From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Wed, 6 May 2020 04:53:35 -0400
Subject: [PATCH] Optimize Network Manager and add advanced packet support

Adds ability for 1 packet to bundle other packets to follow it
Adds ability for a packet to delay sending more packets until a state is ready.

Removes synchronization from sending packets
Removes processing packet queue off of main thread
  - for the few cases where it is allowed, order is not necessary nor
    should it even be happening concurrently in first place (handshaking/login/status)

Ensures packets sent asynchronously are dispatched on main thread

This helps ensure safety for ProtocolLib as packet listeners
are commonly accessing world state. This will allow you to schedule
a packet to be sent async, but itll be dispatched sync for packet
listeners to process.

This should solve some deadlock risks

Also adds Netty Channel Flush Consolidation to reduce the amount of flushing

Also avoids spamming closed channel exception by rechecking closed state in dispatch
and then catch exceptions and close if they fire.

Part of this commit was authored by: Spottedleaf, sandtechnology

diff --git a/src/main/java/net/minecraft/network/Connection.java b/src/main/java/net/minecraft/network/Connection.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/network/Connection.java
+++ b/src/main/java/net/minecraft/network/Connection.java
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     private static final ProtocolInfo<ServerHandshakePacketListener> INITIAL_PROTOCOL = HandshakeProtocols.SERVERBOUND;
     private final PacketFlow receiving;
     private volatile boolean sendLoginDisconnect = true;
-    private final Queue<Consumer<Connection>> pendingActions = Queues.newConcurrentLinkedQueue();
+    private final Queue<WrappedConsumer> pendingActions = Queues.newConcurrentLinkedQueue(); // Paper
     public Channel channel;
     public SocketAddress address;
     // Spigot Start
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     public java.net.InetSocketAddress virtualHost;
     private static boolean enableExplicitFlush = Boolean.getBoolean("paper.explicit-flush"); // Paper - Disable explicit network manager flushing
     // Paper end
+    // Paper start - Optimize network
+    public boolean isPending = true;
+    public boolean queueImmunity;
+    // Paper end - Optimize network
 
     // Paper start - add utility methods
     public final net.minecraft.server.level.ServerPlayer getPlayer() {
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     }
 
     public void send(Packet<?> packet, @Nullable PacketSendListener callbacks, boolean flush) {
-        if (this.isConnected()) {
-            this.flushQueue();
+        // Paper start - Optimize network: Handle oversized packets better
+        final boolean connected = this.isConnected();
+        if (!connected && !this.preparing) {
+            return;
+        }
+
+        packet.onPacketDispatch(this.getPlayer());
+        if (connected && (InnerUtil.canSendImmediate(this, packet)
+            || (io.papermc.paper.util.MCUtil.isMainThread() && packet.isReady() && this.pendingActions.isEmpty()
+            && (packet.getExtraPackets() == null || packet.getExtraPackets().isEmpty())))) {
             this.sendPacket(packet, callbacks, flush);
         } else {
-            this.pendingActions.add((networkmanager) -> {
-                networkmanager.sendPacket(packet, callbacks, flush);
-            });
-        }
+            // Write the packets to the queue, then flush - antixray hooks there already
+            final java.util.List<Packet<?>> extraPackets = InnerUtil.buildExtraPackets(packet);
+            final boolean hasExtraPackets = extraPackets != null && !extraPackets.isEmpty();
+            if (!hasExtraPackets) {
+                this.pendingActions.add(new PacketSendAction(packet, callbacks, flush));
+            } else {
+                final java.util.List<PacketSendAction> actions = new java.util.ArrayList<>(1 + extraPackets.size());
+                actions.add(new PacketSendAction(packet, null, false)); // Delay the future listener until the end of the extra packets
+
+                for (int i = 0, len = extraPackets.size(); i < len;) {
+                    final Packet<?> extraPacket = extraPackets.get(i);
+                    final boolean end = ++i == len;
+                    actions.add(new PacketSendAction(extraPacket, end ? callbacks : null, end)); // Append listener to the end
+                }
+
+                this.pendingActions.addAll(actions);
+            }
 
+            this.flushQueue();
+            // Paper end - Optimize network
+        }
     }
 
     public void runOnceConnected(Consumer<Connection> task) {
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
             this.flushQueue();
             task.accept(this);
         } else {
-            this.pendingActions.add(task);
+            this.pendingActions.add(new WrappedConsumer(task)); // Paper - Optimize network
         }
 
     }
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     }
 
     private void doSendPacket(Packet<?> packet, @Nullable PacketSendListener callbacks, boolean flush) {
+        // Paper start - Optimize network
+        final net.minecraft.server.level.ServerPlayer player = this.getPlayer();
+        if (!this.isConnected()) {
+            packet.onPacketDispatchFinish(player, null);
+            return;
+        }
+        try {
+        // Paper end - Optimize network
         ChannelFuture channelfuture = flush ? this.channel.writeAndFlush(packet) : this.channel.write(packet);
 
         if (callbacks != null) {
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
             });
         }
 
+        // Paper start - Optimize network
+        if (packet.hasFinishListener()) {
+            channelfuture.addListener((ChannelFutureListener) channelFuture -> packet.onPacketDispatchFinish(player, channelFuture));
+        }
         channelfuture.addListener(ChannelFutureListener.FIRE_EXCEPTION_ON_FAILURE);
+        } catch (final Exception e) {
+            LOGGER.error("NetworkException: {}", player, e);
+            this.disconnect(Component.translatable("disconnect.genericReason", "Internal Exception: " + e.getMessage()));
+            packet.onPacketDispatchFinish(player, null);
+        }
+        // Paper end - Optimize network
     }
 
     public void flushChannel() {
         if (this.isConnected()) {
             this.flush();
         } else {
-            this.pendingActions.add(Connection::flush);
+            this.pendingActions.add(new WrappedConsumer(Connection::flush)); // Paper - Optimize network
         }
 
     }
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
 
     }
 
-    private void flushQueue() {
-        if (this.channel != null && this.channel.isOpen()) {
-            Queue queue = this.pendingActions;
-
+    // Paper start - Optimize network: Rewrite this to be safer if ran off main thread
+    private boolean flushQueue() {
+        if (!this.isConnected()) {
+            return true;
+        }
+        if (io.papermc.paper.util.MCUtil.isMainThread()) {
+            return this.processQueue();
+        } else if (this.isPending) {
+            // Should only happen during login/status stages
             synchronized (this.pendingActions) {
-                Consumer consumer;
+                return this.processQueue();
+            }
+        }
+        return false;
+    }
+
+    private boolean processQueue() {
+        if (this.pendingActions.isEmpty()) {
+            return true;
+        }
 
-                while ((consumer = (Consumer) this.pendingActions.poll()) != null) {
-                    consumer.accept(this);
+        // If we are on main, we are safe here in that nothing else should be processing queue off main anymore
+        // But if we are not on main due to login/status, the parent is synchronized on packetQueue
+        final java.util.Iterator<WrappedConsumer> iterator = this.pendingActions.iterator();
+        while (iterator.hasNext()) {
+            final WrappedConsumer queued = iterator.next(); // poll -> peek
+
+            // Fix NPE (Spigot bug caused by handleDisconnection())
+            if (queued == null) {
+                return true;
+            }
+
+            if (queued.isConsumed()) {
+                continue;
+            }
+
+            if (queued instanceof PacketSendAction packetSendAction) {
+                final Packet<?> packet = packetSendAction.packet;
+                if (!packet.isReady()) {
+                    return false;
                 }
+            }
 
+            iterator.remove();
+            if (queued.tryMarkConsumed()) {
+                queued.accept(this);
             }
         }
+        return true;
     }
+    // Paper end - Optimize network
 
     private static final int MAX_PER_TICK = io.papermc.paper.configuration.GlobalConfiguration.get().misc.maxJoinsPerTick; // Paper - Buffer joins to world
     private static int joinAttemptsThisTick; // Paper - Buffer joins to world
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     public void disconnect(Component disconnectReason) {
         // Spigot Start
         this.preparing = false;
+        this.clearPacketQueue(); // Paper - Optimize network
         // Spigot End
         if (this.channel == null) {
             this.delayedDisconnect = disconnectReason;
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     public void handleDisconnection() {
         if (this.channel != null && !this.channel.isOpen()) {
             if (this.disconnectionHandled) {
-                Connection.LOGGER.warn("handleDisconnection() called twice");
+                // Connection.LOGGER.warn("handleDisconnection() called twice"); // Paper - Don't log useless message
             } else {
                 this.disconnectionHandled = true;
                 PacketListener packetlistener = this.getPacketListener();
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
 
                     packetlistener1.onDisconnect(ichatbasecomponent);
                 }
-                this.pendingActions.clear(); // Free up packet queue.
+                this.clearPacketQueue(); // Paper - Optimize network
                 // Paper start - Add PlayerConnectionCloseEvent
                 final PacketListener packetListener = this.getPacketListener();
                 if (packetListener instanceof net.minecraft.server.network.ServerCommonPacketListenerImpl commonPacketListener) {
@@ -0,0 +0,0 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     public void setBandwidthLogger(LocalSampleLogger log) {
         this.bandwidthDebugMonitor = new BandwidthDebugMonitor(log);
     }
+
+    // Paper start - Optimize network
+    public void clearPacketQueue() {
+        final net.minecraft.server.level.ServerPlayer player = getPlayer();
+        for (final Consumer<Connection> queuedAction : this.pendingActions) {
+            if (queuedAction instanceof PacketSendAction packetSendAction) {
+                final Packet<?> packet = packetSendAction.packet;
+                if (packet.hasFinishListener()) {
+                    packet.onPacketDispatchFinish(player, null);
+                }
+            }
+        }
+        this.pendingActions.clear();
+    }
+
+    private static class InnerUtil { // Attempt to hide these methods from ProtocolLib, so it doesn't accidently pick them up.
+
+        @Nullable
+        private static java.util.List<Packet<?>> buildExtraPackets(final Packet<?> packet) {
+            final java.util.List<Packet<?>> extra = packet.getExtraPackets();
+            if (extra == null || extra.isEmpty()) {
+                return null;
+            }
+
+            final java.util.List<Packet<?>> ret = new java.util.ArrayList<>(1 + extra.size());
+            buildExtraPackets0(extra, ret);
+            return ret;
+        }
+
+        private static void buildExtraPackets0(final java.util.List<Packet<?>> extraPackets, final java.util.List<Packet<?>> into) {
+            for (final Packet<?> extra : extraPackets) {
+                into.add(extra);
+                final java.util.List<Packet<?>> extraExtra = extra.getExtraPackets();
+                if (extraExtra != null && !extraExtra.isEmpty()) {
+                    buildExtraPackets0(extraExtra, into);
+                }
+            }
+        }
+
+        private static boolean canSendImmediate(final Connection networkManager, final net.minecraft.network.protocol.Packet<?> packet) {
+            return networkManager.isPending || networkManager.packetListener.protocol() != ConnectionProtocol.PLAY ||
+                packet instanceof net.minecraft.network.protocol.common.ClientboundKeepAlivePacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundPlayerChatPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundSystemChatPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundCommandSuggestionsPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundSetTitleTextPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundSetSubtitleTextPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundSetActionBarTextPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundSetTitlesAnimationPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundClearTitlesPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundSoundPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundSoundEntityPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundStopSoundPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundLevelParticlesPacket ||
+                packet instanceof net.minecraft.network.protocol.game.ClientboundBossEventPacket;
+        }
+    }
+
+    private static class WrappedConsumer implements Consumer<Connection> {
+        private final Consumer<Connection> delegate;
+        private final java.util.concurrent.atomic.AtomicBoolean consumed = new java.util.concurrent.atomic.AtomicBoolean(false);
+
+        private WrappedConsumer(final Consumer<Connection> delegate) {
+            this.delegate = delegate;
+        }
+
+        @Override
+        public void accept(final Connection connection) {
+            this.delegate.accept(connection);
+        }
+
+        public boolean tryMarkConsumed() {
+            return consumed.compareAndSet(false, true);
+        }
+
+        public boolean isConsumed() {
+            return consumed.get();
+        }
+    }
+
+    private static final class PacketSendAction extends WrappedConsumer {
+        private final Packet<?> packet;
+
+        private PacketSendAction(final Packet<?> packet, @Nullable final PacketSendListener packetSendListener, final boolean flush) {
+            super(connection -> connection.sendPacket(packet, packetSendListener, flush));
+            this.packet = packet;
+        }
+    }
+    // Paper end - Optimize network
 }
diff --git a/src/main/java/net/minecraft/network/protocol/Packet.java b/src/main/java/net/minecraft/network/protocol/Packet.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/network/protocol/Packet.java
+++ b/src/main/java/net/minecraft/network/protocol/Packet.java
@@ -0,0 +0,0 @@ public interface Packet<T extends PacketListener> {
     static <B extends ByteBuf, T extends Packet<?>> StreamCodec<B, T> codec(StreamMemberEncoder<B, T> encoder, StreamDecoder<B, T> decoder) {
         return StreamCodec.ofMember(encoder, decoder);
     }
+
+    // Paper start
+    /**
+     * @param player Null if not at PLAY stage yet
+     */
+    default void onPacketDispatch(@org.jetbrains.annotations.Nullable net.minecraft.server.level.ServerPlayer player) {
+    }
+
+    /**
+     * @param player Null if not at PLAY stage yet
+     * @param future Can be null if packet was cancelled
+     */
+    default void onPacketDispatchFinish(@org.jetbrains.annotations.Nullable net.minecraft.server.level.ServerPlayer player, @org.jetbrains.annotations.Nullable io.netty.channel.ChannelFuture future) {}
+
+    default boolean hasFinishListener() {
+        return false;
+    }
+
+    default boolean isReady() {
+        return true;
+    }
+
+    @org.jetbrains.annotations.Nullable
+    default java.util.List<Packet<?>> getExtraPackets() {
+        return null;
+    }
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/server/network/ServerConnectionListener.java b/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
+++ b/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
@@ -0,0 +0,0 @@ public class ServerConnectionListener {
     final List<Connection> connections = Collections.synchronizedList(Lists.newArrayList());
     // Paper start - prevent blocking on adding a new connection while the server is ticking
     private final java.util.Queue<Connection> pending = new java.util.concurrent.ConcurrentLinkedQueue<>();
+    private static final boolean disableFlushConsolidation = Boolean.getBoolean("Paper.disableFlushConsolidate"); // Paper - Optimize network
     private final void addPending() {
         Connection connection;
         while ((connection = pending.poll()) != null) {
             connections.add(connection);
+            connection.isPending = false; // Paper - Optimize network
         }
     }
     // Paper end - prevent blocking on adding a new connection while the server is ticking
@@ -0,0 +0,0 @@ public class ServerConnectionListener {
                         ;
                     }
 
+                    if (!disableFlushConsolidation) channel.pipeline().addFirst(new io.netty.handler.flush.FlushConsolidationHandler()); // Paper - Optimize network
                     ChannelPipeline channelpipeline = channel.pipeline().addLast("timeout", new ReadTimeoutHandler(30));
 
                     if (ServerConnectionListener.this.server.repliesToStatus()) {
