Add feature flags to AsyncPlayerConfigurationEvent

src/main/java/net/minestom/server/event/player/AsyncPlayerConfigurationEvent.java

@@ -1,12 +1,18 @@
 package net.minestom.server.event.player;
 
+import it.unimi.dsi.fastutil.objects.ObjectArraySet;
+import it.unimi.dsi.fastutil.objects.ObjectSets;
 import net.minestom.server.entity.Player;
 import net.minestom.server.event.trait.PlayerEvent;
 import net.minestom.server.instance.Instance;
 import net.minestom.server.network.packet.server.configuration.ResetChatPacket;
+import net.minestom.server.network.packet.server.configuration.UpdateEnabledFeaturesPacket;
+import net.minestom.server.utils.NamespaceID;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.Set;
+
 /**
  * Called when a player enters the configuration state (either on first connection, or if they are
  * sent back to configuration later). The player is moved to the play state as soon as all event
@@ -20,6 +26,7 @@ public class AsyncPlayerConfigurationEvent implements PlayerEvent {
     private final Player player;
     private final boolean isFirstConfig;
 
+    private final ObjectArraySet<NamespaceID> featureFlags = new ObjectArraySet<>();
     private boolean hardcore;
     private boolean clearChat;
     private boolean sendRegistryData;
@@ -29,6 +36,8 @@ public class AsyncPlayerConfigurationEvent implements PlayerEvent {
         this.player = player;
         this.isFirstConfig = isFirstConfig;
 
+        this.featureFlags.add(NamespaceID.from("minecraft:vanilla")); // Vanilla feature-set, without this you get nothing at all. Kinda wacky!
+
         this.hardcore = false;
         this.clearChat = false;
         this.sendRegistryData = isFirstConfig;
@@ -55,6 +64,42 @@ public class AsyncPlayerConfigurationEvent implements PlayerEvent {
         this.hardcore = hardcore;
     }
 
+    /**
+     * Add a feature flag, see <a href="https://wiki.vg/Protocol#Feature_Flags">Wiki.vg Feature Flags</a> for a list of applicable features
+     * Note: the flag "minecraft:vanilla" is already included by default.
+     *
+     * @param feature A minecraft feature flag
+     *
+     * @see UpdateEnabledFeaturesPacket
+     */
+    public void addFeatureFlag(@NotNull NamespaceID feature) {
+        this.featureFlags.add(feature);
+    }
+
+    /**
+     * Remove a feature flag, see <a href="https://wiki.vg/Protocol#Feature_Flags">Wiki.vg Feature Flags</a> for a list of applicable features
+     * Note: removing the flag "minecraft:vanilla" may result in weird behavior
+     *
+     * @param feature A minecraft feature flag
+     * @return if the feature specified existed prior to being removed
+     *
+     * @see UpdateEnabledFeaturesPacket
+     */
+    public boolean removeFeatureFlag(@NotNull NamespaceID feature) {
+        return this.featureFlags.remove(feature); // Should this have sanity checking to see if the feature was actually contained in the list?
+    }
+
+    /**
+     * The list of currently added feature flags. This is an unmodifiable copy of what will be sent to the client.
+     *
+     * @return An unmodifiable set of feature flags
+     *
+     * @see UpdateEnabledFeaturesPacket
+     */
+    public @NotNull Set<NamespaceID> getFeatureFlags() {
+        return ObjectSets.unmodifiable(this.featureFlags);
+    }
+
     /**
      * If true, the player's chat will be cleared when exiting the configuration state, otherwise
      * it will be preserved. The default is not to clear the chat.

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

@@ -18,6 +18,7 @@ import net.minestom.server.network.packet.server.common.TagsPacket;
 import net.minestom.server.network.packet.server.configuration.FinishConfigurationPacket;
 import net.minestom.server.network.packet.server.configuration.ResetChatPacket;
 import net.minestom.server.network.packet.server.configuration.SelectKnownPacksPacket;
+import net.minestom.server.network.packet.server.configuration.UpdateEnabledFeaturesPacket;
 import net.minestom.server.network.packet.server.login.LoginSuccessPacket;
 import net.minestom.server.network.packet.server.play.StartConfigurationPacket;
 import net.minestom.server.network.player.PlayerConnection;
@@ -277,6 +278,8 @@ public final class ConnectionManager {
             EventDispatcher.call(event);
             if (!player.isOnline()) return; // Player was kicked during config.
 
+            player.sendPacket(new UpdateEnabledFeaturesPacket(event.getFeatureFlags())); // send player features that were enabled or disabled during async config event
+
             final Instance spawningInstance = event.getSpawningInstance();
             Check.notNull(spawningInstance, "You need to specify a spawning instance in the AsyncPlayerConfigurationEvent");