System.Net.Http.ResponseStream.ReadAsync C# (CSharp) Method

        public override async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            VerifyBuffer(buffer, offset, count, allowEmpty: false);
            CancellationTokenRegistration registration = cancellationToken.Register(Abort);
            await _readLock.WaitAsync(cancellationToken).NotOnCapturedContext();
            try
            {
                int totalRead = 0;
                do
                {
                    // Don't drained buffered data on abort.
                    CheckAborted();
                    if (_topBuffer.Count <= 0)
                    {
                        byte[] topBuffer;
                        while (!_bufferedData.TryDequeue(out topBuffer))
                        {
                            if (_disposed)
                            {
                                CheckAborted();
                                // Graceful close
                                return totalRead;
                            }
                            await WaitForDataAsync().NotOnCapturedContext();
                        }
                        _topBuffer = new ArraySegment<byte>(topBuffer);
                    }
                    int actualCount = Math.Min(count, _topBuffer.Count);
                    Buffer.BlockCopy(_topBuffer.Array, _topBuffer.Offset, buffer, offset, actualCount);
                    _topBuffer = new ArraySegment<byte>(_topBuffer.Array,
                        _topBuffer.Offset + actualCount,
                        _topBuffer.Count - actualCount);
                    totalRead += actualCount;
                    offset += actualCount;
                    count -= actualCount;
                }
                while (count > 0 && (_topBuffer.Count > 0 || _bufferedData.Count > 0));
                // Keep reading while there is more data available and we have more space to put it in.
                return totalRead;
            }
            finally
            {
                registration.Dispose();
                _readLock.Release();
            }
        }