Move FMLHandshakeFilter into 1.12.2 project

versions/1.12.2/src/main/java/com/replaymod/recording/handler/FMLHandshakeFilter.java

@@ -0,0 +1,29 @@
+package com.replaymod.recording.handler;
+
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.SimpleChannelInboundHandler;
+import net.minecraftforge.fml.common.network.handshake.FMLHandshakeMessage;
+
+/**
+ * Filters out all handshake packets that were sent for recording but must
+ * not actually be handled.
+ * This handler is only present when connected to the integrated server as
+ * otherwise all packets must be handled.
+ *
+ * When in single player, the game state packets must never be handled
+ * otherwise wired bugs related to semi-singletons can occur.
+ * See https://bugs.replaymod.com/show_bug.cgi?id=44
+ */
+public class FMLHandshakeFilter extends SimpleChannelInboundHandler<FMLHandshakeMessage> {
+    @Override
+    protected void channelRead0(ChannelHandlerContext ctx, FMLHandshakeMessage msg) throws Exception {
+        //#if MC>=10800
+        if (!(msg instanceof FMLHandshakeMessage.RegistryData)) {
+        //#else
+        //$$ if (!(msg instanceof FMLHandshakeMessage.ModIdData)) {
+        //#endif
+            // Pass on everything but RegistryData messages
+            ctx.fireChannelRead(msg);
+        }
+    }
+}