Cheat detector for platform-like games in VRChat.

JLChnToZ.VRC.CheatDetector.cs

using System;
using UdonSharp;
using UnityEngine;
using VRC.SDKBase;
using VRC.Udon;

namespace JLChnToZ.VRC {
    [UdonBehaviourSyncMode(BehaviourSyncMode.NoVariableSync)]
    public class CheatDetector : UdonSharpBehaviour {
        [Tooltip("Detects open menu stucking cheat.")]
        [SerializeField] bool menuCheatDetect = true;
        [Tooltip("Interval of actively challenges player opening main menu, 0 to disable.")]
        [SerializeField] float menuCheatCheckInterval = 5;

        [Space, Tooltip("Detects flying avatar. Requires a non-kinematic rigidbody and a slightly downward offsetted small collider attached to this game object.")]
        [SerializeField] bool flyingAvatarDetect = true;

        [Space, Tooltip("Game objects with udons that wants to know if player is flying, will send OnFlyingDetected custom event to them when detected. If you are using U#, you can use RegisterCallback(this) instead.")]
        [SerializeField] GameObject[] callbackGameObjects;
        Component[] callbacks;
        new Rigidbody rigidbody;
        VRCPlayerApi localPlayer;
        Vector3 lastPosition;
        int menuHackForgiveness;
        float menuHackStrictForgiveness;

        void Start() {
            if (callbackGameObjects != null)
                foreach (var callbackGO in callbackGameObjects) {
                    var udonBehaviours = callbackGO.GetComponents(typeof(UdonBehaviour));
                    if (udonBehaviours.Length == 0) continue;
                    if (callbacks == null || callbacks.Length == 0) {
                        callbacks = udonBehaviours;
                        continue;
                    }
                    var temp = new Component[callbacks.Length + udonBehaviours.Length];
                    Array.Copy(callbacks, temp, callbacks.Length);
                    Array.Copy(udonBehaviours, 0, temp, callbacks.Length, udonBehaviours.Length);
                    callbacks = temp;
                }
        }

        void OnEnable() {
            Debug.Log("[Cheat Detector] Start initialize cheat detector.");
            if (flyingAvatarDetect) {
                if (rigidbody == null) rigidbody = GetComponent<Rigidbody>();
                rigidbody.isKinematic = false;
                rigidbody.freezeRotation = true;
                rigidbody.mass = 0.00001F; // Extra low mass to minimize affects on other on scene physic objects.
            }
            menuHackForgiveness = 0;
            menuHackStrictForgiveness = 0;
            lastPosition = new Vector3(float.NaN, float.NaN, float.NaN);
            Debug.Log("[Cheat Detector] Initialize completed, start detecting cheats.");
        }

        void OnDisable() {
            Debug.Log("[Cheat Detector] Cheat detector disabled.");
            if (flyingAvatarDetect) {
                rigidbody.isKinematic = true;
            }
        }

        void FixedUpdate() {
            if (!Utilities.IsValid(localPlayer)) return;
            var position = localPlayer.GetPosition();
            var velocity = localPlayer.GetVelocity();
            var deltaTime = Time.fixedUnscaledDeltaTime;

            // Menu hack detection
            if (menuCheatDetect) {
                if (position == lastPosition) {
                    // If player stays at the exact same position but it is not grounded for certain amount of time, ban!
                    if (!localPlayer.IsPlayerGrounded()) {
                        if(++menuHackForgiveness > 5)
                            FlyingDetected();
                    } else {
                        // Actively challenges player to set velocity, if grounded state is still setted afterwards, ban!
                        if (menuCheatCheckInterval > 0 && (menuHackStrictForgiveness += deltaTime) >= menuCheatCheckInterval) {
                            localPlayer.SetVelocity(velocity);
                            if (localPlayer.IsPlayerGrounded())
                                FlyingDetected();
                            menuHackStrictForgiveness = 0;
                        }
                        menuHackForgiveness = 0;
                    }
                } else {
                    menuHackForgiveness = 0;
                    menuHackStrictForgiveness = 0;
                }
                lastPosition = position;
            }

            // Flying avatar detector update position
            if (flyingAvatarDetect) {
                if (velocity.y < 0) position += new Vector3(0, velocity.y * deltaTime, 0);
                transform.position = position;
                rigidbody.position = position;
                rigidbody.velocity = Vector3.zero;
            }
        }

        public void RegisterCallback(UdonSharpBehaviour ub) {
            if (callbacks == null || callbacks.Length == 0) {
                callbacks = new [] { ub };
                return;
            }
            var temp = new Component[callbacks.Length + 1];
            Array.Copy(callbacks, temp, callbacks.Length);
            temp[callbacks.Length] = ub;
            callbacks = temp;
        }

        public override void OnPlayerJoined(VRCPlayerApi player) {
            if (player.isLocal) localPlayer = player;
        }

        // Flying avatar detection: If any extra non-trigger colliders under the player's capsule, ban!
        public override void OnPlayerCollisionEnter(VRCPlayerApi player) {
            if (flyingAvatarDetect && player == localPlayer) FlyingDetected();
        }

        void FlyingDetected() {
            Debug.Log("[Cheat Detector] <color=#FF0000>Flying detected!</color>");
            if (callbacks != null)
                foreach (var ub in callbacks)
                    ((UdonBehaviour)ub).SendCustomEvent("OnFlyingDetected");
        }
    }
}