System.Net.Http.Headers.RangeItemHeaderValue.GetRangeItemListLength C# (CSharp) Method

        internal static int GetRangeItemListLength(string? input, int startIndex,
            ICollection<RangeItemHeaderValue> rangeCollection)
        {
            Debug.Assert(rangeCollection != null);
            Debug.Assert(startIndex >= 0);

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

            // Empty segments are allowed, so skip all delimiter-only segments (e.g. ", ,").
            bool separatorFound = false;
            int current = HeaderUtilities.GetNextNonEmptyOrWhitespaceIndex(input, startIndex, true, out separatorFound);
            // It's OK if we didn't find leading separator characters. Ignore 'separatorFound'.

            if (current == input.Length)
            {
                return 0;
            }

            RangeItemHeaderValue? range;
            while (true)
            {
                int rangeLength = GetRangeItemLength(input, current, out range);

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

                rangeCollection.Add(range!);

                current = current + rangeLength;
                current = HeaderUtilities.GetNextNonEmptyOrWhitespaceIndex(input, current, true, out separatorFound);

                // If the string is not consumed, we must have a delimiter, otherwise the string is not a valid
                // range list.
                if ((current < input.Length) && !separatorFound)
                {
                    return 0;
                }

                if (current == input.Length)
                {
                    return current - startIndex;
                }
            }
        }

        internal static int GetRangeLength(string input, int startIndex, out object parsedValue)
        {
            Contract.Requires(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);
        }