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


diff --git a/src/main/java/net/minecraft/server/network/ServerCommonPacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerCommonPacketListenerImpl.java
index a8edeb5a40cd9aac933805259407e32c544d181e..26ccb217b846410c826cb1da017b45903d9c5469 100644
--- a/src/main/java/net/minecraft/server/network/ServerCommonPacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerCommonPacketListenerImpl.java
@@ -73,6 +73,7 @@ public abstract class ServerCommonPacketListenerImpl implements ServerCommonPack
     private long keepAliveChallenge;
     private long closedListenerTime;
     private boolean closed = false;
+    private it.unimi.dsi.fastutil.longs.LongList keepAlives = new it.unimi.dsi.fastutil.longs.LongArrayList(); // Purpur
     private int latency;
     private volatile boolean suspendFlushingOnServerThread = false;
     public final java.util.Map<java.util.UUID, net.kyori.adventure.resource.ResourcePackCallback> packCallbacks = new java.util.concurrent.ConcurrentHashMap<>(); // Paper - adventure resource pack callbacks
@@ -124,6 +125,16 @@ public abstract class ServerCommonPacketListenerImpl implements ServerCommonPack
 
     @Override
     public void handleKeepAlive(ServerboundKeepAlivePacket packet) {
+        // Purpur start
+        if (org.purpurmc.purpur.PurpurConfig.useAlternateKeepAlive) {
+            long id = packet.getId();
+            if (keepAlives.size() > 0 && keepAlives.contains(id)) {
+                int ping = (int) (Util.getMillis() - id);
+                this.latency = (this.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.serverLevel()); // CraftBukkit // Paper - handle ServerboundKeepAlivePacket async
         if (this.keepAlivePending && packet.getId() == this.keepAliveChallenge) {
             int i = (int) (Util.getMillis() - this.keepAliveTime);
@@ -260,6 +271,21 @@ public abstract class ServerCommonPacketListenerImpl implements ServerCommonPack
         long currentTime = Util.getMillis();
         long elapsedTime = currentTime - this.keepAliveTime;
 
+        // Purpur start
+        if (org.purpurmc.purpur.PurpurConfig.useAlternateKeepAlive) {
+            if (elapsedTime >= 1000L) { // 1 second
+                if (!processedDisconnect && keepAlives.size() * 1000L >= KEEPALIVE_LIMIT) {
+                    LOGGER.warn("{} was kicked due to keepalive timeout!", this.player.getScoreboardName());
+                    disconnect(ServerCommonPacketListenerImpl.TIMEOUT_DISCONNECTION_MESSAGE, org.bukkit.event.player.PlayerKickEvent.Cause.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.isSingleplayerOwner() && elapsedTime >= 15000L) { // Paper - use vanilla's 15000L between keep alive packets
             if (this.keepAlivePending && !this.processedDisconnect && elapsedTime >= KEEPALIVE_LIMIT) { // Paper - check keepalive limit, don't fire if already disconnected
                 this.disconnect(ServerCommonPacketListenerImpl.TIMEOUT_DISCONNECTION_MESSAGE, org.bukkit.event.player.PlayerKickEvent.Cause.TIMEOUT); // Paper - kick event cause
diff --git a/src/main/java/org/purpurmc/purpur/PurpurConfig.java b/src/main/java/org/purpurmc/purpur/PurpurConfig.java
index 876a4ea0beeae5baca62822eec2e18a4cf3ef09b..bf45bdc2126b320a4954a3d546ec9d4d30660527 100644
--- a/src/main/java/org/purpurmc/purpur/PurpurConfig.java
+++ b/src/main/java/org/purpurmc/purpur/PurpurConfig.java
@@ -198,6 +198,11 @@ public class PurpurConfig {
         laggingThreshold = getDouble("settings.lagging-threshold", laggingThreshold);
     }
 
+    public static boolean useAlternateKeepAlive = false;
+    private static void useAlternateKeepAlive() {
+        useAlternateKeepAlive = getBoolean("settings.use-alternate-keepalive", useAlternateKeepAlive);
+    }
+
     public static int barrelRows = 3;
     public static boolean enderChestSixRows = false;
     public static boolean enderChestPermissionRows = false;