From 7fc14d8956157a735dcba939418b80ef3d1cb48a Mon Sep 17 00:00:00 2001
From: Camotoy <20743703+DoctorMacc@users.noreply.github.com>
Date: Fri, 31 Jul 2020 19:47:23 -0400
Subject: [PATCH] Add customizable MTU support (#1068)

* Add customizable MTU support

Fixes clients being unable to connect in rare instances.

* Make config.yml nicer
---
 .../geysermc/platform/sponge/GeyserSpongeConfiguration.java | 5 +++++
 .../main/java/org/geysermc/connector/GeyserConnector.java   | 5 +++++
 .../connector/configuration/GeyserConfiguration.java        | 2 ++
 .../connector/configuration/GeyserJacksonConfiguration.java | 3 +++
 connector/src/main/resources/config.yml                     | 6 +++++-
 5 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/bootstrap/sponge/src/main/java/org/geysermc/platform/sponge/GeyserSpongeConfiguration.java b/bootstrap/sponge/src/main/java/org/geysermc/platform/sponge/GeyserSpongeConfiguration.java
index 27c54326..279aca54 100644
--- a/bootstrap/sponge/src/main/java/org/geysermc/platform/sponge/GeyserSpongeConfiguration.java
+++ b/bootstrap/sponge/src/main/java/org/geysermc/platform/sponge/GeyserSpongeConfiguration.java
@@ -253,6 +253,11 @@ public class GeyserSpongeConfiguration implements GeyserConfiguration {
         }
     }
 
+    @Override
+    public int getMtu() {
+        return node.getNode("mtu").getInt(1400);
+    }
+
     @Override
     public int getConfigVersion() {
         return node.getNode("config-version").getInt(0);
diff --git a/connector/src/main/java/org/geysermc/connector/GeyserConnector.java b/connector/src/main/java/org/geysermc/connector/GeyserConnector.java
index ee687dbb..6224dfcd 100644
--- a/connector/src/main/java/org/geysermc/connector/GeyserConnector.java
+++ b/connector/src/main/java/org/geysermc/connector/GeyserConnector.java
@@ -27,6 +27,7 @@ package org.geysermc.connector;
 
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.nukkitx.network.raknet.RakNetConstants;
 import com.nukkitx.protocol.bedrock.BedrockPacketCodec;
 import com.nukkitx.protocol.bedrock.BedrockServer;
 import com.nukkitx.protocol.bedrock.v407.Bedrock_v407;
@@ -168,6 +169,10 @@ public class GeyserConnector {
         if (config.isAboveBedrockNetherBuilding())
             DimensionUtils.changeBedrockNetherId(); // Apply End dimension ID workaround to Nether
 
+        // https://github.com/GeyserMC/Geyser/issues/957
+        RakNetConstants.MAXIMUM_MTU_SIZE = (short) config.getMtu();
+        logger.debug("Setting MTU to " + config.getMtu());
+
         bedrockServer = new BedrockServer(new InetSocketAddress(config.getBedrock().getAddress(), config.getBedrock().getPort()));
         bedrockServer.setHandler(new ConnectorServerEventHandler(this));
         bedrockServer.bind().whenComplete((avoid, throwable) -> {
diff --git a/connector/src/main/java/org/geysermc/connector/configuration/GeyserConfiguration.java b/connector/src/main/java/org/geysermc/connector/configuration/GeyserConfiguration.java
index 57b4d739..94322db9 100644
--- a/connector/src/main/java/org/geysermc/connector/configuration/GeyserConfiguration.java
+++ b/connector/src/main/java/org/geysermc/connector/configuration/GeyserConfiguration.java
@@ -118,6 +118,8 @@ public interface GeyserConfiguration {
         String getUniqueId();
     }
 
+    int getMtu();
+
     int getConfigVersion();
 
     static void checkGeyserConfiguration(GeyserConfiguration geyserConfig, GeyserLogger geyserLogger) {
diff --git a/connector/src/main/java/org/geysermc/connector/configuration/GeyserJacksonConfiguration.java b/connector/src/main/java/org/geysermc/connector/configuration/GeyserJacksonConfiguration.java
index c31e9d2f..d6eaf934 100644
--- a/connector/src/main/java/org/geysermc/connector/configuration/GeyserJacksonConfiguration.java
+++ b/connector/src/main/java/org/geysermc/connector/configuration/GeyserJacksonConfiguration.java
@@ -138,6 +138,9 @@ public abstract class GeyserJacksonConfiguration implements GeyserConfiguration
         private String uniqueId;
     }
 
+    @JsonProperty("mtu")
+    private int mtu = 1400;
+
     @JsonProperty("config-version")
     private int configVersion;
 }
diff --git a/connector/src/main/resources/config.yml b/connector/src/main/resources/config.yml
index c587b21d..d8961270 100644
--- a/connector/src/main/resources/config.yml
+++ b/connector/src/main/resources/config.yml
@@ -110,5 +110,9 @@ metrics:
   # UUID of server, don't change!
   uuid: generateduuid
 
-# DO NOT TOUCH!
+# ADVANCED OPTIONS - DO NOT TOUCH UNLESS YOU KNOW WHAT YOU ARE DOING! 
+# The internet supports a maximum MTU of 1492 but could cause issues with packet fragmentation.
+# 1400 is the default.
+# mtu: 1400
+
 config-version: 3