Sync server config changes to the connected clients

gradle.properties

@@ -15,22 +15,23 @@ neoform_version=20240808.144430
 neoforge_snapshot_next_stable=22.0
 
 mergetool_version=2.0.0
+# TODO: does this get bumped because of FML?
 accesstransformers_version=10.0.1
 coremods_version=6.0.4
 eventbus_version=8.0.1
 modlauncher_version=11.0.4
 securejarhandler_version=3.0.8
 bootstraplauncher_version=2.0.2
-asm_version=9.5
+asm_version=9.7
 installer_version=2.1.+
 mixin_version=0.14.0+mixin.0.8.6
 terminalconsoleappender_version=1.3.0
 nightconfig_version=3.8.0
-jetbrains_annotations_version=24.0.1
+jetbrains_annotations_version=24.1.0
 slf4j_api_version=2.0.7
 apache_maven_artifact_version=3.8.5
 jarjar_version=0.4.1
-fancy_mod_loader_version=4.0.24
+fancy_mod_loader_version=4.0.26-sync-config-changes
 mojang_logging_version=1.1.1
 log4j_version=2.22.1
 guava_version=31.1.2-jre

src/main/java/net/neoforged/neoforge/common/NeoForgeEventHandler.java

@@ -35,6 +35,7 @@
 import net.neoforged.neoforge.event.level.ChunkEvent;
 import net.neoforged.neoforge.event.level.LevelEvent;
 import net.neoforged.neoforge.event.tick.ServerTickEvent;
+import net.neoforged.neoforge.network.ConfigSync;
 import net.neoforged.neoforge.network.PacketDistributor;
 import net.neoforged.neoforge.network.payload.RegistryDataMapSyncPayload;
 import net.neoforged.neoforge.registries.DataMapLoader;
@@ -77,6 +78,7 @@ public void preServerTick(ServerTickEvent.Pre event) {
     @SubscribeEvent
     public void postServerTick(ServerTickEvent.Post event) {
         WorldWorkerManager.tick(false);
+        ConfigSync.syncPendingConfigs(event.getServer());
     }
 
     @SubscribeEvent

src/main/java/net/neoforged/neoforge/internal/NeoForgeBindings.java

@@ -7,11 +7,24 @@
 
 import net.neoforged.bus.api.IEventBus;
 import net.neoforged.fml.IBindingsProvider;
+import net.neoforged.fml.config.IConfigSpec;
+import net.neoforged.fml.config.ModConfig;
 import net.neoforged.neoforge.common.NeoForge;
+import net.neoforged.neoforge.network.ConfigSync;
+import org.jetbrains.annotations.Nullable;
 
 public class NeoForgeBindings implements IBindingsProvider {
     @Override
     public IEventBus getGameBus() {
         return NeoForge.EVENT_BUS;
     }
+
+    @Override
+    public void onConfigChanged(ModConfig modConfig, @Nullable IConfigSpec.ILoadedConfig loadedConfig) {
+        if (modConfig.getType() != ModConfig.Type.SERVER || loadedConfig == null) {
+            return;
+        }
+
+        ConfigSync.addPendingConfig(modConfig, loadedConfig);
+    }
 }

src/main/java/net/neoforged/neoforge/network/ConfigSync.java

@@ -6,23 +6,46 @@
 package net.neoforged.neoforge.network;
 
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
-import java.util.List;
+import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Optional;
+import java.util.WeakHashMap;
 import java.util.stream.Collectors;
 import net.minecraft.client.Minecraft;
+import net.minecraft.network.Connection;
+import net.minecraft.network.protocol.configuration.ServerConfigurationPacketListener;
+import net.minecraft.server.MinecraftServer;
 import net.neoforged.fml.config.ConfigTracker;
+import net.neoforged.fml.config.IConfigSpec;
 import net.neoforged.fml.config.ModConfig;
 import net.neoforged.fml.config.ModConfigs;
+import net.neoforged.neoforge.network.configuration.SyncConfig;
 import net.neoforged.neoforge.network.payload.ConfigFilePayload;
 import org.jetbrains.annotations.ApiStatus;
 
 @ApiStatus.Internal
 public final class ConfigSync {
+    private static final Object lock = new Object();
+    /**
+     * Connection -> Config file name -> byte[] of the config serialized to TOML.
+     *
+     * <p>Pending config updates get sent to players in the PLAY phase only,
+     * but start being tracked as soon as the {@link SyncConfig} configuration task runs.
+     * This ensures that all updates during the configuration phase will eventually arrive to the clients.
+     *
+     * <p>Connections get removed when GC'ed thanks to the WeakHashMap.
+     */
+    private static final Map<Connection, Map<String, byte[]>> configsToSync = new WeakHashMap<>();
+
     private ConfigSync() {}
 
-    public static List<ConfigFilePayload> syncConfigs() {
+    public static void syncAllConfigs(ServerConfigurationPacketListener listener) {
+        synchronized (lock) {
+            configsToSync.put(listener.getConnection(), new LinkedHashMap<>());
+        }
+
         final Map<String, byte[]> configData = ModConfigs.getConfigSet(ModConfig.Type.SERVER).stream().collect(Collectors.toMap(ModConfig::getFileName, mc -> {
             try {
                 return Files.readAllBytes(mc.getFullPath());
@@ -31,9 +54,33 @@ public static List<ConfigFilePayload> syncConfigs() {
             }
         }));
 
-        return configData.entrySet().stream()
-                .map(e -> new ConfigFilePayload(e.getKey(), e.getValue()))
-                .toList();
+        for (var entry : configData.entrySet()) {
+            listener.send(new ConfigFilePayload(entry.getKey(), entry.getValue()));
+        }
+    }
+
+    public static void addPendingConfig(ModConfig modConfig, IConfigSpec.ILoadedConfig loadedConfig) {
+        var bytes = loadedConfig.config().configFormat().createWriter().writeToString(loadedConfig.config()).getBytes(StandardCharsets.UTF_8);
+        synchronized (lock) {
+            for (var toSync : configsToSync.values()) {
+                toSync.put(modConfig.getFileName(), bytes);
+            }
+        }
+    }
+
+    public static void syncPendingConfigs(MinecraftServer server) {
+        synchronized (lock) {
+            for (var player : server.getPlayerList().getPlayers()) {
+                var toSync = configsToSync.get(player.connection.getConnection());
+                if (toSync == null) {
+                    throw new IllegalStateException("configsToSync should contain an entry for player " + player.getName());
+                }
+                toSync.forEach((fileName, data) -> {
+                    PacketDistributor.sendToPlayer(player, new ConfigFilePayload(fileName, data));
+                });
+                toSync.clear();
+            }
+        }
     }
 
     public static void receiveSyncedConfig(final byte[] contents, final String fileName) {

src/main/java/net/neoforged/neoforge/network/NetworkInitialization.java

@@ -40,7 +40,7 @@ private static void register(final RegisterPayloadHandlersEvent event) {
         final PayloadRegistrar registrar = event.registrar("1") // Update this version if the payload semantics change.
                 .optional();
         registrar
-                .configurationToClient(
+                .commonToClient(
                         ConfigFilePayload.TYPE,
                         ConfigFilePayload.STREAM_CODEC,
                         ClientPayloadHandler::handle)

src/main/java/net/neoforged/neoforge/network/configuration/SyncConfig.java

@@ -25,7 +25,7 @@ public record SyncConfig(ServerConfigurationPacketListener listener) implements
 
     @Override
     public void run(Consumer<CustomPacketPayload> sender) {
-        ConfigSync.syncConfigs().forEach(sender);
+        ConfigSync.syncAllConfigs(listener);
         listener().finishCurrentTask(type());
     }