internal static int GetRangeItemLength(string input, int startIndex, out RangeItemHeaderValue parsedValue)
        {
            Debug.Assert(startIndex >= 0);

            // This parser parses number ranges: e.g. '1-2', '1-', '-2'.

            parsedValue = null;

            if (string.IsNullOrEmpty(input) || (startIndex >= input.Length))
            {
                return(0);
            }

            // Caller must remove leading whitespace. If not, we'll return 0.
            int current = startIndex;

            // Try parse the first value of a value pair.
            int fromStartIndex = current;
            int fromLength     = HttpRuleParser.GetNumberLength(input, current, false);

            if (fromLength > HttpRuleParser.MaxInt64Digits)
            {
                return(0);
            }

            current = current + fromLength;
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            // After the first value, the '-' character must follow.
            if ((current == input.Length) || (input[current] != '-'))
            {
                // We need a '-' character otherwise this can't be a valid range.
                return(0);
            }

            current++; // skip the '-' character
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            int toStartIndex = current;
            int toLength     = 0;

            // If we didn't reach the end of the string, try parse the second value of the range.
            if (current < input.Length)
            {
                toLength = HttpRuleParser.GetNumberLength(input, current, false);

                if (toLength > HttpRuleParser.MaxInt64Digits)
                {
                    return(0);
                }

                current = current + toLength;
                current = current + HttpRuleParser.GetWhitespaceLength(input, current);
            }

            if ((fromLength == 0) && (toLength == 0))
            {
                return(0); // At least one value must be provided in order to be a valid range.
            }

            // Try convert first value to int64
            long from = 0;

            if ((fromLength > 0) && !HeaderUtilities.TryParseInt64(input, fromStartIndex, fromLength, out from))
            {
                return(0);
            }

            // Try convert second value to int64
            long to = 0;

            if ((toLength > 0) && !HeaderUtilities.TryParseInt64(input, toStartIndex, toLength, out to))
            {
                return(0);
            }

            // 'from' must not be greater than 'to'
            if ((fromLength > 0) && (toLength > 0) && (from > to))
            {
                return(0);
            }

            parsedValue = new RangeItemHeaderValue((fromLength == 0 ? (long?)null : (long?)from),
                                                   (toLength == 0 ? (long?)null : (long?)to));
            return(current - startIndex);
        }