From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: William Blake Galbreath <blake.galbreath@gmail.com>
Date: Fri, 11 Oct 2019 00:17:39 -0500
Subject: [PATCH] Alternative Keepalive Handling

Original code by PurpurMC, licensed under MIT
You can find the original code on https://github.com/PurpurMC/Purpur

diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index ca245019669591a5468de2df6dedc3080b61282e..507cc0d0322bff3e2536629b89339982cdc8352f 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -260,6 +260,7 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
     private long keepAliveTime = Util.getMillis();
     private boolean keepAlivePending;
     private long keepAliveChallenge;
+    private java.util.List<Long> keepAlives = new java.util.ArrayList<>(); // Purpur
     // CraftBukkit start - multithreaded fields
     private final AtomicInteger chatSpamTickCount = new AtomicInteger();
     private final java.util.concurrent.atomic.AtomicInteger tabSpamLimiter = new java.util.concurrent.atomic.AtomicInteger(); // Paper - configurable tab spam limits
@@ -407,6 +408,21 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
         long currentTime = Util.getMillis();
         long elapsedTime = currentTime - this.keepAliveTime;
 
+        // Purpur start
+        if (wtf.etil.mirai.MiraiConfig.useAlternateKeepAlive) {
+            if (elapsedTime >= 1000L) { // 1 second
+                if (!processedDisconnect && keepAlives.size() > KEEPALIVE_LIMIT) {
+                    LOGGER.warn("{} was kicked due to keepalive timeout!", player.getName());
+                    disconnect(Component.translatable("disconnect.timeout"));
+                } else {
+                    keepAliveTime = currentTime; // hijack this field for 1 second intervals
+                    keepAlives.add(currentTime); // currentTime is ID
+                    send(new ClientboundKeepAlivePacket(currentTime));
+                }
+            }
+        } else
+        // Purpur end
+
         if (this.keepAlivePending) {
             if (!this.processedDisconnect && elapsedTime >= KEEPALIVE_LIMIT) { // check keepalive limit, don't fire if already disconnected
                 ServerGamePacketListenerImpl.LOGGER.warn("{} was kicked due to keepalive timeout!", this.player.getScoreboardName()); // more info
@@ -3597,6 +3613,16 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
 
     @Override
     public void handleKeepAlive(ServerboundKeepAlivePacket packet) {
+        // Purpur start
+        if (wtf.etil.mirai.MiraiConfig.useAlternateKeepAlive) {
+            long id = packet.getId();
+            if (keepAlives.size() > 0 && keepAlives.contains(id)) {
+                int ping = (int) (Util.getMillis() - id);
+                player.latency = (player.latency * 3 + ping) / 4;
+                keepAlives.clear(); // we got a valid response, lets roll with it and forget the rest
+            }
+        } else
+        // Purpur end
         //PacketUtils.ensureRunningOnSameThread(packet, this, this.player.getLevel()); // CraftBukkit // Paper - This shouldn't be on the main thread
         if (this.keepAlivePending && packet.getId() == this.keepAliveChallenge) {
             int i = (int) (Util.getMillis() - this.keepAliveTime);
diff --git a/src/main/java/wtf/etil/mirai/MiraiConfig.java b/src/main/java/wtf/etil/mirai/MiraiConfig.java
index 992ab312e6e2b8283ef8187bcbeeb35dd51858a1..ffbee643991ff36bb3a0b8de937fcf518c25a294 100644
--- a/src/main/java/wtf/etil/mirai/MiraiConfig.java
+++ b/src/main/java/wtf/etil/mirai/MiraiConfig.java
@@ -159,4 +159,11 @@ public class MiraiConfig {
                                         "Whether or not server should send entity packets with null movements.");
     }
 
+    public static boolean useAlternateKeepAlive;
+    private static void alternateKeepAlive() {
+        useAlternateKeepAlive = getBoolean("use-alternate-keepalive", true,
+                                    "Whether or not server should use an alternative keepalive algorithm.",
+                                    "This can drastically reduce players timeouts due to a bad connection.");
+    }
+
 }
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