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

        private async Task<WebSocketReceiveResult> HandleReceivedCloseAsync(
            MessageHeader header, CancellationToken cancellationToken)
        {
            lock (StateUpdateLock)
            {
                _receivedCloseFrame = true;
                if (_state < WebSocketState.CloseReceived)
                {
                    _state = WebSocketState.CloseReceived;
                }
            }

            WebSocketCloseStatus closeStatus = WebSocketCloseStatus.NormalClosure;
            string closeStatusDescription = string.Empty;

            // Handle any payload by parsing it into the close status and description.
            if (header.PayloadLength == 1)
            {
                // The close payload length can be 0 or >= 2, but not 1.
                await CloseWithReceiveErrorAndThrowAsync(WebSocketCloseStatus.ProtocolError, WebSocketError.Faulted, cancellationToken).ConfigureAwait(false);
            }
            else if (header.PayloadLength >= 2)
            {
                if (_receiveBufferCount < header.PayloadLength)
                {
                    await EnsureBufferContainsAsync((int)header.PayloadLength, cancellationToken).ConfigureAwait(false);
                }

                if (_isServer)
                {
                    ApplyMask(_receiveBuffer, _receiveBufferOffset, header.Mask, 0, header.PayloadLength);
                }

                closeStatus = (WebSocketCloseStatus)(_receiveBuffer[_receiveBufferOffset] << 8 | _receiveBuffer[_receiveBufferOffset + 1]);
                if (!IsValidCloseStatus(closeStatus))
                {
                    await CloseWithReceiveErrorAndThrowAsync(WebSocketCloseStatus.ProtocolError, WebSocketError.Faulted, cancellationToken).ConfigureAwait(false);
                }

                if (header.PayloadLength > 2)
                {
                    try
                    {
                        closeStatusDescription = s_textEncoding.GetString(_receiveBuffer, _receiveBufferOffset + 2, (int)header.PayloadLength - 2);
                    }
                    catch (DecoderFallbackException exc)
                    {
                        await CloseWithReceiveErrorAndThrowAsync(WebSocketCloseStatus.ProtocolError, WebSocketError.Faulted, cancellationToken, exc).ConfigureAwait(false);
                    }
                }
                ConsumeFromBuffer((int)header.PayloadLength);
            }

            // Store the close status and description onto the instance.
            _closeStatus = closeStatus;
            _closeStatusDescription = closeStatusDescription;

            // And return them as part of the result message.
            return new WebSocketReceiveResult(0, WebSocketMessageType.Close, true, closeStatus, closeStatusDescription);
        }