Newtonsoft.Json.JsonTextReader.ReadData C# (CSharp) Method

        private int ReadData(bool append, int charsRequired)
        {
            if (_isEndOfFile)
            {
                return 0;
            }

            // char buffer is full
            if (_charsUsed + charsRequired >= _chars.Length - 1)
            {
                if (append)
                {
                    // copy to new array either double the size of the current or big enough to fit required content
                    int newArrayLength = Math.Max(_chars.Length * 2, _charsUsed + charsRequired + 1);

                    // increase the size of the buffer
                    char[] dst = BufferUtils.RentBuffer(_arrayPool, newArrayLength);

                    BlockCopyChars(_chars, 0, dst, 0, _chars.Length);

                    BufferUtils.ReturnBuffer(_arrayPool, _chars);

                    _chars = dst;
                }
                else
                {
                    int remainingCharCount = _charsUsed - _charPos;

                    if (remainingCharCount + charsRequired + 1 >= _chars.Length)
                    {
                        // the remaining count plus the required is bigger than the current buffer size
                        char[] dst = BufferUtils.RentBuffer(_arrayPool, remainingCharCount + charsRequired + 1);

                        if (remainingCharCount > 0)
                        {
                            BlockCopyChars(_chars, _charPos, dst, 0, remainingCharCount);
                        }

                        BufferUtils.ReturnBuffer(_arrayPool, _chars);

                        _chars = dst;
                    }
                    else
                    {
                        // copy any remaining data to the beginning of the buffer if needed and reset positions
                        if (remainingCharCount > 0)
                        {
                            BlockCopyChars(_chars, _charPos, _chars, 0, remainingCharCount);
                        }
                    }

                    _lineStartPos -= _charPos;
                    _charPos = 0;
                    _charsUsed = remainingCharCount;
                }
            }

            int attemptCharReadCount = _chars.Length - _charsUsed - 1;

            int charsRead = _reader.Read(_chars, _charsUsed, attemptCharReadCount);

            _charsUsed += charsRead;

            if (charsRead == 0)
            {
                _isEndOfFile = true;
            }

            _chars[_charsUsed] = '\0';
            return charsRead;
        }