Online Subsystem Steam

The Online Subsystem Steam API enables you to ship Unreal Engine 4 (UE4) applications to Valve's Steam platform. The main purpose of the Steam module is to help you distribute your application with a set of features (such as matchmaking and leaderboards) to Steam users. Additionally, the Steam module implements several of the interfaces being exposed by the Online Subsystem, supporting most of what is offered by the Steamworks Software Development Kit (SDK).

Some of the available Steam Interfaces include:

• Matchmaking (Lobbies and GameServer APIs)
• Leaderboards
• Achievements
• Voice
• UserCloud
• SharedCloud
• External UI

Meeting Valve's Requirements

The Steam Subsystem requires additional setup through Valve Steamworks. Please contact Valve and reference their Steamworks SDK Documentation to make sure that your application meets Valve's requirements before attempting to use Steam with UE4.

Downloading Steamworks

If your application meets Valve's requirements, go ahead and download the latest version of the Steamworks SDK. The SDK needs to be unzipped and copied to /YourUnrealEnginePath/Engine/Source/ThirdParty/Steamworks/Steam[Current Version]/sdk

Compiling UE4

If you're compiling Unreal Engine 4 from source, the following steps should be taken:

1. Open "OnlineSubsystemSteamPrivatePCH.h" (located in "..\..\Plugins\Online\OnlineSubsystemSteam\Source\Private\"), where you'll find the following line of code, defining the root location of the Steamworks SDK:

   #define STEAM_SDK_ROOT_PATH TEXT("Binaries/ThirdParty/Steamworks")
   	

2. You'll want to modify the line to read:

   #define STEAM_SDK_VER TEXT("Steam[Current Version]")
   	

Setting up the Steamworks SDK

Using Steam against the precompiled version of the engine should only require copying some of the dynamically linked libraries (*.dll) from Valve's SDK into the appropriate folders. If you intend to recompile the engine against the source, putting the SDK in the right place is required as well. Now, copy the relevant redistributable files from the /redistributable_bin/ directory of the SDK to the following locations:

Steam App ID

All games using the Steam Online Subsystem must have a valid application ID because the Steamworks API won't initialize if it doesn't know your application's Steam App ID. Before initializing Steam, UE4 will generate steam_appid.txt (during a graceful shutdown of the engine, UE4 deletes this file). It's important to note that steam_appid.txt must be located in the same directory as your application's executable file because Steam will look for the text file in the current working directory. Additionally, the file should not be included in any Steam images.

If you open steam_appid.txt, you'll see a SteamDevAppId entry, which is a field that hints your application's ID to Steam. This makes it unnecessary to launch the game using the Steam client (although it must be running).

Shipping Builds

In shipping builds, the engine will check to make sure that the logged-in user is properly subscribed to the game and will shutdown if the engine's test returns false (this is one way to help secure the game). Additionally, using Steam DRM (see the Steamworks SDK) should further protect the game from being tampered with.

Configuring your Application's Settings

Now that you've set up the Steamworks SDK for your application (along with setting up the Steam App ID), you're ready to configure your application's settings to use Online Subsystem Steam.

Steps

1. Open your project's DefaultEngine.ini file and add the following setting:

   [/Script/Engine.GameEngine]
   +NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemSteam.SteamNetDriver",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")
   	

   NetDriverDefinitions describes the net drivers available to UE4 with the following properties being defined:
   • DefName is the unique name of this net driver definition.
   • DriverClassName is the class name of the primary net driver.
   • DriverClassNameFallBack is the class name of the fallback net driver if the primary net driver class fails to initialize.
2. To tell UE4 to use Online Subsystem Steam, add the following setting:

   [OnlineSubsystem]
   DefaultPlatformService=Steam
   	

3. Now that you've told UE4 that you want your application to use the Steam Online Subsystem, you'll need to configure the OnlineSubsystemSteam module by adding the following settings:

   [OnlineSubsystemSteam]
   bEnabled=true
   SteamDevAppId=480
   	

4. Finally, you'll want to specify the Steam class to the Net Driver for the application's connections:

   [/Script/OnlineSubsystemSteam.SteamNetDriver]
   NetConnectionClassName="OnlineSubsystemSteam.SteamNetConnection"
   	

End Result

At the end of this brief guide, your application's DefaultEngine.ini file should look like the following setting block. If you want to see how other projects set up and use the Online Subsystem, please refer to our library of Sample Projects.

Finished Settings

DefaultEngine.ini

[/Script/Engine.GameEngine]
+NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemSteam.SteamNetDriver",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")

[OnlineSubsystem]
DefaultPlatformService=Steam

[OnlineSubsystemSteam]
bEnabled=true
SteamDevAppId=480

[/Script/OnlineSubsystemSteam.SteamNetDriver]
NetConnectionClassName="OnlineSubsystemSteam.SteamNetConnection"

Steam Online Authentication

Enabling SteamAuth

To enable SteamAuth, add the following to "DefaultEngine.ini", or to the platform-specific engine .ini file (such as "WindowsEngine.ini", "LinuxEngine.ini", or "MacEngine.ini") for each platform that is intended to support Steam Online Authentication:

[PacketHandlerComponents]
+Components=OnlineSubsystemSteam.SteamAuthComponentModuleInterface

Once enabled, the Steam Online Subsystem interface (SteamOSS) function, GetAuthInterface, can be used to access SteamAuth functionality.

SteamAuth Delegates

There are two Delegates in the SteamAuth system that developers may wish to override: OverrideFailureDelegate and OnAuthenticationResultDelegate.

OverrideFailureDelegate is called with the FUniqueNetId of a player when that player attempts to join the server without Steam authentication, or when that player loses Steam authentication during the session. By default, SteamAuth will kick the player from the game. However, if this Delegate is bound, the default behavior will be suspended, so developers will have to kick the player manually if that behavior is still desired.

OnAuthenticationResultDelegate handles responses from Steam's authentication service, providing the FUniqueNetId of the player and a boolean indicating whether the authentication attempt succeeded.

Additional Notes

Module Setup

Make sure to include the Unreal Engine Steam module as part of your project (see UnrealBuildTool Target Files for additional help). Specifically, adding the following line in the construtor for mygame.build.cs should be enough to make sure that the Steam module is built along with your game.

DynamicallyLoadedModuleNames.Add("OnlineSubsystemSteam");