System.Net.Http.Headers.StringWithQualityHeaderValue.GetStringWithQualityLength C# (CSharp) Method

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

            parsedValue = null;

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

            // Parse the value string: <value> in '<value>; q=<quality>'
            int valueLength = HttpRuleParser.GetTokenLength(input, startIndex);

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

            StringWithQualityHeaderValue result = new StringWithQualityHeaderValue();
            result._value = input.Substring(startIndex, valueLength);
            int current = startIndex + valueLength;
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            if ((current == input.Length) || (input[current] != ';'))
            {
                parsedValue = result;
                return current - startIndex; // we have a valid token, but no quality.
            }

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

            // If we found a ';' separator, it must be followed by a quality information
            if (!TryReadQuality(input, result, ref current))
            {
                return 0;
            }

            parsedValue = result;
            return current - startIndex;
        }