Implement PlayerNegotiationEvent (#8599)

src/main/java/net/minecraftforge/event/entity/player/PlayerNegotiationEvent.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) Forge Development LLC and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.minecraftforge.event.entity.player;
+
+import com.mojang.authlib.GameProfile;
+import net.minecraft.network.Connection;
+import net.minecraftforge.common.MinecraftForge;
+import net.minecraftforge.eventbus.api.Event;
+
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Future;
+
+/**
+ * This event is fired on the server when a connection has started the Forge handshake,
+ * Forge will wait for all enqueued work to be completed before proceeding further with the login process.
+ * <br>
+ * This event can be used to delay the player login until any necessary work such as preloading user data has completed.
+ * <br>
+ * This event is fired on the {@link MinecraftForge#EVENT_BUS}.
+ */
+public class PlayerNegotiationEvent extends Event
+{
+
+    private final Connection connection;
+    private final GameProfile profile;
+    private final List<Future<Void>> futures;
+
+    public PlayerNegotiationEvent(Connection connection, GameProfile profile, List<Future<Void>> futures)
+    {
+        this.connection = connection;
+        this.profile = profile;
+        this.futures = futures;
+    }
+
+    /**
+     * Enqueue work to be completed asynchronously before the login proceeds.
+     */
+    public void enqueueWork(Runnable runnable)
+    {
+        enqueueWork(CompletableFuture.runAsync(runnable));
+    }
+
+    /**
+     * Enqueue work to be completed asynchronously before the login proceeds.
+     */
+    public void enqueueWork(Future<Void> future)
+    {
+        futures.add(future);
+    }
+
+    public Connection getConnection()
+    {
+        return connection;
+    }
+
+    public GameProfile getProfile()
+    {
+        return profile;
+    }
+}

src/main/java/net/minecraftforge/network/HandshakeHandler.java

@@ -6,6 +6,7 @@
 package net.minecraftforge.network;
 
 import com.google.common.collect.Multimap;
+import com.mojang.authlib.GameProfile;
 import net.minecraft.network.Connection;
 import net.minecraft.network.protocol.handshake.ClientIntentionPacket;
 import net.minecraft.network.protocol.login.ClientboundCustomQueryPacket;
@@ -13,7 +14,9 @@ import net.minecraft.network.protocol.login.ServerboundCustomQueryPacket;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.network.chat.TextComponent;
 import net.minecraft.server.network.ServerLoginPacketListenerImpl;
+import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.common.util.LogMessageAdapter;
+import net.minecraftforge.event.entity.player.PlayerNegotiationEvent;
 import net.minecraftforge.network.simple.SimpleChannel;
 import net.minecraftforge.registries.ForgeRegistry;
 import net.minecraftforge.registries.GameData;
@@ -25,7 +28,10 @@ import org.apache.logging.log4j.MarkerManager;
 import com.google.common.collect.Maps;
 
 import java.util.*;
+import java.util.concurrent.CancellationException;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.BiConsumer;
 import java.util.function.IntSupplier;
@@ -99,6 +105,8 @@ public class HandshakeHandler
     private Map<ResourceLocation, ForgeRegistry.Snapshot> registrySnapshots;
     private Set<ResourceLocation> registriesToReceive;
     private Map<ResourceLocation, String> registryHashes;
+    private boolean negotiationStarted = false;
+    private final List<Future<Void>> pendingFutures = new ArrayList<>();
 
     private HandshakeHandler(Connection networkManager, NetworkDirection side)
     {
@@ -281,6 +289,13 @@ public class HandshakeHandler
      */
     public boolean tickServer()
     {
+        if (!negotiationStarted) {
+            GameProfile profile = ((ServerLoginPacketListenerImpl) manager.getPacketListener()).gameProfile;
+            PlayerNegotiationEvent event = new PlayerNegotiationEvent(manager, profile, pendingFutures);
+            MinecraftForge.EVENT_BUS.post(event);
+            negotiationStarted = true;
+        }
+
         if (packetPosition < messageList.size()) {
             NetworkRegistry.LoginPayload message = messageList.get(packetPosition);
 
@@ -290,8 +305,24 @@ public class HandshakeHandler
             packetPosition++;
         }
 
+        pendingFutures.removeIf(future -> {
+            if (!future.isDone()) {
+                return false;
+            }
+
+            try {
+                future.get();
+            } catch (ExecutionException ex) {
+                LOGGER.error("Error during negotiation", ex.getCause());
+            } catch (CancellationException | InterruptedException ex) {
+                // no-op
+            }
+
+            return true;
+        });
+
         // we're done when sentMessages is empty
-        if (sentMessages.isEmpty() && packetPosition >= messageList.size()-1) {
+        if (sentMessages.isEmpty() && packetPosition >= messageList.size()-1 && pendingFutures.isEmpty()) {
             // clear ourselves - we're done!
             this.manager.channel().attr(NetworkConstants.FML_HANDSHAKE_HANDLER).set(null);
             LOGGER.debug(FMLHSMARKER, "Handshake complete!");

src/main/resources/META-INF/accesstransformer.cfg

@@ -271,6 +271,7 @@ public net.minecraft.server.level.ServerLevel m_142646_()Lnet/minecraft/world/le
 public net.minecraft.server.level.ServerPlayer f_8940_ # containerCounter
 public net.minecraft.server.level.ServerPlayer m_143399_(Lnet/minecraft/world/inventory/AbstractContainerMenu;)V # initMenu
 public net.minecraft.server.level.ServerPlayer m_9217_()V # nextContainerCounter
+public net.minecraft.server.network.ServerLoginPacketListenerImpl f_10021_ # gameProfile
 public net.minecraft.server.packs.AbstractPackResources f_10203_ # file
 public net.minecraft.server.packs.resources.FallbackResourceManager f_10599_ # fallbacks
 public net.minecraft.tags.Tag$BuilderEntry <init>(Lnet/minecraft/tags/Tag$Entry;Ljava/lang/String;)V # constructor

src/test/java/net/minecraftforge/debug/entity/player/PlayerNegotiationEventTest.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) Forge Development LLC and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.minecraftforge.debug.entity.player;
+
+import net.minecraftforge.event.entity.player.PlayerNegotiationEvent;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
+import net.minecraftforge.fml.common.Mod;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+/**
+ * Tests {@link PlayerNegotiationEvent} by listening for and then enqueuing work to be done asynchronously,
+ * details regarding the work execution is printed out and exceptions are thrown to ensure proper handling.
+ */
+@Mod("player_negotiation_event_test")
+@Mod.EventBusSubscriber()
+public class PlayerNegotiationEventTest
+{
+    private static final boolean ENABLE = false;
+    private static final Logger LOGGER = LogManager.getLogger(PlayerNegotiationEventTest.class);
+
+    @SubscribeEvent
+    public static void onPlayerNegotiation(PlayerNegotiationEvent event)
+    {
+        if (!ENABLE) return;
+        LOGGER.info("{} ({})[{}] started negotiation", event.getProfile().getName(), event.getProfile().getId(), event.getConnection().getRemoteAddress());
+        event.enqueueWork(() -> {
+            // This log message should be printed on the fork-join-pool.
+            LOGGER.info("Hello from {}", Thread.currentThread().getName());
+        });
+        event.enqueueWork(() -> {
+            // This exception should be logged by Forge.
+            throw new RuntimeException("Test Exception from PlayerNegotiationEventTest");
+        });
+    }
+}

src/test/resources/META-INF/mods.toml

@@ -218,5 +218,7 @@ license="LGPL v2.1"
     modId="server_world_creation_test"
 [[mods]]
     modId="valid_railshape_test"
+[[mods]]
+    modId="player_negotiation_event_test"
 
 # ADD ABOVE THIS LINE