Optimize bandwidth + fix keep alive

src/main/java/net/minestom/server/UpdateManager.java

@@ -1,5 +1,7 @@
 package net.minestom.server;
 
+import net.kyori.text.TextComponent;
+import net.kyori.text.format.TextColor;
 import net.minestom.server.entity.EntityManager;
 import net.minestom.server.entity.Player;
 import net.minestom.server.instance.InstanceManager;
@@ -12,6 +14,9 @@ import java.util.concurrent.ExecutorService;
 
 public class UpdateManager {
 
+    private static final long KEEP_ALIVE_DELAY = 10_000;
+    private static final long KEEP_ALIVE_KICK = 30_000;
+
     private ExecutorService mainUpdate = new MinestomThread(MinecraftServer.THREAD_COUNT_MAIN_UPDATE, MinecraftServer.THREAD_NAME_MAIN_UPDATE);
     private boolean stopRequested;
 
@@ -33,9 +38,14 @@ public class UpdateManager {
                 final long time = System.currentTimeMillis();
                 final KeepAlivePacket keepAlivePacket = new KeepAlivePacket(time);
                 for (Player player : connectionManager.getOnlinePlayers()) {
-                    if (time - player.getLastKeepAlive() > 10000) {
+                    final long lastKeepAlive = time - player.getLastKeepAlive();
+                    if (lastKeepAlive > KEEP_ALIVE_DELAY && player.didAnswerKeepAlive()) {
                         player.refreshKeepAlive(time);
                         player.getPlayerConnection().sendPacket(keepAlivePacket);
+                    } else if (lastKeepAlive >= KEEP_ALIVE_KICK) {
+                        TextComponent textComponent = TextComponent.of("No Keep Alive answer")
+                                .color(TextColor.RED);
+                        player.kick(textComponent);
                     }
                 }
 

src/main/java/net/minestom/server/entity/Entity.java

@@ -266,6 +266,8 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer {
     public boolean addViewer(Player player) {
         Check.notNull(player, "Viewer cannot be null");
         boolean result = this.viewers.add(player);
+        if (!result)
+            return false;
         player.viewableEntities.add(this);
         return result;
     }

src/main/java/net/minestom/server/entity/EntityCreature.java

@@ -142,6 +142,9 @@ public abstract class EntityCreature extends LivingEntity {
     @Override
     public boolean addViewer(Player player) {
         boolean result = super.addViewer(player);
+        if (!result)
+            return false;
+
         PlayerConnection playerConnection = player.getPlayerConnection();
 
         EntityPacket entityPacket = new EntityPacket();

src/main/java/net/minestom/server/entity/ObjectEntity.java

@@ -30,6 +30,10 @@ public abstract class ObjectEntity extends Entity {
 
     @Override
     public boolean addViewer(Player player) {
+        boolean result = super.addViewer(player);
+        if (!result)
+            return false;
+
         PlayerConnection playerConnection = player.getPlayerConnection();
 
         SpawnEntityPacket spawnEntityPacket = new SpawnEntityPacket();
@@ -46,7 +50,7 @@ public abstract class ObjectEntity extends Entity {
             playerConnection.sendPacket(getPassengersPacket());
         }
 
-        return super.addViewer(player); // Add player to viewers list
+        return result;
     }
 
 }

src/main/java/net/minestom/server/entity/Player.java

@@ -54,6 +54,7 @@ import java.util.function.Consumer;
 public class Player extends LivingEntity {
 
     private long lastKeepAlive;
+    private boolean answerKeepAlive;
 
     private String username;
     protected PlayerConnection playerConnection;
@@ -144,6 +145,9 @@ public class Player extends LivingEntity {
 
         setCanPickupItem(true); // By default
 
+        // Allow the server to send the next keep alive packet
+        refreshAnswerKeepAlive(true);
+
         this.gameMode = GameMode.SURVIVAL;
         this.dimension = Dimension.OVERWORLD;
         this.levelType = LevelType.DEFAULT;
@@ -337,11 +341,10 @@ public class Player extends LivingEntity {
         // Tick event
         callEvent(PlayerTickEvent.class, playerTickEvent);
 
-
         // Multiplayer sync
-        if (!getViewers().isEmpty()) {
+        final boolean positionChanged = position.getX() != lastX || position.getY() != lastY || position.getZ() != lastZ;
-            final boolean positionChanged = position.getX() != lastX || position.getZ() != lastZ || position.getY() != lastY;
         final boolean viewChanged = position.getYaw() != lastYaw || position.getPitch() != lastPitch;
+        if (!getViewers().isEmpty() && (positionChanged || viewChanged)) {
             ServerPacket updatePacket = null;
             ServerPacket optionalUpdatePacket = null;
             if (positionChanged && viewChanged) {
@@ -483,6 +486,9 @@ public class Player extends LivingEntity {
             return false;
 
         boolean result = super.addViewer(player);
+        if (!result)
+            return false;
+
         PlayerConnection viewerConnection = player.getPlayerConnection();
         String property = "eyJ0aW1lc3RhbXAiOjE1NjU0ODMwODQwOTYsInByb2ZpbGVJZCI6ImFiNzBlY2I0MjM0NjRjMTRhNTJkN2EwOTE1MDdjMjRlIiwicHJvZmlsZU5hbWUiOiJUaGVNb2RlOTExIiwidGV4dHVyZXMiOnsiU0tJTiI6eyJ1cmwiOiJodHRwOi8vdGV4dHVyZXMubWluZWNyYWZ0Lm5ldC90ZXh0dXJlL2RkOTE2NzJiNTE0MmJhN2Y3MjA2ZTRjN2IwOTBkNzhlM2Y1ZDc2NDdiNWFmZDIyNjFhZDk4OGM0MWI2ZjcwYTEifX19";
         SpawnPlayerPacket spawnPlayerPacket = new SpawnPlayerPacket();
@@ -1566,6 +1572,15 @@ public class Player extends LivingEntity {
      */
     public void refreshKeepAlive(long lastKeepAlive) {
         this.lastKeepAlive = lastKeepAlive;
+        this.answerKeepAlive = false;
+    }
+
+    public boolean didAnswerKeepAlive() {
+        return answerKeepAlive;
+    }
+
+    public void refreshAnswerKeepAlive(boolean answerKeepAlive) {
+        this.answerKeepAlive = answerKeepAlive;
     }
 
     /**

src/main/java/net/minestom/server/inventory/Inventory.java

@@ -121,7 +121,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
      * Refresh the inventory for all viewers
      */
     public void update() {
-        PacketWriterUtils.writeAndSend(getViewers(), getWindowItemsPacket());
+        PacketWriterUtils.writeAndSend(getViewers(), createWindowItemsPacket());
     }
 
     /**
@@ -134,7 +134,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
         if (!getViewers().contains(player))
             return;
 
-        PacketWriterUtils.writeAndSend(player, getWindowItemsPacket());
+        PacketWriterUtils.writeAndSend(player, createWindowItemsPacket());
     }
 
     @Override
@@ -145,8 +145,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
     @Override
     public boolean addViewer(Player player) {
         boolean result = this.viewers.add(player);
-        WindowItemsPacket windowItemsPacket = getWindowItemsPacket();
+        PacketWriterUtils.writeAndSend(player, createWindowItemsPacket());
-        player.getPlayerConnection().sendPacket(windowItemsPacket);
         return result;
     }
 
@@ -174,7 +173,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
         }
     }
 
-    private WindowItemsPacket getWindowItemsPacket() {
+    private WindowItemsPacket createWindowItemsPacket() {
         WindowItemsPacket windowItemsPacket = new WindowItemsPacket();
         windowItemsPacket.windowId = getWindowId();
         windowItemsPacket.count = (short) itemStacks.length;

src/main/java/net/minestom/server/listener/KeepAliveListener.java

@@ -18,6 +18,8 @@ public class KeepAliveListener {
             return;
         }
 
+        player.refreshAnswerKeepAlive(true);
+
         // Update latency
         int latency = (int) (System.currentTimeMillis() - packet.id);
         player.refreshLatency(latency);

src/main/java/net/minestom/server/network/PacketWriterUtils.java

@@ -26,8 +26,7 @@ public class PacketWriterUtils {
 
     public static void writeAndSend(Collection<Player> players, ServerPacket serverPacket) {
         batchesPool.execute(() -> {
-            int size = players.size();
+            if (players.isEmpty())
-            if (size == 0)
                 return;
 
             ByteBuf buffer = PacketUtils.writePacket(serverPacket);