How to send message to client by client ID

Hi everyone.
I am new in Colyseus. I am learning to create a simple game.
All players will join only one room - Lobby
Then choose one in other players to invite to dule ( 1 vs 1 game)
If the invited player accepts, other players will see this two players are marked "Duling"
Then this two players will moved to Game screen to dule.
But i have problem in two steps

1. How to send message to chosen player?
   I am going to use foreach to check all clients in the room with chosen player client ID. But i think it is bad solution.
2. I don't know one client can connect to many room or not.
   Because as i understood, these two players will be moved to Game room that only has 2 players. But i still want to keep their name and status in Lobby screen.
   What is best solution?
   Thanks you so much.

hi @deadwind88, welcome!

yes, clients can join multiple rooms. each room connection has its own websocket connection.

you'd need exchange messages between client and server during the Lobby room.

• sending messages from client to server
• onMessage in the client-side
• onMessage in the server-side

once your custom "handshake" between two clients has established on Lobby handler, you can send a "dule code" to the two players, and make the players join the same "dule" session.

client.join("dule", { code: "bothPlayersShouldJoinThisCode" });

on Dule room handler, you should only allow clients with the same dule code do join toguether:

maxClients = 2;

onInit (options) {
  this.code = options.code;
}

// on dule room handler
requestJoin(options) {
  return this.code === options.code;
}

I haven't tested the code, you can play around and modify as you see fit! Hope this helps, cheers!

@endel Thank you so much.
But i still not understand how to send the code to player who is invited.
For example:
Player A login, and see this lists
B, C, D
A want to invite C to duel, A send a message to Server "Hey, I want to make a duel with C"
I don't know how to make Server to send message to C "Hey A want to make a dule with C" and C can accept or not.
This is my code

// When a client sends a message
    onMessage (client, message) {
        switch (message.action) {
            //A send request to invite C to make a duel
            case 'request_dule':
                let guestId = message.data.guest_id;
                let guest = this.state.players[guestId];
                //find a client has id equal with C's client id
                for (let i = 0; i < this.clients.length; i++) {
                    if (this.clients[i].id == guest.client_Id) {
                        //send request to C's client and wait C accepting
                        this.send(this.clients[i], {action: 'request_dule', data: {host: client.id}});
                        break;
                    }
                }
                break;
            default:
                break;
        }
    }

Looking forward your advice. Thanks

@deadwind88 I think I can help with this.

You need to create an onMessage handler on your client side. Refer to this https://docs.colyseus.io/client-room/#onmessage
so lets say your server code is working fine, in the client, you'd need to extract that message.
ex: onMessage(…) {
if (message.action === "request_dule") {…}
}