From 6498d625add48ad35c289bf420f9744998da33ad Mon Sep 17 00:00:00 2001
From: johni0702 <me@johni0702.de>
Date: Sat, 24 Dec 2016 11:22:01 +0100
Subject: [PATCH] Fix server game data snapshot being restored in singleplayer
 (fixes #44)

---
 .../recording/handler/FMLHandshakeFilter.java | 25 +++++++++++++++++
 .../mixin/MixinNetworkDispatcher.java         | 27 ++++++++++++++++---
 2 files changed, 48 insertions(+), 4 deletions(-)
 create mode 100644 src/main/java/com/replaymod/recording/handler/FMLHandshakeFilter.java

diff --git a/src/main/java/com/replaymod/recording/handler/FMLHandshakeFilter.java b/src/main/java/com/replaymod/recording/handler/FMLHandshakeFilter.java
new file mode 100644
index 00000000..79553b3b
--- /dev/null
+++ b/src/main/java/com/replaymod/recording/handler/FMLHandshakeFilter.java
@@ -0,0 +1,25 @@
+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 (!(msg instanceof FMLHandshakeMessage.RegistryData)) {
+            // Pass on everything but RegistryData messages
+            ctx.fireChannelRead(msg);
+        }
+    }
+}
diff --git a/src/main/java/com/replaymod/recording/mixin/MixinNetworkDispatcher.java b/src/main/java/com/replaymod/recording/mixin/MixinNetworkDispatcher.java
index 9ef0b6da..c6e2e4d5 100644
--- a/src/main/java/com/replaymod/recording/mixin/MixinNetworkDispatcher.java
+++ b/src/main/java/com/replaymod/recording/mixin/MixinNetworkDispatcher.java
@@ -1,7 +1,11 @@
 package com.replaymod.recording.mixin;
 
+import com.replaymod.recording.handler.FMLHandshakeFilter;
+import io.netty.channel.ChannelPipeline;
 import io.netty.channel.embedded.EmbeddedChannel;
+import net.minecraftforge.fml.common.network.handshake.FMLHandshakeCodec;
 import net.minecraftforge.fml.common.network.handshake.NetworkDispatcher;
+import net.minecraftforge.fml.relauncher.Side;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.Shadow;
 import org.spongepowered.asm.mixin.injection.At;
@@ -11,17 +15,32 @@ import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 @Mixin(value = NetworkDispatcher.class, remap = false)
 public abstract class MixinNetworkDispatcher {
 
+    @Shadow
+    private Side side;
+
     @Shadow
     private EmbeddedChannel handshakeChannel;
 
     /**
-     * Always sets fml:isLocal to false.
+     * Always sets fml:isLocal to false on the server side.
      * This effectively removes the difference in the FML handshake between SP and MP
      * and forces the block/item ids, etc. to always be send.
-     * This might have undesired side effects but at least it works at all.
+     * Injects a {@link FMLHandshakeFilter} on the client side to filter out
+     * those extra, unexpected packets.
      */
     @Inject(method = "insertIntoChannel", at=@At("HEAD"))
-    public void replayModRecording_forceIsLocalToFalse(CallbackInfo cb) {
-        handshakeChannel.attr(NetworkDispatcher.IS_LOCAL).set(false);
+    public void replayModRecording_setupForLocalRecording(CallbackInfo cb) {
+        // If we're in multiplayer, everything is fine as is
+        if (!handshakeChannel.attr(NetworkDispatcher.IS_LOCAL).get()) return;
+
+        if (side == Side.SERVER) {
+            // On the server side, force all packets to be sent
+            handshakeChannel.attr(NetworkDispatcher.IS_LOCAL).set(false);
+        } else {
+            // On the client side, discard additional packets
+            ChannelPipeline pipeline = handshakeChannel.pipeline();
+            pipeline.addAfter(pipeline.context(FMLHandshakeCodec.class).name(),
+                    "replaymod_filter", new FMLHandshakeFilter());
+        }
     }
 }