Sprinting Into Wall Causes Anti-Cheat Flagging

[lowercasebtw]

General Information

https://dump.viaversion.com/34ef146dd45671d8eabd0aab9f7b9bb35e96c1eaf34621bc4eabd3c1a6134a8f

Bug Description

In 1.8 and below, when sprinting into a wall, it flags anticheat GrimAC.

Steps to Reproduce

Join eu.loyisa.cn w/ version 1.8
Go to a block, spam W (w/ toggle sprint enabled, also happens even without toggle sprint)

Expected Behavior

No flagging

[Exterminate5573]

BadPacketsX seems to flag due to duplicate packets

    public void onPacketReceive(PacketReceiveEvent event) {
        if (player.gamemode == GameMode.SPECTATOR || isTickPacket(event.getPacketType())) {
            sprint = sneak = false;
            return;
        }

        if (event.getPacketType() == PacketType.Play.Client.ENTITY_ACTION) {
            switch (new WrapperPlayClientEntityAction(event).getAction()) {
                case START_SNEAKING, STOP_SNEAKING -> {
                    if (sneak) {
                        if (player.canSkipTicksPreVia() || flagAndAlert()) {
                            flags++;
                        }
                    }

                    sneak = true;
                }
                case START_SPRINTING, STOP_SPRINTING -> {
                    if (player.inVehicle()) {
                        return;
                    }

                    if (sprint) {
                        if (player.canSkipTicksPreVia() || flagAndAlert()) {
                            flags++;
                        }
                    }

                    sprint = true;
                }
            }
        }
    }

[FlorianMichael]

Yeah, it's multiple actions in one tick. The other BadPackets check is checking for very close position updates. My assumption was sendMovementPackets() or tick() inside the ClientPlayerEntity to be called too often?

[Exterminate5573]

I may have found the cause for this

Latest:

        profiler.push("rest");
        boolean bl = !MathHelper.approximatelyEquals(movement.x, vec3d.x);
        boolean bl2 = !MathHelper.approximatelyEquals(movement.z, vec3d.z);
        this.horizontalCollision = bl || bl2;

17w46a (Pre-Collision change)

        this.world.profiler.push("rest");
        this.setPositionFromShape();
        this.collidingHorizontally = n != x || p != z;

This is in the Entity Class under the move func

[lowercasebtw]

Looks interesting even if it doesn’t fix it, should probably still be fixed / added if not already

[Exterminate5573]

I just did some testing with viaproxy and was unable to flag BadPacketsX even on latest, it's definitely a VFP change that is causing the flag.

[FlorianMichael]

Oh well, that's bad lol

[FlorianMichael]

I may have found the cause for this

Latest:

        profiler.push("rest");
        boolean bl = !MathHelper.approximatelyEquals(movement.x, vec3d.x);
        boolean bl2 = !MathHelper.approximatelyEquals(movement.z, vec3d.z);
        this.horizontalCollision = bl || bl2;

17w46a (Pre-Collision change)

        this.world.profiler.push("rest");
        this.setPositionFromShape();
        this.collidingHorizontally = n != x || p != z;

This is in the Entity Class under the move func

Seems important, but it doesn't seem to fix the issue sadly. Still would be good to add