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

        private int WriteFrameToSendBuffer(MessageOpcode opcode, bool endOfMessage, ArraySegment<byte> payloadBuffer)
        {
            // Grow our send buffer as needed.  We reuse the buffer for all messages, with it protected by the send frame lock.
            EnsureBufferLength(ref _sendBuffer, payloadBuffer.Count + MaxMessageHeaderLength);

            // Write the message header data to the buffer.
            int headerLength;
            int? maskOffset = null;
            if (_isServer)
            {
                // The server doesn't send a mask, so the mask offset returned by WriteHeader
                // is actually the end of the header.
                headerLength = WriteHeader(opcode, _sendBuffer, payloadBuffer, endOfMessage, useMask: false);
            }
            else
            {
                // We need to know where the mask starts so that we can use the mask to manipulate the payload data,
                // and we need to know the total length for sending it on the wire.
                maskOffset = WriteHeader(opcode, _sendBuffer, payloadBuffer, endOfMessage, useMask: true);
                headerLength = maskOffset.GetValueOrDefault() + MaskLength;
            }

            // Write the payload
            if (payloadBuffer.Count > 0)
            {
                Buffer.BlockCopy(payloadBuffer.Array, payloadBuffer.Offset, _sendBuffer, headerLength, payloadBuffer.Count);

                // If we added a mask to the header, XOR the payload with the mask.  We do the manipulation in the send buffer so as to avoid
                // changing the data in the caller-supplied payload buffer.
                if (maskOffset.HasValue)
                {
                    ApplyMask(_sendBuffer, headerLength, _sendBuffer, maskOffset.Value, 0, payloadBuffer.Count);
                }
            }

            // Return the number of bytes in the send buffer
            return headerLength + payloadBuffer.Count;
        }