Using javassist add compatibility for Spigot builds with protocol compatibility (eg. 1.9.1 & 1.9.2)

Also fix issue with protocol passthrough
*whew*

src/main/java/us/myles/ViaVersion/ViaVersionPlugin.java

@@ -20,6 +20,7 @@ import us.myles.ViaVersion.api.command.ViaVersionCommand;
 import us.myles.ViaVersion.api.data.UserConnection;
 import us.myles.ViaVersion.api.protocol.ProtocolRegistry;
 import us.myles.ViaVersion.boss.ViaBossBar;
+import us.myles.ViaVersion.classgenerator.ClassGenerator;
 import us.myles.ViaVersion.commands.ViaCommandHandler;
 import us.myles.ViaVersion.handlers.ViaVersionInitializer;
 import us.myles.ViaVersion.protocols.base.ProtocolInfo;
@@ -48,6 +49,7 @@ public class ViaVersionPlugin extends JavaPlugin implements ViaVersionAPI, ViaVe
     private List<Pair<Field, Object>> injectedLists = new ArrayList<>();
     private ViaCommandHandler commandHandler;
     private boolean debug = false;
+    private boolean compatSpigotBuild = false;
 
     @Override
     public void onLoad() {
@@ -65,8 +67,16 @@ public class ViaVersionPlugin extends JavaPlugin implements ViaVersionAPI, ViaVe
 
             }
         }
+        // Check if it's a spigot build with a protocol mod
+        try {
+            compatSpigotBuild = ReflectionUtil.nms("PacketEncoder").getDeclaredField("version") != null;
+        } catch (Exception e){
+            compatSpigotBuild = false;
+        }
+        // Generate classes needed (only works if it's compat)
+        ClassGenerator.generate();
 
-        getLogger().info("ViaVersion " + getDescription().getVersion() + " is now loaded, injecting.");
+        getLogger().info("ViaVersion " + getDescription().getVersion() + (compatSpigotBuild ? "compat" : "") + " is now loaded, injecting.");
         injectPacketHandler();
     }
 
@@ -348,6 +358,11 @@ public class ViaVersionPlugin extends JavaPlugin implements ViaVersionAPI, ViaVe
         return commandHandler;
     }
 
+    @Override
+    public boolean isCompatSpigotBuild() {
+        return compatSpigotBuild;
+    }
+
     public boolean isCheckForUpdates() {
         return getConfig().getBoolean("checkforupdates", true);
     }

src/main/java/us/myles/ViaVersion/api/PacketWrapper.java

@@ -174,7 +174,7 @@ public class PacketWrapper {
         readableObjects.clear();
         // If the buffer has readable bytes, copy them.
         if(inputBuffer.readableBytes() > 0){
-            read(Type.REMAINING_BYTES);
+            passthrough(Type.REMAINING_BYTES);
         }
     }
 
@@ -318,4 +318,13 @@ public class PacketWrapper {
             PipelineUtil.getContextBefore("decompress", user().getChannel().pipeline()).fireChannelRead(output);
         }
     }
+
+    @Override
+    public String toString() {
+        return "PacketWrapper{" +
+                "packetValues=" + packetValues +
+                ", readableObjects=" + readableObjects +
+                ", id=" + id +
+                '}';
+    }
 }

src/main/java/us/myles/ViaVersion/api/ViaVersionAPI.java

@@ -101,4 +101,12 @@ public interface ViaVersionAPI {
      * @return command handler
      */
     ViaVersionCommand getCommandHandler();
+
+    /**
+     * Get if this version is a compatibility build for spigot.
+     * Eg. 1.9.1 / 1.9.2 allow certain versions to connect
+     *
+     * @return True if it is
+     */
+    boolean isCompatSpigotBuild();
 }

src/main/java/us/myles/ViaVersion/api/data/UserConnection.java

@@ -1,12 +1,9 @@
 package us.myles.ViaVersion.api.data;
 
-import com.google.gson.Gson;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.socket.SocketChannel;
 import lombok.Data;
-import lombok.Getter;
-import lombok.Setter;
 import org.bukkit.Bukkit;
 import org.bukkit.ChatColor;
 import org.bukkit.entity.Player;

src/main/java/us/myles/ViaVersion/classgenerator/BasicHandlerConstructor.java

@@ -0,0 +1,20 @@
+package us.myles.ViaVersion.classgenerator;
+
+import io.netty.handler.codec.ByteToMessageDecoder;
+import io.netty.handler.codec.MessageToByteEncoder;
+import us.myles.ViaVersion.api.data.UserConnection;
+import us.myles.ViaVersion.classgenerator.HandlerConstructor;
+import us.myles.ViaVersion.handlers.ViaDecodeHandler;
+import us.myles.ViaVersion.handlers.ViaEncodeHandler;
+
+public class BasicHandlerConstructor implements HandlerConstructor {
+    @Override
+    public ViaEncodeHandler newEncodeHandler(UserConnection info, MessageToByteEncoder minecraftEncoder) {
+        return new ViaEncodeHandler(info, minecraftEncoder);
+    }
+
+    @Override
+    public ViaDecodeHandler newDecodeHandler(UserConnection info, ByteToMessageDecoder minecraftDecoder) {
+        return new ViaDecodeHandler(info, minecraftDecoder);
+    }
+}

src/main/java/us/myles/ViaVersion/classgenerator/ClassGenerator.java

@@ -0,0 +1,88 @@
+package us.myles.ViaVersion.classgenerator;
+
+import javassist.*;
+import javassist.expr.ConstructorCall;
+import javassist.expr.ExprEditor;
+import us.myles.ViaVersion.api.ViaVersion;
+import us.myles.ViaVersion.handlers.ViaDecodeHandler;
+import us.myles.ViaVersion.handlers.ViaEncodeHandler;
+import us.myles.ViaVersion.util.ReflectionUtil;
+
+public class ClassGenerator {
+    private static HandlerConstructor constructor = new BasicHandlerConstructor();
+
+    public static HandlerConstructor getConstructor() {
+        return constructor;
+    }
+
+    public static void generate() {
+        if(!ViaVersion.getInstance().isCompatSpigotBuild()) return; // Use Basic Handler as not needed.
+
+        try {
+            ClassPool pool = ClassPool.getDefault();
+            pool.insertClassPath(new LoaderClassPath(ClassGenerator.class.getClassLoader()));
+            // Generate the classes
+            transformSuperclass(pool, ViaDecodeHandler.class, ReflectionUtil.nms("PacketDecoder"));
+            transformSuperclass(pool, ViaEncodeHandler.class, ReflectionUtil.nms("PacketEncoder"));
+
+            // Implement Constructor
+            CtClass generated = pool.makeClass("us.myles.ViaVersion.classgenerator.generated.GeneratedConstructor");
+            CtClass handlerInterface = pool.get(HandlerConstructor.class.getName());
+
+            generated.setInterfaces(new CtClass[]{handlerInterface});
+            // Import required classes
+            pool.importPackage("us.myles.ViaVersion.classgenerator.generated");
+            pool.importPackage("us.myles.ViaVersion.classgenerator");
+            pool.importPackage("us.myles.ViaVersion.api.data");
+            pool.importPackage("io.netty.handler.codec");
+            // Implement Methods
+            generated.addMethod(CtMethod.make("public MessageToByteEncoder newEncodeHandler(UserConnection info, MessageToByteEncoder minecraftEncoder) {\n" +
+                    "        return new ViaEncodeHandler(info, minecraftEncoder);\n" +
+                    "    }", generated));
+            generated.addMethod(CtMethod.make("public ByteToMessageDecoder newDecodeHandler(UserConnection info, ByteToMessageDecoder minecraftDecoder) {\n" +
+                    "        return new ViaDecodeHandler(info, minecraftDecoder);\n" +
+                    "    }", generated));
+
+            constructor = (HandlerConstructor) generated.toClass(HandlerConstructor.class.getClassLoader()).newInstance();
+        } catch (ClassNotFoundException e) {
+            e.printStackTrace();
+        } catch (CannotCompileException e) {
+            e.printStackTrace();
+        } catch (NotFoundException e) {
+            e.printStackTrace();
+        } catch (InstantiationException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+    }
+
+    private static Class transformSuperclass(ClassPool pool, Class input, Class superclass) {
+        String newName = "us.myles.ViaVersion.classgenerator.generated." + input.getSimpleName();
+
+        try {
+            CtClass toExtend = pool.get(superclass.getName());
+            CtClass generated = pool.getAndRename(input.getName(), newName);
+            generated.setSuperclass(toExtend);
+            // Modify constructor to call super
+            if(generated.getConstructors().length != 0) {
+                generated.getConstructors()[0].instrument(new ExprEditor() {
+                    @Override
+                    public void edit(ConstructorCall c) throws CannotCompileException {
+                        if (c.isSuper()) {
+                            // Constructor for both has a stats thing.
+                            c.replace("super(null);");
+                        }
+                        super.edit(c);
+                    }
+                });
+            }
+            return generated.toClass(HandlerConstructor.class.getClassLoader());
+        } catch (NotFoundException e) {
+            e.printStackTrace();
+        } catch (CannotCompileException e) {
+            e.printStackTrace();
+        }
+        return null;
+    }
+}

src/main/java/us/myles/ViaVersion/classgenerator/HandlerConstructor.java

@@ -0,0 +1,10 @@
+package us.myles.ViaVersion.classgenerator;
+
+import io.netty.handler.codec.ByteToMessageDecoder;
+import io.netty.handler.codec.MessageToByteEncoder;
+import us.myles.ViaVersion.api.data.UserConnection;
+
+public interface HandlerConstructor {
+    public MessageToByteEncoder newEncodeHandler(UserConnection info, MessageToByteEncoder minecraftEncoder);
+    public ByteToMessageDecoder newDecodeHandler(UserConnection info, ByteToMessageDecoder minecraftDecoder);
+}

src/main/java/us/myles/ViaVersion/handlers/ViaEncodeHandler.java

@@ -4,6 +4,7 @@ import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.handler.codec.MessageToByteEncoder;
 import us.myles.ViaVersion.api.PacketWrapper;
+import us.myles.ViaVersion.api.ViaVersion;
 import us.myles.ViaVersion.api.data.UserConnection;
 import us.myles.ViaVersion.api.type.Type;
 import us.myles.ViaVersion.exception.CancelException;
@@ -11,6 +12,7 @@ import us.myles.ViaVersion.packets.Direction;
 import us.myles.ViaVersion.protocols.base.ProtocolInfo;
 import us.myles.ViaVersion.util.PipelineUtil;
 
+import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 
 public class ViaEncodeHandler extends MessageToByteEncoder {
@@ -25,6 +27,11 @@ public class ViaEncodeHandler extends MessageToByteEncoder {
 
     @Override
     protected void encode(final ChannelHandlerContext ctx, Object o, final ByteBuf bytebuf) throws Exception {
+        if (ViaVersion.getInstance().isCompatSpigotBuild()) {
+            Field ver = minecraftEncoder.getClass().getDeclaredField("version");
+            ver.setAccessible(true);
+            ver.set(minecraftEncoder, ver.get(this));
+        }
         // handle the packet type
         if (!(o instanceof ByteBuf)) {
             // call minecraft encoder

src/main/java/us/myles/ViaVersion/handlers/ViaVersionInitializer.java

@@ -7,6 +7,8 @@ import io.netty.handler.codec.ByteToMessageDecoder;
 import io.netty.handler.codec.MessageToByteEncoder;
 import us.myles.ViaVersion.api.data.UserConnection;
 import us.myles.ViaVersion.api.protocol.ProtocolPipeline;
+import us.myles.ViaVersion.classgenerator.ClassGenerator;
+import us.myles.ViaVersion.classgenerator.HandlerConstructor;
 
 import java.lang.reflect.Method;
 
@@ -36,9 +38,11 @@ public class ViaVersionInitializer extends ChannelInitializer<SocketChannel> {
         new ProtocolPipeline(info);
         // Add originals
         this.method.invoke(this.original, socketChannel);
+
+        HandlerConstructor constructor = ClassGenerator.getConstructor();
         // Add our transformers
-        ViaEncodeHandler encoder = new ViaEncodeHandler(info, (MessageToByteEncoder) socketChannel.pipeline().get("encoder"));
-        ViaDecodeHandler decoder = new ViaDecodeHandler(info, (ByteToMessageDecoder) socketChannel.pipeline().get("decoder"));
+        MessageToByteEncoder encoder = constructor.newEncodeHandler(info, (MessageToByteEncoder) socketChannel.pipeline().get("encoder"));
+        ByteToMessageDecoder decoder = constructor.newDecodeHandler(info, (ByteToMessageDecoder) socketChannel.pipeline().get("decoder"));
         ViaPacketHandler chunkHandler = new ViaPacketHandler(info);
 
         socketChannel.pipeline().replace("encoder", "encoder", encoder);