Lobby

A lobby is a group of players who are connected to each other so their mods can talk. One player hosts it, and the others join. There is one lobby for all mods at a time.

Lobby host, join and watch the lobby

Call Host to make a lobby, Join to enter one, and Leave to get out. MemberJoined, MemberLeft and OwnerChanged tell you when players come and go.

public static class Lobby
{
    public const int MaxMembers = 32;
    public static bool IsAvailable { get; }
    public static LobbyStatus Status { get; }
    public static string Error { get; }
    public static List<ulong> Members { get; }
    public static ulong Owner { get; }
    public static bool IsHost { get; }
    public static bool Host(string gameTag, string version, int maxMembers, bool openInvite);
    public static bool Join(ulong lobby, string gameTag, string version);
    public static bool Leave();
    public static bool Leave(string gameTag);
    public static bool Invite();
    public static string MemberName(ulong member);
    public static bool IsRefused(ulong member);
    public static event Action<ulong> MemberJoined;
    public static event Action<ulong> MemberLeft;
    public static event Action<ulong, ulong> OwnerChanged;
    public static event Action<ulong> JoinRequested;
}

Method	Returns	What it does
Host(gameTag, version, maxMembers, openInvite)	bool	Makes a lobby.
Join(lobby, gameTag, version)	bool	Joins a lobby.
Leave()	bool	Leaves any lobby.
Leave(gameTag)	bool	Leaves only when the lobby belongs to this game tag.
Invite()	bool	Opens the invite window for the lobby you host.
MemberName(member)	string	A member’s name. "" when not in a lobby.
IsRefused(member)	bool	true when the host refused this member because of a version mismatch.

Property	Type	What it means
MaxMembers	int	The most players a lobby can hold.
IsAvailable	bool	true while Steam is ready.
Status	LobbyStatus	Where you are now.
Error	string	The text of the last failure. "" when there is none.
Members	List<ulong>	Everyone in the lobby, including you and any player that was refused.
Owner	ulong	The host’s SteamID64. 0 when you are not in a lobby or Steam is not ready.
IsHost	bool	true when you are in a lobby and you are its host.

Event	Gives you	When it fires
MemberJoined	The player’s SteamID64.	A checked player has joined.
MemberLeft	The player’s SteamID64.	A checked player has left or was refused.
OwnerChanged	The previous host and the new host.	The host changes.
JoinRequested	The lobby’s id.	The player accepts a Steam invite.

LobbyStatus where you are in a lobby

Lobby.Status gives you this. Check it before you host or join, because only one lobby is allowed at a time.

public enum LobbyStatus
{
    Offline,
    Pending,
    Hosting,
    Joined
}

Value	Meaning
Offline	You are not in a lobby.
Pending	A host or join request is still working.
Hosting	You made the lobby.
Joined	You are in someone else’s lobby.

Things to know

• gameTag and version name your mod’s game. Players can only join a lobby that has the same tag and the same version as theirs.
• gameTag also keeps one mod from ending another mod’s lobby (see Leave).
• Host makes a lobby that only friends can join. openInvite opens the Steam invite window for you. (It sets the lobby data game to gameTag, v to version and core to the framework version, and it sets the connect rich presence, which is what lets friends join from Steam.)
• If you are already hosting a lobby with the same game tag, version and size, Host only opens the invite window (when openInvite is set) and returns true.
• Join joins a lobby by its id. It needs your game tag and version because the framework checks that the host runs the same ones. It leaves your current lobby first. It returns true when you are already in that lobby.
• After Steam confirms the join, Status stays Pending for up to 3 seconds while the lobby’s information arrives.
• The framework does not join a lobby by itself when the player accepts an invite. JoinRequested tells your mod that the player accepted one, and your mod decides to call Join. If nothing subscribes to the event, the request is ignored. (It is raised for a Steam invite and for the launch option +connect_lobby <id>.)
• Leave ends whatever you are doing with the lobby. It cancels a waiting request, leaves the lobby, closes the connection to each checked player, and raises MemberLeft for each of them. It returns true.
• Leave(gameTag) is the safe version, so use it instead of Leave(). It does nothing and returns false when the lobby or a waiting request belongs to another game tag, so one mod can’t end another mod’s session. Otherwise it works like Leave().
• There is one lobby at a time for all mods. Check Status before you host or join.
• Invite opens the invite window for the lobby you host. It returns false when Status is not Hosting.
• MemberName returns a player’s lobby name. If that is missing, it returns their Steam name, and otherwise "". It never throws.
• Every player sets their own name when they host or join, capped at 64 characters, so a name can be missing or late. Show a fallback until it arrives. The text is cleaned the same way as the other text from other players (see “Presence”).
• Members is refreshed every second and whenever Steam reports a change. It includes players that were refused for a version mismatch, because Steam has no way to kick someone from a lobby. Use Net.Peers for the players you can really talk to.
• Owner reads the host from Steam each time you ask. It is 0 while Status is Offline or Pending, so a join is not reported as hosted until it is checked. IsHost is true only when Owner is not 0 and is you.
• OwnerChanged fires when the host changes. The first host seen after you join is reported as (0, owner), so ignore events where the previous host is 0. (It is raised from the Members refresh, every second and on each Steam member change, when Owner differs from the last owner seen. The last owner resets to 0 on Leave and when the lobby is cleared.)
• When you become the host because the old one left, Status becomes Hosting and the connect rich presence is set, as Host does, so Invite works.
• Lobby.IsAvailable is the same as Steam.IsReady. The lobby has no changes to the game of its own, so it works whenever Steam is ready.

Limits

• gameTag and version must be 1 to 32 characters of letters, digits, ., _ and -.
• maxMembers is from 1 to 32. With any other values (a different game tag, version or size from the lobby you already host), Host returns false and leaves the lobby as it is, so leave the lobby first. It also returns false while a request is waiting, and when you are in someone else’s lobby.
• Join returns false for a lobby id of 0 or while a request is waiting. A lobby that is already for another game tag is refused at once.
• If a Join leaves your current lobby, or a Host is refused because the lobby you host has other settings, the framework writes a warning with both game tags to the log.
• A request that takes more than 20 seconds fails. Error then says “The lobby request timed out.”, and a success that arrives late is left at once.