System.Xml.XmlTextReaderImpl.InitStreamInput C# (CSharp) Method

        private void InitStreamInput(Uri baseUri, string baseUriStr, Stream stream, byte[] bytes, int byteCount, Encoding encoding)
        {
            Debug.Assert(_ps.charPos == 0 && _ps.charsUsed == 0 && _ps.textReader == null);
            Debug.Assert(baseUriStr != null);
            Debug.Assert(baseUri == null || (baseUri.ToString().Equals(baseUriStr)));

            _ps.stream = stream;
            _ps.baseUri = baseUri;
            _ps.baseUriStr = baseUriStr;

            // take over the byte buffer allocated in XmlReader.Create, if available
            int bufferSize;
            if (bytes != null)
            {
                _ps.bytes = bytes;
                _ps.bytesUsed = byteCount;
                bufferSize = _ps.bytes.Length;
            }
            else
            {
                // allocate the byte buffer 
                if (_laterInitParam != null && _laterInitParam.useAsync)
                {
                    bufferSize = AsyncBufferSize;
                }
                else
                {
                    bufferSize = XmlReader.CalcBufferSize(stream);
                }
                if (_ps.bytes == null || _ps.bytes.Length < bufferSize)
                {
                    _ps.bytes = new byte[bufferSize];
                }
            }

            // allocate char buffer
            if (_ps.chars == null || _ps.chars.Length < bufferSize + 1)
            {
                _ps.chars = new char[bufferSize + 1];
            }

            // make sure we have at least 4 bytes to detect the encoding (no preamble of System.Text supported encoding is longer than 4 bytes)
            _ps.bytePos = 0;
            while (_ps.bytesUsed < 4 && _ps.bytes.Length - _ps.bytesUsed > 0)
            {
                int read = stream.Read(_ps.bytes, _ps.bytesUsed, _ps.bytes.Length - _ps.bytesUsed);
                if (read == 0)
                {
                    _ps.isStreamEof = true;
                    break;
                }
                _ps.bytesUsed += read;
            }

            // detect & setup encoding
            if (encoding == null)
            {
                encoding = DetectEncoding();
            }
            SetupEncoding(encoding);

            // eat preamble 
            byte[] preamble = _ps.encoding.GetPreamble();
            int preambleLen = preamble.Length;
            int i;
            for (i = 0; i < preambleLen && i < _ps.bytesUsed; i++)
            {
                if (_ps.bytes[i] != preamble[i])
                {
                    break;
                }
            }
            if (i == preambleLen)
            {
                _ps.bytePos = preambleLen;
            }

            _documentStartBytePos = _ps.bytePos;

            _ps.eolNormalized = !_normalize;

            // decode first characters
            _ps.appendMode = true;
            ReadData();
        }