From c900fddebb1bbe7539c16204f74c9565840d4427 Mon Sep 17 00:00:00 2001
From: Techcable <Techcable@techcable.net>
Date: Thu, 19 May 2016 17:09:22 -0600
Subject: [PATCH] Allow invalid packet ids for forge servers

Some forge mods (COFH) use negative packet ids instead of plugin channels for 'reasons'.
Vanilla servers still error on negative/invalid packets.

Original issue: https://github.com/WaterfallMC/Waterfall-Old/issues/11

diff --git a/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java b/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java
index d79d5e5c..250e7620 100644
--- a/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java
+++ b/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java
@@ -18,6 +18,14 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf>
     private final boolean server;
     @Setter
     private int protocolVersion;
+    @Setter
+    private boolean supportsForge = false;
+
+    public MinecraftDecoder(Protocol protocol, boolean server, int protocolVersion) {
+        this.protocol = protocol;
+        this.server = server;
+        this.protocolVersion = protocolVersion;
+    }
 
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception
@@ -36,7 +44,7 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf>
         {
             int packetId = DefinedPacket.readVarInt( in );
 
-            DefinedPacket packet = prot.createPacket( packetId, protocolVersion );
+            DefinedPacket packet = prot.createPacket( packetId, protocolVersion, supportsForge );
             if ( packet != null )
             {
                 packet.read( in, protocol, prot.getDirection(), protocolVersion );
diff --git a/protocol/src/main/java/net/md_5/bungee/protocol/Protocol.java b/protocol/src/main/java/net/md_5/bungee/protocol/Protocol.java
index 2eeca50b..9bd62ceb 100644
--- a/protocol/src/main/java/net/md_5/bungee/protocol/Protocol.java
+++ b/protocol/src/main/java/net/md_5/bungee/protocol/Protocol.java
@@ -751,14 +751,23 @@ public enum Protocol
             return protocol;
         }
 
+        public boolean hasPacket(int i, boolean supportsForge) {
+            return supportsForge || i >= 0 && i <= MAX_PACKET_ID;
+        }
+
         public final DefinedPacket createPacket(int id, int version)
+        {
+            return createPacket(id, version, true);
+        }
+
+        public final DefinedPacket createPacket(int id, int version, boolean supportsForge)
         {
             ProtocolData protocolData = getProtocolData( version );
             if ( protocolData == null )
             {
                 throw new BadPacketException( "Unsupported protocol version " + version );
             }
-            if ( id > MAX_PACKET_ID || id < 0 )
+            if ( !hasPacket(id, supportsForge) )
             {
                 throw new BadPacketException( "Packet with id " + id + " outside of range" );
             }
diff --git a/proxy/src/main/java/net/md_5/bungee/ServerConnector.java b/proxy/src/main/java/net/md_5/bungee/ServerConnector.java
index ce925db2..6db704bd 100644
--- a/proxy/src/main/java/net/md_5/bungee/ServerConnector.java
+++ b/proxy/src/main/java/net/md_5/bungee/ServerConnector.java
@@ -224,6 +224,12 @@ public class ServerConnector extends PacketHandler
     public static void handleLogin(ProxyServer bungee, ChannelWrapper ch, UserConnection user, BungeeServerInfo target, ForgeServerHandler handshakeHandler, ServerConnection server, Login login) throws Exception
     {
         ServerConnectedEvent event = new ServerConnectedEvent( user, server );
+
+        if (server.isForgeServer() && user.isForgeUser()) {
+            ((net.md_5.bungee.protocol.MinecraftDecoder) server.getCh().getHandle().pipeline().get(net.md_5.bungee.netty.PipelineUtils.PACKET_DECODER)).setSupportsForge(true);
+            ((net.md_5.bungee.protocol.MinecraftDecoder) user.getCh().getHandle().pipeline().get(net.md_5.bungee.netty.PipelineUtils.PACKET_DECODER)).setSupportsForge(true);
+        }
+
         bungee.getPluginManager().callEvent( event );
 
         ch.write( BungeeCord.getInstance().registerChannels( user.getPendingConnection().getVersion() ) );
diff --git a/proxy/src/main/java/net/md_5/bungee/entitymap/EntityMap.java b/proxy/src/main/java/net/md_5/bungee/entitymap/EntityMap.java
index 9a47f2ec..b768d54a 100644
--- a/proxy/src/main/java/net/md_5/bungee/entitymap/EntityMap.java
+++ b/proxy/src/main/java/net/md_5/bungee/entitymap/EntityMap.java
@@ -340,6 +340,12 @@ public abstract class EntityMap
         int packetId = DefinedPacket.readVarInt( packet );
         int packetIdLength = packet.readerIndex() - readerIndex;
 
+        if (packetId < 0 || packetId > ints.length || packetId > varints.length) { // Invalid packet id
+            // Ignore these invalid packets for compatibility reasons
+            packet.readerIndex( readerIndex );
+            return;
+        }
+
         if ( ints[packetId] )
         {
             rewriteInt( packet, oldId, newId, readerIndex + packetIdLength );
-- 
2.42.1