InjectMyau

Myau for Minecraft 1.8.9, loaded into a game that is already running instead of installed as a mod.

The point of doing it this way is that it works on launchers that will not take a mod file: Badlion and Lunar ship their own closed clients, and neither has a mods folder you can drop something into. An injector does not need one. Start the game, press a button, and the client is inside it.

Forge still works too — the same build runs there, and that is the easiest place to develop against.

Layout

InjectMyau/
├── OpenMyau-Inject/    the client itself (Java, Gradle, Forge 1.8.9)
└── myau-natives/       the loader and the injected DLL (C++, CMake, Windows)

The two build separately and meet once: the loader embeds the client jar as a resource, so the Gradle build has to run first and the CMake build picks its output up from ../OpenMyau-Inject/build/libs.

Requirements

Building the client	JDK 17
The client itself	targets Java 8 — Gradle handles this with a toolchain, no second JDK needed
Building the loader	CMake 3.15+, Visual Studio 2022 (or another MSVC toolchain), Windows
Running	Windows, 64-bit

JDK 17 is not a preference. The Gradle build pulls in architectury-pack200, which refuses to run on anything below 16, and 21 and above break other parts of the toolchain. Point JAVA_HOME at a 17 and leave it.

Building

1. The client

cd OpenMyau-Inject
./gradlew build

The jar lands in OpenMyau-Inject/build/libs/. On Windows use gradlew.bat.

2. The loader

cd myau-natives
cmake -S . -B build -G "Visual Studio 17 2022" -A x64 -DJAVA_INCLUDE="<your-jdk>/include"
cmake --build build --config Release

JAVA_INCLUDE is only needed if JAVA_HOME is not already pointing at a JDK — the build reads it from there by default. It has to be a JDK and not a JRE, because the injected DLL is a JVMTI agent and needs jni.h and jvmti.h.

The configure step fails outright if it cannot find a client jar. That is deliberate: a loader with no client in it looks like it works and then does nothing.

The result is myau-natives/build/Release/myau_loader.exe, with the DLL and the client jar built into it. It is the only file you need to keep.

Using it

1. Start Minecraft 1.8.9 — Forge, Badlion or Lunar.
2. Get to the main menu. Do not join a server yet.
3. Run myau_loader.exe and press Load.

The loader looks for a running java.exe or javaw.exe that is a Minecraft process, writes the DLL and the client jar to %TEMP%, and attaches. It says Loaded when the client is in.

Once it is in, RSHIFT opens the menu and .help in chat lists the commands.

Injecting twice into the same game does nothing the second time — the classes are already loaded and will not be read again. To pick up a new build, close Minecraft, start it again, and inject the new loader.

If something goes wrong

The client writes to %TEMP%\myau-native.log, and that is the first place to look. It records every hook it installed and every name it failed to resolve. System.out is not a substitute: Badlion sends it somewhere you cannot read.

How it works

The loader is a JVMTI agent. It attaches to the running JVM and asks it to hand back the classes it has already loaded so they can be rewritten — ClassFileLoadHook plus RetransformClasses. The rewriting is plain ASM, injecting calls to the client's own callbacks at chosen points in vanilla methods. There are no Mixins at runtime.

The one genuinely awkward part is that the three launchers do not agree on what anything is called:

	Classes	Members
Forge	MCP (net.minecraft.client.Minecraft)	SRG (func_71410_x)
Lunar	MCP	MCP (getMinecraft)
Badlion	obfuscated (ave)	obfuscated (aw)

So the client ships mapping tables and remaps its own references as its classes load, in whichever direction that particular game needs. A Mixin build of the same source exists alongside the injected one and is what runs in a development environment, where Forge names everything itself.

Development

./gradlew runClient starts a Forge development client with the Mixin build, which is a much shorter loop than rebuilding the loader for every change. The injected path and the Mixin path are separate implementations of the same hooks, so anything touching one usually has to touch the other — they are src/main/java/myau/inject/ and src/main/java/myau/mixin/.

Credits

Based on Myau 250910, and on OpenMyau. The click GUI came from Raven b3 by blowsy. Various modules are ported from Raven and Rise, and are marked as such in the source.