public async Task SendMessage(string sessionKey, string socketId, string message)
        {
            WebsocketSession session = this.GetSessionByKey(sessionKey);

            if (session == null)
            {
                throw new Exception("Unknown Session requested: " + sessionKey);
            }

            WebsocketSessionPeer sessionSocket = session.GetPeerById(socketId);

            if (sessionSocket == null)
            {
                throw new Exception("Unknown Socket requested: " + socketId);
            }

            await SendMessage(sessionSocket.Socket, message);
        }
        public virtual async Task <WebsocketSessionPeer> JoinSession(HttpContext context, string sessionType, string sessionKey)
        {
            WebsocketSession targetSession = GetSessionByKey(sessionKey);

            if (targetSession == null)
            {
                targetSession = this.CreateSession(sessionType, sessionKey);
            }

            WebSocket socket = await context.WebSockets.AcceptWebSocketAsync();

            WebsocketSessionPeer sessionSocket = targetSession.AddPeer(socket);

            string hostId = sessionSocket.Token.PeerId;

            if (targetSession.GetPeers().Count == 1)
            {
                targetSession.SetAttribute("hostId", hostId);
            }
            else
            {
                hostId = targetSession.GetAttributeValue <string>("hostId");
            }

            // alert requester of their own token, the hosts token and other existing peers
            WebsocketSessionPeerToken hostToken = targetSession.GetPeerById(hostId).Token;

            WebsocketSessionPeerToken[] participants = targetSession.GetPeers().Where(pair => pair.Value.Token.PeerId != sessionSocket.Token.PeerId).Select(pair => pair.Value.Token).ToArray();

            WebsocketSessionGreeting greeting = new WebsocketSessionGreeting {
                SessionKey = sessionKey, HostToken = hostToken, Token = sessionSocket.Token, Peers = participants
            };
            WebsocketSessionMessageResponse greetingResponse = CreateWebsocketResponseMessage(WebsocketSessionMessageType.Greeting, greeting);

            SendMessage(sessionSocket, greetingResponse);

            return(sessionSocket);
        }