Don't allow the sub-MOTD to be empty (GeyserMC#1933)

As of 1.16.210.59, the sub-MOTD cannot be blank: https://bugs.mojang.com/browse/MCPE-117979

This workaround will be implemented now so the widest range of Geyser versions will properly show a ping in 1.16.210 - better an 'outdated server' message than 'unable to connect to world.'

connector/src/main/java/org/geysermc/connector/network/ConnectorServerEventHandler.java

@@ -42,6 +42,15 @@
 import java.nio.charset.StandardCharsets;
 
 public class ConnectorServerEventHandler implements BedrockServerEventHandler {
+    /*
+    The following constants are all used to ensure the ping does not reach a length where it is unparsable by the Bedrock client
+     */
+    private static final int MINECRAFT_VERSION_BYTES_LENGTH = BedrockProtocol.DEFAULT_BEDROCK_CODEC.getMinecraftVersion().getBytes(StandardCharsets.UTF_8).length;
+    private static final int BRAND_BYTES_LENGTH = GeyserConnector.NAME.getBytes(StandardCharsets.UTF_8).length;
+    /**
+     * The MOTD, sub-MOTD and Minecraft version ({@link #MINECRAFT_VERSION_BYTES_LENGTH}) combined cannot reach this length.
+     */
+    private static final int MAGIC_RAKNET_LENGTH = 338;
 
     private final GeyserConnector connector;
 
@@ -72,13 +81,13 @@ public BedrockPong onQuery(InetSocketAddress inetSocketAddress) {
         pong.setGameType("Survival"); // Can only be Survival or Creative as of 1.16.210.59
         pong.setNintendoLimited(false);
         pong.setProtocolVersion(BedrockProtocol.DEFAULT_BEDROCK_CODEC.getProtocolVersion());
-        pong.setVersion(BedrockProtocol.DEFAULT_BEDROCK_CODEC.getMinecraftVersion()); // Required to not be empty as of 1.16.210.59
+        pong.setVersion(BedrockProtocol.DEFAULT_BEDROCK_CODEC.getMinecraftVersion()); // Required to not be empty as of 1.16.210.59. Can only contain . and numbers.
         pong.setIpv4Port(config.getBedrock().getPort());
 
         if (config.isPassthroughMotd() && pingInfo != null && pingInfo.getDescription() != null) {
             String[] motd = MessageTranslator.convertMessageLenient(pingInfo.getDescription()).split("\n");
             String mainMotd = motd[0]; // First line of the motd.
-            String subMotd = (motd.length != 1) ? motd[1] : ""; // Second line of the motd if present, otherwise blank.
+            String subMotd = (motd.length != 1) ? motd[1] : GeyserConnector.NAME; // Second line of the motd if present, otherwise default.
 
             pong.setMotd(mainMotd.trim());
             pong.setSubMotd(subMotd.trim()); // Trimmed to shift it to the left, prevents the universe from collapsing on us just because we went 2 characters over the text box's limit.
@@ -95,22 +104,28 @@ public BedrockPong onQuery(InetSocketAddress inetSocketAddress) {
             pong.setMaximumPlayerCount(config.getMaxPlayers());
         }
 
-        if (pong.getMotd() == null) {
-            pong.setMotd("");
+        // Fallbacks to prevent errors and allow Bedrock to see the server
+        if (pong.getMotd() == null || pong.getMotd().trim().isEmpty()) {
+            pong.setMotd(GeyserConnector.NAME);
         }
-        if (pong.getSubMotd() == null) {
-            pong.setSubMotd("");
+        if (pong.getSubMotd() == null || pong.getSubMotd().trim().isEmpty()) {
+            // Sub-MOTD cannot be empty as of 1.16.210.59
+            pong.setSubMotd(GeyserConnector.NAME);
         }
 
         // The ping will not appear if the MOTD + sub-MOTD is of a certain length.
         // We don't know why, though
         byte[] motdArray = pong.getMotd().getBytes(StandardCharsets.UTF_8);
-        if (motdArray.length + pong.getSubMotd().getBytes(StandardCharsets.UTF_8).length > 338) {
-            // Remove the sub-MOTD first since that only appears locally
-            pong.setSubMotd("");
-            if (motdArray.length > 338) {
+        int subMotdLength = pong.getSubMotd().getBytes(StandardCharsets.UTF_8).length;
+        if (motdArray.length + subMotdLength > (MAGIC_RAKNET_LENGTH - MINECRAFT_VERSION_BYTES_LENGTH)) {
+            // Shorten the sub-MOTD first since that only appears locally
+            if (subMotdLength > BRAND_BYTES_LENGTH) {
+                pong.setSubMotd(GeyserConnector.NAME);
+                subMotdLength = BRAND_BYTES_LENGTH;
+            }
+            if (motdArray.length > (MAGIC_RAKNET_LENGTH - MINECRAFT_VERSION_BYTES_LENGTH - subMotdLength)) {
                 // If the top MOTD is still too long, we chop it down
-                byte[] newMotdArray = new byte[339];
+                byte[] newMotdArray = new byte[MAGIC_RAKNET_LENGTH - MINECRAFT_VERSION_BYTES_LENGTH - subMotdLength];
                 System.arraycopy(motdArray, 0, newMotdArray, 0, newMotdArray.length);
                 pong.setMotd(new String(newMotdArray, StandardCharsets.UTF_8));
             }

connector/src/main/resources/config.yml

@@ -18,8 +18,9 @@ bedrock:
   # This option is for the plugin version only.
   clone-remote-port: false
   # The MOTD that will be broadcasted to Minecraft: Bedrock Edition clients. This is irrelevant if "passthrough-motd" is set to true
-  motd1: "GeyserMC"
-  motd2: "Another GeyserMC forced host."
+  # If either of these are empty, the respective string will default to "Geyser"
+  motd1: "Geyser"
+  motd2: "Another Geyser server."
   # The Server Name that will be sent to Minecraft: Bedrock Edition clients. This is visible in both the pause menu and the settings menu.
   server-name: "Geyser"
 remote: