Implement packet send/receive events

src/main/java/emu/grasscutter/server/event/Event.java

@@ -18,10 +18,9 @@ public abstract class Event {
     /**
      * Cancels the event if possible.
      */
-    public void cancel() throws IllegalAccessException {
-        if(!(this instanceof Cancellable))
-            throw new IllegalAccessException("Event is not cancellable.");
-        this.cancelled = true;
+    public void cancel() {
+        if(this instanceof Cancellable)
+            this.cancelled = true;
     }
 
     /**

src/main/java/emu/grasscutter/server/event/game/ReceivePacketEvent.java

+package emu.grasscutter.server.event.game;
+
+import emu.grasscutter.server.event.Cancellable;
+import emu.grasscutter.server.event.ServerEvent;
+import emu.grasscutter.server.game.GameSession;
+
+public final class ReceivePacketEvent extends ServerEvent implements Cancellable {
+    private final GameSession gameSession;
+    private final int packetId;
+    private byte[] packetData;
+    
+    public ReceivePacketEvent(GameSession gameSession, int packetId, byte[] packetData) {
+        super(Type.GAME);
+        
+        this.gameSession = gameSession;
+        this.packetId = packetId;
+        this.packetData = packetData;
+    }
+    
+    public GameSession getGameSession() {
+        return this.gameSession;
+    }
+    
+    public int getPacketId() {
+        return this.packetId;
+    }
+    
+    public void setPacketData(byte[] packetData) {
+        this.packetData = packetData;
+    }
+    
+    public byte[] getPacketData() {
+        return this.packetData;
+    }
+}

src/main/java/emu/grasscutter/server/event/game/SendPacketEvent.java

+package emu.grasscutter.server.event.game;
+
+import emu.grasscutter.net.packet.GenshinPacket;
+import emu.grasscutter.server.event.Cancellable;
+import emu.grasscutter.server.event.ServerEvent;
+import emu.grasscutter.server.game.GameSession;
+
+public final class SendPacketEvent extends ServerEvent implements Cancellable {
+    private final GameSession gameSession;
+    private GenshinPacket packet;
+
+    public SendPacketEvent(GameSession gameSession, GenshinPacket packet) {
+        super(Type.GAME);
+
+        this.gameSession = gameSession;
+        this.packet = packet;
+    }
+
+    public GameSession getGameSession() {
+        return this.gameSession;
+    }
+
+    public void setPacket(GenshinPacket packet) {
+        this.packet = packet;
+    }
+
+    public GenshinPacket getPacket() {
+        return this.packet;
+    }
+}

src/main/java/emu/grasscutter/server/game/GameServerPacketHandler.java

@@ -2,6 +2,7 @@ package emu.grasscutter.server.game;
 
 import java.util.Set;
 
+import emu.grasscutter.server.event.game.ReceivePacketEvent;
 import org.reflections.Reflections;
 
 import emu.grasscutter.Grasscutter;
@@ -48,9 +49,7 @@ public class GameServerPacketHandler {
 	}
 	
 	public void handle(GameSession session, int opcode, byte[] header, byte[] payload) {
-		PacketHandler handler = null;
-		
-		handler = this.handlers.get(opcode);
+		PacketHandler handler = this.handlers.get(opcode);
 		
 		if (handler != null) {
 			try {
@@ -77,8 +76,10 @@ public class GameServerPacketHandler {
 					}
 				}
 				
-				// Handle
-				handler.handle(session, header, payload);				
+				// Invoke event.
+				ReceivePacketEvent event = new ReceivePacketEvent(session, opcode, payload); event.call();
+				if(!event.isCanceled()) // If event is not canceled, continue.
+					handler.handle(session, header, event.getPacketData());				
 			} catch (Exception ex) {
 				// TODO Remove this when no more needed
 				ex.printStackTrace();

src/main/java/emu/grasscutter/server/game/GameSession.java

@@ -10,6 +10,7 @@ import emu.grasscutter.game.GenshinPlayer;
 import emu.grasscutter.net.packet.GenshinPacket;
 import emu.grasscutter.net.packet.PacketOpcodesUtil;
 import emu.grasscutter.netty.MihoyoKcpChannel;
+import emu.grasscutter.server.event.game.SendPacketEvent;
 import emu.grasscutter.utils.Crypto;
 import emu.grasscutter.utils.FileUtils;
 import emu.grasscutter.utils.Utils;
@@ -161,16 +162,15 @@ public class GameSession extends MihoyoKcpChannel {
     		genshinPacket.buildHeader(this.getNextClientSequence());
     	}
     	
-    	// Build packet
-    	byte[] data = genshinPacket.build();
-    	
     	// Log
     	if (Grasscutter.getConfig().getGameServerOptions().LOG_PACKETS) {
     		logPacket(genshinPacket);
     	}
-    	
-    	// Send
-    	send(data);
+		
+		// Invoke event.
+		SendPacketEvent event = new SendPacketEvent(this, genshinPacket); event.call();
+    	if(!event.isCanceled()) // If event is not cancelled, continue.
+			this.send(event.getPacket().build());
     }
     
     private void logPacket(int opcode) {