Atto Server

Table of Contents

• Dependencies
• Features
• Supported Online Subsystem interfaces
• Configuration
• Futher development ideas
• Command-line options
• Usage scenario
• Why not just use Steam OSS?

Atto is an Unreal Engine plugin that implements a minimalistic backend / meta service.

Important

Atto is not intended for high-load production use. Also, Atto server API can be exploited to break things. Project goal is just to have a meta service for early game development.

Atto aims to be fully compatible with Unreal Engine Online Subsystems, so you should not need to write Atto-specific code in your game. If you do have for some reason, either you’re using OSS API wrong, or there could be a bug in Atto. If you’re sure it’s the latter, consider reporting it to Atto issue tracker.

Dependencies

This project relies on C++20 features. Tested against Unreal Engine 5.5.

Features

• Auto-starts in editor, so it is immediately available for PIE

• Provides online subsystem implementation

• Zero cloud dependencies

• Absolutely free and open-source

Supported Online Subsystem interfaces

• Identity. Authentication is just a stub, it accepts any login/password pair if they are equal.

• Sessions: create, start, end, destroy, find, start/cancel matchmaking

• Time service

Configuration

Put Atto plugin into Plugins directory of your game.

Set Atto as default online subsystem:

Config/DefaultEngine.ini

[OnlineSubsystem]
DefaultPlatformService=Atto

Add login credentials for PIE:

Config/EditorPerProjectUserSettings.ini

[/Script/OnlineSubsystemUtils.OnlinePIESettings]
bOnlinePIEEnabled=True
+Logins=(Id="user1",Type="Atto",TokenBytes=(227,203,173,173,239,219,173,172,239,143,173,222,239,0,0,0))
+Logins=(Id="user2",Type="Atto",TokenBytes=(227,203,173,173,239,219,173,172,239,140,173,222,239,190,173,222))
+Logins=(Id="user3",Type="Atto",TokenBytes=(227,203,173,173,239,219,173,172,239,141,173,222,239,0,0,0))
+Logins=(Id="user4",Type="Atto",TokenBytes=(227,203,173,173,239,219,173,172,239,138,173,222,239,190,173,222))

Futher development ideas

• Persistent data storage

• Implement more OSS interfaces

• Add OnlineServices implementation

• Add API for game-specific logic

Command-line options

-DisableAttoServer

Disables Atto server in cases where it would normally start (for example, in editor).

-EnableAttoServer

Enables Atto server in cases where it would normally not start (for example, game client)

-AttoListenPort=27777

Specifies network port for Atto server

-AttoBindAddress=0.0.0.0

Specifies bind address for Atto server

-AttoUrl=ws://localhost:27777

Specifies Atto server address to connect to

-AttoPublicAddress=<ip_address>

When creating online session, this parameter allows specifying which IP address it will announce for incoming connections

-AttoPublicPort=<port>

When creating online session, this parameter allows specifying which network port it will announce for incoming connections

Usage scenario

Suppose, you want to start a separate Atto server, connect one or more dedicated servers to it and one or more game clients.

First, create client and dedicated server builds of your game.

Now, start Atto server:

$ ./Binaries/<PLATFORM>/<PROJECT_NAME>Server AttoServer -EnableAttoServer -log

You may pass additional command-line options to configure it.

Verify that Atto server is listening to incoming connections by looking for a relevant log entry:

LogAtto: Atto Server started accepting connections on :27777

Next, start dedicated server instance:

$ ./Binaries/<PLATFORM>/<PROJECT_NAME>Server <YOUR_GAME_MAP> -AttoUrl=ws://localhost:27777 -log

Atto plugin provides a reference AttoGame map with BP_AttoGame game mode that uses AttoGameSession class. AttoGameSession auto-creates online session when map is loaded and destroys when map is unloaded. Alternatively, you will need to manage online session in your game code.

You might need to alter -AttoUrl=…​ argument if your Atto server is running on a different port or machine.

Ensure that dedicated server has properly connected to Atto server and created online session by looking for a relevant entry in dedicated server logs:

LogOnline: OSS: Atto server url: ws://localhost:27777
LogOnline: OSS: Created online subsystem instance for: Atto
LogOnline: OSS: TryLoadSubsystemAndSetDefault: Loaded subsystem for type [Atto]
...
LogAtto: Creating game session: GameSession
LogAtto: OnCreateSessionComplete GameSession bSuccess: 1

Finally, start your game client:

$ ./Binaries/<PLATFORM>/<PROJECT_NAME> -AttoUrl=ws://localhost:27777

You might need to alter -AttoUrl=…​ argument if your Atto server is running on a different port or machine.

Ensure that client has properly connected to Atto server by looking for a relevant entry in client server logs:

LogOnline: OSS: Atto server url: ws://localhost:27777
LogOnline: OSS: Created online subsystem instance for: Atto
LogOnline: OSS: TryLoadSubsystemAndSetDefault: Loaded subsystem for type [Atto]
...
LogOnline: OSS: Successfully logged into Atto server, userId=<value>

What’s next?

You can use AdvancedSessions plugin or built-in Online Subsystem blueprint nodes or just use OnlineSubsystem from C++.

Why not just use Steam OSS?

• Because it doesn’t allow to run multiple game instances on the same computer simultaneously

• Because it expects dedicated server to have public IP address

• Because it is nontrivial to run multiple dedicated servers on the same machine

• Because it doesn’t work in PIE