• Start Client -> Join World -> Exit World -> Join World = crash: screen says IndeOutOfBoundException (present in original forge version as well) but log only shows what seems like a problem handling the packet kicking you for crashing Received class net.minecraft.network.protocol.game.ClientboundDisconnectPacket that couldn't be processed java.lang.ClassCastException: class net.minecraft.server.network.ServerGamePacketListenerImpl cannot be cast to class net.minecraft.network.protocol.game.ClientGamePacketListener

Any parts of the fabric api that are used must be reimplemented in this package. The api classes must have exactly the same names, methods and package structure. Then their functionality is reimplemented using forge events or mixins.

The signature of methods and fields must match the fabric api exactly to avoid NoSuchFieldError/NoSuchMethodError. For example, it is not enough for ServerPlayConnectionEvents#register to accept a TriConsumer<ServerPlayNetworkHandler, PacketSender, MinecraftServer>, it must take a Join which is a functional interface that exposes a onPlayReady method corresponding to that consumer. Also, interfaces must be in the same package/class as they are in the fabric api. In that example, the PackeSender must be an inner class since it will not be found if it is its own file in the package. Make sure the return types of methods are the same! Even though the result is never used by the mod, ServerPlayNetworking#registerGlobalReceiver must return a boolean or the method will not be recognised.

• The structure of the api is from Fabric API under the Apache License 2.0.
• Luke's code reimplimenting that is under the Creative Commons Zero License.