Pseudo Authoritative Server Using Unity’s HLAPI

I was looking at Unity’s Simple Multiplayer Example. It’s rather easy to set up and runs pretty good. They mentioned it was an “authoritative server” which confused me because the client is the one deciding where it moves. I was hoping we could fix that somewhat by using clientMoveCallback3D.

The below code will take the client’s new position and check to make sure it’s not too far from its last known position on the server. We also check to make sure they haven’t moved inside anything. If they are too far or inside a wall, we’ll tell them to move back.

// Only called on one client
// Call if client was found in illegal spot
// Fix me: can this be abused?
[TargetRpc]
void TargetSetPosition(NetworkConnection target, Vector3 position)
{
    Debug.Log("Setting position to " + position);
    transform.position = position;
}

// Only called by the server
public bool ValidateMove(ref Vector3 position, ref Vector3 velocity, ref Quaternion rotation)
{
    if (position == transform.position) // Don't bother if they didn't move
        return true;

    // Did they move too far away?
    // Fix me: what if we want them to transport?
    // Fix me: what if they are falling?
    if (Vector3.Distance(transform.position, position) > 0.5f)
    {
        // Tell client to move to last known good position
        TargetSetPosition(connectionToClient, transform.position);
        return false;
    }

    // Are they moving inside anything?
    // Fix me: what if they're trapped inside something already?
    Collider[] colliders = Physics.OverlapBox(position, m_collider.bounds.extents);
    if (colliders.Length > 1)
    {
        // Tell client to move to last known good position
        TargetSetPosition(connectionToClient, transform.position);
        return false;
    }

    // Everything's good, accept client move
    return true;
}

If we return false on a ValidateMove, then the server will not update the client’s move and it won’t let other clients know about the new position either. The client that moved illegally will be in the new position on their computer, however. I’m using TargetRpcAttribute to tell the client to set themselves back to the old spot.

Here’s the updated PlayerController.cs:

using UnityEngine;
using UnityEngine.Networking;

public class PlayerController : NetworkBehaviour
{
    private Collider m_collider;
    private string m_log;

    void Start()
    {
        m_collider = GetComponent<Collider>();
    }

    // Get client input
    void FixedUpdate()
    {
        if (!isLocalPlayer)
            return;

        var x = Input.GetAxis("Horizontal") * Time.deltaTime * 150.0f;
        var z = Input.GetAxis("Vertical") * Time.deltaTime * 3.0f;
        if (Input.GetButton("Jump")) // Move fast like we're cheating
            z *= 10.0f;

        transform.Rotate(0, x, 0);
        // Don't move into things
        Collider[] colliders = Physics.OverlapBox(transform.TransformPoint(0, 0, z), m_collider.bounds.extents);
        if (colliders.Length == 1) // We'll always detect our own collider
            transform.Translate(0, 0, z);
    }

    // Only called on one client
    // Call if client was found in illegal spot
    // Fix me: can this be abused?
    [TargetRpc]
    void TargetSetPosition(NetworkConnection target, Vector3 position)
    {
        Debug.Log("Setting position to " + position);
        transform.position = position;
    }

    // Only called by the server
    public bool ValidateMove(ref Vector3 position, ref Vector3 velocity, ref Quaternion rotation)
    {
        if (position == transform.position) // Don't bother if they didn't move
            return true;

        // Did they move too far away?
        // Fix me: what if we want them to transport?
        // Fix me: what if they are falling?
        if (Vector3.Distance(transform.position, position) > 0.5f)
        {
            // Tell client to move to last known good position
            TargetSetPosition(connectionToClient, transform.position);
            return false;
        }

        // Are they moving inside anything?
        // Fix me: what if they're trapped inside something already?
        Collider[] colliders = Physics.OverlapBox(position, m_collider.bounds.extents);
        if (colliders.Length > 1)
        {
            // Tell client to move to last known good position
            TargetSetPosition(connectionToClient, transform.position);
            return false;
        }

        // Everything's good, accept client move
        return true;
    }

    public override void OnStartServer()
    {
        GetComponent<NetworkTransform>().clientMoveCallback3D = ValidateMove;
    }

    public override void OnStartLocalPlayer()
    {
        GetComponent<MeshRenderer>().material.color = Color.blue;

        // Hook up for Debug messages
        Application.logMessageReceived += HandleLog;
    }

    private void HandleLog(string condition, string stackTrace, LogType type)
    {
        if (type == LogType.Log)
        {
            if (m_log.Split('\n').Length > 20)
                m_log = "";
            m_log += "\n" + condition;
        }
    }

    public void OnGUI()
    {
        GUI.Label(new Rect(0, 0, Screen.width, Screen.height), m_log);
    }
}

If you know of a way to improve this, please let me know. Sample code at GitHub.