Paper/patches/server/0448-Buffer-joins-to-world.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Shane Freeder <theboyetronic@gmail.com>
Date: Wed, 19 Aug 2020 05:05:54 +0100
Subject: [PATCH] Buffer joins to world

This patch buffers the number of logins which will attempt to join
the world per tick, this attempts to reduce the impact that join floods
has on the server

diff --git a/src/main/java/net/minecraft/network/Connection.java b/src/main/java/net/minecraft/network/Connection.java
index 81e49a770fd8a10e987f3e67a5ab99fc39d5e47f..a147c5e1929e8034b28af56f561f86478684fd08 100644
--- a/src/main/java/net/minecraft/network/Connection.java
+++ b/src/main/java/net/minecraft/network/Connection.java
@@ -403,14 +403,29 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
         }
     }
 
+    private static final int MAX_PER_TICK = io.papermc.paper.configuration.GlobalConfiguration.get().misc.maxJoinsPerTick; // Paper
+    private static int joinAttemptsThisTick; // Paper
+    private static int currTick; // Paper
     public void tick() {
         this.flushQueue();
+        // Paper start
+        if (Connection.currTick != net.minecraft.server.MinecraftServer.currentTick) {
+            Connection.currTick = net.minecraft.server.MinecraftServer.currentTick;
+            Connection.joinAttemptsThisTick = 0;
+        }
+        // Paper end
         PacketListener packetlistener = this.packetListener;
 
         if (packetlistener instanceof TickablePacketListener) {
             TickablePacketListener tickablepacketlistener = (TickablePacketListener) packetlistener;
 
+            // Paper start - limit the number of joins which can be processed each tick
+            if (!(this.packetListener instanceof net.minecraft.server.network.ServerLoginPacketListenerImpl loginPacketListener)
+                || loginPacketListener.state != net.minecraft.server.network.ServerLoginPacketListenerImpl.State.READY_TO_ACCEPT
+                || Connection.joinAttemptsThisTick++ < MAX_PER_TICK) {
             tickablepacketlistener.tick();
+            }
+            // Paper end
         }
 
         if (!this.isConnected() && !this.disconnectionHandled) {