This is a conceptual work. Not tested in production.
This is a simple server browser example using Gdmaster - Open masterlist server written in Godot's gdscript.
For reasons, hosting a game in godot requires atleast two ports: 1) Game port - port where the godot game is hosted at using high level multiplayer API. This port is used by multiplayer peers to connect to the hosted game; 2) Listener port - port on which server information is served at. This port is used by clients retrieving server information during the server browser refresh;
It is best practice to serve Gdmaster (masterlist) server your hosted game's listener port, so that this IP:PORT combo would be served back to clients, upon get servers request, from Gdmaster (masterlist).
Everything starts from main.tscn scene which has lobby.tscn, server_browser.tscn and player_data.tscn nodes. PlayerData node holds information about current lobby, and is referenced in both Lobby and ServerBrowser nodes via exported variables. Both Lobby and ServerBrowser nodes have references to each other via exported variables. This is important. Without these references you wont be able to switch between these scenes during runtime.
Lobby node holds data about Gdmaster server, player and lobby/game. Here you define your game parameters for Gdmaster, lobby parameters. Onece you press "Host game" button, a "create_game()" function will create game and serve server information on listener port and will send game information to Gdmaster. Also check GdmasterClient node for more configuration. By default this will work with default configuration of Gdmaster server. But Gdmaster client must match Gdmaster server configurations. See more info on Gdmaster server configuration Gdmaster.
ServerBrowser node holds data about servers, retreived form Gdmaster (masterlist) server. Here you need to specify Gdmaster server information and information about the game you want to request from Gdmaster. By pressing button "Get servers" Gdmaster will server you a list of available games based on the requested game parameters. After that you can refresh listed server datas by pressing "Refresh servers".
The main idea is this: - A game is created using Godots high level multiplayer API. - Server information listener is launched on a different port. - The game data is sent through GdmasterClient to Gdmaster (masterlist) server to hold the hosted game info, IP and listener port (this is important). - A Godot multiplayer peer client makes a request server list request through GdmasterClient on Gdmaster (masterlist) server for currently available servers with given game parameters. - A list of servers then is parsed by ServerBrowser node and for each server item, and AddressItem is created. - Upon the creation of AddressItem, server info request is made to the IP:PORT (Listener port on the hosted game machine). - Server information is served back at AddressItem. - AddressItem then displays current server information on the server browser. - Client/multiplayer peer then presses the "Join" button on the AddressItem in ServerBrowser node and is connected to the game. - A server info request by AddressItem is emmited, to get the updated information about the server. - AddressItem "Join" button text is then updated to "In game".
Of course more things happen during all these steps. Main thing I didn't mention- the lobby_id is the main property that gets set in PlayerData node once a peer is connected to the hosted game. This lobby_id is used by the ServerInfoRequester in AddressItem to test with funtion "is_joined" if the peer is connected to this AddressItem so that the AddressItem "Join" button could be renamed appropriately.
Due to how high-level multiplayer works in Godot, there are number of hacks that you need to implement in order to have fluid code progression.
One such area is in "peer.create_server()" function where you need to specify max number of peers that are allowed to join the game. This number does not include the host, so in total there will be max number of peers + host of player in the game. You can't have a game of 1/1 players. The minimum player limit for multiplayer game is 2.
Another thing to consider is to manage the "peer.create_client()" timeouts. Once you create client, it wont throw error if the client was refused by the server or something else. The multiplayer API will still be valid object. So you have to run a timer to check and see currect "PeerState".
This was my attempt to solve the good ol' question - Will it blen.. How to server browser in Godot? I think i did pretty well for a nobody, with somehelp from both Godotforums and Xonotic communities. Im sure there are better ways to do things.