System.Net.WebSockets.WebSocketHttpListenerDuplexStream.ReadAsyncCore C# (CSharp) Method

        private async Task<int> ReadAsyncCore(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            if (NetEventSource.IsEnabled)
            {
                NetEventSource.Enter(this, WebSocketValidate.GetTraceMsgForParameters(offset, count, cancellationToken));
            }

            CancellationTokenRegistration cancellationTokenRegistration = new CancellationTokenRegistration();

            int bytesRead = 0;
            try
            {
                if (cancellationToken.CanBeCanceled)
                {
                    cancellationTokenRegistration = cancellationToken.Register(s_OnCancel, this, false);
                }

                if (!_inOpaqueMode)
                {
                    bytesRead = await _inputStream.ReadAsync(buffer, offset, count, cancellationToken).SuppressContextFlow<int>();
                }
                else
                {
#if DEBUG
                    // When using fast path only one outstanding read is permitted. By switching into opaque mode
                    // via IWebSocketStream.SwitchToOpaqueMode (see more detailed comments in interface definition)
                    // caller takes responsibility for enforcing this constraint.
                    Debug.Assert(Interlocked.Increment(ref _outstandingOperations._reads) == 1,
                        "Only one outstanding read allowed at any given time.");
#endif
                    _readTaskCompletionSource = new TaskCompletionSource<int>();
                    _readEventArgs.SetBuffer(buffer, offset, count);
                    if (!ReadAsyncFast(_readEventArgs))
                    {
                        if (_readEventArgs.Exception != null)
                        {
                            throw _readEventArgs.Exception;
                        }

                        bytesRead = _readEventArgs.BytesTransferred;
                    }
                    else
                    {
                        bytesRead = await _readTaskCompletionSource.Task.SuppressContextFlow<int>();
                    }
                }
            }
            catch (Exception error)
            {
                if (s_CanHandleException(error))
                {
                    cancellationToken.ThrowIfCancellationRequested();
                }

                throw;
            }
            finally
            {
                cancellationTokenRegistration.Dispose();

                if (NetEventSource.IsEnabled)
                {
                    NetEventSource.Exit(this, bytesRead);
                }
            }

            return bytesRead;
        }