More skipping conditions for "set back on tick".

* The player is at the coordinates.
* The last received ACK for an outgoing teleport has been received on
packet level. This is experimental, to be confirmed to a) do something
b) not allow abuse.

NCPCore/src/main/java/fr/neatmonster/nocheatplus/checks/moving/MovingData.java

@@ -45,6 +45,7 @@
 import fr.neatmonster.nocheatplus.compat.blocks.changetracker.BlockChangeReference;
 import fr.neatmonster.nocheatplus.components.data.ICanHandleTimeRunningBackwards;
 import fr.neatmonster.nocheatplus.components.entity.IEntityAccessDimensions;
+import fr.neatmonster.nocheatplus.components.location.IGetPosition;
 import fr.neatmonster.nocheatplus.components.location.IPositionWithLook;
 import fr.neatmonster.nocheatplus.utilities.CheckUtils;
 import fr.neatmonster.nocheatplus.utilities.TickTask;
@@ -740,6 +741,20 @@ public boolean isTeleportedPosition(final Location loc) {
         return loc != null && teleported != null && TrigUtil.isSamePos(teleported, loc);
     }
 
+    /**
+     * Check if the given location has the same coordinates like the
+     * 'teleported' (set back) location. This is more light-weight and more
+     * lenient than isTeleported, because world and yaw and pitch are all
+     * ignored.
+     * 
+     * @param loc
+     * @return In case of either loc or teleported being null, false is
+     *         returned, otherwise TrigUtil.isSamePos(pos, teleported).
+     */
+    public boolean isTeleportedPosition(final IGetPosition pos) {
+        return pos != null && teleported != null && TrigUtil.isSamePos(pos, teleported);
+    }
+
     /**
      * Set teleport-to location to recognize NCP set backs. This copies the coordinates and world.
      * @param loc

NCPCore/src/main/java/fr/neatmonster/nocheatplus/checks/net/model/TeleportQueue.java

@@ -49,6 +49,7 @@ public static enum AckResolution {
     private long maxAge = 4000; // TODO: configurable
     private int maxQueueSize = 60; // TODO: configurable
 
+    private CountableLocation lastAck = null;
 
     /**
      * Maximum age in milliseconds, older entries expire.
@@ -57,13 +58,18 @@ public static enum AckResolution {
     public long getMaxAge() {
         return maxAge;
     }
+
+    public CountableLocation getLastAck() {
+        return lastAck;
+    }
 
     /**
      * Call for Bukkit events (expect this packet to be sent).
      * @param packetData
      */
     public void onTeleportEvent(final double x, final double y, final double z, final float yaw, final float pitch) {
         lock.lock();
+        lastAck = null;
         expectOutgoing = new DataLocation(x, y, z, yaw, pitch);
         lock.unlock();
     }
@@ -174,6 +180,7 @@ else if (packetData.isSameLocation(ref)) {
                 if (--ref.count <= 0) { // (Lots of safety margin.)
                     expectIncoming.removeFirst(); // Do not use the iterator here.
                 }
+                lastAck = ref;
                 return AckResolution.ACK;
             }
             else {

NCPCore/src/main/java/fr/neatmonster/nocheatplus/utilities/TickTask.java

@@ -26,14 +26,19 @@
 import java.util.concurrent.locks.ReentrantLock;
 
 import org.bukkit.Bukkit;
+import org.bukkit.Location;
 import org.bukkit.entity.Player;
 import org.bukkit.plugin.Plugin;
 
 import fr.neatmonster.nocheatplus.checks.CheckType;
 import fr.neatmonster.nocheatplus.checks.ViolationData;
 import fr.neatmonster.nocheatplus.checks.access.ICheckData;
 import fr.neatmonster.nocheatplus.checks.combined.Improbable;
+import fr.neatmonster.nocheatplus.checks.moving.MovingConfig;
 import fr.neatmonster.nocheatplus.checks.moving.MovingData;
+import fr.neatmonster.nocheatplus.checks.moving.player.PlayerSetBackMethod;
+import fr.neatmonster.nocheatplus.checks.net.NetData;
+import fr.neatmonster.nocheatplus.checks.net.model.CountableLocation;
 import fr.neatmonster.nocheatplus.compat.BridgeMisc;
 import fr.neatmonster.nocheatplus.components.registry.feature.TickListener;
 import fr.neatmonster.nocheatplus.logging.StaticLog;
@@ -648,6 +653,10 @@ public static void reset() {
     }
 
     // Instance methods (meant private).
+
+    /** Temporary use only, beware of nesting. Cleanup with setWorld(null). */
+    private final Location useLoc = new Location(null, 0, 0, 0);
+
     /**
      * 
      * Notify all listeners. A copy of the listeners under lock, then processed without lock. Theoretically listeners can get processed though they have already been unregistered.
@@ -693,11 +702,43 @@ private void processPlayerSetBackIds() {
                 }
                 continue;
             }
-            if (!player.teleport(data.getTeleported(), BridgeMisc.TELEPORT_CAUSE_CORRECTION_OF_POSITION)) {
+            // (teleported is set.).
+            final Location loc = player.getLocation(useLoc);
+            if (data.isTeleportedPosition(loc)) {
+                // Skip redundant teleport.
+                if (data.debug) {
+                    CheckUtils.debug(player, CheckType.MOVING, "Player set back on tick: Skip teleport, player is there, already.");
+                }
+                continue;
+            }
+            // (player is somewhere else.)
+            // TODO: Consider to skip packet level, if not available (plus optimize access to the information).
+            final PlayerSetBackMethod method = MovingConfig.getConfig(player).playerSetBackMethod;
+            if (method.shouldCancel() || method.shouldSetTo()) {
+                /*
+                 * Another leniency option: Skip, if we have already received an
+                 * ACK for this position on packet level.
+                 */
+                // (CANCEL + UPDATE_FROM mean a certain teleport to the set back, still could be repeated tp.)
+                final CountableLocation cl = ((NetData) CheckType.NET.getDataFactory().getData(player)).teleportQueue.getLastAck();
+                if (data.isTeleportedPosition(cl)) {
+                    if (data.debug) {
+                        CheckUtils.debug(player, CheckType.MOVING, "Player set back on tick: Skip teleport, having received an ACK for the teleport on packet level.");
+                    }
+                    continue;
+                }
+            }
+
+            // (No ACK received yet.)
+            final Location teleported = data.getTeleported();
+            if (!player.teleport(teleported, BridgeMisc.TELEPORT_CAUSE_CORRECTION_OF_POSITION)) {
                 if (data .debug) {
                     CheckUtils.debug(player, CheckType.MOVING, "Player set back on tick: Teleport failed.");
                 }
             }
+            // Cleanup.
+            useLoc.setWorld(null);
+
             // (Data resetting is done during PlayerTeleportEvent handling.)
         }
         // (There could be ids kept on errors !?)