False Positive: SurvivalFly when walking with right clicked (charged) spear

[Phoenix616]

Complete output of the ncp version command (please prefer text here)

[15:48:59 INFO]: »Version information«
[15:48:59 INFO]: Server:
[15:48:59 INFO]: 1.21.11-100-4873e3f ~MC: 1.21.11~
[15:48:59 INFO]: Detected: 1.21.11
[15:48:59 INFO]: NoCheatPlus:
[15:48:59 INFO]: Plugin: 3.17.1-SNAPSHOT-Updated-2026_02_02-14_40
[15:48:59 INFO]: MCAccess: 1.13-1.21 / Bukkit-API
[15:48:59 INFO]: Features:
[15:48:59 INFO]: blocks: BlocksMC1_4, BlocksMC1_5, BlocksMC1_6_1, BlocksMC1_7_2, BlocksMC1_8, BlocksMC1_9, BlocksMC1_10, BlocksMC1_11, BlocksMC1_12, BlocksMC1_13, BlocksMC1_14, BlocksMC1_15, BlocksMC1_16, BlocksMC1_17, BlocksMC1_19, BlocksMC1_20, BlocksMC1_21, MCAccessBukkitModern
[15:48:59 INFO]: checks: HotFixFallingBlockPortalEnter
[15:48:59 INFO]: defaults: pvpKnockBackVelocity
[15:48:59 INFO]: Hooks:
AllViolations~NCP~ 1.0, ViolationFrequency~NCP~ 1.1
[15:48:59 INFO]: »Related Plugins«
[15:48:59 INFO]: ProtocolLib v5.2.1-SNAPSHOT-689, ViaVersion v5.4.1

Server is Paper 1.21.11 b100, plugin is built from the latest source state

Short description of the issue and how to reproduce (is it random / always happens / side conditions ?)

Charging spear (holding right click) causes SurvivalFly violations and setbacks even though walking with it charged should be allowed (that's the whole point of it, running/walking/riding into entities to do damage)

Have you made any (noteworthy) changes to the default configuration of NCP?

No, default config generated from latest version

Do you run any other special plugins that affect game mechanics next to NC+ (skills, machines, adding/changing blocks, other anti-cheating)?

No.

Provide additional information: for bypasses, vulnerabilities and reproducible issues, we request a debug log. Use GitHub gists or PasteBin or similar for errors and huge logs, or attach a (zip-) file here.

https://gist.github.com/Phoenix616/ca40aa6c1b9de841cc65fde7d09dacbb

[Phoenix616]

The reason for this seems to be that the itemInUse is null in the PlayerData which is used to check for whether the player is getting slowed down in BridgeMisc#isSlowedDownByUsingAnItem

[Phoenix616]

Ok, looks like that should be using Player#getItemInUse like the isUsingItem method (as the manual tracking seems to not have been necessary since 1.17). I will PR my fix but I noticed another false positive with trying to sprint while the spear is charged after applying that fix so will look into that too.

[Phoenix616]

I'm not 100% sure what's causing the sprint bug but it seems to be related to the estimated hAllowedDistance distance being lower than the actual distance (not sure why the spear influences that when the speed is the same as normal sprinting). I tracked the values it's using down to the part in SurvivalFly which add the acceleration vector to the momentum but the source might be further up (didn't see anything obvious to using items though).

I assume there is a place where it checks for item usage instead of using the slow down check before that which sets the wrong expected movement vector.

[Phoenix616]

Can't really figure out the second issue unfortunately :S Will PR my current state to at least fix this issue right here and then open a new issue one with debug logs if I can't find anything in the next couple days.

[Lysandr0]

Gonna keep the issue open as spear handling isn't properly implemented yet.
I've pieced together the logic/functions for the lunging mechanic but I haven't had the time to fully study nms code.
From what I've understood and observed on the server-side, left clicking with a spear in hand won't slow the player down like it normally happens with any other item, although I haven't been able to spot this exemption in NMS; just from empirical testing.

NoCheatPlus/NCPCore/src/main/java/fr/neatmonster/nocheatplus/checks/combined/CombinedListener.java

Lines 416 to 430 in ddb128d

	@EventHandler(priority = EventPriority.MONITOR)
	public void onLeftClickingBlocksOrAir(final PlayerInteractEvent event) {
	final Player player = event.getPlayer();
	if (event.getAction() != Action.LEFT_CLICK_AIR && event.getAction() != Action.LEFT_CLICK_BLOCK) {
	return;
	}
	if (BridgeMisc.mayLungeForward(player)) {
	final IPlayerData pData = DataManager.getPlayerData(player);
	final PlayerMoveData thisMove = pData.getGenericInstance(MovingData.class).playerMoves.getCurrentMove();
	thisMove.lungingForward = true;
	if (pData.isDebugActive(CheckType.MOVING)) {
	debug(player, "Set lunging forward flag in this move.");
	}
	}
	}

If the spear is released and has Lunge, the player will lunge forward horizontally (but not vertically(!)):

NoCheatPlus/NCPCore/src/main/java/fr/neatmonster/nocheatplus/utilities/location/PlayerLocation.java

Lines 245 to 264 in 959f815

	/**
	* From {@code ApplyEntityImpulse.java} and {@code Enchantments.java}.<br>
	* Gets the lunging motion vector for the player.
	* @return
	*/
	public Vector tryApplyLungingMotion() {
	// (same as entity.getLookAngle() in vanilla).
	Vector lookVec = TrigUtil.getLookingDirection(getLocation(), player);
	// Convert local direction to world coordinates using player's rotation.
	// TODO: ISSUE: this eye loc isn't updated to split moves!
	Location eye = player.getEyeLocation();
	float pitch = eye.getPitch();
	float yaw = eye.getYaw();
	Vector worldLocal = TrigUtil.applyLocalCoordinatesToRotation(pitch, yaw, new Vector(0.0, 0.0, 1.0)); // The new Vector represents the Local direction (0,0,1)
	// sum = lookVec + worldLocal
	Vector sum = lookVec.clone().add(worldLocal);
	// Multiply with coordinateScale (vec3 1.0,0.0,1.0): x *= sx, y *= sy, z *= sz
	Vector scaled = new Vector(sum.getX() * 1.0, sum.getY() * 0.0, sum.getZ() * 1.0);
	// final delta, scaled to magnitude level
	return scaled.multiply(0.458 * BridgeEnchant.getLungeLevel(player));

The function might be wrong.
There's also the issue of the lunging sequence in the movement processing pipeline, which is likely not correct.

NoCheatPlus/NCPCore/src/main/java/fr/neatmonster/nocheatplus/checks/moving/player/SurvivalFly.java

Lines 1147 to 1154 in ddb128d

	// Lunging forward if applicable: the effect only adds the lunging motion on the current delta.
	// TODO: TOTALLY RANDOM PLACEMENT !
	// The addition is called on any left click, provided the player has a Spear in hand with Lunge enchant.
	// NOTE: Does not need to be brute forced, since lunging is supported only by clients that can send WASD inputs.
	if (thisMove.lungingForward) {
	Vector lungeVelocity = to.tryApplyLungingMotion(); // Use to as we're working with rotations here
	thisMove.xAllowedDistance += lungeVelocity.getX();
	thisMove.zAllowedDistance += lungeVelocity.getZ();