fix noslow with invalid drop item packets

Author: ManInMyVan

common/src/main/java/ac/grim/grimac/checks/Check.java

@@ -8,6 +8,7 @@
 import com.github.retrooper.packetevents.protocol.packettype.PacketType;
 import com.github.retrooper.packetevents.protocol.packettype.PacketTypeCommon;
 import com.github.retrooper.packetevents.protocol.player.ClientVersion;
+import com.github.retrooper.packetevents.protocol.player.DiggingAction;
 import lombok.Getter;
 import lombok.Setter;
 import org.jetbrains.annotations.NotNull;
@@ -207,4 +208,10 @@ public boolean isTickPacketIncludingNonMovement(PacketTypeCommon packetType) {
         return isFlying(packetType);
     }
 
+    // prevent causing exploits with packet cancelling (ie noslow)
+    public boolean canCancel(DiggingAction action) {
+        return action != DiggingAction.RELEASE_USE_ITEM
+                // we check client version here because 1.8- doesn't predict dropping items, so we can cancel them. (see CompensatedInventory)
+                && (action != DiggingAction.DROP_ITEM && action != DiggingAction.DROP_ITEM_STACK || player.getClientVersion().isOlderThanOrEquals(ClientVersion.V_1_8));
+    }
 }

common/src/main/java/ac/grim/grimac/checks/impl/badpackets/BadPacketsL.java

@@ -43,7 +43,7 @@ public void onPacketReceive(PacketReceiveEvent event) {
                         + ", face=" + packet.getBlockFace()
                         + ", sequence=" + packet.getSequence()
                         + ", action=" + packet.getAction().toString().toLowerCase(Locale.ROOT)
-                ) && shouldModifyPackets() && packet.getAction() != DiggingAction.RELEASE_USE_ITEM) {
+                ) && shouldModifyPackets() && canCancel(packet.getAction())) {
                     event.setCancelled(true);
                     player.onPacketCancel();
                 }

common/src/main/java/ac/grim/grimac/checks/impl/packetorder/PacketOrderF.java

@@ -7,7 +7,6 @@
 import ac.grim.grimac.utils.anticheat.update.PredictionComplete;
 import com.github.retrooper.packetevents.event.PacketReceiveEvent;
 import com.github.retrooper.packetevents.protocol.packettype.PacketType;
-import com.github.retrooper.packetevents.protocol.player.DiggingAction;
 import com.github.retrooper.packetevents.wrapper.play.client.WrapperPlayClientClientStatus;
 import com.github.retrooper.packetevents.wrapper.play.client.WrapperPlayClientPlayerDigging;
 
@@ -42,7 +41,7 @@ && new WrapperPlayClientClientStatus(event).getAction() == WrapperPlayClientClie
             if (!player.canSkipTicks()) {
                 if (flagAndAlert(verbose) && shouldModifyPackets()) {
                     if (event.getPacketType() == PacketType.Play.Client.PLAYER_DIGGING
-                            && new WrapperPlayClientPlayerDigging(event).getAction() == DiggingAction.RELEASE_USE_ITEM
+                            && !canCancel(new WrapperPlayClientPlayerDigging(event).getAction())
                     ) return; // don't cause a noslow
 
                     event.setCancelled(true);

common/src/main/java/ac/grim/grimac/checks/impl/packetorder/PacketOrderG.java

@@ -48,7 +48,7 @@ && new WrapperPlayClientClientStatus(event).getAction() == WrapperPlayClientClie
                         + ", picking=" + player.packetOrderProcessor.isPicking()
                         + ", digging=" + player.packetOrderProcessor.isDigging();
                 if (!player.canSkipTicks()) {
-                    if (flagAndAlert(verbose) && shouldModifyPackets()) {
+                    if (flagAndAlert(verbose) && shouldModifyPackets() && canCancel(action)) {
                         event.setCancelled(true);
                         player.onPacketCancel();
                     }

common/src/main/java/ac/grim/grimac/events/packets/PacketPlayerDigging.java

@@ -1,7 +1,6 @@
 package ac.grim.grimac.events.packets;
 
 import ac.grim.grimac.GrimAPI;
-import ac.grim.grimac.checks.impl.movement.NoSlow;
 import ac.grim.grimac.player.GrimPlayer;
 import ac.grim.grimac.utils.item.ItemBehaviour;
 import ac.grim.grimac.utils.item.ItemBehaviourRegistry;