FOnlineSessionNull::RegisterPlayers Fails to Update Session State When Session Name is Not "Game"

Development Programming & Scripting Multiplayer & Networking
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The null subsystem includes code for updating certain session state in RegisterPlayers. It updates thing like NumOpenPublicConnections which is how I found the bug.

Reproduction steps

  1. Setup a multiplayer project with the NULL subsystem.
  2. Create a session with any name but “Game”.
  3. Find the session from another game instance.
  4. Notice that the session that comes back will have NumOpenPublicConnections == SessionSettings.NumPublicConnections

Reason for the behaviour

The calling code for RegisterPlayers up the hierarchy is APlayerState::RegisterPlayerWithSession. This gets a default PlayerState with GetDefault<APlayerState>(). Apparently, this session name is not set to the actual session this player is trying to join. This does not seem like intended behaviour.

Suggested fix

The SessionName passed to UOnlineEngineInterface::Get()->RegisterPlayer() should be populated from the actual session name that we are trying to join, not the PlayerState default.

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