System.Net.Http.Headers.ProductInfoHeaderValue.GetProductInfoLength C# (CSharp) Method

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

            parsedValue = null;

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

            int current = startIndex;

            // Caller must remove leading whitespace.
            string comment = null;
            ProductHeaderValue product = null;
            if (input[current] == '(')
            {
                int commentLength = 0;
                if (HttpRuleParser.GetCommentLength(input, current, out commentLength) != HttpParseResult.Parsed)
                {
                    return 0;
                }

                comment = input.Substring(current, commentLength);

                current = current + commentLength;
                current = current + HttpRuleParser.GetWhitespaceLength(input, current);
            }
            else
            {
                // Trailing whitespace is removed by GetProductLength().
                int productLength = ProductHeaderValue.GetProductLength(input, current, out product);

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

                current = current + productLength;
            }

            parsedValue = new ProductInfoHeaderValue();
            parsedValue._product = product;
            parsedValue._comment = comment;
            return current - startIndex;
        }

        public override bool TryParseValue(string value, object storeValue, ref int index, out object parsedValue)
        {
            parsedValue = null;

            if (string.IsNullOrEmpty(value) || (index == value.Length))
            {
                return(false);
            }

            // Skip leading whitespace
            int current = index + HttpRuleParser.GetWhitespaceLength(value, index);

            if (current == value.Length)
            {
                return(false); // whitespace-only values are not valid
            }

            ProductInfoHeaderValue result = null;
            int length = ProductInfoHeaderValue.GetProductInfoLength(value, current, out result);

            if (length == 0)
            {
                return(false);
            }

            // GetProductInfoLength() already skipped trailing whitespace. No need to do it here again.
            current = current + length;

            // If we have more values, make sure we saw a whitespace before. Values like "product/1.0(comment)" are
            // invalid since there must be a whitespace between the product and the comment value.
            if (current < value.Length)
            {
                // Note that for \r\n to be a valid whitespace, it must be followed by a space/tab. I.e. it's enough if
                // we check whether the char before the next value is space/tab.
                char lastSeparatorChar = value[current - 1];
                if ((lastSeparatorChar != ' ') && (lastSeparatorChar != '\t'))
                {
                    return(false);
                }
            }

            // Separators for "User-Agent" and "Server" headers are whitespace. This is different from most other headers
            // where comma/semicolon is used as separator.
            index       = current;
            parsedValue = result;
            return(true);
        }