Support plugin message in configuration stage (#1096)

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/ConfigSessionHandler.java

@@ -45,7 +45,6 @@ import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import java.io.IOException;
 import java.util.concurrent.CompletableFuture;
 import java.util.regex.Pattern;
-import net.kyori.adventure.text.Component;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
@@ -193,10 +192,7 @@ public class ConfigSessionHandler implements MinecraftSessionHandler {
           PluginMessageUtil.rewriteMinecraftBrand(packet, server.getVersion(),
               serverConn.getPlayer().getProtocolVersion()));
     } else {
-      // TODO: Change this so its usable for mod loaders
-      serverConn.disconnect();
-      resultFuture.complete(ConnectionRequestResults.forDisconnect(
-          Component.translatable("multiplayer.disconnect.missing_tags"), serverConn.getServer()));
+      serverConn.getPlayer().getConnection().write(packet.retain());
     }
     return true;
   }

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientConfigSessionHandler.java

@@ -17,6 +17,7 @@
 
 package com.velocitypowered.proxy.connection.client;
 
+import com.velocitypowered.api.event.player.PlayerClientBrandEvent;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
@@ -25,9 +26,11 @@ import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.StateRegistry;
 import com.velocitypowered.proxy.protocol.packet.ClientSettings;
 import com.velocitypowered.proxy.protocol.packet.KeepAlive;
+import com.velocitypowered.proxy.protocol.packet.PingIdentify;
 import com.velocitypowered.proxy.protocol.packet.PluginMessage;
 import com.velocitypowered.proxy.protocol.packet.ResourcePackResponse;
 import com.velocitypowered.proxy.protocol.packet.config.FinishedUpdate;
+import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import io.netty.buffer.ByteBuf;
 import java.util.concurrent.CompletableFuture;
 import net.kyori.adventure.text.Component;
@@ -105,6 +108,31 @@ public class ClientConfigSessionHandler implements MinecraftSessionHandler {
     return true;
   }
 
+  @Override
+  public boolean handle(PluginMessage packet) {
+    VelocityServerConnection serverConn = player.getConnectionInFlight();
+    if (serverConn != null) {
+      if (PluginMessageUtil.isMcBrand(packet)) {
+        String brand = PluginMessageUtil.readBrandMessage(packet.content());
+        server.getEventManager().fireAndForget(new PlayerClientBrandEvent(player, brand));
+        player.setClientBrand(brand);
+        // Client sends `minecraft:brand` packet immediately after Login,
+        // but at this time the backend server may not be ready, just discard it.
+      } else {
+        serverConn.ensureConnected().write(packet.retain());
+      }
+    }
+    return true;
+  }
+
+  @Override
+  public boolean handle(PingIdentify packet) {
+    if (player.getConnectionInFlight() != null) {
+      player.getConnectionInFlight().ensureConnected().write(packet);
+    }
+    return true;
+  }
+
   @Override
   public void handleGeneric(MinecraftPacket packet) {
     VelocityServerConnection serverConnection = player.getConnectedServer();