Lobby Sessions (Online Subsystem)

The EOSCore Online Subsystem can use EOS Lobbies instead of EOS Sessions behind the normal IOnlineSession interface. The same Create, Find, Join, Update, Destroy and invite functions work. They talk to the EOS Lobby interface when the session settings ask for it.

Lobby sessions are meant for player hosted games, such as parties, listen servers and peer-to-peer games. Dedicated servers cannot own a lobby, so use EOS Sessions for them.

Requirements

• The local user is logged in with EOS Connect (a Product User Id).
• Players connect to the lobby owner over EOS P2P, so use the EOSCore NetDriver with bIsUsingP2PSockets=true. See Configuring Online Subsystem.
• Create the session before you open the level with listen. The host listens on a P2P socket named after the lobby id.

Creating a Lobby Session

Set bUseLobbiesIfAvailable in the session settings.

FOnlineSessionSettings Settings;
Settings.NumPublicConnections = 4;
Settings.bShouldAdvertise = true;
Settings.bUsesPresence = true;
Settings.bAllowJoinViaPresence = true;
Settings.bAllowInvites = true;
Settings.bUseLobbiesIfAvailable = true;
Settings.bUseLobbiesVoiceChatIfAvailable = false;
Settings.Set(SETTING_HOST_MIGRATION, true, EOnlineDataAdvertisementType::DontAdvertise);
Settings.Set(FName(TEXT("GAMEMODE")), FString(TEXT("Coop")), EOnlineDataAdvertisementType::ViaOnlineService);

SessionInterface->CreateSession(0, NAME_GameSession, Settings);

Setting	Lobby option
NumPublicConnections + NumPrivateConnections	Max lobby members (EOS allows up to 64)
NumPublicConnections > 0	Public advertised lobby
NumPublicConnections == 0 and bAllowJoinViaPresence	Join via presence
Otherwise	Invite only
bUsesPresence	Lobby presence, so friends can join from the EOS overlay
bAllowInvites	Invites allowed
bUseLobbiesVoiceChatIfAvailable	Creates the lobby RTC voice room. The platform must be created with RTC enabled
SETTING_HOST_MIGRATION	Host migration, on by default
SessionIdOverride (UE 5.1+)	Custom lobby id, 4 to 32 characters

Settings advertised with ViaOnlineService or ViaOnlineServiceAndPing become lobby attributes. MemberSettings for the local user become member attributes.

Finding Lobby Sessions

Set SEARCH_LOBBIES to true in the query settings. The other query settings are used as lobby search filters.

SessionSearch = MakeShared<FOnlineSessionSearch>();
SessionSearch->MaxSearchResults = 50;
SessionSearch->QuerySettings.Set(SEARCH_LOBBIES, true, EOnlineComparisonOp::Equals);
SessionSearch->QuerySettings.Set(FName(TEXT("GAMEMODE")), FString(TEXT("Coop")), EOnlineComparisonOp::Equals);

SessionInterface->FindSessions(0, SessionSearch.ToSharedRef());

FindFriendSession finds the lobby a friend is in, and FindSessionById looks for a lobby with that id first and then for an EOS session.

Joining and Connecting

Join a search result with JoinSession. When OnJoinSessionComplete reports success, get the connect string and travel:

FString ConnectString;
if (SessionInterface->GetResolvedConnectString(NAME_GameSession, ConnectString))
{
	PlayerController->ClientTravel(ConnectString, TRAVEL_Absolute);
}

The connect string is an EOS P2P address for the lobby owner, EOS:<OwnerProductUserId>:<LobbyId>:<Channel>.

Updates, Members and Invites

• UpdateSession updates the lobby. Only the owner can change lobby settings and attributes. Other members only update their own member attributes.
• Lobby changes call OnSessionSettingsUpdated. Members joining and leaving call OnSessionParticipantJoined and OnSessionParticipantLeft (UE 5.2+) or OnSessionParticipantsChange (older engines). Member attribute changes call OnSessionParticipantSettingsUpdated.
• SendSessionInviteToFriend sends a lobby invite. Received invites call OnSessionInviteReceived. Accepted invites and Join in the EOS overlay call OnSessionUserInviteAccepted.
• Leave in the EOS overlay calls OnDestroySessionRequested (UE 5.5+). On older engines the session is destroyed directly.
• DestroySession leaves the lobby. If the owner leaves with host migration on, EOS promotes another member, and that member's session becomes the owner. If the lobby is closed or the local user is kicked, the session is removed and OnDestroySessionComplete is called.