System.Net.Http.Headers.RangeHeaderValue.GetRangeLength C# (CSharp) Method

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

            parsedValue = null;

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

            // Parse the unit string: <unit> in '<unit>=<from1>-<to1>, <from2>-<to2>'
            int unitLength = HttpRuleParser.GetTokenLength(input, startIndex);

            if (unitLength == 0)
            {
                return 0;
            }

            RangeHeaderValue result = new RangeHeaderValue();
            result._unit = input.Substring(startIndex, unitLength);
            int current = startIndex + unitLength;
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            if ((current == input.Length) || (input[current] != '='))
            {
                return 0;
            }

            current++; // skip '=' separator
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            int rangesLength = RangeItemHeaderValue.GetRangeItemListLength(input, current, result.Ranges);

            if (rangesLength == 0)
            {
                return 0;
            }

            current = current + rangesLength;
            Debug.Assert(current == input.Length, "GetRangeItemListLength() should consume the whole string or fail.");

            parsedValue = result;
            return current - startIndex;
        }