Provide a system property to set the keepalive limit

add a system property to allow people to tweak how long the server
will wait for a reply. There is a compromise here between lower and higher
values, lower values will mean that dead connections can be closed sooner,
whereas higher values will make this less sensitive to issues such as spikes
from networking or during connections flood of chunk packets on slower clients,
at the cost of dead connections being kept open for longer.

Spigot-Server-Patches/AsyncTabCompleteEvent.patch

@@ -14,7 +14,7 @@ completion, such as offline players.
 Also adds isCommand and getLocation to the sync TabCompleteEvent
 
 diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
-index 5a620f3fd..ead0994f8 100644
+index d0ab87d0f..ca054afcf 100644
 --- a/src/main/java/net/minecraft/server/PlayerConnection.java
 +++ b/src/main/java/net/minecraft/server/PlayerConnection.java
 @@ -0,0 +0,0 @@ public class PlayerConnection implements PacketListenerPlayIn, ITickable {

Spigot-Server-Patches/revert-serverside-behavior-of-keepalives.patch

@@ -1,7 +1,7 @@
 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
 From: Shane Freeder <theboyetronic@gmail.com>
 Date: Sun, 15 Oct 2017 00:29:07 +0100
-Subject: [PATCH] Increase time allowed for a keepalive reply
+Subject: [PATCH] revert serverside behavior of keepalives
 
 This patch intends to bump up the time that a client has to reply to the
 server back to 30 seconds as per pre 1.12.2, which allowed clients
@@ -9,10 +9,25 @@ more than enough time to reply potentially allowing them to be less
 tempermental due to lag spikes on the network thread, e.g. that caused
 by plugins that are interacting with netty.
 
+We also add a system property to allow people to tweak how long the server
+will wait for a reply. There is a compromise here between lower and higher
+values, lower values will mean that dead connections can be closed sooner,
+whereas higher values will make this less sensitive to issues such as spikes
+from networking or during connections flood of chunk packets on slower clients,
+ at the cost of dead connections being kept open for longer.
+
 diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
-index a92bf8967..5a620f3fd 100644
+index a92bf8967..d0ab87d0f 100644
 --- a/src/main/java/net/minecraft/server/PlayerConnection.java
 +++ b/src/main/java/net/minecraft/server/PlayerConnection.java
+@@ -0,0 +0,0 @@ public class PlayerConnection implements PacketListenerPlayIn, ITickable {
+     private int receivedMovePackets;
+     private int processedMovePackets;
+     private AutoRecipe H = new AutoRecipe();
++    private static final long KEEPALIVE_LIMIT = Long.getLong("paper.playerconnection.keepalive", 30) * 1000; // Paper - provide property to set keepalive limit
+ 
+     public PlayerConnection(MinecraftServer minecraftserver, NetworkManager networkmanager, EntityPlayer entityplayer) {
+         this.minecraftServer = minecraftserver;
 @@ -0,0 +0,0 @@ public class PlayerConnection implements PacketListenerPlayIn, ITickable {
          }
  
@@ -33,7 +48,7 @@ index a92bf8967..5a620f3fd 100644
 +        long elapsedTime = currentTime - this.getLastPing();
 +        if (this.isPendingPing()) {
 +            // We're pending a ping from the client
-+            if (!this.processedDisconnect && elapsedTime >= 30000L) { // 30 seconds for a ping reply also, don't fire if already disconnected
++            if (!this.processedDisconnect && elapsedTime >= KEEPALIVE_LIMIT) { // check keepalive limit, don't fire if already disconnected
 +                PlayerConnection.LOGGER.warn("{} was kicked due to keepalive timeout!", this.player.getName()); // more info
 +                this.disconnect(new ChatMessage("disconnect.timeout"));
 +            }