Prevent vanilla clients from joining servers that require modded registry entries. (#3992)

* Prevent vanilla clients from joining servers that require modded registry entries

fabric-networking-api-v1/src/main/java/net/fabricmc/fabric/impl/networking/server/ServerConfigurationNetworkAddon.java

@@ -20,8 +20,11 @@ import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 
+import org.jetbrains.annotations.Nullable;
+
 import net.minecraft.network.NetworkPhase;
 import net.minecraft.network.PacketCallbacks;
+import net.minecraft.network.packet.BrandCustomPayload;
 import net.minecraft.network.packet.CustomPayload;
 import net.minecraft.network.packet.Packet;
 import net.minecraft.network.packet.s2c.common.CommonPingS2CPacket;
@@ -44,6 +47,8 @@ public final class ServerConfigurationNetworkAddon extends AbstractChanneledNetw
 	private final MinecraftServer server;
 	private final ServerConfigurationNetworking.Context context;
 	private RegisterState registerState = RegisterState.NOT_SENT;
+	@Nullable
+	private String clientBrand = null;
 
 	public ServerConfigurationNetworkAddon(ServerConfigurationNetworkHandler handler, MinecraftServer server) {
 		super(ServerNetworkingImpl.CONFIGURATION, ((ServerCommonNetworkHandlerAccessor) handler).getConnection(), "ServerConfigurationNetworkAddon for " + handler.getDebugProfile().getName());
@@ -55,6 +60,16 @@ public final class ServerConfigurationNetworkAddon extends AbstractChanneledNetw
 		this.registerPendingChannels((ChannelInfoHolder) this.connection, NetworkPhase.CONFIGURATION);
 	}
 
+	@Override
+	public boolean handle(CustomPayload payload) {
+		if (payload instanceof BrandCustomPayload brandCustomPayload) {
+			clientBrand = brandCustomPayload.brand();
+			return false;
+		}
+
+		return super.handle(payload);
+	}
+
 	@Override
 	protected void invokeInitEvent() {
 	}
@@ -169,6 +184,10 @@ public final class ServerConfigurationNetworkAddon extends AbstractChanneledNetw
 		handler.send(packet, callback);
 	}
 
+	public @Nullable String getClientBrand() {
+		return clientBrand;
+	}
+
 	private enum RegisterState {
 		NOT_SENT,
 		SENT,

fabric-registry-sync-v0/src/main/java/net/fabricmc/fabric/impl/registry/sync/RegistrySyncManager.java

@@ -41,7 +41,6 @@ import org.jetbrains.annotations.VisibleForTesting;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import net.minecraft.nbt.NbtCompound;
 import net.minecraft.network.packet.Packet;
 import net.minecraft.registry.Registries;
 import net.minecraft.registry.Registry;
@@ -59,6 +58,7 @@ import net.minecraft.util.thread.ThreadExecutor;
 import net.fabricmc.fabric.api.event.registry.RegistryAttribute;
 import net.fabricmc.fabric.api.event.registry.RegistryAttributeHolder;
 import net.fabricmc.fabric.api.networking.v1.ServerConfigurationNetworking;
+import net.fabricmc.fabric.impl.networking.server.ServerNetworkingImpl;
 import net.fabricmc.fabric.impl.registry.sync.packet.DirectRegistryPacketHandler;
 import net.fabricmc.fabric.impl.registry.sync.packet.RegistryPacketHandler;
 
@@ -66,9 +66,14 @@ public final class RegistrySyncManager {
 	public static final boolean DEBUG = Boolean.getBoolean("fabric.registry.debug");
 
 	public static final DirectRegistryPacketHandler DIRECT_PACKET_HANDLER = new DirectRegistryPacketHandler();
-
 	private static final Logger LOGGER = LoggerFactory.getLogger("FabricRegistrySync");
 	private static final boolean DEBUG_WRITE_REGISTRY_DATA = Boolean.getBoolean("fabric.registry.debug.writeContentsAsCsv");
+	private static final Text INCOMPATIBLE_FABRIC_CLIENT_TEXT = Text.literal("This server requires ").append(Text.literal("Fabric API").formatted(Formatting.GREEN))
+			.append(" installed on your client!").formatted(Formatting.YELLOW)
+			.append(Text.literal("\nContact server's administrator for more information!").formatted(Formatting.GOLD));
+	private static final Text INCOMPATIBLE_VANILLA_CLIENT_TEXT = Text.literal("This server requires ").append(Text.literal("Fabric Loader and Fabric API").formatted(Formatting.GREEN))
+			.append(" installed on your client!").formatted(Formatting.YELLOW)
+			.append(Text.literal("\nContact server's administrator for more information!").formatted(Formatting.GOLD));
 
 	//Set to true after vanilla's bootstrap has completed
 	public static boolean postBootstrap = false;
@@ -81,11 +86,6 @@ public final class RegistrySyncManager {
 			return;
 		}
 
-		if (!ServerConfigurationNetworking.canSend(handler, DIRECT_PACKET_HANDLER.getPacketId())) {
-			// Don't send if the client cannot receive
-			return;
-		}
-
 		final Map<Identifier, Object2IntMap<Identifier>> map = RegistrySyncManager.createAndPopulateRegistryMap();
 
 		if (map == null) {
@@ -93,6 +93,17 @@ public final class RegistrySyncManager {
 			return;
 		}
 
+		if (!ServerConfigurationNetworking.canSend(handler, DIRECT_PACKET_HANDLER.getPacketId())) {
+			// Disconnect incompatible clients
+			Text message = switch (ServerNetworkingImpl.getAddon(handler).getClientBrand()) {
+			case "fabric" -> INCOMPATIBLE_FABRIC_CLIENT_TEXT;
+			case null, default -> INCOMPATIBLE_VANILLA_CLIENT_TEXT;
+			};
+
+			handler.disconnect(message);
+			return;
+		}
+
 		handler.addTask(new SyncConfigurationTask(handler, map));
 	}
 
@@ -148,9 +159,9 @@ public final class RegistrySyncManager {
 	}
 
 	/**
-	 * Creates a {@link NbtCompound} used to sync the registry ids.
+	 * Creates a {@link Map} used to sync the registry ids.
 	 *
-	 * @return a {@link NbtCompound} to sync, null when empty
+	 * @return a {@link Map} to sync, null when empty
 	 */
 	@Nullable
 	public static Map<Identifier, Object2IntMap<Identifier>> createAndPopulateRegistryMap() {