Add customizable MTU support (#1068)

* Add customizable MTU support

Fixes clients being unable to connect in rare instances.

* Make config.yml nicer

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);

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) -> {

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) {

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;
 }

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