[WIP] Prevent older clients from connecting

Prevents older clients from connecting, which would cause desync issues.
My mind is exhausted from trying to figure out how this should work, so I'm just pushing it as-is.

Author: halotroop2288

common/src/main/java/com/fox2code/foxloader/loader/packet/ServerHello.java

@@ -1,5 +1,6 @@
 package com.fox2code.foxloader.loader.packet;
 
+import com.fox2code.foxloader.loader.ModLoader;
 import com.fox2code.foxloader.registry.EntityTypeRegistryEntry;
 import com.fox2code.foxloader.registry.RegistryEntry;
 
@@ -8,10 +9,20 @@
 import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.logging.Level;
 
 public final class ServerHello extends FoxPacket {
-    public static final int SERVER_HELLO_VERSION = 1;
-    private static final int SERVER_HELLO_VERSION_NEXT = 1;
+    /**
+	 * <p>The current version of the Server Hello packet.</p>
+     * <b>V0</b> - <i>Block and Item registry entries and metadata</i>.<br/>
+     * <b>V1</b> - <i>Entity type registry metadata appended to the end</i>.
+     */
+    public static final short SERVER_HELLO_VERSION = 1;
+    /**
+     * <p>The minimum version of ServerHello on older clients for the server to be compatible with.</p>
+     * V0 clients will always expect exactly {@literal 0}.
+     */
+    private static final short CLIENT_BACKWARD_COMPATIBILITY_VERSION = 0;
 
     public HashMap<String, RegistryEntry> registryEntries;
     public HashMap<String, String> metadata;
@@ -30,13 +41,15 @@ public ServerHello(HashMap<String, RegistryEntry> registryEntries,
         this.entityTypeRegistryEntries = entityTypeRegistryEntries;
     }
 
+	/**
+	 * @throws IOException if the data cannot be read as instructed.
+	 */
     @Override
     public void readData(DataInputStream inStream) throws IOException {
         int serverHelloVersion = inStream.readUnsignedShort();
-        if (serverHelloVersion >= SERVER_HELLO_VERSION_NEXT &&
-                // Next field is how much backward compatible is the packet
-                inStream.readUnsignedShort() > SERVER_HELLO_VERSION_NEXT) {
-            throw new RuntimeException("Client is critically out of date, please update FoxLoader");
+        int clientBackwardCompatibilityVersion = inStream.readUnsignedShort();
+        if (SERVER_HELLO_VERSION < clientBackwardCompatibilityVersion) {
+            throw new IOException("Client is critically out of date, please update FoxLoader.");
         }
 
         int entries = inStream.readUnsignedShort();
@@ -51,6 +64,7 @@ public void readData(DataInputStream inStream) throws IOException {
         if (inStream.available() < 2) {
             // Too few bytes to read the next short.
             this.metadata = new HashMap<>();
+            ModLoader.getModLoaderLogger().log(Level.WARNING, "Server Hello: Too few bytes to read metadata.");
         } else {
             entries = inStream.readUnsignedShort();
             metadata = new HashMap<>();
@@ -60,8 +74,8 @@ public void readData(DataInputStream inStream) throws IOException {
         }
 
         if (inStream.available() < 4) {
-            // Too few bytes to read the next integer.
             this.entityTypeRegistryEntries = new HashMap<>();
+            ModLoader.getModLoaderLogger().log(Level.WARNING, "Server Hello: Too few bytes to read entity data.");
         } else {
             int entityEntries = inStream.readInt();
             entityTypeRegistryEntries = new HashMap<>(entityEntries);
@@ -76,6 +90,7 @@ public void readData(DataInputStream inStream) throws IOException {
     @Override
     public void writeData(DataOutputStream outStream) throws IOException {
         outStream.writeShort(SERVER_HELLO_VERSION);
+        outStream.writeShort(CLIENT_BACKWARD_COMPATIBILITY_VERSION);
 
         outStream.writeShort(this.registryEntries.size());
         for (RegistryEntry registryEntry : registryEntries.values()) {