System.Net.WebSockets.ManagedWebSocket.EnsureBufferContainsAsync C# (CSharp) Method

        private async Task EnsureBufferContainsAsync(int minimumRequiredBytes, CancellationToken cancellationToken, bool throwOnPrematureClosure = true)
        {
            Debug.Assert(minimumRequiredBytes <= _receiveBuffer.Length, $"Requested number of bytes {minimumRequiredBytes} must not exceed {_receiveBuffer.Length}");

            // If we don't have enough data in the buffer to satisfy the minimum required, read some more.
            if (_receiveBufferCount < minimumRequiredBytes)
            {
                // If there's any data in the buffer, shift it down.  
                if (_receiveBufferCount > 0)
                {
                    Buffer.BlockCopy(_receiveBuffer, _receiveBufferOffset, _receiveBuffer, 0, _receiveBufferCount);
                }
                _receiveBufferOffset = 0;

                // While we don't have enough data, read more.
                while (_receiveBufferCount < minimumRequiredBytes)
                {
                    int numRead = await _stream.ReadAsync(_receiveBuffer, _receiveBufferCount, _receiveBuffer.Length - _receiveBufferCount, cancellationToken).ConfigureAwait(false);
                    Debug.Assert(numRead >= 0, $"Expected non-negative bytes read, got {numRead}");
                    _receiveBufferCount += numRead;
                    if (numRead == 0)
                    {
                        // The connection closed before we were able to read everything we needed.
                        // If it was due to use being disposed, fail.  If it was due to the connection
                        // being closed and it wasn't expected, fail.  If it was due to the connection
                        // being closed and that was expected, exit gracefully.
                        if (_disposed)
                        {
                            throw new ObjectDisposedException(nameof(ClientWebSocket));
                        }
                        else if (throwOnPrematureClosure)
                        {
                            throw new WebSocketException(WebSocketError.ConnectionClosedPrematurely);
                        }
                        break;
                    }
                }
            }
        }