[BUG] Client brand not sent to backend when reconnecting back from limbo

[metabrixkt]

The bug

Velocity doesn't send the client brand to the backend when reconnecting back from limbo.

Related code in LimboAPI:

LimboAPI/plugin/src/main/java/net/elytrium/limboapi/server/LimboPlayerImpl.java

Lines 301 to 303 in be15850

	// Rollback original CONFIG handler
	this.connection.setActiveSessionHandler(StateRegistry.CONFIG,
	new ClientConfigSessionHandler(this.plugin.getServer(), this.player));

This happens because Velocity expects ClientConfigSessionHandler's private String brandChannel field to be set in ClientConfigSessionHandler#handle(PluginMessageEvent) during initial configuration — the client sends the brand only during its first configuration that comes right after the login phase. The issue isn't present when changing servers because Velocity reuses the same ClientConfigSessionHandler after one was created: https://github.com/PaperMC/Velocity/blob/4aa9ee77351531430019b4725427c5d9e5bed913/proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java#L397-L399

Expected behavior

LimboAPI follows Velocity behavior for configuration phase and reuses the same ClientConfigSessionHandler; or, at least, preserves the brandChannel field.

Proposed fix

diff --git a/plugin/src/main/java/net/elytrium/limboapi/injection/login/LoginTasksQueue.java b/plugin/src/main/java/net/elytrium/limboapi/injection/login/LoginTasksQueue.java
index bc027db..be00a88 100644
--- a/plugin/src/main/java/net/elytrium/limboapi/injection/login/LoginTasksQueue.java
+++ b/plugin/src/main/java/net/elytrium/limboapi/injection/login/LoginTasksQueue.java
@@ -89,7 +89,7 @@ public class LoginTasksQueue {
   private static final BiConsumer<Object, MinecraftConnection> MC_CONNECTION_SETTER;
   private static final MethodHandle CONNECT_TO_INITIAL_SERVER_METHOD;
   private static final MethodHandle SET_CLIENT_BRAND;
-  private static final BiConsumer<ClientConfigSessionHandler, String> BRAND_CHANNEL_SETTER;
+  public static final BiConsumer<ClientConfigSessionHandler, String> BRAND_CHANNEL_SETTER;
 
   private final LimboAPI plugin;
   private final Object handler;
diff --git a/plugin/src/main/java/net/elytrium/limboapi/server/LimboPlayerImpl.java b/plugin/src/main/java/net/elytrium/limboapi/server/LimboPlayerImpl.java
index f26767f..cc16a49 100644
--- a/plugin/src/main/java/net/elytrium/limboapi/server/LimboPlayerImpl.java
+++ b/plugin/src/main/java/net/elytrium/limboapi/server/LimboPlayerImpl.java
@@ -43,6 +43,7 @@ import net.elytrium.limboapi.api.protocol.item.ItemComponentMap;
 import net.elytrium.limboapi.api.protocol.packets.data.AbilityFlags;
 import net.elytrium.limboapi.api.protocol.packets.data.MapData;
 import net.elytrium.limboapi.api.protocol.packets.data.MapPalette;
+import net.elytrium.limboapi.injection.login.LoginTasksQueue;
 import net.elytrium.limboapi.protocol.packets.s2c.ChangeGameStatePacket;
 import net.elytrium.limboapi.protocol.packets.s2c.MapDataPacket;
 import net.elytrium.limboapi.protocol.packets.s2c.PlayerAbilitiesPacket;
@@ -299,8 +300,9 @@ public class LimboPlayerImpl implements LimboPlayer {
     if (this.connection.getProtocolVersion().compareTo(ProtocolVersion.MINECRAFT_1_20_2) >= 0) {
       this.sessionHandler.disconnectToConfig(() -> {
         // Rollback original CONFIG handler
-        this.connection.setActiveSessionHandler(StateRegistry.CONFIG,
-            new ClientConfigSessionHandler(this.plugin.getServer(), this.player));
+        ClientConfigSessionHandler handler = new ClientConfigSessionHandler(this.plugin.getServer(), this.player);
+        LoginTasksQueue.BRAND_CHANNEL_SETTER.accept(handler, "minecraft:brand");
+        this.connection.setActiveSessionHandler(StateRegistry.CONFIG, handler);
         this.player.createConnectionRequest(server).fireAndForget();
       });
     } else {

going to PR that soon

Server info

• LimboAPI 1.1.27, dev build be15850: https://modrinth.com/plugin/limboapi/version/be15850
• Test plugin that uses LimboAPI to reproduce the bug

Additional info

This seems to have been a bug ever since the configuration phase was added in Minecraft 1.20.2.