proof-of-concept extensible bytecode transformation for a block game

Currently, the only supported platform is Bukkit.

Spigot already transforms plugins' bytecode in the name of backwards compatibility, so why not take advantage of this for something more mischievous? In post-flattening Bukkit (1.13+), plugins have their bytecode transformed with a public "API" (UnsafeValues#processClass, formerly just hidden in the Commodore class). This "API" is implemented by the CraftMagicNumbers singleton, with its instance being stored in its public static final UnsafeValues INSTANCE field. You should already know where this is going.

You can replace the singleton instance with sun.misc.Unsafe for your own UnsafeValues implementation, which allows you to transform every plugin class that's loaded after yours. Now, I know that using Java's Unsafe is very bad, which is why I've also made the bukkit-agent module, which is a premain Java agent that strips the final modifier from the field, so it can be accessed and replaced with plain Reflection. Unlimited power!

The reference implementation can be found in the bukkit module, build it with ./gradlew :ray-bukkit:shadowJar (output is in bukkit/build/libs/ray-bukkit-<version>-all.jar, pay attention to the JAR classifier).

The plugin discovers me.kcra.ray.transform.Transformer (from the api module) services in JARs in the plugins/ray/transformers directory, these are then added to the class transformation pipeline.

A reference implementation for a transformer JAR can be found in the transform/reobf module, this one reads the /META-INF/mappings/reobf.tiny resource, which modern Paper installations bundle to deobfuscate stacktraces, and reobfuscates Mojang-mapped plugins using it. You can test this with any dev-classified JAR from a paperweight-userdev-based plugin.

This project is licensed under the Apache License, Version 2.0.