Add LazyPacket

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

@@ -27,6 +27,7 @@ import net.minestom.server.instance.InstanceManager;
 import net.minestom.server.instance.block.Block;
 import net.minestom.server.instance.block.BlockHandler;
 import net.minestom.server.network.packet.server.CachedPacket;
+import net.minestom.server.network.packet.server.LazyPacket;
 import net.minestom.server.network.packet.server.ServerPacket;
 import net.minestom.server.network.packet.server.play.*;
 import net.minestom.server.permission.Permission;
@@ -431,7 +432,7 @@ public class Entity implements Viewable, Tickable, Schedulable, TagHandler, Perm
     public void updateNewViewer(@NotNull Player player) {
         player.sendPacket(getEntityType().registry().spawnType().getSpawnPacket(this));
         if (hasVelocity()) player.sendPacket(getVelocityPacket());
-        player.sendPacket(getMetadataPacket());
+        player.sendPacket(new LazyPacket(this::getMetadataPacket));
         // Passengers
         final Set<Entity> passengers = this.passengers;
         if (!passengers.isEmpty()) {

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

@@ -19,6 +19,7 @@ import net.minestom.server.instance.EntityTracker;
 import net.minestom.server.inventory.EquipmentHandler;
 import net.minestom.server.item.ItemStack;
 import net.minestom.server.network.ConnectionState;
+import net.minestom.server.network.packet.server.LazyPacket;
 import net.minestom.server.network.packet.server.play.CollectItemPacket;
 import net.minestom.server.network.packet.server.play.EntityAnimationPacket;
 import net.minestom.server.network.packet.server.play.EntityPropertiesPacket;
@@ -514,8 +515,8 @@ public class LivingEntity extends Entity implements EquipmentHandler {
     @Override
     public void updateNewViewer(@NotNull Player player) {
         super.updateNewViewer(player);
-        player.sendPacket(getEquipmentsPacket());
-        player.sendPacket(getPropertiesPacket());
+        player.sendPacket(new LazyPacket(this::getEquipmentsPacket));
+        player.sendPacket(new LazyPacket(this::getPropertiesPacket));
         if (getTeam() != null) player.sendPacket(getTeam().createTeamsCreationPacket());
     }
 

src/main/java/net/minestom/server/network/packet/server/LazyPacket.java

@@ -0,0 +1,34 @@
+package net.minestom.server.network.packet.server;
+
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.function.Supplier;
+
+/**
+ * Represents a packet that is lazily allocated. Potentially in a different thread.
+ * <p>
+ * Supplier must be thread-safe.
+ */
+@ApiStatus.Internal
+public final class LazyPacket implements SendablePacket {
+    private final Supplier<ServerPacket> packetSupplier;
+    private volatile ServerPacket packet;
+
+    public LazyPacket(@NotNull Supplier<@NotNull ServerPacket> packetSupplier) {
+        this.packetSupplier = packetSupplier;
+    }
+
+    public @NotNull ServerPacket packet() {
+        ServerPacket packet = this.packet;
+        if (packet == null) {
+            synchronized (this) {
+                packet = this.packet;
+                if (packet == null) {
+                    packet = this.packet = packetSupplier.get();
+                }
+            }
+        }
+        return packet;
+    }
+}

src/main/java/net/minestom/server/network/packet/server/SendablePacket.java

@@ -9,7 +9,7 @@ import org.jetbrains.annotations.NotNull;
  */
 @ApiStatus.Experimental
 public sealed interface SendablePacket
-        permits ServerPacket, CachedPacket, FramedPacket {
+        permits CachedPacket, FramedPacket, LazyPacket, ServerPacket {
 
     @ApiStatus.Experimental
     static @NotNull ServerPacket extractServerPacket(@NotNull SendablePacket packet) {
@@ -19,6 +19,8 @@ public sealed interface SendablePacket
             return cachedPacket.packet();
         } else if (packet instanceof FramedPacket framedPacket) {
             return framedPacket.packet();
+        } else if (packet instanceof LazyPacket lazyPacket) {
+            return lazyPacket.packet();
         } else {
             throw new RuntimeException("Unknown packet type: " + packet.getClass().getName());
         }

src/main/java/net/minestom/server/network/player/PlayerSocketConnection.java

@@ -357,6 +357,8 @@ public class PlayerSocketConnection extends PlayerConnection {
             writeFramedPacketSync(framedPacket);
         } else if (packet instanceof CachedPacket cachedPacket) {
             writeBufferSync(cachedPacket.body());
+        } else if (packet instanceof LazyPacket lazyPacket) {
+            writeServerPacketSync(lazyPacket.packet(), compressed);
         } else {
             throw new RuntimeException("Unknown packet type: " + packet.getClass().getName());
         }