Fix memory leak in CustomPayloadS2CPacket

This is technically a bug in vanilla, however vanilla is saved from this bug due to pure dumb luck: it extensively abuses unpooled heap buffers, so the buffer just gets picked up by the garbage collector and we have nothing to worry about. However, with pooled direct buffers (as with Krypton), the copy is a big problem since it will occupy precious direct buffer space. Worse still, the copy isn't even needed at all. Change it to a slice, which is what it should've been in the first place.

While we're at it, add a new mixin to allow the resource leak detection level to be changed via the normal system property.

src/main/java/me/steinborn/krypton/mixin/shared/bugfix/CustomPayloadS2CPacketFixMemoryLeakMixin.java

@@ -0,0 +1,17 @@
+package me.steinborn.krypton.mixin.shared.bugfix;
+
+import io.netty.buffer.ByteBuf;
+import net.minecraft.network.PacketByteBuf;
+import net.minecraft.network.packet.s2c.play.CustomPayloadS2CPacket;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Redirect;
+
+@Mixin(CustomPayloadS2CPacket.class)
+public class CustomPayloadS2CPacketFixMemoryLeakMixin {
+
+    @Redirect(method = "getData", at = @At(value = "INVOKE", target = "Lnet/minecraft/network/PacketByteBuf;copy()Lio/netty/buffer/ByteBuf;"))
+    private ByteBuf getData$copyShouldBeSlice(PacketByteBuf instance) {
+        return instance.slice();
+    }
+}

src/main/java/me/steinborn/krypton/mixin/shared/debugaid/ResourceLeakDetectorDisableConditionalMixin.java

@@ -0,0 +1,19 @@
+package me.steinborn.krypton.mixin.shared.debugaid;
+
+import io.netty.util.ResourceLeakDetector;
+import net.minecraft.SharedConstants;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Redirect;
+
+@Mixin(SharedConstants.class)
+public class ResourceLeakDetectorDisableConditionalMixin {
+    @Redirect(method = "<clinit>", at = @At(value = "INVOKE", target = "Lio/netty/util/ResourceLeakDetector;setLevel(Lio/netty/util/ResourceLeakDetector$Level;)V"))
+    private static void clinit$resourceLeakDetectorDisableConditional(ResourceLeakDetector.Level level) {
+        if (System.getProperty("io.netty.leakDetection.level") == null) {
+            // Allow the user to override the leak detection level in the Minecraft server with the
+            // io.netty.leakDetection.level system property.
+            ResourceLeakDetector.setLevel(level);
+        }
+    }
+}

src/main/java/me/steinborn/krypton/mod/shared/KryptonSharedInitializer.java

@@ -20,12 +20,6 @@ public class KryptonSharedInitializer implements ModInitializer {
         if (System.getProperty("io.netty.allocator.maxOrder") == null) {
             System.setProperty("io.netty.allocator.maxOrder", "9");
         }
-
-        // Disable the resource leak detector by default as it reduces performance. Allow the user to
-        // override this if desired.
-        if (System.getProperty("io.netty.leakDetection.level") == null) {
-            ResourceLeakDetector.setLevel(ResourceLeakDetector.Level.DISABLED);
-        }
     }
 
     @Override

src/main/resources/krypton.mixins.json

@@ -9,6 +9,8 @@
   ],
   "mixins": [
     "server.fastchunkentityaccess.ServerWorldMixin",
+    "shared.bugfix.CustomPayloadS2CPacketFixMemoryLeakMixin",
+    "shared.debugaid.ResourceLeakDetectorDisableConditionalMixin",
     "shared.fastchunkentityaccess.EntityTrackingSectionAccessor",
     "shared.fastchunkentityaccess.SectionedEntityCacheMixin",
     "shared.network.avoidwork.ThreadedAnvilChunkStorageMixin",