Add join-interrupt-timer per-arena setting.

This commit adds a new per-arena setting, join-interrupt-timer, which, when set to a positive number, will introduce a delay to the join and spec commands. During this delay, if the player takes damage or moves more than one block's distance, the command will be interrupted.

Closes #482

changelog.md

@@ -12,6 +12,7 @@ These changes will (most likely) be included in the next version.
 
 ## [Unreleased]
 - It is now possible to add a fixed delay (in seconds) between waves with the new per-arena setting `next-wave-delay`.
+- The new per-arena setting `join-interrupt-timer` makes it possible to add a "delay" to the join and spec commands. If the player moves or takes damage during this delay, the command is interrupted. This should help prevent exploits on PvP servers.
 - Right-clicking is now allowed in the lobby. This makes it possible to activate blocks like buttons and levers.
 - Snow and ice no longer melts in arenas.
 

src/main/java/com/garbagemule/MobArena/ArenaMasterImpl.java

@@ -6,6 +6,7 @@ import static com.garbagemule.MobArena.util.config.ConfigUtils.parseLocation;
 import com.garbagemule.MobArena.framework.Arena;
 import com.garbagemule.MobArena.framework.ArenaMaster;
 import com.garbagemule.MobArena.things.Thing;
+import com.garbagemule.MobArena.util.JoinInterruptTimer;
 import com.garbagemule.MobArena.util.config.ConfigUtils;
 import org.bukkit.Bukkit;
 import org.bukkit.Location;
@@ -44,6 +45,8 @@ public class ArenaMasterImpl implements ArenaMaster
     
     private boolean enabled;
 
+    private JoinInterruptTimer joinInterruptTimer;
+
     /**
      * Default constructor.
      */
@@ -60,6 +63,8 @@ public class ArenaMasterImpl implements ArenaMaster
         this.spawnsPets = new SpawnsPets(Material.BONE, Material.RAW_FISH);
         
         this.enabled = config.getBoolean("global-settings.enabled", true);
+
+        this.joinInterruptTimer = new JoinInterruptTimer();
     }
 
     /*
@@ -114,6 +119,10 @@ public class ArenaMasterImpl implements ArenaMaster
         return allowedCommands.contains(command);
     }
 
+    public JoinInterruptTimer getJoinInterruptTimer() {
+        return joinInterruptTimer;
+    }
+
     /*
      * /////////////////////////////////////////////////////////////////////////
      * // // Arena getters //

src/main/java/com/garbagemule/MobArena/Msg.java

@@ -30,6 +30,9 @@ public enum Msg {
     JOIN_PLAYER_LIMIT_REACHED("The player limit of this arena has been reached."),
     JOIN_STORE_INV_FAIL("Failed to store inventory. Try again."),
     JOIN_EXISTING_INV_RESTORED("Your old inventory items have been restored."),
+    JOIN_AFTER_DELAY("Joining arena in &c%&r seconds..."),
+    JOIN_INTERRUPTED_BY_DAMAGE("Join aborted due to taking damage."),
+    JOIN_INTERRUPTED_BY_MOVEMENT("Join aborted due to movement."),
     JOIN_PLAYER_JOINED("You joined the arena. Have fun!"),
     LEAVE_NOT_PLAYING("You are not in the arena."),
     LEAVE_NOT_READY("You did not ready up in time! Next time, ready up by clicking an iron block."),

src/main/java/com/garbagemule/MobArena/commands/user/JoinCommand.java

@@ -1,5 +1,6 @@
 package com.garbagemule.MobArena.commands.user;
 
+import com.garbagemule.MobArena.MobArena;
 import com.garbagemule.MobArena.Msg;
 import com.garbagemule.MobArena.commands.Command;
 import com.garbagemule.MobArena.commands.CommandInfo;
@@ -31,26 +32,43 @@ public class JoinCommand implements Command
         
         // Run some rough sanity checks, and grab the arena to join.
         Arena toArena = Commands.getArenaToJoinOrSpec(am, p, arg1);
-        if (toArena == null) {
+        if (toArena == null || !canJoin(p, toArena)) {
             return true;
         }
         
-        // Deny joining from other arenas
-        Arena fromArena = am.getArenaWithPlayer(p);
-        if (fromArena != null && (fromArena.inArena(p) || fromArena.inLobby(p))) {
-            fromArena.getMessenger().tell(p, Msg.JOIN_ALREADY_PLAYING);
-            return true;
-        }
-        
-        // Per-arena sanity checks
-        if (!toArena.canJoin(p)) {
-            return true;
-        }
-
-        // Force leave previous arena
-        if (fromArena != null) fromArena.playerLeave(p);
-        
         // Join the arena!
-        return toArena.playerJoin(p, p.getLocation());
+        int seconds = toArena.getSettings().getInt("join-interrupt-timer", 0);
+        if (seconds > 0) {
+            boolean started = am.getJoinInterruptTimer().start(p, toArena, seconds, () -> tryJoin(p, toArena));
+            if (started) {
+                toArena.getMessenger().tell(p, Msg.JOIN_AFTER_DELAY, String.valueOf(seconds));
+            } else {
+                toArena.getMessenger().tell(p, Msg.JOIN_ALREADY_PLAYING);
+            }
+        } else {
+            tryJoin(p, toArena);
+        }
+        return true;
+    }
+
+    private boolean canJoin(Player player, Arena arena) {
+        MobArena plugin = arena.getPlugin();
+        ArenaMaster am = plugin.getArenaMaster();
+        if (am.getJoinInterruptTimer().isWaiting(player)) {
+            plugin.getGlobalMessenger().tell(player, Msg.JOIN_ALREADY_PLAYING);
+            return false;
+        }
+        Arena current = am.getArenaWithPlayer(player);
+        if (current != null) {
+            current.getMessenger().tell(player, Msg.JOIN_ALREADY_PLAYING);
+            return false;
+        }
+        return arena.canJoin(player);
+    }
+
+    private void tryJoin(Player player, Arena arena) {
+        if (canJoin(player, arena)) {
+            arena.playerJoin(player, player.getLocation());
+        }
     }
 }

src/main/java/com/garbagemule/MobArena/commands/user/SpecCommand.java

@@ -1,5 +1,6 @@
 package com.garbagemule.MobArena.commands.user;
 
+import com.garbagemule.MobArena.MobArena;
 import com.garbagemule.MobArena.Msg;
 import com.garbagemule.MobArena.commands.Command;
 import com.garbagemule.MobArena.commands.CommandInfo;
@@ -31,27 +32,43 @@ public class SpecCommand implements Command
         
         // Run some rough sanity checks, and grab the arena to spec.
         Arena toArena = Commands.getArenaToJoinOrSpec(am, p, arg1);
-        if (toArena == null) {
+        if (toArena == null || !canSpec(p, toArena)) {
             return true;
         }
 
-        // Deny spectating from other arenas
-        Arena fromArena = am.getArenaWithPlayer(p);
-        if (fromArena != null && (fromArena.inArena(p) || fromArena.inLobby(p))) {
-            fromArena.getMessenger().tell(p, Msg.SPEC_ALREADY_PLAYING);
-            return true;
-        }
-        
-        // Per-arena sanity checks
-        if (!toArena.canSpec(p)) {
-            return true;
-        }
-
-        // Force leave previous arena
-        if (fromArena != null) fromArena.playerLeave(p);
-        
         // Spec the arena!
-        toArena.playerSpec(p, p.getLocation());
+        int seconds = toArena.getSettings().getInt("join-interrupt-timer", 0);
+        if (seconds > 0) {
+            boolean started = am.getJoinInterruptTimer().start(p, toArena, seconds, () -> trySpec(p, toArena));
+            if (started) {
+                toArena.getMessenger().tell(p, Msg.JOIN_AFTER_DELAY, String.valueOf(seconds));
+            } else {
+                toArena.getMessenger().tell(p, Msg.SPEC_ALREADY_PLAYING);
+            }
+        } else {
+            trySpec(p, toArena);
+        }
         return true;
     }
+
+    private boolean canSpec(Player player, Arena arena) {
+        MobArena plugin = arena.getPlugin();
+        ArenaMaster am = plugin.getArenaMaster();
+        if (am.getJoinInterruptTimer().isWaiting(player)) {
+            plugin.getGlobalMessenger().tell(player, Msg.SPEC_ALREADY_PLAYING);
+            return false;
+        }
+        Arena current = arena.getPlugin().getArenaMaster().getArenaWithPlayer(player);
+        if (current != null) {
+            current.getMessenger().tell(player, Msg.SPEC_ALREADY_PLAYING);
+            return false;
+        }
+        return arena.canSpec(player);
+    }
+
+    private void trySpec(Player player, Arena arena) {
+        if (canSpec(player, arena)) {
+            arena.playerSpec(player, player.getLocation());
+        }
+    }
 }

src/main/java/com/garbagemule/MobArena/framework/ArenaMaster.java

@@ -4,6 +4,7 @@ import com.garbagemule.MobArena.ArenaClass;
 import com.garbagemule.MobArena.Messenger;
 import com.garbagemule.MobArena.MobArena;
 import com.garbagemule.MobArena.SpawnsPets;
+import com.garbagemule.MobArena.util.JoinInterruptTimer;
 import org.bukkit.Location;
 import org.bukkit.World;
 import org.bukkit.entity.Entity;
@@ -88,6 +89,8 @@ public interface ArenaMaster
     
     boolean isAllowed(String command);
 
+    JoinInterruptTimer getJoinInterruptTimer();
+    
     
     
     /*/////////////////////////////////////////////////////////////////////////

src/main/java/com/garbagemule/MobArena/util/JoinInterruptTimer.java

@@ -0,0 +1,154 @@
+package com.garbagemule.MobArena.util;
+
+import com.garbagemule.MobArena.Msg;
+import com.garbagemule.MobArena.framework.Arena;
+import org.bukkit.Bukkit;
+import org.bukkit.Location;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.Listener;
+import org.bukkit.event.entity.EntityDamageEvent;
+import org.bukkit.event.player.PlayerKickEvent;
+import org.bukkit.event.player.PlayerMoveEvent;
+import org.bukkit.event.player.PlayerQuitEvent;
+import org.bukkit.scheduler.BukkitRunnable;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.UUID;
+
+public class JoinInterruptTimer {
+    private Set<UUID> waiting;
+
+    public JoinInterruptTimer() {
+        this.waiting = new HashSet<>();
+    }
+
+    public boolean isWaiting(Player player) {
+        return waiting.contains(player.getUniqueId());
+    }
+
+    public boolean start(Player player, Arena arena, int seconds, Runnable completed) {
+        if (isWaiting(player)) {
+            return false;
+        }
+
+        UUID id = player.getUniqueId();
+        waiting.add(id);
+
+        TimedInterruptListener listener = new TimedInterruptListener(
+            player,
+            arena,
+            () -> waiting.remove(id),
+            completed
+        );
+        listener.runTaskLater(arena.getPlugin(), seconds * 20);
+        Bukkit.getPluginManager().registerEvents(listener, arena.getPlugin());
+
+        return true;
+    }
+
+    static class TimedInterruptListener extends BukkitRunnable implements Listener {
+        Player player;
+        Location location;
+        Arena arena;
+        Runnable stopped;
+        Runnable completed;
+
+        boolean done;
+
+        TimedInterruptListener(Player player, Arena arena, Runnable stopped, Runnable completed) {
+            this.player = player;
+            this.location = player.getLocation();
+            this.arena = arena;
+            this.stopped = stopped;
+            this.completed = completed;
+
+            this.done = false;
+        }
+
+        @Override
+        public void run() {
+            complete();
+        }
+
+        @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+        public void on(EntityDamageEvent event) {
+            if (done || !event.getEntity().equals(player)) {
+                return;
+            }
+            arena.getMessenger().tell(player, Msg.JOIN_INTERRUPTED_BY_DAMAGE);
+            interrupt();
+        }
+
+        @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+        public void on(PlayerMoveEvent event) {
+            if (done || !event.getPlayer().equals(player)) {
+                return;
+            }
+            if (location.getWorld() == event.getTo().getWorld() && location.distanceSquared(event.getTo()) < 1) {
+                return;
+            }
+            arena.getMessenger().tell(player, Msg.JOIN_INTERRUPTED_BY_MOVEMENT);
+            interrupt();
+        }
+
+        @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+        public void on(PlayerQuitEvent event) {
+            if (done || !event.getPlayer().equals(player)) {
+                return;
+            }
+            interrupt();
+        }
+
+        @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+        public void on(PlayerKickEvent event) {
+            if (done || !event.getPlayer().equals(player)) {
+                return;
+            }
+            interrupt();
+        }
+
+        void complete() {
+            if (done) {
+                return;
+            }
+            done = true;
+
+            try {
+                HandlerList.unregisterAll(this);
+                stopped.run();
+                completed.run();
+            } finally {
+                clear();
+            }
+        }
+
+        void interrupt() {
+            if (done) {
+                return;
+            }
+            done = true;
+
+            try {
+                HandlerList.unregisterAll(this);
+                stopped.run();
+                super.cancel();
+            } catch (IllegalStateException e) {
+                // Swallow this exception from super.cancel()
+            } finally {
+                clear();
+            }
+        }
+
+        void clear() {
+            player = null;
+            location = null;
+            arena = null;
+            stopped = null;
+            completed = null;
+        }
+    }
+}

src/main/resources/res/settings.yml

@@ -20,6 +20,7 @@ share-items-in-arena: true
 min-players: 0
 max-players: 0
 max-join-distance: 0
+join-interrupt-timer: 0
 first-wave-delay: 5
 next-wave-delay: 0
 wave-interval: 15