DarkflameServer/docs/Matchmaking.md

Activity matchmaking

Activity lobbies (survival, racing, Battle of Nimbus Station, the other activities whose Activities.instanceMapID is another zone) are kept by the chat server, across every world. Players on different instances of a zone who join the same activity wait in the same lobby and are sent to the same new instance of the activity's zone.

Live worked this way: in the 2014 captures of an Avant Gardens survival lobby, the lobby's other players never appear in the joining player's world (18 other players are constructed there, none of them from the lobby), and the four who stayed in the lobby are then all constructed together in the same survival instance (zone 1101). The chat service's message list has MATCH_REQUEST (52), the world to chat message for this.

Flow

1. The client sends the game message MatchRequest (type 0, value = activity ID) to its world. The world answers MatchResponse 0 (not for quickbuild activities, as before), saves the zone to come back to, and sends chat ChatPackets::MatchRequest JOIN with the player's name, the client's choices text and the activity's settings as the world read them (instanceMapID, minTeams, maxTeams, minTeamSize, maxTeamSize, waitTime, startDelay, with the world's overrides: solo_racing, transferZoneID). Chat needs no CDClient.
2. Ready (MatchRequest type 1) is answered with MatchResponse 0 (as live) and sent to chat as READY. The LobbyExit message box button sends LEAVE.
3. Chat keeps the lobbies (dChatServer/Matchmaking.{h,cpp}, no network code) and sends the MatchUpdate game messages to the clients through their worlds (WORLD_ROUTE_PACKET, ClientPackets::MatchUpdate, byte for byte the world's GameMessages::MatchUpdate).
4. When a lobby's countdown runs out, chat asks master for a new instance of the zone (the usual REQUEST_ZONE_TRANSFER with a random clone ID) and sends each world that has players of the match MATCH_TRANSFER (DLU, chat id 71) with the instance's zone, address and that world's players. The world checks each player's activity cost, records the activity instance and sends them TransferToWorld.
5. Chat makes the players a team when there are 2 to 3 of them (as the world did before: CreateTeam holds at most 3 members).

A player leaves their lobby when their world reports them gone (UNEXPECTED_DISCONNECT from the world they are in) or when they load into a world (LOGIN_SESSION_NOTIFY).

Lobby rules

Lobby key	activity ID and instanceMapID
Capacity	maxTeams when maxTeamSize is 1, else maxTeamSize
Minimum	minTeams when maxTeamSize is 1, else minTeamSize
Joining	the oldest lobby of the activity with room, else a new one with the timer at waitTime
Countdown	runs only while the lobby has its minimum; players leaving below it pause it, it does not start over
All ready	with the minimum, the timer drops to startDelay
Start	timer at 0: every player in the lobby goes to one instance
Joining another activity	leaves the first lobby

MatchUpdate messages

When	To	Type	Text
Join	joining player	PLAYER_ADDED for themselves, then for each waiting player followed by PLAYER_READY if that player is ready	[droppedItem=9:<id>\n]player=9:<id>\nplayerName=0:<name>
Join	the others	PLAYER_ADDED	same
Join while counting	joining player	PHASE_WAIT_READY	time=3:<seconds left>
Countdown starts	everyone	PHASE_WAIT_READY	time=3:<seconds>
Ready / not ready	everyone	PLAYER_READY / PLAYER_NOT_READY	player=9:<id>
All ready	everyone	PHASE_WAIT_START	time=3:<startDelay>
Leave	everyone, the leaver included	PLAYER_REMOVED	player=9:<id>

droppedItem is the racing car the client names in its MatchRequest choices (droppedItem=13:<id>); live showed it to the lobby as an object ID before the player's line.

Differences from the world lobbies DLU had before: the joining player gets only the ready players' states (live) where every state went to everyone; the all-ready cut needs the lobby's minimum; the ready request gets a MatchResponse.

Limits

• Lobbies live in the chat server: a chat restart (live update) empties them, and players waiting have to join again. Without a chat server nobody can join a lobby.