rfc3339ToTimestamp(String rfc3339)

Parses an RFC 3339 string into a google.protobuf.Timestamp.

Accepts strings like "1972-01-01T10:00:20.021Z" or without fractional seconds like "2000-01-01T00:00:00Z".

Returns {"seconds": int, "nanos": int}.

Implementation

Map<String, Object?> rfc3339ToTimestamp(String rfc3339) {
  // Strict RFC 3339 (proto3 JSON): a 4-digit year, the uppercase 'T'
  // separator, and either an uppercase 'Z' or a numeric offset with a colon
  // (±HH:MM). Rejects lenient variants (missing T/Z, lowercase z, offset
  // without a colon).
  if (!RegExp(
    r'^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[+-]\d{2}:\d{2})$',
  ).hasMatch(rfc3339)) {
    throw FormatException('Invalid RFC 3339 timestamp: "$rfc3339"');
  }

  // Extract fractional seconds from the string to preserve full nanosecond
  // precision (DateTime only holds microseconds). protobuf nanos are ALWAYS in
  // [0, 999999999] — even for negative timestamps — so the fraction is parsed
  // separately and the whole-second part is floored, not truncated.
  int nanos = 0;
  String forParse = rfc3339;
  final dotIndex = rfc3339.indexOf('.');
  if (dotIndex != -1) {
    // Find the end of the fractional part (before 'Z' or timezone offset).
    int endIndex = rfc3339.length;
    for (int i = dotIndex + 1; i < rfc3339.length; i++) {
      if (rfc3339[i] == 'Z' ||
          rfc3339[i] == 'z' ||
          rfc3339[i] == '+' ||
          rfc3339[i] == '-') {
        endIndex = i;
        break;
      }
    }
    final fracStr = rfc3339.substring(dotIndex + 1, endIndex).padRight(9, '0');
    nanos = int.parse(fracStr.substring(0, 9));
    // Strip the fraction so the parsed instant lands on a whole second; this
    // makes `~/ 1000` exact (a negative fractional time would otherwise
    // truncate toward zero, e.g. -1.5s -> -1s instead of the correct -2s+0.5).
    forParse = rfc3339.substring(0, dotIndex) + rfc3339.substring(endIndex);
  }

  final dt = DateTime.parse(forParse);
  final seconds = dt.millisecondsSinceEpoch ~/ 1000;
  return {'seconds': seconds, 'nanos': nanos};
}