ChristianTucker

public class CharacterController : MonoBehaviour 
{
    private ClientInputState inputState;
    private Vector3 velocity = Vector3.zero;
    private int simulationFrame;
    
    private void Start()
    {
        NetworkClient.RegisterHandler<SimulationState>(OnServerSimulationStateReceived); 
    }

ChristianTucker

public class SimulationState : Message 
{
    public Vector3 position;
    public Vector3 velocity;
    public int simulationFrame;
}

ChristianTucker

public class ClientInputState : Message 
{
    public List<KeyCode> keysPressed;
    public List<KeyCode> keysDown;
    public List<KeyCode> keysReleased;
    public int simulationFrame; 
}

ChristianTucker

// Psuedo implementation to send data to a client. 
NetworkServer.SendToClient(NetworkConnection connection, Message message);

// Psuedo implementation to send data to the server.  
NetworkClient.Send(Message message);

// Psuedo implementation to register incoming message handlers.
NetworkClient.RegisterHandler<T>(Action<NetworkConnection, T> handler);
NetworkServer.RegisterHandler<T>(Action<NetworkConnection, T> handler);