getRetryAfter function

Duration? getRetryAfter(Map<String, String> headers)

Extracts the retry duration from the HTTP response headers when a rate limit (429) error occurs.

• If the Retry-After header contains a number, it is interpreted as seconds.
• If the header contains a valid date string, the function computes the duration from now to that time.
• If the header is missing or invalid, returns null.

Implementation

Duration? getRetryAfter(Map<String, String> headers) {
  // final retryAfterValue = headers[HttpHeaders.retryAfterHeader];
  final retryAfterValue = headers.entries
      .firstWhere(
        (e) => e.key.toLowerCase() == HttpHeaders.retryAfterHeader,
        orElse: () => const MapEntry('', ''),
      )
      .value;

  if (retryAfterValue.isEmpty) {
    return null; // No Retry-After header present
  }

  // Check if the value is a number (seconds)
  final seconds = int.tryParse(retryAfterValue);
  if (seconds != null) {
    return Duration(seconds: seconds);
  }

  // Check if the value is a valid HTTP date
  try {
    final retryAfterDate = HttpDate.parse(retryAfterValue);
    final now = DateTime.now().toUtc();

    if (retryAfterDate.isAfter(now)) {
      return retryAfterDate.difference(now);
    }
  } catch (_) {
    // Ignore parsing errors and return null
  }

  return null; // Invalid Retry-After value
}