Matchmaking API

Introduction

One key requirement while creating a multiplayer game is to easily be able to match together players with similar skills, level, or that wants to play the same game type or map, making the overall experience in-game as enjoyable as possible.
For this purpose, Photon Fusion exposes a set of API calls that can be used to create the best experience for players looking for the perfect match.

Photon Fusion works with the Photon Cloud transparently, so most of the interactions with the Photon backend services are done automatically internally.
On this page it is described the Fusion Matchmaking API, which is used to create a Game Session optionally with custom properties that can be used by players to filter/join the best Session based on their desired game play experience.

Glossary

In order to fully understand the API, below are described some terms used along this document that are directly related to the correct usage of the Matchmaking API.

• Game Session: or just Session is where Players meet to play a match or communicate. This is what gets published in the Photon Cloud and it is made available so other clients can search, filter, and join a particular game. Communication outside of any Session is not possible and any client can only be active in one Session. Game Sessions have the following properties and methods: can be created and joined by name, Custom Properties, has a maximum amount of players, can be hidden (does not show in a Lobby) or visible, can be closed (no one can join) or opened. In PUN and Photon Realtime, it was formerly called a Room.
• Lobby: is a virtual container or "list" of Sessions. It is possible to use multiple lobbies to split the sessions between different game types, for example, as it is basically a way to have a Game Session listed within an arbitrary set of sessions. Clients can't communicate in the Lobby and they never know that another client is also in the lobby. A client can only be in a Lobby, a Game Session or neither.

Creating and Joining a Game Session

The Game Session creation and joining are two parts of the same procedure, and the rules are simple:
1. if there is no Session with the specified SessionName, a new one will be created (not in all cases as explained below) with that SessionName.
2. if there is already a Session with that SessionName, the peer will join it.

In terms of API, all of this is done automatically when a new Fusion Simulation is started.
Below are listed the main arguments that can be used to customize the Session when creating a new one or used as a filter when looking for a Session to join:

C#

NetworkRunner.StartGame(new StartGameArgs {
  // ...
  // Arguments related to the Matchmaking between peers
  SessionName = [string],
  SessionProperties = [Dictionary<string, SessionProperty>],
  CustomLobbyName = [string],
  EnableClientSessionCreation = [bool],
  PlayerCount = [int],
  IsOpen = [bool],
  IsVisible = [bool],
  MatchmakingMode = [MatchmakingMode],
});

All the matchmaking related arguments are optional and the default values each one will take are described below:

• SessionName: the Game Session's Name or ID, it will identify the session on the Photon Cloud and it must be unique within a Region. If no name is set, Fusion will generate a random GUID to identify the Session.
• SessionProperties: the Session's Custom Properties are the way to include metadata on your Game Session, like the game mode/type or the current map, for example. Keep in mind that all properties are always published to the Lobby when creating the Session and those properties can be used as matching filters when a peer is joining a random Session (read more below). As a suggestion, always try to keep the Property Keys as short as possible in order to minimize traffic. By default, the Session Custom Properties are empty and no extra information is included.
• CustomLobbyName: this argument is used to set custom Lobby Name which the Session will be associated with. By default, Fusion already separates a Session based on the GameMode (ClientServer Lobby when starting in Host, Server, or Client, and Shared Lobby when starting in Shared game mode).
• EnableClientSessionCreation: this flag changes which Client peer types can create a new Game Session or only join one. See below for more info.
• PlayerCount: defines the max number of clients that can join a Session. This parameter is only used when creating a new Session and by default, it takes the value from the Default Players field on the NetworkProjectConfig/Simulation.
• IsOpen: defines if the Game Session being created (when applies), will be set as Open for any other players to join. See Getting and Updating the Game Session information for more info.
• IsVisible: defines if the Game Session being created (when applies), will be Visible other players. See Getting and Updating the Game Session information for more info.
• MatchmakingMode: defines the matchmaking mode used when trying to join a Random Game Session.
  • FillRoom: Fills up rooms (oldest first) to get players together as fast as possible. Default.
  • SerialMatching: Distributes players across available rooms sequentially but takes filter into account. Without filter, rooms get players evenly distributed.
  • RandomMatching: Joins a (fully) random room. Expected properties must match but aside from this, any available room might be selected.

It is possible to create and join a Game Session, either at random or with a specific SessionName (useful for Game Invites, for example), and also enables Session filtering using custom properties, in order to only join games with specific configurations.
This already provides a lot of flexibility when managing the sessions.

The following table summarizes how Fusion handles the Game Session creation and joining, as it depends on the SessionName, GameMode and if the EnableClientSessionCreation is enabled or not when starting the simulation.

GameMode	Session Name
	Valid			Empty/Null
Server/Host	Create or Join specific Session			Create or Join Session with Random ID
	EnableClientSessionCreation
	Null (default)	True	False	Null (default)	True	False
Client	Join Session	Create or Join Session	Join Session	Join Random Session	Join Random or Create	Join Random Session
Shared	Create or Join Session	Create or Join Session	Join Session	Join Random or Create	Join Random or Create	Join Random Session
AutoHostOrClient	Create or Join Session	Create or Join Session	Join Session	Join Random or Create	Join Random or Create	Join Random Session

Getting and Updating the Game Session information

Fusion provides a lot of information about the currently connected Game Session like its Name and Region.
These data are directly available in NetworkRunner through the SessionInfo property.
Below are listed all available fields of the SessionInfo type:

• IsValid [bool{get}]: signal if the SessionInfo is ready for read/write.
• Name [string{get}]: the Session Name.
• Region [string{get}]: the currently connected Region.
• Properties [Dictionary<string, SessionProperty>{get}]: a read only dictionary with the current Session Custom Properties. In order to update these properties, just use the SessionInfo.UpdateCustomProperties(Dictionary<string, SessionProperty>) method and pass the a new set of properties.
• IsVisible [bool{get,set}]: signal if the Session is Visible on Lobby. Making a Session invisible is just a matter of changing this property.
• IsOpen [bool{get,set}]: signal if the Session is Open to join. In order to close or open a Sesion, just alter this property.
• PlayerCount [int{get}]: the current number of Players in the Session. Only available in the Lobby.
• MaxPlayers [int{get}]: Max Number of peers hat can join the Session, this value also includes a slot of the Server/Host peer. Only available in the Lobby.

Keep in mind that the Session information and mainly the Custom Properties, should be used for Matchmaking purposes only and never to synchronize game state information with the game clients, for example. We highly discourage such uses.
If you need to exchange information session-wide that is related to gameplay, Fusion offers plenty of options, like having a global NetworkObjects or using RPCs for one-shot data.

The NetworkRunner also provides some other Session and Photon Cloud related properties that can be used in-game, like:

• NetworkRunner.IsCloudReady: signal if the Local Peer is connected to Photon Cloud and is able to Create/Join a Room or join a Lobby.
• NetworkRunner.UserId: holds the UserId associated with the Local Peer after it gets authenticated. This information comes from Authentication Service used by your application.
• NetworkRunner.AuthenticationValues: holds the reference of the AuthenticationValues used to authenticate the local peer when starting Fusion.
• NetworkRunner.CurrentConnectionType: describes the current Connection Type used by the peer, either a Direct or Relayed connection with the remote Server. Keep in mind that in SharedMode, the clients always connect via relay.
• NetworkRunner.NATType: when the NAT Punchthrough System is enabled, Fusion will try to determine the current NAT Type of the current network where the local peer is running, this property exposes this information. NAT Types can be: Invalid, UdpBlocked, OpenInternet, FullCone or Symmetric.
• NetworkRunner.IsSharedModeMasterClient: boolean flag that describes if the local peer is also the Master Client of a Shared Game Session. This is only valid when running in SharedMode and can be used to determine in which peer certain actions should happen based on the differentiation between other clients and the Master Client.

Another related field is the NetworkRunner.LobbyInfo, that exposes infomation about the current Lobby the peer is connected to (keep in mind that a peer can only be in a Lobby, a Game Session or disconnected). Here we list the main properties of the LobbyInfo:

• IsValid [bool{get}]: signal if the LobbyInfo is ready for read/write.
• Name [string{get}]: contains the name of the current Lobby.

Game Session Browser

Game Session browsers were popular in the 90s and early 2000s. The fundamental design is still valid but nowadays their main purpose (finding a suitable game and joining it quickly) has been replaced with Matchmaking.

There are multiple reasons why Game Session browsers are discouraged:

• there are present security concerns;
• retrieving a list of active Game Session is a performance heavy operation for the servers;
• the lists are always specific to the region to which a player is currently connected; and,
• most importantly it is an antiquated design pattern and better UX options are available today.

The up-to-date alternatives offered by Fusion Matchmaking API are:

1. To fill / join a Game Session quickly: Join a random open room.
2. To join a certain type of match: Join a random open room while also filtering using the Game Session properties.
3. To have specific players join up and play together: Create an invite code and / or join a Game Session by name.

Unless the game has an abundance of community servers running which have their own custom / modded modes and maps, there is little to no reason to request a full list of rooms and make them available to the user through a Game Session browser.

Examples of API usage

Join a Random Session

In order to join any Session, in cases where players just want to quickly join a Game, simply start the NetworkRunner and let it find an available Game Session without any extra parameters:

C#

public async Task StartPlayer(NetworkRunner runner) {

  var result = await runner.StartGame(new StartGameArgs() {
    GameMode = GameMode.AutoHostOrClient, // or GameMode.Shared
  });
  
  if (result.Ok) {
    // all good 
  } else {
    Debug.LogError($"Failed to Start: {result.ShutdownReason}");
  }
}

This way, the local peer will start and connect to a Random Game Session, if none can be found, it will create a new one with a random Session Name (because it is using the GameMode.AutoHostOrClient). This is also valid if starting the NetworkRunner using the GameMode.Shared, for Sessions in Shared Mode.

Starting a new Game Session with Custom Properties

In this example a Host will create a Game Session with some custom properties, so later, Clients can filter the Sessions using those properties.

C#

// Some predefined types used as values for the Game Session Properties
public enum GameType : int {
  FreeForAll,
  Team,
  Timed
}

public enum GameMap : int {
  Forest,
  City,
  Desert
}

// Utility method to start a Host using a defined GameMap and GameType
public async Task StartHost(NetworkRunner runner, GameMap gameMap, GameType gameType) {

  var customProps = new Dictionary<string, SessionProperty>();

  customProps["map"] = (int)gameMap;
  customProps["type"] = (int)gameType;

  var result = await runner.StartGame(new StartGameArgs() {
    GameMode = GameMode.Host,
    SessionProperties = customProps,
  });

  if (result.Ok) {
    // all good 
  } else {
    Debug.LogError($"Failed to Start: {result.ShutdownReason}");
  }
}

The sample code shows the use of Enums for the Custom Properties values of the Game Session, but this is just one way to add meaning to the values.
Calling the runner.StartGame as a Host (GameMode = GameMode.Host) is enough to start a new session with a Random Name (as the SessionName argument was not passed) and by using the SessionProperties argument, Fusion will include those properties in the Session.

Join a Random Session with Filters

Considering the example code above, here it is shown how to start a Client that will join any Game Session on any GameMap, but with a specific GameType.
The startup code is basically the same, just the GameMode that is now set to GameMode.Client, and the customProps contains only the type key with the desired gameType value.

C#

public async Task StartClient(NetworkRunner runner, GameType gameType) {

  var customProps = new Dictionary<string, SessionProperty>() {
    { "type", (int)gameType }
  };

  var result = await runner.StartGame(new StartGameArgs() {
    GameMode = GameMode.Client,
    SessionProperties = customProps,
  });
  
  if (result.Ok) {
    // all good 
  } else {
    Debug.LogError($"Failed to Start: {result.ShutdownReason}");
  }
}

That is enough to make your client join a random Session with that specific GameType.

Join a Session from a Lobby

Another way to find the right Game Session is to provide a list of Sessions, allowing the player to choose one to join.
Joining a Lobby is the way to go in this case, although we highly suggest avoiding this method if it is really not necessary.
For most game types, joining a Session based on property filters is the best way, but Fusion makes Session listing pretty easy too.

Instead of using the usual flow and starting Fusion as described above, the Session listing follows a slightly different flow:

1. Join a Lobby: using a Fusion Runner reference, just call NetworkRunner.JoinSessionLobby([SessionLobby], [string]) in order to make the peer connect to the Photon Cloud and join a specific Lobby. This method receives two arguments:
   • SessionLobby: which can be one of the following values:
     1. ClientServer to join the default ClientServer Lobby;
     2. Shared to join the default Shared Lobby; and,
     3. Custom, used in conjunction with a custom LobbyName.
   • LobbyName: this should be a Custom Lobby Name used when creating a Game Session previously.

C#

// Utility method to Join the ClientServer Lobby
public async Task JoinLobby(NetworkRunner runner) {

  var result = await runner.JoinSessionLobby(SessionLobby.ClientServer);

  if (result.Ok) {
    // all good 
  } else {
    Debug.LogError($"Failed to Start: {result.ShutdownReason}");
  }
}

And as described before, it is possible for a Client to join the ClientServer, Shared or Custom lobbies this way.
Just as an example, it is shown below how a Server/Host can create a Session in a custom Lobby:

C#

public async Task StartHost(NetworkRunner runner) {

  var result = await runner.StartGame(new StartGameArgs() {
    GameMode = GameMode.Host,
    CustomLobbyName = "MyCustomLobby"
  });

  if (result.Ok) {
    // all good 
  } else {
    Debug.LogError($"Failed to Start: {result.ShutdownReason}");
  }
}

And how a Client can join that custom Lobby:

C#

// Utility method to Join a Custom Lobby
public async Task JoinLobby(NetworkRunner runner) {

  var result = await runner.JoinSessionLobby(SessionLobby.Custom, "MyCustomLobby");

  if (result.Ok) {
    // all good 
  } else {
    Debug.LogError($"Failed to Start: {result.ShutdownReason}");
  }
}

2. Get a list of Game Sessions: when working with Fusion, one of the main API entry points is the INetworkRunnerCallbacks, a special interface that Fusion uses to surface a series of different events, including the list of sessions from a Lobby. The OnSessionListUpdated(NetworkRunner runner, List<SessionInfo> sessionList) callback will be invoked with the complete list of Sessions from the Lobby every time the sessions change, either by the creation/removal of sessions or when the properties of a session are updated. The SessionInfo is of the same type described above. The list can then be shown, filtered, ordered, etc.

3. Join a Session: with a selected Session to join, Fusion can be started using the usual NetworkRunner.StartGame(), but in this case, the SessionName used to start the client must be the one from the Session. That way the Client will join that particular Game Session.

   • Select the right GameMode as usual, as the peer is joining the Session it must be either GameMode.Client or GameMode.Shared modes.
   • The SessionName field must be set to SessionInfo.Name, as this is the identifier of the Game Session.
   • All other parameters are optional and should be initialized accordingly.

C#

public class MyBehaviour : Fusion.Behaviour, INetworkRunnerCallbacks {

  // other callbacks...

  // Receive the List of Sessions from the current Lobby
  public void OnSessionListUpdated(NetworkRunner runner, List<SessionInfo> sessionList) {

    Debug.Log($"Session List Updated with {sessionList.Count} session(s)");

    // Example
    // Join first session from the list

    // Check if there are any Sessions to join
    if (sessionList.Count > 0) {

      // Get first Session from the list
      var session = sessionList[0];

      Debug.Log($"Joining {session.Name}");

      // Join
      runner.StartGame(new StartGameArgs() {
        GameMode = GameMode.Client, // Client GameMode, could be Shared as well
        SessionName = session.Name, // Session to Join
        // ...
      });
    }

    // OR

    // Example
    // Search the list for a Session with a specific Property

    // Store the target session
    SessionInfo session = null;

    foreach (var sessionItem in sessionList) {

      // Check for a specific Custom Property
      if (sessionItem.Properties.TryGetValue("type", out var propertyType) && propertyType.IsInt) {

        var gameType = (int)propertyType.PropertyValue;

        // Check for the desired Game Type
        if (gameType == 1) {

          // Store the session info
          session = sessionItem;
          break;
        }
      }
    }

    // Check if there is any valid session
    if (session != null) {
      Debug.Log($"Joining {session.Name}");

      // Join
      runner.StartGame(new StartGameArgs() {
        GameMode = GameMode.Client, // Client GameMode, could be Shared as well
        SessionName = session.Name, // Session to Join
        // ...
      });
    }
  }
}

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