Send larger messages than 126 bytes websockets in C#
public void sendMessage(Stream stream, string message)
    {
        try
        {
            List<byte> lb = new List<byte>();
            string aux = message;
            bool flagStart = false;
            int size;
            while (message.Length > _maxLengthMessage)
            {
                lb = new List<byte>();
                // I cut the mesasge in smaller pieces to send
                message = aux.Substring(0, _maxLengthMessage);
                aux = aux.Substring(_maxLengthMessage);
                if (!flagStart)
                {
                    // In doc of Websockets i sign this piece: not the end, text
                    lb.Add(0x01);
                    flagStart = !flagStart;
                }
                else
                {
                    // In doc of Websockets i sign this piece: not the end, continuation
                    lb.Add(0x00);
                }
                size = message.Length;

                lb.Add((byte)size);
                lb.AddRange(Encoding.UTF8.GetBytes(message));
                stream.Write(lb.ToArray(), 0, size + 2);
            }
            lb = new List<byte>();
            if (!flagStart)
            {
                // If is this the only message we mark with: end of message, text
                lb.Add(0x81);
                flagStart = !flagStart;
            }
            else
            {
                //else Is the end of the message but is the continuation frame
                lb.Add(0x80);
            }
            size = aux.Length;

            lb.Add((byte)size);
            lb.AddRange(Encoding.UTF8.GetBytes(aux));
            //lb.AddRange(Encoding.UTF8.GetBytes(i.ToString()));
            stream.Write(lb.ToArray(), 0, size+2);

        }
        catch (Exception ex)
        {
            throw ex;
        }

    }