Newtonsoft.Json.Bson.BsonReader.ReadString C# (CSharp) Method

        private string ReadString()
        {
            EnsureBuffers();

            StringBuilder builder = null;

            int totalBytesRead = 0;
            // used in case of left over multibyte characters in the buffer
            int offset = 0;
            while (true)
            {
                int count = offset;
                byte b;
                while (count < MaxCharBytesSize && (b = _reader.ReadByte()) > 0)
                {
                    _byteBuffer[count++] = b;
                }
                int byteCount = count - offset;
                totalBytesRead += byteCount;

                if (count < MaxCharBytesSize && builder == null)
                {
                    // pref optimization to avoid reading into a string builder
                    // if string is smaller than the buffer then return it directly
                    int length = Encoding.UTF8.GetChars(_byteBuffer, 0, byteCount, _charBuffer, 0);

                    MovePosition(totalBytesRead + 1);
                    return new string(_charBuffer, 0, length);
                }
                else
                {
                    // calculate the index of the end of the last full character in the buffer
                    int lastFullCharStop = GetLastFullCharStop(count - 1);

                    int charCount = Encoding.UTF8.GetChars(_byteBuffer, 0, lastFullCharStop + 1, _charBuffer, 0);

                    if (builder == null)
                    {
                        builder = new StringBuilder(MaxCharBytesSize * 2);
                    }

                    builder.Append(_charBuffer, 0, charCount);

                    if (lastFullCharStop < byteCount - 1)
                    {
                        offset = byteCount - lastFullCharStop - 1;
                        // copy left over multi byte characters to beginning of buffer for next iteration
                        Array.Copy(_byteBuffer, lastFullCharStop + 1, _byteBuffer, 0, offset);
                    }
                    else
                    {
                        // reached end of string
                        if (count < MaxCharBytesSize)
                        {
                            MovePosition(totalBytesRead + 1);
                            return builder.ToString();
                        }

                        offset = 0;
                    }
                }
            }
        }